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مفاهیم پایه شیمی آلی Basic Concepts from Organic Chemistry

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C    H5A    P    T    E    R

 

 

 

Basic Concepts from Organic Chemistry

 

 

 

 

۵٫۱ | INTRODUCTION

 

The fundamental information that environmental engineers and scientists need con- cerning organic chemistry differs considerably from that which the organic chemist requires. This difference is due to the fact that chemists are concerned principally with the synthesis of compounds, whereas environmental engineers and scientists are con- cerned, in the main, with how the organic compounds in liquid, solid, and gaseous wastes can be destroyed and how they react in the environment. Another major differ- ence lies in the fact that the organic chemist is usually concerned with the product of the reaction: the by-products of a reaction are of little interest to him or her. Since few organic reactions give better than 85 percent yields, the amount of by-products and unreacted raw materials that represent processing wastes is of considerable magni- tude. In addition, many raw materials contain impurities that do not enter the desired reaction and, of course, add to the organic load in waste streams. A classical example is formaldehyde, which normally contains about 5 percent of methanol unless special precautions are taken in its manufacture. Unfortunately, organic chemists have pre- sented very little information on the nature of the by-products of reactions to aid envi- ronmental engineers and scientists in solving industrial and hazardous waste prob- lems. Fortunately, this is changing because of the large liabilities that companies now face from discharge of environmental pollutants. Awards are now being given for “green chemistry,” that is, for changing the ways chemicals are produced in order to reduce the environmental harm they or their production cause.

The environmental engineer and scientist, like the biochemist, must have a fun- damental knowledge of organic chemistry. It is not important for either to know a multiplicity of ways of preparing a given organic compound and the yields to be ex- pected from each. Rather, the important consideration is how the compounds react in the atmosphere, in the soil, in water, and in treatment reactors, especially when serving as a source of energy for living organisms. It is from this viewpoint that or- ganic chemistry will be treated in this chapter, and considerations will be from the viewpoint of classes rather than individual compounds.

 

۲۱۲

 

 

 

History

 

Organic chemistry deals with the compounds of carbon. The science of organic chemistry is considered to have originated in 1685 with the publication by Lémery1 of a chemistry book that classified substances according to their origin as mineral, vegetable, or animal. Compounds derived from plants and animals became known as organic and those derived from nonliving sources were inorganic.

Until 1828 it was believed that organic compounds could not be formed except by living plants and animals. This was known as the vital-force theory, and belief in it severely limited the development of organic chemistry. Wöhler,2 in 1828, by acci- dent, found that application of heat to ammonium cyanate, an inorganic compound, caused it to change to urea, a compound considered organic in nature. This discovery dealt a death blow to the vital-force theory, and by 1850 modern organic chemistry became well established. Today about 13 million organic compounds are known.3

Many of these are products of synthetic chemistry, and similar compounds are not known in nature. Approximately 70,000 organic chemicals are in commercial use.

 

Elements

 

All organic compounds contain carbon in combination with one or more elements. The hydrocarbons contain only carbon and hydrogen. A great many compounds contain carbon, hydrogen, and oxygen, and they are considered to be the major ele- ments. Minor elements in naturally occurring compounds are nitrogen, phosphorus, and sulfur, and sometimes halogens and metals. Compounds produced by synthesis may contain, in addition, a wide variety of other elements.

 

Properties

 

Organic compounds, in general, differ greatly from inorganic compounds in seven respects:

 

۱٫    Organic compounds are usually combustible.

۲٫    Organic compounds, in general, have lower melting and boiling points.

۳٫    Organic compounds are usually less soluble in water.

۴٫     Several organic compounds may exist for a given formula. This is known as isomerism.

۵٫     Reactions of organic compounds are usually molecular rather than ionic. As a result, they are often quite slow.

۶٫     The molecular weights of organic compounds may be very high, often well over 1000.

۷٫    Most organic compounds can serve as a source of food for bacteria.

 

 

 

۱Nicholas Lémery (1645–۱۷۱۵), French physician and chemist.

۲Freidrich Wöhler (1800–۱۸۸۲), German chemist.

۳R. Chang, “Chemistry,” ۷th ed., McGraw-Hill, New York, 2002.

 

 

 

Sources

 

Organic compounds are derived from three sources:

 

۱٫     Nature:  fibers, vegetable oils, animal oils and fats, alkaloids, cellulose, starch, sugars, and so on.

۲٫     Synthesis: A wide variety of compounds and materials prepared by manufacturing processes.

۳٫     Fermentation: Alcohols, acetone, glycerol, antibiotics, acids, and the like are derived by the action of microorganisms upon organic matter.

 

The wastes produced in the processing of natural organic materials and from the synthetic organic and fermentation industries constitute a major part of the indus- trial and hazardous waste problems that environmental engineers and scientists are called upon to solve.

 

The Carbon Atom

 

A question commonly asked is: How is it possible to have so many compounds of car- bon? There are two reasons. In the first place, carbon normally has four covalent bonds (four electrons to share). This factor alone allows many possibilities, but the most im- portant reason is concerned with the ability of carbon atoms to link together by cova- lent bonding in a wide variety of ways They may be in a continuous open chain,

 

 

ˆ C ˆ C ˆ C ˆ C ˆ C ˆ

 

 

or a chain with branches,

 

 

ˆ C ˆ

 

ˆ Cˆ C ˆ C ˆ C ˆ C ˆ C ˆ

 

ˆ C ˆ

 

 

or in a ring,

 

 

C

ˆ C        C ˆ

 

ˆ C        C ˆ

C

 

 

or in chains or rings containing other elements,

 

 

 

 

 

 

ˆ C ˆ C ˆ Oˆ C ˆ C ˆ


ˆ Cˆ C

N

ˆ Cˆ C

 

 

 

These examples will serve to show the tremendous number of possibilities that exist.

 

Isomerism

 

In inorganic chemistry, a molecular formula is specific for one compound. In or- ganic chemistry, most molecular formulas do not represent any particular com- pound. For example, the molecular formula C3H6O3  represents at least four separate compounds and therefore is of little value in imparting information other than that the compound contains carbon, hydrogen, and oxygen. Four compounds having the formula C3H6O3  are

 

 

H

 

H    O    O

 

 

 

H    H    O

 

Hˆ C ˆ C ˆ C ˆ Oˆ H H      H


Hˆ O ˆC ˆ C ˆ C ˆ Oˆ H H           H

 

 

H     O            H                                            O H             H

 

HˆOˆ C ˆ C ˆ O ˆ C ˆ H


Hˆ C ˆ O ˆ Cˆ C ˆ OH

 

H            H H                   H

 

Compounds having the same molecular formula are known as isomers. In the case just cited, the first two isomers are hydroxy acids, the third is an ester of a hy- droxy acid, and the fourth is a methoxy acid. To the organic chemist, each of the formulas represents a chemical compound with definite physical and chemical properties. The term structural formulas is applied to molecular representations as drawn for the four compounds. They are as useful to a chemist as blueprints are to an engineer.

In many cases structural formulas may be simplified as condensed formulas so as to use only one line. Thus, the formula

 

H    H    H

 

Hˆ C ˆ C ˆ C ˆ Oˆ H

 

 

 

 

may be written as

 

H    H    H

 

 

CH3ˆCH2ˆCH2OH        or       CH3CH2CH2OH

 

thereby saving a great deal of space.

 

 

 

There are three major types of organic compounds, the aliphatic, aromatic, and heterocyclic. The aliphatic compounds are those in which the characteristic groups are linked to a straight or branched carbon chain. The aromatic compounds have these groups linked to a particular type of six-member carbon ring that contains three alter- nating double bonds. Such rings have peculiar stability and chemical character and are present in a wide variety of important compounds. The heterocyclic compounds have a ring structure with or without the alternating double-bond structure of aromatic compounds, and in which at least one member is an element other than carbon.

 

 

ALIPHATIC COMPOUNDS

 

۵٫۲ | HYDROCARBONS

 

The hydrocarbons are compounds of carbon and hydrogen. There are two types, saturated and unsaturated. Saturated hydrocarbons are those in which adjacent car- bon atoms are joined by a single covalent bond and all other bonds are satisfied by hydrogen.

H    H    H

 

Hˆ C ˆ C ˆ C ˆ H

 

H    H    H

A saturated compound

 

Unsaturated hydrocarbons have at least two carbon atoms that are joined by more than one covalent bond and all remaining bonds are satisfied by hydrogen.

 

H    H    H

Hˆ C ˆ C ¨ C ˆ H       HC˜ CH H

Unsaturated compounds

 

 

Saturated Hydrocarbons

 

The saturated hydrocarbons form a whole series of compounds starting with one carbon atom and increasing one carbon atom, stepwise. These compounds are called alkanes, or the methane series. The principal source is petroleum. Gasoline is a mixture containing several of them; diesel fuel is another such mixture.

The hydrocarbons serve as feedstocks for the preparation of a wide variety of organic chemicals. This knowledge serves as the basis of the great petrochemical industry within the petroleum industry. Saturated hydrocarbons are quite inert to- ward most chemical reagents. For this reason they were termed “paraffins” by early chemists (from the Latin parum affinis, meaning “little affinity”).

 

Methane (CH4) is the simplest hydrocarbon. It is a gas of considerable importance to environmental engineers and scientists since it is a major end product of the anaerobic treatment process as applied to sewage sludge and other organic

 

 

 

waste materials. It is a component of marsh gas and of natural gas and, in a mixture with air containing from 5 to 15 percent methane, it is highly explosive. This property allows its use as fuel for gas engines. Methane is commonly called “firedamp” by miners and makes their work particularly hazardous. Methane is also considered to be an important greenhouse gas; its concentration in the stratosphere affects the earth’s heat balance, and thus temperature. On a per molecule basis, it is

۲۱ times more effective at trapping heat in the atmosphere than carbon dioxide, the primary greenhouse gas.

Ethane (CH3ˆCH3) is the second member of the series.

Propane (CH3ˆCH2ˆCH3) is the third member of the series.

Butane (C4H10) is the fourth member of the series and is of interest because it occurs in two isomeric forms:

 

 

H    H    H    H


H    H    H

 

 

Hˆ C ˆ C ˆ Cˆ C ˆ H

 

Hˆ C ˆ C ˆ Cˆ H

 

 

H    H    H    H

 

H HCH H H

 

n-Butane


Isobutane

 

 

Pentane (C5H12) is the fifth member of the series and exists in three isomeric forms:

 

 

 

 

H    H    H    H    H

 

 

H    H    H    H

 

H HCH

H           H

 

HCˆ Cˆ C ˆ C ˆ CH


HCˆ Cˆ C ˆ CH


HCˆ Cˆ CH

 

H    H    H    H    H


H             H    H HCH

H

 

H           H HCH

H

 

n-Pentane bp, 36.2°C


Isopentane bp, 28°C


Neopentane bp, 9.5°C

 

 

 

The third isomer of pentane might also be called tetramethylmethane or dimethylpropane, as the reader will shortly recognize.

As the number of carbon atoms increases in the molecule, the number of possi- ble  isomers  increases  accordingly.  There  are  five  possible  isomers  of  hexane (C6H14) and 75 possible isomers of decane (C10H22).

 

Physical Properties    Table 5.1 lists the names and physical constants of the nor- mal saturated hydrocarbons of 1 to 10 carbon atoms per molecule. The term “nor- mal” applies to the isomer that has all its carbon atoms linked in a straight chain. The others are referred to as branched-chain compounds. The branched form of bu- tane and the simplest branched form of pentane are commonly given the prefix iso-.

The saturated hydrocarbons are colorless, practically odorless, and quite insolu- ble in water, particularly those with five or more carbon atoms. They dissolve read-

 

 

 

Table 5.1 | Physical constants of some normal alkanes

 

Name

Formula

Mp,  C

Bp,  C

Sp. gr.,

۲۰ *

Calcd. no. of isomers

Methane           CH4                       ۱۸۲٫۴               ۱۶۱٫۵           ۰٫۴۲۳   ۱۶۲                        ۱

Ethane

C2H6

 ۱۸۲٫۸

 ۸۸٫۶

۰٫۵۴۵ ۸۹

۱

Propane

C3H8

 ۱۸۷٫۶

 ۴۲٫۱

۰٫۴۹۳۲۵

۱

Butane

C4H10

 ۱۳۸٫۲

 ۰٫۵

۰٫۵۷۳۲۵

۲

Pentane

C5H12

 ۱۲۹٫۷

۳۶٫۰

۰٫۶۲۶

۳

Hexane

C6H14

 ۹۵٫۳

۶۸٫۷

۰٫۶۵۵

۵

Heptane

C7H16

 ۹۰٫۶

۹۸٫۵

۰٫۶۸۴

۹

Octane

C8H18

 ۵۶٫۸

۱۲۵٫۶

۰٫۶۹۹۲۵

۱۸

Nonane

C9H20

 ۵۳٫۵

۱۵۰٫۸

۰٫۷۱۸

۳۵

Decane

C10H22

 ۲۹٫۷

۱۷۴٫۱

۰٫۷۳۰

۷۵

*Density of compound at 20 C (or at the temperature noted by superscript) over the maximum density of water, which is at 4 C.

Source: D. R. Linde (ed.): “Handbook of Chemistry and Physics,” ۸۲nd ed., CRC Press LLC, Boca

Raton, 2001.

 

ily in many organic solvents. At room temperature all members through C5  are gases, those from C6 to C17 are liquids, and those above C17 are solids. Data in Table

۵٫۱ show that as molecular size increases, the melting and boiling points of alkanes increase. Solubility in water in general decreases with increasing size. Such rela- tionships are important in understanding the behavior of organic compounds in the environment and in engineered reactors (Sec. 5.34).

Homologous Series    It will be noted from Table 5.1 that each successive member of the series differs from the previous member by CH2. When the formulas of a se- ries of compounds differ by a common increment, such as CH2, the series is referred to as being a homologous series. Such compounds can be expressed by a general formula. That for the alkane series is CnH2n   ۲٫

 

Radicals    The inert character of the alkanes has been mentioned; however, they may be made to react under the proper conditions, and a wide variety of compounds results. It becomes necessary, therefore, to establish some form of nomenclature to identify the products formed. When one hydrogen is replaced from a molecule of an alkane, the -ane ending is dropped and a -yl is added. The names of some radicals are shown in Table 5.2. The system serves quite well for the normal compounds but is of little value in naming derivatives of the isomers.

 

Nomenclature     The alkanes are characterized by names ending in -ane. The straight-chain compounds are termed normal compounds. The branched-chain

 

Table 5.2 | Names of alkane-series radicals (alkyl groups)

 

Parent compound

Radical

Formula

Methane

Methyl

CH3ˆ

Ethane

Ethyl

C2H5ˆ

Propane

n-Propyl

C3H7ˆ

Propane

Isopropyl

(CH3)2CHˆ

n-Butane

n-Butyl

C4H9ˆ

 

 

 

compounds and the derivatives of both straight- and branched-chain compounds are difficult to name with any degree of specificity. The IUPAC system, as pro- posed by the International Union of Pure and Applied Chemistry, is commonly used. In this system the compounds are named in terms of the longest continuous chain of carbon atoms in the molecule. A few examples will illustrate the method.

 

H    H    H    H    H

HCˆ Cˆ C ˆ C ˆ CH

H    H    H    H    H

n-Pentane

 

 

H    H    H

 

H    H    H

 

HCˆ Cˆ C ˆ CˆC ˆ CH

 

H    H    H


H    H    H

 

n-Hexane

 

 

H    H    H


H    H    H

 

HCˆ Cˆ C ˆ CˆC ˆ CH

H     H           H    H    H HCH

H

۳-Methylhexane

(an isomer of heptane)

 

H    H    H    H    H    H    H     H     H

HCˆ Cˆ C ˆ CˆC ˆC ˆC ˆ C ˆ CH

 

H    H    H


H    H    H     H     H

H HCˆ CH

 

H    H

۴-Ethylnonane

(an isomer of undecane)

 

H    H    H    H    H    H

HCˆ Cˆ Cˆ Cˆ Cˆ CH

 

H

HCH H


H             H    H HCH

H

 

۲,۴-Dimethylhexane

(an isomer of octane)

 

It will be noted that a chain is numbered from the end nearest the attached radi- cal. The rule is to make the numbers as small as possible. The IUPAC system is ap- plied to other compounds as well as to hydrocarbons.

 

Chemical Reactions   Strong bases, acids, or aqueous solutions of oxidizing agents do not react with saturated hydrocarbons at room temperature. At elevated tempera- tures, strong oxidizing agents, such as concentrated sulfuric acid, oxidize the com- pounds to carbon dioxide and water. Other reactions of importance are as follows:

 

۱٫    Oxidation with oxygen or air:

CH4     ۲O2 l CO2     ۲H2O                                    (۵٫۱)

 

 

 

۲٫    Substitution of hydrogen by halogens:

 

CH4     Cl2 l HC1     CH3Cl                                    (۵٫۲) This reaction does not ordinarily occur in aqueous solutions and therefore is of

little significance in environmental engineering and science.

۳٫     Pyrolysis or cracking:  High-molecular-weight hydrocarbons may be broken into smaller molecules by heat treatment. The process is used in the petroleum industry to increase the yield of light boiling fractions, suitable for sale as gasoline or for chemical synthesis. Heat treatment results in disruption of the large molecules as follows:

 

 

 

High- mol.- wt

 

 

heat


alkanes of lower mol. wt

alkenes

 

 

(۵٫۳)

 

alkanes   p¶resslure    hydrogen     naphthenes

  carbon

۴٫     Biological oxidation:  Hydrocarbons are oxidized by certain bacteria under aerobic conditions. The oxidation proceeds through several steps. The first step is very slow biologically and involves conversion to alcohols with attack occurring on terminal carbon atoms, i.e., omega oxidation.

 

 

۲CH3CH2CH3     O2 ¶baclt.    ۲CH3CH2CH2OH

 

(۵٫۴)

 

Hydrocarbon


Alcohol

 

 

Through additional oxidative steps, which will be discussed in Chap. 6, microorganisms convert the hydrocarbon to carbon dioxide and water and derive energy in the process.

 

 

CH3CH2CH3     ۵O2 ¶baclt.

 

۳CO2     ۴H2O                          (۵٫۵)

 

Such reactions, particularly the intermediate steps, are of great interest to environmental engineering and science.

 

Unsaturated Hydrocarbons

The unsaturated hydrocarbons are usually separated into four classes.

Alkenes    Each member of the alkane group except methane can lose hydrogen to form an unsaturated compound or alkene. The alkenes all contain one double bond between two adjacent carbon atoms,

 

H   H

H    H  H    H

 

Hˆ C¨ Cˆ H


HCˆ C¨ Cˆ CH

 

 

Ethylene or ethene

 

H                 H

Butylene or

۲-butene

 

 

and their names all end in -ylene (older nomenclature) or -ene. The alkenes are also called olefins. Alkenes, particularly ethene, propene, and butene are formed in great quantities during the cracking or pyrolysis of petroleum.

The  names,  formulas,  and  physical  constants  of  a  number  of  important alkenes are given in Table 5.3. In naming specific alkenes, the IUPAC system

 

 

 

 

Table 5.3 | Physical constants of selected alkenes

 

 

Calcd. Sp. gr.,             no. of

 

IUPAC name       Formula                           Mp,  C        Bp,  C         ۲۰ C/4 C*        isomers

 

 

Propene

CH2¨CHCH3

 ۱۸۵٫۲

 ۴۷٫۶

۰٫۵۰۵۲۵

۱

۱-Butene

CH2¨CHCH2CH3

 ۱۸۵٫۳

 ۶٫۲

۰٫۵۸۸۲۵

۳

۱-Pentene

CH2¨CH(CH2)2CH3

 ۱۶۵٫۲

۲۹٫۹

۰٫۶۴۰

۵

۱-Hexene

CH2¨CH(CH2)3CH3

 ۱۳۹٫۷

۶۳٫۴

۰٫۶۷۳

۱۳

۱-Heptene

CH2¨CH(CH2)4CH3

 ۱۱۹٫۷

۹۳٫۶

۰٫۶۹۷

۲۷

۱-Octene

CH2¨CH(CH2)5CH3

 ۱۰۱٫۷

۱۲۱٫۲

۰٫۷۱۵

۶۶

۱-Nonene

CH2¨CH(CH2)6CH3

 ۸۱٫۳

۱۴۹٫۹

۰٫۷۲۵۲۵

۱۵۳

۱-Decene

CH2¨CH(CH2)7CH3

 ۶۶٫۳

۱۷۰٫۵

۰٫۷۴۱

۳۷۷

 

Ethene                     CH2¨CH2                                         ۱۶۹              ۱۰۳٫۷
۰٫۵۶۸   ۱۰۴                       ۱

 

 

 

 

 

 

 

 

 

*Density of compound at 20 C (or at the temperature noted by superscript) over the maximum density of water, which is at 4 C.

Source: D. R. Linde (ed.): “Handbook of Chemistry and Physics,” ۸۲nd ed., CRC Press LLC, Boca Raton, 2001.

 

 

must be employed on all compounds with over three carbon atoms. The nomen- clature  becomes  quite  complicated  with  branched-chain  isomers.  Fortunately, there is little reason to differentiate between normal and branched-chain com- pounds in this series.

Diolefins   When aliphatic compounds contain two double bonds in the molecule, they are called alkadienes, some times dienes for short. The compound 1,3-butadi- ene is an important example:

 

CH2¨CHCH¨CH2

It has been used to make polymers.

Alkadienes    Some organic compounds contain more than two double bonds per molecule. The red coloring matter of tomatoes, lycopene, and the yellow coloring matter of carrots are examples.

 

 

CH3

 

CH3

 

CH3

 

CH3

 

CH3C ¨ CH(CH2)2C¨ CHCH ¨ CHC ¨ CHCH¨ CHC ¨ CHCH CH3C ¨ CH(CH2)2C¨ CHCH ¨ CHC ¨ CHCH¨ CHC ¨ CHCH

 

 

CH3

 

CH3

 

CH3

Lycopene (C40H56)

 

CH3

 

 

These compounds are of interest because of their occurrence in industrial wastes produced in the preparation of vegetables for canning. The oxidant (e.g., chlorine) demand of such wastes is extremely high.

Alkynes    The alkynes have a triple bond between adjacent carbon atoms.

 

HˆC˜CˆH

 

These compounds are found to some extent in industrial wastes from certain indus- tries, particularly those from the manufacture of some types of synthetic rubber.

 

 

 

Chemical Reactions   Unsaturated linkages occur in many types of organic com- pounds and exhibit many properties in common, regardless of the type of compound in which they exist. Unsaturated compounds undergo several reactions with relative ease.

 

۱.     Oxidation: The compounds are easily oxidized in aqueous solution by oxidizing agents such as potassium permanganate. A glycol is the normal product.

۲٫     Reduction:  Under special conditions of temperature, pressure, and catalysis, hydrogen may be caused to add at double or triple bonds. This reaction is of considerable importance commercially in the conversion of vegetable oils to solid fats. Many vegetable shortenings are made by this process.

۳٫     Addition:  Halogen acids, hypochlorous acid, and halogens will add across unsaturated linkages.

 

 

OH Cl

 

CH3 ˆ C¨ CˆH   HOCl  l CH3 ˆ C ˆ Cˆ H

 

 

 

(۵٫۶)

 

 

H   H                                        H    H

 

The reaction with hypochlorous acid is most important. Industrial wastes containing appreciable amounts of unsaturated compounds exhibit high chlorine-demand values because of such reactions.

۴٫     Polymerization:  Molecules of certain compounds having unsaturated linkages are prone to combine with each other to form polymers of higher molecular weight.

 

high temperature

nCH2¨CH2   ¶and¶pr¶essulre      (C2H4)n

Polyethylene

 

n     ۷۰ to 700                  (۵٫۷)

 

 

Similar reactions serve as the basis for many industrial products, e.g., synthetic resins, synthetic fibers, synthetic rubber, and synthetic detergents. Industrial wastes from such industries can be expected to contain a wide variety of polymers and usually exhibit a high chlorine demand. Historically such wastes were treated by chlorination. This practice is currently discouraged because the chlorinated organic compounds so formed have adverse impacts to human health and the environment.

۵.     Bacterial oxidation: It is generally considered that organic compounds possessing unsaturated linkages are more prone to bacterial oxidation than corresponding saturated compounds because of the ease of oxidation at the double bonds.

 

 

۵٫۳ | ALCOHOLS

 

Alcohols are considered the primary oxidation product of hydrocarbons.

 

 

CH4

Methane

 

 

۲    ۲

۱O  l

CH3OH

Methyl alcohol or methanol

 

(۵٫۸)

 

 

 

۳               ۲               ۳        ۲    ۲                 ۳               ۲               ۲

CH ˆ CH ˆ CH      ۱O  l CH ˆ CH ˆ CH OH

(۵٫۹)

 

Propane


n-Propyl alcohol or propanol

 

 

 

They cannot be prepared in this manner, however, because the reaction cannot be stopped with alcohols as the end product. Nevertheless, the reaction illustrates an initial step in biological degradation of hydrocarbons under aerobic conditions.

Alcohols may be considered as hydroxy alkyl compounds. For convenience, the alkyl group in alcohols and other organic compounds is often represented by Rˆ, and the general formula for alcohols is RˆOH. The OH group does not easily ion- ize; consequently, alcohols are neutral in reaction. The chemistry of alcohols is re- lated entirely to the OH group.

 

Classification

 

Alcohols are classified into three groups: primary, secondary, and tertiary, depend- ing upon where the OH group is attached to the molecule. If the OH group is on a terminal (primary) carbon atom, it is a primary alcohol.

 

H    H                     H    H    H    H

 

HC ˆ C ˆ OH


HCˆ C ˆ Cˆ C ˆ OH


Rˆ OH

 

H    H                     H    H    H    H

Primary alcohols

 

If the OH group is attached to a carbon atom that is joined to two other carbon atoms, it is a secondary alcohol, and the carbon atom to which it is attached is a sec- ondary carbon atom.

 

 

H    H    H


H    H    H    H          R

 

HC ˆ C ˆ CH


HC ˆ C ˆ C ˆ CH


CHOH

 

H           H             H    H           H          R

O                                  O

H                                  H

Secondary alcohols

 

If the OH group is attached to a carbon atom that is joined to three other carbon atoms, it is a tertiary alcohol, and the carbon atom to which it is attached is a ter- tiary carbon atom.

C H

HCH                             C               R H           H

 

HCˆ C ˆ CH


CˆCˆ C ˆ C


Rˆ Cˆ OH

 

H           H

O                                O H                                H

Tertiary alcohols


R

 

 

The chemistry of the primary, secondary, and tertiary alcohols differs considerably (e.g., bacterial oxidation of tertiary alcohols is much more difficult than of primary alcohols). Therefore, it is important to know how to differentiate among them.

 

Common Alcohols

 

The alcohols of greatest commercial importance are methyl, ethyl, isopropyl, and

n-butyl.

 

 

 

Methanol (CH3OH)    Methanol (also called methyl alcohol) is used to a consider- able extent for synthesis of organic compounds. It has been used as an antifreeze for automobiles. It is prepared mainly by synthesis from natural gas and steam as follows:

 

  pressure

CH4     H2O ¶ca¶talylst

 

CH3OH     H2                                                 (۵٫۱۰)

 

but may be manufactured from carbon monoxide and hydrogen.

 

Ethanol (CH3CH2OH)    Ethanol (ethyl alcohol) is used for the synthesis of organic compounds, the production of beverages, and the manufacture of medicines. Re- cently it has found use as a fuel oxygenate for reformulated gasoline (Sec. 3.8). It is prepared largely by fermentation processes. Alcohol intended for beverages is often manufactured by the fermentation of starch derived from a variety of materials, such as corn, wheat, rye, rice, and potatoes. The reactions involved are as follows:

enzyme

 

Starch     water ¶of¶mallt


maltose                                (۵٫۱۱)

 

 

 

enzyme

C12H22O11     H2O  ¶of¶yealst

Maltose

 

۲ glucose                            (۵٫۱۲)

 

 

Fermentation of the glucose yields carbon dioxide and alcohol.

 

fermentation

C6H12O6   ¶¶l 2CO2     ۲C2H5OH                            (۵٫۱۳)

Glucose

 

Wine is produced from the fermentation of sugars in grapes. Industrial alcohol is produced largely from the fermentation of solutions containing sugars that are difficult to reclaim, such as molasses and, sometimes, even spent sulfite liquor.

 

 

invertase

C12H22O11     H2O ¶¶l C6H12O6     C6H12O6

 

(۵٫۱۴)

 

 

yeast


Glucose


Fructose

 

C6H12O6 ¶l 2CO2     ۲C2H5OH

Glucose

Fructose

 

The residues remaining after distillation of the desired product, ethanol, consti- tute some of the most potent industrial wastes in terms of strength with which the environmental engineer has to deal.

 

Isopropanol (CH3CHOHCH3)   Isopropanol (isopropyl alcohol) is widely used in organic synthesis, and considerable amounts are sold as “dry gas” to prevent separa- tion of water in the fuel tanks of automobiles. It is prepared by hydration of propy- lene derived from the cracking of petroleum.

 

n-Butanol (CH3CH2CH2CH2OH)   Normal butanol (n-butyl alcohol) is used to prepare butyl acetate, an excellent solvent. It is often referred to as “synthetic ba- nana oil” because of its odor which resembles natural banana oil, amyl acetate. Nor- mal butanol is prepared from cornstarch by a fermentation process utilizing a partic- ular microorganism, Clostridium acetobutylicum. Considerable amounts of acetone

 

 

 

and some ethanol and hydrogen are produced during the fermentation. The liquid wastes remaining after distillation of the desired products are classed as industrial wastes, and their treatment and ultimate disposal usually fall to the lot of the envi- ronmental engineer. They are similar in character to the residues from the produc- tion of ethanol but offer less promise of by-product recovery. While methanol, ethanol, and isopropanol are completely miscible with water, n-butanol has a some- what limited solubility in water.

 

Physical Properties of Alcohols

 

The short-chain alcohols are completely soluble in water due in part to the increased polarity caused by the hydroxyl group. As with alkanes and alkenes, as alcohol mol- ecular size increases, melting and boiling points increase while water solubility de- creases. The miscibility of C1–C3  alcohols makes them useful as cosolvents for re- mediation of contaminated subsurface environments (Sec. 3.8). Alcohols with more than 12 carbon atoms are colorless waxy solids and very poorly soluble in water. The physical constants of several alcohols are given in Table 5.4.

 

Nomenclature

 

The alcohols of commercial significance are usually called by their common names. The IUPAC system must be employed, however, to differentiate among isomers and to name the higher members, such as hexadecanol. In this terminology, the names of all alcohols end in -ol. The formulas, common names, and IUPAC names of several alcohols are given in Tables 5.4 and 5.5. In this system, the longest car- bon chain containing the hydroxyl group determines the name. The locations of alkyl groups and the hydroxyl group are described by number; e.g., isobutanol is described as 2-methyl-1-propanol.

 

 

Table 5.4 | Physical constants of normal primary alcohols

 

Name          IUPAC                                                                                                Calcd. of                name of                                                                           Sp. gr.,        no. of radical        alcohol             Formula        Mp,  C        Bp,  C        ۲۰ *        isomers

 

Methyl

Methanol

CH3OH

 ۹۷٫۶

۶۴٫۶

۰٫۷۹۱

۱

Ethyl

Ethanol

C2H5OH

 ۱۱۴٫۱

۷۸٫۲

۰٫۷۸۹

۱

Propyl

۱-Propanol

C3H7OH

 ۱۲۶٫۱

۹۷٫۲

۰٫۸۰۰۲۵

۲

Butyl

۱-Butanol

C4H9OH

 ۸۹٫۸

۱۱۷٫۷

۰٫۸۱۰

۴

Pentyl

۱-Pentanol

C5H11OH

 ۷۸٫۹

۱۳۷٫۹

۰٫۸۱۴

۸

Hexyl

۱-Hexanol

C6H13OH

 ۴۴٫۶

۱۵۷٫۶

۰٫۸۱۴

۱۷

Heptyl

۱-Heptanol

C7H15OH

 ۳۴

۱۷۶٫۴

۰٫۸۲۲

۳۹

Octyl

۱-Octanol

C8H17OH

 ۱۵٫۵

۱۹۵٫۱

۰٫۸۲۶۲۵

۸۹

Nonyl

۱-Nonanol

C9H19OH

 ۵

۲۱۳٫۳

۰٫۸۲۷

۲۱۱†

Decyl

۱-Decanol

C10H21OH

۶٫۹

۲۳۱٫۱

۰٫۸۳۰

۵۰۷

*Density of compound at 20 C (or at the temperature noted by superscript) over the maximum density of water, which is at 4 C.

†These numbers are for all the isomers of a given carbon content.

Source: D. R. Linde (ed.): “Handbook of Chemistry and Physics,” ۸۲nd ed., CRC Press LLC, Boca

Raton, 2001.

 

 

 

Table 5.5 | Nomenclature of alcohols

 

Formula                                              Common name                        IUPAC name

 

CH3OH C2H5OH CH3CH2CH2OH CH3

CHOH CH3

CH3CH2CH2CH2OH

CH3

CHCH2OH CH3

CH3

CHOH C2H5

(CH3)3COH


Methyl alcohol                          Methanol

Ethyl alcohol                             Ethanol

n-Propyl alcohol                       ۱-Propanol Isopropyl alcohol                      ۲-Propanol n-Butyl alcohol                         ۱-Butanol

Isobutyl alcohol                        ۲-Methyl-1-propanol

 

 

 

sec-Butyl alcohol                      ۲-Butanol

 

tert-Butyl alcohol                      ۲-Methyl-2-propanol

 

 

Polyhydroxy Alcohols

 

Those alcohols having two hydroxyl groups per molecule are known as glycols. The principal glycol of commercial significance is ethylene glycol (1,2-ethanediol), which is prepared from ethene. Ethene adds hypochlorous acid to form ethylene chlorohydrin.

H    H

 

CH2 ¨ CH2      HOCl  l


HC ˆ CH

 

(۵٫۱۵)

 

Cl   OH

Ethylene chlorohydrin

 

and treatment of the chlorohydrin with sodium bicarbonate produces ethylene glycol.

 

H2C ˆ CH2


NaHCO3


l NaCl


   CO2     H2C ˆ CH2

 

(۵٫۱۶)

 

 

Cl   OH

 

OH OH

Ethylene glycol

 

It is used extensively as a nonevaporative, radiator antifreeze compound.

Glycerol or glycerin is a trihydroxy alcohol (1,2,3-trihydroxypropane).

H2    H    H2

C ˆ Cˆ C

 

OH OH OH

Glycerol

 

It was formerly produced in large quantities in the soap industry through saponifica- tion of fats and oils. Presently, considerable amounts are produced by chemical syn- thesis. Glycerol is used in a wide variety of commercial products: foods, cosmetics, medicines, tobaccos, and so on. It is used for the manufacture of nitroglycerin, an important component of dynamite.

 

 

 

Chemical Reactions of Alcohols

 

Alcohols undergo two types of reactions of special interest.

 

Ester Formation    Alcohols react with acids, both inorganic and organic, to form esters. Inorganic hydroxy acids yield “inorganic” esters:

 

ROH     H2SO4 7 H2O     ROSO3H                            (۵٫۱۷) Organic acids yield organic esters:

ROH     R1CO2H 7 H2O     R1CO2R                            (۵٫۱۸) Organic esters are discussed in Sec. 5.6.

Oxidation    Most alcohols are readily oxidized by strong oxidizing agents and by many microorganisms. The product of the oxidation depends upon the class of alco- hol involved.

Primary alcohols are oxidized to aldehydes. The general equation is

 

 

 

 

۲

RCH2OH       ۱O2Primary alcohol


H

l H2O       RC¨ O

An aldehyde

 

(۵٫۱۹)

 

 

Care must be used in selecting the oxidizing agent, or the aldehyde may be oxidized still further to an acid.

Secondary alcohols are oxidized to ketones.

 

 

OH

 

 

۲

H3Cˆ C ˆCH3      ۱O2
O

 

l H2O      H3C ˆ C ˆ CH3

 

H

Isopropyl alcohol                                                      Acetone

(a ketone)

 

 

(۵٫۲۰)

 

 

The ketones are not easily oxidized and can usually be recovered completely.

Tertiary alcohols are not oxidized by ordinary agents in aqueous solution. When attacked by very strong oxidizing agents, they are converted to carbon diox- ide and water.

Microorganisms oxidize primary and secondary alcohols readily under aerobic conditions. The end products are carbon dioxide and water, but aldehydes and ke- tones are believed to exist as intermediates. Present evidence indicates that tertiary alcohols are very resistant to microbial degradation and are oxidized initially through terminal methyl groups, as with the hydrocarbons.

 

 

۵٫۴ | ALDEHYDES AND KETONES

 

Aldehydes are the oxidation products of primary alcohols (ROH). Ketones are the oxidation products of secondary alcohols.

 

 

 

Aldehydes

The oxidation of primary alcohols to aldehydes is as follows: H

 

۲

RCH2OH       ۱O2
l Rˆ C¨ O       H2O

H


(۵٫۲۱)

 

All aldehydes have the characteristic carbonyl group, —C ¨O. The general struc-

tural formula for an aldehyde is RˆCHO,  where R represents any alkyl group: CH3ˆ, C2H5ˆ, and so on.

Aldehydes can also be formed from unsaturated hydrocarbons by ozonation.

The hydrocarbons are first converted to an ozonide by ozone.

 

O

 

 

RCH ¨ CHR‘      O3 l

 

RCH

 

 

OˆO

 

CHR

 

An ozonide

 

The ozonides react readily with water to form aldehydes.

 

O


(۵٫۲۲)

 

 

RCH               CHR

OˆO

 

H2O  l

 

RCHO       RCHO       H2O2

 

(۵٫۲۳)

 

 

These reactions are particularly significant in air pollution, where aldehydes are formed when unsaturated hydrocarbons discharged in automobile exhausts combine with ozone catalytically produced by reactions of oxygen with sunlight in the presence of oxides of nitrogen. The aldehydes so formed cause eye irritation, one of the most serious problems associated with air pollution. The oxides of nitrogen required for cat- alyzing ozone formation are produced in great quantities during high-temperature combustion of fossil fuels in steam power plants and internal combustion engines. Automobile and truck engine exhaust gases are a particularly significant source be- cause of wide distribution at ground level where contact with human, animal, and plant life is most probable.

Although a wide variety of aldehydes can be formed from primary alcohols, only a few are of commercial importance. Aldehydes can also be produced by re- duction of carboxylic acids.

 

Formaldehyde    Formaldehyde is formed by the oxidation of methanol.

 

H

 

۲

CH3OH      ۱O2
l HC ¨ O      H2O

Formaldehyde

 

(۵٫۲۴)

 

 

It is used extensively in organic synthesis. It is very toxic to microorganisms, and, because of this property, it is used in embalming fluids and fluids used for the preservation of biological specimens. Industrial wastes containing formaldehyde were considered at one time to be too toxic for treatment by biological methods.

 

 

 

Through dilution of such wastes to reduce the concentration of formaldehyde below

۱۵۰۰ mg/L, it was found that microorganisms could use the formaldehyde as food and oxidize it to carbon dioxide and water. This experience has led to the concept of toxicity thresholds in industrial waste treatment practice. It means that below certain concentrations all materials are nontoxic. The completely mixed activated sludge system is designed to take advantage of this concept.

 

Acetaldehyde    Acetaldehyde is formed by the oxidation of ethanol.

 

H

 

 

۲

CH3CH2OH       ۱O2
l CH3 ˆ C¨ O      H2O

Acetaldehyde


(۵٫۲۵)

 

 

It is used extensively in organic synthesis. A major industrial use involves its con- densation with formaldehyde to produce pentaerythritol [C(CH2OH)4], an important intermediate for the production of a wide variety of products, including aldehyde resin paints. Development of a biological treatment process for the formaldehyde- bearing industrial wastes from the manufacture of pentaerythritol led to the concept of toxicity threshold mentioned earlier.

A wide variety of aldehydes are of commercial interest. The names and formu- las of several of them are given in Table 5.6. The IUPAC names of all aldehydes end in -al.

 

Ketones

 

Ketones are prepared by the oxidation of secondary alcohols.

 

 

H O

 

۲

Rˆ C ˆ R‘       ۱O2   l

H

 

O

 

Rˆ C ˆ R

Ketone

 

 

 

H2O

 

 

O

 

 

 

 

(۵٫۲۶)

 

 

Ketones have two alkyl groups attached to the carbonyl group,

 

ˆ C ˆ , while alde-

 

hydes have one R group and a hydrogen atom. The R groups in ketones may be the same or different.

 

Table 5.6 | Common aldehydes

 

Common name

IUPAC name

Formula

Formaldehyde

Methanal

HCHO

Acetaldehyde

Propionaldehyde Butyraldehyde Valeraldehyde Caproaldehyde Heptaldehyde Acrolein

Citral

Citronellal

Ethanal

n-Propanal

n-Butanal

n-Pentanal n-Hexanal n-Heptanal

CH3CHO C2H5CHO C3H7CHO C4H9CHO C5H11CHO C6H13CHO CH2¨CHCHO C9H15CHO C9H17CHO

 

 

 

Acetone    Acetone (dimethyl ketone) is the simplest ketone and is produced by the oxidation of isopropyl alcohol (2-propanol).

 

H

 

O

 

CH ˆ C ˆ CH

 

 

۱O2

 

O

 

l CH3 ˆ C ˆ CH3      H2O

 

 

(۵٫۲۷)

 

۳                            ۳           ۲

 

H

 

Acetone

 

 

Methyl ethyl ketone   Methyl ethyl ketone is prepared by the oxidation of 2-butanol.

 

H

 

O

 

CH ˆ C ˆ CH CH

 

 

۱O2

 

O

 

l CH3 ˆ C ˆ C2H5      H2O

 

 

(۵٫۲۸)

 

۳                            ۲         ۳           ۲

H

 

Methyl ethyl ketone

 

 

Ketones are used as solvents in industry and for the synthesis of a wide variety of products. The names of a few ketones are given in Table 5.7.

 

Chemical Properties of Aldehydes and Ketones

 

Aldehydes and ketones differ in ease of oxidation.

 

۱٫    Aldehydes are easily oxidized to the corresponding acids.

 

H

 

Rˆ C ¨ O

 

 

 

۲

۱O2

O

 

l Rˆ Cˆ OH

 

 

(۵٫۲۹)

 

 

۲٫    Ketones are more difficult to oxidize. This is because there is no hydrogen attached to the carbonyl group. As a result, further oxidation must initiate in one of the alkyl groups, the molecule is cleaved, and two or more acids are produced.

 

O

 

 

CH3CCH3      ۲O2   l

 

CO2      H2O     CH3COOH

 

(۵٫۳۰)

 

Acetone                                                                  Acetic acid

 

 

Table 5.7 | Common ketones

 

Common name                            IUPAC name

 

Acetone                                          Propanone Methyl ethyl ketone                       Butanone Diethyl ketone                                ۳-Pentanone Methyl propyl ketone                     ۲-Pentanone

Methyl isopropyl ketone                ۳-Methyl-2-butanone

n-Butyl methyl ketone                    ۲-Hexanone Ethyl propyl ketone                        ۳-Hexanone Dipropyl ketone                             ۴-Heptanone Dibutyl ketone                                ۵-Nonanone

 

 

 

In the case of acetone, carbon dioxide and acetic acid are formed. Theoret- ically, formic acid should be formed, but it is so easily oxidized that it is generally converted under the prevailing conditions to carbon dioxide and water. Higher ketones such as diethyl ketone (3-pentanone) are oxidized as follows:

 

H    O                                   O                        O

 

 

R ˆ C ˆ C ˆ R‘ 

 

H

 

 

۲

۳O2

l R ˆ C ˆ OH      Rˆ C ˆ OH

 

(۵٫۳۱)

 

 

Oxidation of both aldehydes and ketones to organic acids is accomplished read- ily by many microorganisms. However, since the organic acids serve as a good food supply, the ultimate end products under aerobic conditions are carbon dioxide and water.

 

 

۵٫۵ | ACIDS

 

Acids represent the highest oxidation state that an organic compound can attain. Further oxidation results in the formation of carbon dioxide and water, which are classed as inorganic compounds, and the organic compound is considered com- pletely destroyed.

 

 

CH4

 

l CH3OH  l

 

H2C ¨ O  l

 

HCOOH l

 

H2O

 

CO2

 

(۵٫۳۲)

 

Hydro- carbon


Alcohol


Aldehyde             Acid                   Products of complete oxidation

 

 

 

 

 

Organic acids typically contain the


O

 

ˆ C ˆ OH

 

 

group. This is called the car-

 

boxyl group and is commonly written ˆCOOH. Acids with one carboxyl group are known as monocarboxylic acids, and those with more than one are polycarboxylic acids. In addition, derivatives of phenol (Sec. 5.14) can act as acids. The acids may be saturated or unsaturated. Some contain hydroxy groups within the molecule.

 

Saturated Monocarboxylic Acids

 

A wide variety of saturated monocarboxylic acids occur in nature as constituents of fats, oils, and waxes. Unsaturated acids are also found in these materials, and, as a result, both types are commonly known as fatty acids. The majority of the fatty acids derived from natural products have an even number of carbon atoms and usu- ally have a straight-chain or normal structure.

 

Physical Properties    The first nine members, C1 to C9, are liquids. All the others are greasy solids. Formic, acetic, and propionic acid have sharp penetrating odors;

 

 

 

the remaining liquid acids have disgusting odors, particularly butyric and valeric. Butyric acid gives rancid butter its characteristic odor. Industrial wastes from the dairy industry must be treated with considerable care to prevent formation of bu- tyric acid and consequent odor problems. The “volatile acids” (C1  to C5) are quite soluble in water.

The names, formulas, and physical constants of the important saturated acids are given in Table 5.8. All the acids are considered weak acids from the viewpoint of ionization. Formic acid is the strongest of all.

 

Nomenclature    The common names are usually used for most of the acids, ex- cept for those with 7, 8, 9, and 10 carbon atoms. The IUPAC names are given in Table 5.8. In naming derivatives of acids, the IUPAC system is frequently aban- doned for a system using Greek letters to identify the carbon atoms. In this system the carboxyl group is the reference point, and carbon atoms are numbered from it as follows:

۵         ۴         ۳         ۲           ۱

CH3CH2CH2CH2  COOH

 

The carbon atom next to the carboxyl group is alpha, the next beta, then gamma, delta, and so on. The terminal carbon atom is also referred to as being in the omega position. The    -amino acids are particularly important compounds and are dis- cussed in Sec. 5.22.

 

Unsaturated Monocarboxylic Acids

 

The principal unsaturated monocarboxylic acids are as follows:

 

Acrylic Acid (CH2¨CHCOOH)    Acrylic acid is used extensively because of its ability to polymerize, a characteristic of many compounds with unsaturated link-

 

 

 

Table 5.8 | Physical constants of some normal monocarboxylic acids

 

Common name

IUPAC

name

Formula

Mp,

 C

Bp,

 C

Sp. gr.,

۲۰ *

pKa at 25

Formic

Methanoic

HCOOH

۸٫۳

۱۰۱

۱٫۲۲۰

۳٫۷۵

Acetic

Ethanoic

CH3COOH

۱۶٫۶

۱۱۷٫۹

۱٫۰۴۵۲۵

۴٫۷۵۶

Propionic

Propanoic

C2H5COOH

 ۲۰٫۷

۱۴۱٫۱

۰٫۹۹۳

۴٫۸۷

Butyric

Butanoic

C3H7COOH

 ۵٫۷

۱۶۳٫۷

۰٫۹۵۸

۴٫۸۳

Valeric

Pentanoic

C4H9COOH

 ۳۴

۱۸۶٫۱

۰٫۹۳۹

۴٫۸۳۲۰

Caproic

Hexanoic

C5H11COOH

 ۳

۲۰۵٫۲

۰٫۹۲۷

۴٫۸۵

Enanthic

Heptanoic

C6H13COOH

 ۷٫۵

۲۲۲٫۲

۰٫۹۱۸

۴٫۸۹

Caprylic

Octanoic

C7H15COOH

۱۶٫۳

۲۳۹

۰٫۹۱۱

۴٫۸۹

Pelargonic

Nonanoic

C8H17COOH

۱۲٫۳

۲۵۴٫۵

۰٫۹۰۵

۴٫۹۶

Capric

Decanoic

C9H19COOH

۳۱٫۹

۲۶۸٫۷

۰٫۸۸۶۴۰

Palmitic

Hexadecanoic

C15H31COOH

۶۳٫۱

۳۵۱٫۵

۰٫۸۵۳۶۲

Stearic

Octadecanoic

C17H35COOH

۶۸٫۸

۲۳۲

۰٫۹۴۱

*Density of compound at 20 C (or at the temperature noted by superscript) over the maximum density of water, which is at 4 C.

Source: D. R. Linde (ed.): “Handbook of Chemistry and Physics,” ۸۲nd ed., CRC Press LLC, Boca Raton, 2001.

 

 

 

ages. Derivatives of the acid are used to form colorless plastics such as Lucite and

Plexiglas.

 

Oleic Acid [CH3(CH2)7CH¨CH(CH2)7COOH]

 

Linoleic Acid [CH3(CH2)4CH¨CHCH2CH¨CH(CH2)7COOH] Linolenic Acid [CH3(CH2CH¨CH)3CH2(CH2)6COOH]

Oleic, linoleic, and linolenic acids are normal constituents of the glycerides of

most fats and oils. A glyceride is the ester (Sec. 5.6) formed by combining glycerol (Sec. 5.3) with these acids. Oleic acid is considered to be an essential acid in the diet of humans and animals. Linoleic and linolenic acids as glycerides are important constituents of linseed and other drying oils. Their value for this purpose is depen- dent upon the multiple double bonds that they possess.

 

Chemical Properties of Acids    The chemical properties of acids are determined largely by the carboxyl group. All form metallic salts that have a wide range of commercial use. In addition, the unsaturated acids have chemical properties charac- terized by the double bond, as described under unsaturated hydrocarbons in Sec.

۵٫۲٫ The unsaturated acids may be reduced with hydrogen to give corresponding saturated acids.

Organic acids serve as food for many microorganisms and are oxidized to car- bon dioxide and water. Ease and rate of oxidation are believed to be enhanced by the presence of unsaturated linkages. The rate of biological attack on high-molecular- weight fatty acids is often limited by their solubility in water. This is a particular problem in sludge digesters where fatty materials tend to float and segregate them- selves in a scum layer.

 

Polycarboxylic Acids

 

The most important of the polycarboxylic acids are those that have two carboxyl groups, one on each end of a normal chain of carbon atoms. The most important acids are listed in Table 5.9.

Adipic acid is of some interest because it is used in the manufacture of nylon

fiber and may be expected to occur in the industrial wastes of that industry.

 

 

Table 5.9 | Dicarboxylic acids

 

Name                       Formula

Oxalic                       (COOH)2

Malonic                     CH2(COOH)2

Succinic                    (CH2)2(COOH)2

Glutaric                     (CH2)3(COOH)2

Adipic                       (CH2)4(COOH)2

Pimelic                      (CH2)5(COOH)2

Suberic                      (CH2)6(COOH)2

 

 

 

Hydroxy Acids

 

Hydroxy acids have OH groups attached to the molecule other than in the carboxyl group. Thus, they act chemically as acids and as alcohols. A number of the hydroxy acids have special names. Some examples are

 

HOCH2COOH                      Hydroxyacetic acid, glycolic acid CH3CHOHCOOH                 -Hydroxypropionic acid, lactic acid HOCH2CH2COOH                 -Hydroxypropionic acid, hydracrylic acid HOCH2CH2CH2COOH          -Hydroxybutyric acid

Lactic acid,   -hydroxypropionic acid, is of special interest since it is formed during bacterial fermentation of milk and therefore is a normal constituent of indus- trial wastes from the dairy industry. Whey from cheese making contains consider- able amounts of lactic acid. It is the principal acid in sauerkraut juice and prevents spoilage of the sauerkraut.

Lactic acid is also of interest because it possesses the property of optical activ- ity. One form of lactic acid is levorotatory, which rotates polarized light in the counterclockwise direction (levo means “to the left”). The other form is dextrorota- tory, which rotates polarized light in a clockwise fashion (dextro means “to the right”). In the past, l was used to name the levorotatory form while d was used to name the dextrorotatory form. Current convention is to use a minus sign (   ) for the l form and a plus sign (   ) for the d form.

Many organic compounds are optically active. In order to be optically active, a compound must generally possess at least one asymmetric carbon atom. An asym- metric carbon atom is one having four dissimilar groups attached to it, as follows:

 

a

dˆ C ˆ b c

 

Such compounds are not superposable on their mirror images. Many other objects lack symmetry and cannot be superposed on their mirror image. For example, the left and right hands are mirror images of each other, but cannot be made to coincide at every point with each other. Objects, including molecules, that are nonsuperposable on their mirror image are said to be chiral. With molecules, the asymmetric carbon atom is termed the chiral center. Chiral compounds may have more than one chiral center.

The different chiral forms of a molecule are called enantiomers. Chiral compounds are of environmental significance in that their enantiomers can differ in biological activity or biodegradability. The most sensational case is that of the drug thalidomide. The (   ) enantiomer was employed as a sedative and antinausea drug around 1960. As is the case with most commercially available chiral molecules, thalidomide was sold as a racemic mixture [approximately equal amounts of the (   ) and (   ) enantiomers; such mixtures carry the symbol (   )]. Unfortunately, the (   ) enantiomer caused serious

birth defects in children born to pregnant women taking the drug during pregnancy.

 

 

 

Environmental engineers and scientists have recently begun to use the properties of chiral molecules to better understand the fate of organic pollutants.4

Lactic acid has one chiral center, and two optically active enantiomers are possible.

 

 

COOH H ˆ C ˆ OH

CH3

 

COOH HOˆ C ˆ H

CH3

 

D-(–)-Lactic Acid5                      L-(+)-Lactic Acid5

 

It is the L form of lactic acid that is commonly produced in living organisms.

 

 

Hydroxy Polycarboxylic Acids

 

There are several hydroxy polycarboxylic acids.

 

 

H2CCOOH

 

 

 

COOH HCOH

 

HOCCOOH H2CCOOH


. H2O


HOCH COOH

 

Citric acid                            L-(+)-Tartaric acid

 

Tartaric acid occurs in many fruits, especially grapes, and is present in canning and winery wastes. Citric acid is the major acid of all citrus fruits: oranges, lemons, limes, and grapefruit. It is, of course, a major component of the liquid wastes of the citrus industry.

 

 

۵٫۶ | ESTERS

 

Esters are compounds formed by the reaction of acids and alcohols, similar to the reactions of acids and bases to form salts in inorganic chemistry. The reaction be- tween low-molecular-weight organic acids and alcohols is never complete. Hydrol- ysis occurs and a reversible reaction results. The reaction may be represented by the general equation

 

 

RCOˆ OH      H ˆ OR1  .


H2O     RCOOR1


(۵٫۳۳)

 

 

 

۴J. J. Ridal et al., Enantiomers of   -Hexachlorocyclohexane as Tracers of Air-Water Gas Exchange in

Lake Ontario, Env. Sci. Tech., 31: 1940–۱۹۴۵, ۱۹۹۷٫

۵The symbols D and L are used to describe the configuration of the groups surrounding the asymmetric carbon and are not to be confused with the     or     designations. Additional configuration information is conveyed by the use of R and S symbols. Details concerning this terminology are beyond the scope of this text. The reader should refer to the organic chemistry texts listed at the end of this chapter for the finer points of chiral nomenclature.

 

 

 

 

The general formula of an ester is

 

 

O

 

Rˆ C ˆ O ˆ R

 

 

A wide variety of esters are used in chemical manufacturing. Most esters have highly pleasing odors. Butyl acetate smells like banana oil (amyl acetate) and is used for solvent purposes. Many esters are used in flavoring extracts and perfumes.

Esters have been used to some extent as immiscible solvents in the separation and purification of antibiotics. Considerable quantities often reach the sewer system and become an industrial waste problem. Enzymes liberated by many microorgan- isms hydrolyze esters to yield the corresponding acid and alcohol.

O

 

 

Rˆ C ˆ OR

 

HOH

 

ˆenz¶ymle

 

RCOOH      Rˆ OH

 

(۵٫۳۴)

 

 

The acid and alcohol serve as bacterial food and are oxidized to carbon dioxide and water, as discussed in Secs. 5.3 and 5.5.

 

 

۵٫۷ | ETHERS

 

Ethers are formed by treatment of alcohols with strong dehydrating agents. In the reaction, one molecule of water is removed from two molecules of alcohol.

 

 

RO H      HO R

 

dˆehˆydˆr¶atinlg

agent

 

R ˆ OˆR

Ether


   H2O


(۵٫۳۵)

 

 

The two fragments of the alcohol join to form an ether. The alkyl groups are joined  through  an  oxygen  atom;  thus,  a  carbon-to-oxygen-to-carbon  bond,

 

ˆCˆ O ˆC ˆ , is established.

 

Ethers are used widely as solvents. The low-molecular-weight ethers are highly flammable. When left exposed to air, they are prone to form peroxides that are ex- tremely explosive, particularly when recovery by distillation is practiced and the distillation is allowed to go to dryness. Diethyl ether has been used widely as an anesthetic.

Ethers are generally resistant to biological oxidation. Fortunately, most are rel- atively insoluble in water and can be separated from industrial wastes by flotation or decantation procedures.

An important ether is methyl tert-butyl ether (MTBE).

 

CH3

 

H3Cˆ O ˆC ˆ CH3

 

CH3

 

 

 

MTBE was first used in the late 1970s as an octane enhancer when lead additives to gasoline were being phased out. More recently it has been added to gasoline as a fuel oxygenate to help reduce carbon monoxide emissions from gasoline combustion. MTBE is very soluble in water, volatile, not strongly sorbed to particulate matter, and relatively nonbiodegradable. Thus, upon release to the environment, it is very mobile. Through leaking storage tanks, pipelines, and other uncontrolled releases to the environment, MTBE has been found in a large number of surface waters and groundwaters. Although the health effects associated with MTBE exposure are not yet completely known, action levels as low as 20   g/L

have been set due to taste and odor considerations.6 Because of these problems,

there is a proposed ban on the use of MTBE as a fuel additive. Ethanol is an alternative for MTBE as a fuel additive. However, it has its own set of potential problems (Sec. 3.8).

 

 

۵٫۸ | ALKYL HALIDES AND OTHER HALOGENATED ALIPHATIC COMPOUNDS

 

The alkyl halides are aliphatic compounds in which a halogen is attached to an alkyl carbon. These are to be distinguished from other halogenated aliphatics where the halogen is attached to a double-bonded carbon. Both types of compounds are dis- cussed here. Halogenated aliphatic compounds are used extensively in organic syn- thesis, and a few of them have important industrial uses. Many are toxic to humans and are of significant environmental concern. They are among the most frequently found hazardous chemicals at abandoned waste sites, refuse disposal areas, and in- dustrial and municipal wastewaters. The U.S. federal government has set drinking water maximum contaminant levels (MCLs) for some of these compounds and is proposing MCLs for others. These are listed in Table 34.1. Most of the halogenated aliphatic compounds are volatile and thus may be significant air pollutants.

 

Simple Alkyl Halides

 

The alkyl halides are of great value in organic synthesis because they react with potassium cyanide to form compounds with an additional carbon atom.

 

 

R .  I      K . CN l

 

KI      R . CN

A nitrile

(alkyl cyanide)

 

(۵٫۳۶)

 

 

The nitrile formed can be hydrolyzed to an acid and then reduced to an alcohol, if desired. The alcohol can be converted to an alkyl halide and the process repeated. In this manner the organic chemist can increase the length of carbon-chain compounds one atom at a time.

 

 

 

۶R. Johnson, et al., MTBE—To What Extent Will Past Releases Contaminate Community Water Supply

Wells, Env. Sci. Tech., 34(9): 210A–۲۱۷A (2000).

 

 

 

Methyl chloride (CH3Cl), also called chloromethane, and ethyl chloride (C2H5Cl), also called chloroethane, were used extensively as refrigerants in the past. Chloroethane is used in the manufacture of tetraethyl lead, great quantities of which were previously used in the production of high-octane, antiknock gasolines.

 

 

۴۰–۶۰

۴C2H5Cl     ۴NaPb (alloy) ¶¶l 4NaCl     ۳Pb     (C2H5)4Pb

Tetraethyl

lead

 

(۵٫۳۷)

 

 

During combustion the lead is converted to lead oxide and is emitted in the exhaust gases, creating a lead pollution problem. The lead also fouls catalytic devices being used to reduce the quantity of unburned fuel discharged to the atmosphere. For these reasons use of leaded gasoline has been eliminated in the United States and is being eliminated in Europe.

Vinyl chloride (CH2¨CHCl), also called monochloroethene, is used in large quantities to produce a wide variety of polyvinylchloride (PVC) products. It is also formed biologically through reduction of polyhalogenated ethenes. Through this route it is frequently found in contaminated groundwaters and in gases emanating from sanitary landfills. This compound is very volatile and is a known carcinogen. A drinking water MCL of 2   g/L has been established (Table 34.1). Because of its volatility, vinyl chloride is a potentially significant air pollutant.

 

Polyhalogen compounds

 

A wide variety of polyhalogen compounds are used for industrial purposes. Because of a variety of public and environmental health problems, use of several of these compounds is being discouraged. The challenge is to find environmentally friendly substitutes.

 

۱,۲-Dibromoethane  This compound has also been called ethylene dibromide (EDB), although it is not actually an alkene. 1,2-Dibromoethane is formed from ethene by addition of bromine.

 

H   H                               H    H

 

HC¨ CH      Br2   l


HCˆ CH


(۵٫۳۸)

 

Br   Br

۱,۲-Dibromoethane

 

۱,۲-Dibromoethane has many industrial uses and has been used as a pesticide in agricultural areas and as an ingredient in ethyl gasoline. In the early 1980s, it was discovered in fumigated fruits and vegetables, and several grain products, causing some commercial products to be removed from stores. It is a commonly detected groundwater contaminant. Because of its potential health effects, a drinking water standard of 0.05   g/L has been established (Table 34.1).

 

Dichloromethane (CH2Cl2)   Dichloromethane, sometimes called methylene chlo- ride, is a volatile liquid that has been used as an industrial solvent, in paint strippers, to decaffeinate coffee, and in the making of polyurethane products. It can be pro-

 

 

 

duced from the chlorination of methane, as can all the chlorinated methanes. Dichloromethane is quite soluble in water, more dense than water, and is fairly volatile. A drinking water MCL of 2   g/L has been established.

 

Chloroform (CHCl3)    Chloroform (trichloromethane) was one of our first anes- thetics (1847) and was widely used until about 1920. It is used in industry as a sol- vent for oils, waxes, and so on. It is nonflammable. Chloroform has been found pre- sent in microgram per liter to milligram per liter concentrations in drinking water supplies as a result of chlorination for disinfection. It is formed through reaction of chlorine with organics of biological origin commonly present in natural waters. Be- cause it is a potential carcinogen, an MCL in drinking water has been established for the sum total of chloroform and other trihalomethanes (THMs) of 80   g/L.

 

Carbon  Tetrachloride  (CCl4)    Carbon  tetrachloride  (tetrachloromethane)  has been widely used as a fire extinguisher in small units (Pyrene) and as a solvent. It is a toxic compound, and its use should be restricted to well-ventilated areas. Its use as a fire extinguisher is fraught with some danger. In contact with hot iron and oxygen, it is converted to phosgene (COCl2), a highly toxic gas. For this reason, trained fire fighters use other types of fire-fighting equipment. An MCL for carbon tetrachloride has been established at 5   g/L.

 

Halogenated Ethanes    Several halogenated ethanes, particularly some chlorinated ethanes, are of environmental significance. For the most part, these compounds are used as industrial solvents. They are volatile, heavier than water, and have varying solubilities in water. Some are important because they are products formed during the  transformation  (chemical  and  biological)  of  other  halogenated  compounds. These aspects are further discussed in Sec. 5.34 and Chap. 6.

۱,۱,۱-Trichloroethane (CCl3CH3) is a widely used industrial solvent and is a commonly detected groundwater contaminant. 1,2-Dichloroethane (CH2ClCH2Cl) is also an industrial solvent. Drinking water MCLs are in place for both of these compounds (200    g/L and 5    g/L, respectively), and for 1,1,2-trichloroethane (CHCl2CH2Cl), another industrial solvent (5   g/L).

 

Halogenated Ethenes   As with the halogenated ethanes, it is the chlorinated ethenes that are of most environmental significance. They are volatile solvents, heavier than water, and have varying solubilities in water. Transformation reactions can convert parent chlorinated ethenes into other ethenes. A classical example is the reductive dechlorination of trichloroethene to dichloroethene, and then to vinyl chloride.

Trichloroethene (TCE: CCl2¨CHCl), also called trichloroethylene, is a non- flammable, volatile liquid that has been used as an industrial solvent and degreaser, a dry-cleaning solvent, and in many household products. In the past it was used to decaffeinate coffee. It is one of the most commonly found groundwater pollutants.

۱,۱-Dichloroethene (CCl2¨CH2), also called 1,1-dichloroethylene, is also a solvent and has been found in the environment as a transformation product of both TCE and

۱,۱,۱-trichloroethane. There are drinking water MCLs for both TCE (5    g/L) and

۱,۱-dichloroethene (7   g/L).

 

 

 

The chlorinated ethenes with the formula CHCl¨CHCl are examples of a spe- cial type of isomerism called geometric isomers. In cis-1,2-dichloroethene the chlo- rines are on the same side of the molecule while in trans-1,2-dichloroethene the chlorines are on the opposite side of the molecule:

 

 

Cl             Cl

C ¨ C

H               H

cis-1,2-Dichloroethene

 

H              Cl

C ¨ C

Cl              H

trans-1,2-Dichloroethene

 

 

It is important to note that the physical properties can be different for geometric iso- mers and thus their behavior in the environment and in engineered reactors can be different. For example, the following are given for the cis and trans isomers of 1,2- dichloroethene (values are for 20 C except for boiling point):

 

 

Property

cis isomer

trans isomer

Boiling point,  C

۶۰٫۳

۴۷٫۵

Density, g/cm3

۱٫۲۸۳۷

۱٫۲۵۶۵

Vapor pressure, atm

۰٫۲۴

۰٫۳۷

Henry’s constant, atm/M

۷٫۴

۶٫۷

Water solubility, mg/L

۳۵۰۰

۶۳۰۰

 

Both cis- and trans-1,2-dichloroethene have been found in the environment as bio- logical transformation products of TCE. Drinking water MCLs have been estab- lished for both (70 and 100   g/L, respectively).

Tetrachloroethene  (CCl2¨CCl2),  also  called  perchloroethene  (PCE),  is  a widely used industrial solvent and is a commonly found groundwater pollutant. It is a regulated drinking water contaminant with an MCL of 5   g/L.

 

Dibromochloropropane (DBCP)    Although there are nine possible isomers of di- bromochloropropane (C3H5Br2Cl), it is 1,2-dibromo-3-chloropropane (CH2BrCH BrCH2Cl) that is most environmentally significant. This isomer has been widely used as a pesticide and is frequently detected in groundwater. It is thought to cause cancer and adverse reproductive outcomes, and for these reasons a drinking water MCL has been established (0.2   g/L).

 

Chlorofluorocarbons  (CFCs)    Chlorofluorocarbon  compounds  are  one-  and two-carbon compounds containing chlorine and fluorine. They are sometimes called by their trade name, Freons. For many years these compounds have been widely used as refrigerants, solvents, and aerosol propellants. They were used because  of  their  stability  and  their  nonflammable  and  nontoxic  properties. The most commonly used CFCs are CCl3F (CFC-11), CCl2F2  (CFC-12), CCl2FCClF2 (CFC-113), CClF2CClF2 (CFC-114), and CClF2CF3 (CFC-115). Re- cently, CFCs have been shown to be involved in the destruction of the stratos-

 

 

 

pheric ozone layer, the “ozone hole” effect, via the following reactions with ul- traviolet radiation.

 

CF2Cl2    h  l Cl    CF2Cl

(Cl atom)

Cl     O3 l ClO     O2

(ozone)  (free radical chlorine oxide)

ClO     O l Cl     O2

(O atom)

O     O3 l O2    O2

 

Chlorofluorocarbons are also known to be greenhouse gases. Because of their role in ozone destruction and the greenhouse effect, manufacture and use of chlorofluo- rocarbons is being eliminated worldwide.

 

Haloacetic Acids (HAA)    Another important group of halogenated aliphatic com- pounds is the haloacetic acids. They are produced during chlorination of drinking waters that contain natural organic matter. An MCL of 60    g/L has been estab- lished for the sum of five haloacetic acids (HAA5), mono-, di-, and trichloroacetic acids and mono- and dibromoacetic acids.

 

 

H

Hˆ C ˆ COOH Cl

 

H

Clˆ C ˆ COOH Cl

 

Cl

Clˆ C ˆ COOH Cl

 

Monochloroacetic acid        Dichloroacetic acid           Trichloroacetic acid

 

Perfluorinated Compounds    Another class of halogenated compounds of emerg- ing concern are the perfluorinated compounds. Here, all CˆH bonds are replaced by CˆF bonds. These bonds are very stable and tend to persist in the environment. Perfluorinated compounds have been used in fabric protectors and in a variety of products ranging from paper plates to semiconductor coatings to airplane hydraulic fluid. A particular group of these compounds that are of emerging concern are those that either use perfluoro-octane-sulfonate (PFOS) in their manufacture or break down to this compound.

 

 

F    F     F    F

 

F    F     F    F

 

 

F ˆ Cˆ C ˆ Cˆ C ˆ Cˆ C ˆ Cˆ Cˆ SO3H

 

 

F    F     F    F

 

F    F     F    F

 

Perfluoro-octane-sulfonate (PFOS)

 

These compounds are known to bioaccumulate and are being found in blood sam- ples from humans and animals far from their known sources.7  Laboratory toxicity

 

۷J. P. Giesy and K. Kannan, Global Distribution of Perfluorooctane Sulfonate in Wildlife, Env. Sci. Tech., 35: 1339–۱۳۴۲ (۲۰۰۱).

 

 

 

studies are showing that these compounds are toxic, causing a variety of effects in the livers of test animals, and perhaps carcinogenic.8,9

 

 

۵٫۹ | SIMPLE COMPOUNDS CONTAINING NITROGEN

 

The simple aliphatic compounds containing nitrogen are of three types: amines, amides, and nitriles (cyanides). Other nitrogen-containing compounds of environ- mental significance include nitrosamines and isocyanates.

 

Amines

 

The amines are alkyl derivatives of ammonia. They are of three types: primary, sec- ondary, and tertiary.

 

 

R

Rˆ NH2                       NH

 

R

NˆR

 

 

 

Primary amine


R‘                R

Secondary10

amine

 

Tertiary10

amine

 

 

In primary amines, one hydrogen atom of ammonia is replaced by an alkyl group such as CH3ˆ, C2H5ˆ, and so on. In secondary amines, two hydrogen atoms of ammonia are replaced by alkyl groups, and in tertiary amines, all three hydrogens are replaced. The amines, like ammonia, are all basic in reaction. The basicity in- creases from primary to tertiary.

The amines are found in certain industrial wastes, particularly those from the fish and beet-sugar industries. It is well known that deamination reactions (removal of ammonia) are easily accomplished with primary amines, and somewhat less eas- ily with secondary amines.

Tertiary amines combine with alkyl halides to form quaternary ammonium salts as follows:

R                             R        +

_

 

RˆN    RCl l

 

R

 

RˆNˆR

 

R


   Cl


(۵٫۳۹)

 

 

The compounds formed are actually chloride salts and ionize to form a quaternary ammonium ion and a chloride ion. The quaternary ammonium salts have bacteri- cidal properties that can be enhanced by the proper choice of the R groups. They

 

 

۸R. Renner, Growing Concern Over Perfluorinated Chemicals, Env. Sci. Tech., 35: 154A–۱۶۰A (2001).

۹R. Renner, Perfluorinated Compounds Linked to Carcinogenicity in Vitro,” Env. Sci. Tech., 35: 180A (2001).

۱۰R, R , R  represent alkyl groups. They may all be different or all alike.

 

 

 

are therefore of interest to public health professionals, who find them useful as disinfecting agents in food- and beverage-dispensing establishments. They are also used as disinfectants in the laundering of babies’ diapers to control infections of bacteria responsible for the rapid hydrolysis of urea. Solutions of the quater- nary ammonium salts are sold for disinfecting purposes under a variety of trade names.

 

Amides

 

The amides may be considered as being derived from organic acids and ammonia under special conditions. The ordinary reaction between ammonia and an organic acid, of course, produces an ammonium salt.

 

 

 

۴

RCOOH   NH3  l RCOO     NH

(۵٫۴۰)

 

 

Under special conditions, an amide results.

 

O                                               O

 

 

Rˆ C ˆ OH      H ˆ NH2

 

l Rˆ C ˆ NH2      H2O

Amide

 

(۵٫۴۱)

 

 

Amides are of considerable significance to organic chemists in synthetic work. When they are caused to react with a halogen (Hofmann reaction), an atom of carbon is lost from the amide, and an amine with one less carbon atom is formed.

CH3CONH2     Br2     ۴NaOH l 2NaBr     Na2CO3     ۲H2O     CH3NH2              (۵٫۴۲) This constitutes a method of reducing a length of a carbon chain by one atom.

Amides as such are of little importance to the environmental engineer, but the

O

 

 

amide group   ˆ C ˆ NH2

 

 

H

is related to an important group of compounds con- O

 

 

taining the peptide linkage  ˆ C ˆNˆ   , as discussed in Sec. 5.22.

 

Urea,

 

 

NH2

C¨O NH2

 

 

is an amide of considerable importance because of its many commercial uses and because it is a normal constituent of urine. It is a constituent of many agricultural fertilizers and is used in the manufacture of synthetic resins.

Although urea was originally considered an organic compound and its acciden- tal production from ammonium cyanate by Wöhler is considered to have initiated the study of organic chemistry, it is in effect an inorganic compound since it cannot be used by saprophytic bacteria as a source of energy. In aqueous solutions contain-

 

 

 

ing soil bacteria, urea is hydrolyzed to carbon dioxide and ammonia. These com- bine to form ammonium carbonate in the presence of water.

 

NH2

 

C¨O     H2O NH2


bact. eˆnz¶ymles


CO2      ۲NH3


(۵٫۴۳)

 

and                                CO2     ۲NH3     H2O 7 (NH4)2CO3                                            (۵٫۴۴) The penetrating odor at latrines, privies, and some urinals is due to bacterial infec-

tions and their action on urea with subsequent release of free ammonia to the atmos- phere. The use of disinfectants will control the decomposition of urea and, thereby, control odors.

 

Nitriles

 

Nitriles, or organic cyanides, are important compounds of industry. They have the general formula RˆCN, and the R group may be saturated or unsaturated. The names and formulas of a few nitriles of industrial importance are given in Table 5.10.

The nitriles are used extensively in the manufacture of synthetic fibers and can be expected to be present in industrial wastes of that industry. Some are quite toxic to microorganisms.

 

Nitrosamines

 

Nitrosamines, or N-nitroso compounds, have the general formula R2ˆNˆN¨O and are environmentally significant because they have been shown to cause cancer. They can be formed in the environment through the action of microorganisms and have been detected in beer and whiskey as well as a variety of foods. In the past these compounds had been used as industrial solvents. Of particular recent concern is N-nitrosodimethylamine (NDMA).

 

 

 

O ¨Nˆ N

 

CH3

 

 

CH3

 

N-Nitrosodimethylamine (NDMA)

 

NDMA has been used in rocket fuel production and for a variety of industrial purposes. It has been found in a variety of foods and can also be formed naturally

 

 

Table 5.10 | Important nitriles

 

Name as nitrile

Name as cyanide

Formula

Acetonitrile Propionitrile Succinonitrile Acrylonitrile

Methyl cyanide

Ethyl cyanide

Vinyl cyanide

CH3ˆCN CH3ˆCH2ˆCN CNˆCH2ˆCH2ˆCN CH2¨CHˆCN

 

 

 

in the environment.11 It is classified as a “probable” human carcinogen. NDMA has been detected in surface waters and treated wastewaters and drinking waters.

Recent evidence suggests that NDMA can be formed as a disinfection by-product during chloramination with dimethylamine (DMA) as the precursor.12

 

Isocyanates

 

Isocyanates have the general formula RˆN¨C¨O and are widely used industrial chemicals. Methyl isocyanate (CH3ˆN¨C¨O) was the material involved in the Bhopal, India, chemical plant explosion in which over 1000 people were killed and many thousands were affected to various degrees. The volatility of these com- pounds makes them potent potential air pollutants.

 

۵٫۱۰ | CYCLIC ALIPHATIC COMPOUNDS

 

A number of cyclic aliphatic hydrocarbons are known. Many of these occur in pe- troleum and are known as naphthenes.

 

 

 

 

CH2

CH2ˆ CH2

 

 

Cyclopropane

 

CH2

CH2      CH2

 

CH2      CH2

 

 

Cyclopentane

 

CH2

CH2      CH2

 

CH2      CH2

CH2

Cyclohexane

 

 

They are characterized by having two atoms of hydrogen attached to each carbon in the ring; i.e., they are saturated.

A wide variety of cyclic alcohols and ketones are known. Examples are cyclo- hexanol and cyclohexanone.

 

 

CH2

 

CH2

 

CH2      CHOH


CH2


C¨ O

 

 

CH2      CH2

CH2

Cyclohexanol

 

CH2      CH2

CH2

Cyclohexanone

 

 

۵٫۱۱ | MERCAPTANS OR THIOALCOHOLS

 

Mercaptans or thioalcohols are aliphatic compounds that contain sulfur. They have a structure similar to alcohols, except that oxygen is replaced by sulfur.

 

 

ROH

Alcohol

 

RSH

Mercaptan

 

 

۱۱M. Alexander, “Biodegradation and Bioremediation,” ۲nd ed., Academic Press, San Diego, 1999.

۱۲I. Najm and R. R. Trussell, NDMA Formation in Water and Wastewater, J. American Water Works

Assoc., 93(2): 92–۹۹ (۲۰۰۱).

 

 

 

Mercaptans are noted for their disagreeable odor and are found in certain industrial wastes, particularly those from the pulping of wood by the Kraft or sulfate process. They are considered to be quite toxic to fish. The odor of skunks is largely due to butyl mercaptan.

 

 

AROMATIC COMPOUNDS

 

۵٫۱۲ | INTRODUCTION

 

The aromatic organic compounds are all ring compounds or have cyclic groups of aromatic nature in their structure. The carbon atoms in these ring compounds have only one covalent bond, in contrast to those in aliphatic compounds with two.

 

C                               C

C        C                    C         C

 

ˆ C         C ˆ

C         C                         C

C

 

 

Aliphatic ring


Aromatic ring

 

 

The simplest aromatic ring is made up of six carbon atoms and is known as the benzene ring. Benzene (C6H6) is known as the parent compound of the aromatic se- ries. Hydrocarbons based on the benzene ring as a structural unit are also called arenes. The benzene ring is usually represented by the Kekule formula.

 

H C

HC        CH

 

HC         CH C

H

 

Kekule benzene formula


Simplified formulas

 

 

This formula shows double bonds between alternate carbon atoms in the ring. The double bonds, however, are not like those in the aliphatic series. For example, halo- gens will not add to such bonds. For purposes of simplicity, most chemists represent the benzene ring as one of the simplified formulas shown.

 

Nomenclature

 

It is important to note that carbon atoms are not shown in the simplified benzene formula. Also, each carbon atom in a ring is like all others, and therefore, when sub- stitution occurs on one carbon atom, the same compound is formed as though sub-

 

 

 

stitution had occurred on any of the other five carbon atoms. Thus, for mono- chlorobenzene (C6H5Cl) there is only one compound, no matter how the structural formula is written.

 

Cl

 

or                          or

Cl                                                Cl

 

When substitution occurs on two or more carbon atoms of a benzene ring, it be- comes necessary to establish some system of nomenclature. Two systems are used.

 

X                    X                    X

۱        X              ۱                                    ۱

۶        ۲                           ۶        ۲                          ۶        ۲

۵        ۳                           ۵        ۳                          ۵        ۳

۴                                     ۴        X              ۴

X

 

۱,۲- or ortho

placement


۱,۳- or meta

placement


۱,۴- or para

placement

 

 

Di-substituted compounds, such as dichlorobenzene, are commonly referred to as ortho, meta, or para, depending on the point of substitution. If substitution is on ad- jacent carbon atoms, the term ortho is used; if on carbon atoms once removed, the term meta is used; and if on carbon atoms opposite each other, the term para is used. Tri- and other poly-substituted compounds must be named by another system. In this system, the carbon atoms of the benzene ring are numbered in a clockwise man- ner. Examples are

 

Cl                                    Cl

۱                                                                 ۱        Cl

۶        ۲                                                       ۶        ۲

۵   ۴   ۳   NO2                                       ۵   ۴   ۳

 

m-Chloronitrobenzene                 o-Dichlorobenzene

 

 

Br

۱

۶       ۲

۵       ۳

۴

CH3

 

NO2

۱       Cl

۶       ۲

۵       ۳

Cl    ۴

 

p-Bromotoluene              ۲,۵-Dichloro-1-nitrobenzene

 

When the benzene ring is attached to aliphatic compounds, the products are also called phenyl derivatives, the phenyl group being C6H5ˆ. Thus ethyl benzene is also phenyl ethane.

 

 

۵٫۱۳ | HYDROCARBONS

 

Two series of homologous aromatic hydrocarbons are known: the benzene and the polyring series.

 

 

 

Benzene Series

 

The benzene series of homologous compounds is made up of alkyl substitution products of benzene. They are found along with benzene in coal tar and in many crude petroleums. Table 5.11 lists the benzene-series hydrocarbons of commercial importance. Toluene, or methylbenzene, is the simplest alkyl derivative of benzene. Xylene is a dimethyl derivative of benzene.

 

 

 

CH3

 

C2H5


CH3

 

CH3


CH3

 

 

 

CH3


CH3

 

 

 

CH3

 

Toluene


Ethylbenzene


o-Xylene


m-Xylene


p-Xylene

 

 

 

It exists in three isomeric forms: ortho-xylene, meta-xylene, and para-xylene. All are isomeric with ethylbenzene in that they have the same general formula, C8H10. Together with benzene, these compounds are commonly referred to as the BTEX group.

The benzene-series hydrocarbons are used extensively as solvents and in chem- ical synthesis, and are common constituents of petroleum products (e.g., gasoline). Although they are relatively insoluble in water, wastewaters and leachates contain- ing 10 to as high as 1000 mg/L for the BTEXs have been observed. These com- pounds are frequently detected in groundwaters, with a major source being leaking underground gasoline storage tanks.

The benzene-series compounds have been implicated in several human health effects, most notably cancer. Benzene is known to cause leukemia. The current drinking water MCLs are 5   g/L for benzene, 700   g/L for ethylbenzene, 1 mg/L for toluene, and 10 mg/L for the sum total of the xylenes.

Styrene (phenyl ethene), a benzene derivative, is an environmentally significant compound. It is used as a monomer in the production of a wide variety of poly-

 

 

 

Table 5.11 | Benzene-series hydrocarbons

 

Name

Formula

Mp,

 C

Bp,

 C

Sp. gr.,

۲۰

Benzene

C6H6

۵٫۵

۸۰٫۰

۰٫۸۷۷

Toluene

C6H5CH3

 ۹۴٫۹

۱۱۰٫۶

۰٫۸۶۷

o-Xylene

C6H4(CH3)2

 ۲۵٫۲

۱۴۴٫۵

۰٫۸۸۰۱۰

m-Xylene

 ۴۷٫۸

۱۳۹٫۱

۰٫۸۶۴

p-Xylene

۱۳٫۲

۱۳۸٫۳

۰٫۸۶۱

Ethylbenzene

C6H5C2H5

 ۹۴٫۹

۱۳۶٫۱

۰٫۸۶۷

Source: D. R. Linde (ed.): “Handbook of Chemistry and Physics,” ۸۲nd ed., CRC Press LLC, Boca

Raton, 2001.

 

 

 

styrene products (e.g., plastics, synthetic rubber). A drinking water MCL of 100

 g/L has been set for styrene.

 

H   H

 

ˆ C¨ C ˆH

 

 

Styrene

 

 

Polyring Hydrocarbons

 

A wide variety of polycyclic aromatic hydrocarbons (PAHs) are known. A few ex- amples will illustrate the possibilities.

 

Naphthalene (C10H8)    Naphthalene is a white crystalline compound derived from coal tar and was formerly used to produce mothballs.

 

 

H       H                        ۴

H                     H          ۴        ۸

۷

۶

H                     H          ۳        ۵

 

 ۱

۱      ۱

۲

۳

۴      ۲

 

H       H

Naphthalene


 ۳        ۲

 

 

It has been displaced largely from this market by paradichlorobenzene. A new system of nomenclature is applied to this type of compound. Carbon atoms adja- cent to those shared in common by the two rings are known as   -carbon atoms and the others are known as    -carbon atoms. The carbon atoms shared by the two rings do not have hydrogen attached to them and so are given no designa- tion. The specific name, naphthalene, should not be confused with naphthene (Sec. 5.10).

 

Anthracene (C14H10) and Phenanthrene (C14H10)   Anthracene and phenanthrene

are isomers.

 

 

 

 

۸             ۹             ۱

۷                                      ۲

۶                                       ۳

۵              ۱۰              ۴

 

Anthracene                           Phenanthrene

 

Their formulas illustrate the possible ways in which polycyclic aromatic hydrocar- bons may occur. Many other more complex compounds, such as  benzo(a)pyrene

 

 

 

and picene, are known. Benzo(a)pyrene is a potent carcinogen, and has a drinking water MCL of 0.2   g/L.

 

 

 

 

 

 

 

 

 

Benzo(a)pyrene                                         Picene

 

It should be remembered that hydrogen atoms occur on all carbon atoms of these compounds that are not common to two rings.

Naphthalene and anthracene are widely used in the manufacture of dye-stuffs. The phenanthrene nucleus is found in important alkaloids, such as morphine, vita- min D, sex hormones, and other compounds of great biological significance.

PAHs are associated with combustion products, and are believed to be the cause of the first recognized chemically related cancer that was found in chimney sweeps in the late eighteenth century. They are common residual contaminants at sites where coal was used to manufacture consumer gas (also called coal gas or town gas) in the early twentieth century, and where creosote, which is manufactured from coal, has been used to preserve wood. The larger compounds (five or more aromatic rings) tend not only to be carcinogenic, but are also the more difficult ones for bacteria to degrade.

 

Chlorinated Aromatic Hydrocarbons

 

There are many chlorinated aromatic hydrocarbons (also called aryl halides) of impor- tance. They are common industrial chemicals that through their widespread use and relative environmental persistence have become significant environmental problems, much in the same manner as the chlorinated aliphatic compounds. In general, as chlo- rine atoms are added to the benzene ring, water solubility decreases hydrophobicity increases, and the molecule’s vapor pressure decreases. Two of the most important classes are the chlorinated benzenes and the polychlorinated biphenyls.

 

Chlorinated Benzenes    Chlorinated benzenes are benzenes with one or more of the hydrogens replaced with chlorine. They are widely used industrial chemicals that have solvent and pesticide properties. Like the chlorinated aliphatics, they have been found at abandoned waste sites and in many wastewaters and leachates. They are fairly volatile, slightly to moderately soluble, and hydrophobic.

Chlorobenzene (monochlorobenzene) has a drinking water MCL of 100   g/L. There are three dichlorobenzene isomers: 1,2-dichlorobenzene (ortho isomer), 1,3- dichlorobenzene (meta isomer), and 1,4-dichlorobenzene (para isomer). The current MCLs are 75   g/L for p-dichlorobenzene and 600   g/L for o-dichlorobenzene; the meta isomer is not regulated at this time. There are also three trichlorobenzene iso- mers: 1,2,3-trichlorobenzene, 1,2,4-trichlorobenzene, and 1,3,5-trichlorobenzene. A drinking water MCL of 70   g/L has been established for 1,2,4-trichlorobenzene.

 

 

 

Hexachlorobenzene (C6Cl6) has been used in the synthesis of several chlorinated benzenes and is a commonly found groundwater contaminant. Its MCL is 1   g/L.

 

Polychlorinated  Biphenyls  (PCBs)    Polychlorinated  biphenyls  are  chlorinated benzenes with the general structure:

 

X  X       X  X

 

Xˆ            ˆ   ˆ X

 

X  X       X  X

 

where X can be either a chlorine or a hydrogen. There are 209 possible PCBs (called congeners). Groups of congeners with similar average numbers of chlorine atoms are typically described with the name Aroclor and a corresponding number, for example, Aroclor 1260. PCBs are very stable compounds of low vapor pressure and high di- electric constants. They were widely used as coolants in transformers and capacitors, plasticizers, solvents, and hydraulic fluids. PCBs are very hydrophobic and tend to bioconcentrate. Significant concentrations of PCBs have been found in higher levels of the food chain (e.g., fish and birds). Because of human health and environmental effects associated with PCBs, their manufacture in the United States was banned in

۱۹۷۷٫ The drinking water MCL for total PCBs is 0.5   g/L. PCBs have recently been implicated as endocrine disruptors. Endocrine-disrupting chemicals (EDC), also called hormonally active agents, are those chemicals that have been reported to be associated with adverse reproductive and developmental effects in humans and wildlife. Additional discussion of EDCs is given in Sec. 5.32. The disposal of PCB wastes is strictly controlled and continues to be problematical. Some PCB congeners have been shown to be degraded by microorganisms; the more highly chlorinated congener ones by anaerobic microorganisms, and the less chlorinated ones by aero- bic microorganisms. Transformation rates, however, tend to be very slow such that the compounds are generally considered to be highly resistant to biodegradation.

 

 

۵٫۱۴ | PHENOLS

 

The phenols are among the most important of the aromatic compounds.

 

Monohydroxy Phenols

 

There are several monohydroxy phenols of interest.

 

Phenol (C6H5OH)   The monohydroxy derivative of benzene is known as phenol.

 

H O

 

 

 

Phenol

 

 

 

Its formula and name indicate that it might correspond in the aromatic series to al- cohols in the aliphatic series. This is not the case, however. Phenol is also known as carbolic acid. It ionizes to yield H     to a limited extent (KA     ۱٫۲     ۱۰   ۱۰), and in concentrated solution is quite toxic to bacteria. It has been used widely as a germi- cide, and disinfectants have been rated in terms of “phenol coefficients,” i.e., rela- tive disinfecting power with respect to phenol. The system is considered archaic at the present time.

Phenol is recovered from coal tar, and considerable amounts are manufactured synthetically. It is used extensively in the synthesis of organic products, particularly phenolic-type resins. It occurs as a natural component in industrial wastes from the coal-gas, coal-coking, and petroleum industries as well as in a wide variety of in- dustrial wastes from processes involving the use of phenol as a raw material.

Biological treatment of wastes containing more than 25 mg/L of phenol was considered impossible some years ago. However, research and much practice have demonstrated that phenol will serve as food for aerobic bacteria without serious toxic effects at levels as high as 500 mg/L. Studies with it and with formaldehyde have established the concept of toxicity thresholds. At levels below the threshold, bacteria use the material as food, but above the threshold they find it too toxic for use as food and reproduction of the organisms. Phenol has also been shown to be highly degradable even by anaerobic bacteria, and at levels of up to 2000 mg/L.13

 

Cresols  and  Other  Alkylphenols    The  next  higher  homologs  of  phenol  are cresols.

 

 

OH

CH3

 

OH

 

 

CH3

 

OH

 

 

 

CH3

 

o-Cresol


m-Cresol


p-Cresol

 

 

They are found in coal tar and have a higher germicidal action than phenol. They are less toxic to humans. Lysol is a mixture of cresols which is sold as a household and sickroom disinfectant. Cresols are the major constituents of “creosote” which is used extensively for the preservation of wood.

Industrial wastes containing cresols are somewhat difficult to treat by biologi- cal methods. Research with aerobic14  and anaerobic15  microorganisms has shown the pure cresols to be relatively nontoxic at concentrations of 250 mg/L. The toxic- ity of crude cresols is believed, therefore, to be due to other compounds.

 

 

۱۳D. J. W. Blum, R. Hergenroeder, G. F. Parkin, and R. E. Speece, Anaerobic Treatment of Coal Conversion Wastewater Constituents: Biodegradability and Toxicity, J. Water Pollution Control Federation, 58: 122–۱۳۱ (۱۹۸۶).

۱۴R. E. McKinney, H. D. Tomlinson, and R. L. Wilcox, Metabolism of Aromatic Compounds in

Activated Sludge, Sewage and Ind. Wastes, 28: 547–۵۵۷ (۱۹۵۶).

۱۵Blum et al., Anaerobic Treatment of Coal Conversion Wastewater Constituents: Biodegradability and

Toxicity, J. Water Pollution Control Federation, 58: 122–۱۳۱ (۱۹۸۶).

 

 

 

Alkylphenols have recently been implicated as endocrine disrupters. Alkylphe- nols are combined with ethylene oxide (Secs. 5.17 and 5.25) to produce alkylphenol ethoxylates, which are used as surfactants in products such as detergents, paints, and pesticides. Action by naturally occurring bacteria degrade these molecules releasing the alkylphenols. These compounds have been found in effluents from wastewater treatment plants, wastewater plant sludges, and natural waters.16,17   Nonylphenol is believed to be one of the more potent potential endocrine disruptors.18

 

 

C9H19 ˆ   ˆ OH

 

Nonylphenol

 

The nonyl group may be highly branched, making the compound resistant to biodegradation.

Another phenol that has been implicated as an important endocrine disrupter is bisphenol A.19 Bisphenol A is an important intermediate in the production of a wide variety of industrial products including polymers such as polycarbonate plastics, dyes, epoxy coatings, and flame retardants.

 

 

H3C


CH3

C

 

 

 

HO                                     OH

Bisphenol A

 

Chlorinated Phenols    Chlorinated phenols have been used as wood preservatives. The most commonly used phenol for this purpose is pentachlorophenol.

 

OH

Cl                 Cl

 

 

Cl                 Cl

Cl

Pentachlorophenol

 

The drinking water MCL for pentachlorophenol is 1   g/L.

 

 

 

۱۶B. E. Erickson, Akylphenols in Sewage Sludge Applied to Land, Env. Sci. Tech., 36(1): 10A–۱۱A,

۲۰۰۲٫

۱۷C. Maczka et al., Evaluating Impacts of Hormonally Active Agents in the Environment, Env. Sci. Tech., 34(5): 136A–۱۴۱A, 2000.

۱۸Maczka et al., Evaluating Impacts of Hormonally Active Agents in the Environment.

۱۹Ibid.

 

 

 

Polyhydroxy Phenols

 

Three isomeric dihydroxy phenols are known. All have been shown20  to be readily oxidized by properly acclimated microorganisms.

 

OH                          OH                          OH OH

 

 

 

 

 

Benzene-1,2-diol, pyrocatechol, catechol


OH

 

Benzene-1,3-diol, resorcinol

 

OH

Benzene-1,4-diol, hydroquinone

 

 

Pyrogallol    Pyrogallol, 1,2,3-trihydroxybenzene, is known as pyrogallic acid.

 

 

HO             OH OH

Pyrogallol

 

It is easily oxidized and serves as a photographic developer. Pyrogallol is a minor constituent of spent tan liquors. When they are discharged to streams containing iron, inky black ferric pyrogallate is formed.

 

 

۵٫۱۵ | ALCOHOLS, ALDEHYDES, KETONES, AND ACIDS

 

The aromatic alcohols, aldehydes, ketones, and acids are all formed from alkyl de- rivatives of benzene or one of its homologs. The active group is always in the alkyl group, and therefore the chemistry of the aromatic alcohols, aldehydes, ketones, and acids is very similar to that of the corresponding aliphatic compounds. Common names are usually employed with these compounds, but they may be more properly named as phenyl derivatives of aliphatic compounds.

 

Alcohols

 

The aromatic alcohols compose a homologous series. They are phenyl methyl, phenyl ethyl, phenyl n-propyl, phenyl isopropyl, and so on.

 

H                                H    H    H

 

ˆ Cˆ OH


ˆ C ˆ C ˆ COH

 

H                                H    H    H

 

 

Benzyl alcohol, phenyl methyl alcohol


Phenyl n-propyl alcohol

 

 

 

۲۰Blum et al., Anaerobic Treatment of Coal Conversion Wastewater Constituents: Biodegradability and

Toxicity, J. Water Pollution Control Federation, 58: 122–۱۳۱ (۱۹۸۶).

 

 

 

The aromatic alcohols are subject to chemical and biological oxidation. Oxida- tion of primary alcohols produces aldehydes and oxidation of secondary alcohols produces ketones.

 

Aldehydes

 

The aromatic aldehydes are important compounds in chemical synthesis.

 

H                            H    H    H

 

ˆ C¨ O


ˆ C ˆ C ˆ C ¨ O

 

H    H

 

 

Benzaldehyde


Phenyl propyl aldehyde

 

 

They are easily oxidized to the corresponding acids. Many of the more complex aldehydes have fragrant odors: coumarin, anisaldehyde, vanillin, and so on.

 

Ketones

 

The aromatic ketones are of two types: those that have one phenyl group attached to the carbonyl group and those that have two.

 

 

O

 

ˆ C ˆ CH3

 

 

Acetophenone

 

O

 

ˆC ˆ

 

 

Benzophenone

 

 

Chemical and biological oxidation results in disruption of the molecule, with the formation of lower-molecular-weight acids and, probably, carbon dioxide.

 

Acids

 

A wide variety of aromatic, monocarboxylic acids is known. Oxidation of benzalde- hyde produces benzoic acid. Sodium benzoate is used as a food preservative. Sali- cylic acid is used to prepare aspirin.

 

 

O

 

ˆ CˆOH

 

 

Benzoic acid

 

O

 

ˆ C ˆ OH

ˆ OH

 

Salicylic acid

 

 

Oxidation of naphthalene produces an important dicarboxylic acid, phthalic acid.

 

O

 

 

ˆ COOH

ˆ COOH

 

ˆ C    O

ˆ C

 

O

 

Phthalic acid


Phthalic anhydride

 

 

 

It and its anhydride are important in the manufacture of a variety of organic com- pounds. Phthalates are used as plasticizers in the production of a wide variety of plastics. A drinking water MCL of 6   g/L has been set for di (2-ethylhexyl) phtha- late. Phthalates have also been implicated as endocrine disruptors.

Phenolphthalein, used as a pH indicator in the laboratory, is another example.

 

 

OH

 

 

 

C ¨ O

O      ۲


C                      OH OH  l H2O                         O

 

C¨ O

 

C ¨ O

Phenolphthalein

 

 

Most aromatic acids are subject to biological oxidation. The normal end prod- ucts are carbon dioxide and water. However, some phthalates are resistant to biodegradation.

 

 

۵٫۱۶ | SIMPLE COMPOUNDS CONTAINING NITROGEN

 

The aromatic compounds containing nitrogen are derivatives either of ammonia or of nitric acid. The former are called amines, and the latter are called nitro com- pounds. In addition, many complex nitrogen compounds exist that are outside the scope of this book.

 

Amines

 

The aromatic amines are of two types: those in which the phenyl or other aromatic group is attached directly to nitrogen and those in which the nitrogen occurs in an attached alkyl group. There are three phenyl derivatives of ammonia: primary, sec- ondary, and tertiary amines.

 

 

H N

NH2

 

 

 

 

ˆN ˆ

 

 

Aniline                 Diphenylamine

 

 

 

Triphenylamine

 

The primary form is called aniline and the secondary form is diphenylamine. They are both basic in character, react with strong acids to form salts, and are important

 

 

 

compounds in organic synthesis. Aniline dyes are derived from aniline. Sulfanilic acid, used in the colorimetric determination of nitrites, is made from aniline.

 

 

H3

Nˆ OSO3H

 

۱۸۰°

ˆl

 

 

H2O


NH2

 

(۵٫۴۶)

 

 

 

 

Aniline hydrogen


SO3H

 

sulfate                                                          Sulfanilic acid

 

۱-Naphthylamine HCl is an important compound in water analysis.

 

NH3C l

 

 

 

 

A derivative, N-(1-naphthyl)-ethylenediamine dihydrochloride is used in conjunc- tion with sulfanilic acid in the determination of nitrite nitrogen.

Benzylamine (C6H5CH2NH2) is an example of an aromatic amine that has the

ˆNH2  group attached to the aliphatic part of the molecule. These compounds are

not important commercially.

 

 

Nitro Compounds

 

Nitric acid reacts with benzene and other aromatic compounds to form nitro com- pounds. The reaction is as follows:

 

 

H                               H SO

 

H

H          ˆ NO2

 

۲        ۴

 

H            H

 

H           H


HO NO2


ˆˆˆl

H           H

H


   H2O


(۵٫۴۷)

 

H                                          Nitrobenzene

 

A dehydrating agent, usually sulfuric acid, must be present to remove the water that is formed. One additional nitro group may be added under proper conditions. The principal product is m-dinitrobenzene,

 

NO2                                             CH3

 

 

 

NO2


O2N

 

 

 

NO2


NO2

 

m-Dinitrobenzene


Trinitrotoluene (TNT)

 

 

as the presence of the first nitro group directs the second into the meta position. Trinitrobenzene is very difficult to prepare.

Nitration of toluene results in the formation of trinitrotoluene, or TNT. The first nitro group is directed into the ortho position by the methyl group, and additional nitro groups attach in the meta position with respect to the first nitro group. TNT is

 

 

 

widely used as an ingredient of military explosives. It is relatively resistant to aero- bic biological degradation. However, it is fairly easily reduced to the corresponding amine under reducing conditions.

 

 

HETEROCYCLIC COMPOUNDS

 

۵٫۱۷ | HETEROCYCLIC COMPOUNDS

 

Heterocyclic compounds have one other element in the ring in addition to carbon. A wide variety of compounds exists; some are aliphatic in character, and some are aromatic. Many are of great biological importance, and several are of significance in environmental engineering and science.

Furaldehyde, or furfural, is an example of an aliphatic heterocyclic compound having a five-membered ring containing oxygen. It is produced from pentose sugars by dehydration. Commercially, it is made from oat hulls and corn cobs, waste prod- ucts of the cereal industry.

 

O

HC        C ˆ CHO

 

HCˆˆ CH

Furaldehyde

 

Both were formerly disposed of by burning. Manufacture of furfural yields some liquid wastes of concern to environmental engineers. Furfural has been shown to be biodegradable.

Epoxides are three-membered rings where oxygen is bonded with two carbons. Several epoxides are environmentally significant. For example, ethylene oxide,

 

O

Hˆ C ˆˆ C ˆ H

 

H        H

Ethylene oxide

 

is a toxic epoxide that has been used in chemical synthesis [e.g. alkylphenol ethoxy- lates (Sec. 5.14) and synthetic detergents (Sec. 5.26)] and as a sterilizing agent and pesticide. It is a regulated air pollutant. In general, epoxides are very reactive. They have been shown to be important intermediates in the biotransformation of several organics, for example, trichloroethene.

Pyrrole and pyrrolidine are examples of heterocyclic compounds having five- membered rings containing nitrogen.

 

 

H N

۱

HC        CH

 

H N

H2C        CH2

 

۵

HCˆ۴

 

۲

۳

ˆ CH

H C ˆˆ CH

 

 

Pyrrole


۲                         ۲

Pyrrolidine

 

 

 

The pyrrole or pyrrolidine ring occurs in the structure of many important natural compounds, e.g., nicotine, cocaine, chlorophyll, and hemoglobin.

Pyridine is an example of a six-membered aromatic heterocyclic compound with nitrogen contained in the ring.

N

۶   ۱  ۲

۵        ۳

۴

 

Pyridine

 

It is an especially vile-smelling liquid. It is used as a denaturant in ethyl alcohol, to make it unpalatable, and in chemical synthesis. It is weakly basic in character and forms salts with strong acids. Nicotinic acid is a derivative of pyridine, having a carboxyl group in the    position. It is a key component of a coenzyme, NAD, which is present in all cells and involved in oxidation of organic matter. Nicotinic acid is a vitamin required by humans and many other mammals, a deficiency in the diet of humans causing pellagra.

Purine and pyrimidine are two other ring compounds containing nitrogen and of immense biological importance.

 

 

H

C        N

N        C

CH HC        C

 

N          N H

Purine

 

H C

N        CH

 

HC        CH N

 

Pyrimidine

 

 

Important derivatives of purine are adenine and guanine, and of pyrimidine are cy- tosine, uracil, and thymine. These compounds or bases form the major components of nucleic acids, which carry the genetic information for all life (see Sec. 6.14). In addition, they are components of key biological molecules such as ATP, the pri- mary carrier of chemical energy in all cells, and coenzyme A, which is necessary for fatty acid degradation.

Indole and skatole are examples of heterocyclic compounds that possess a ben- zene nucleus condensed with a pyrrole nucleus.

 

H                         H N                         N

 

 

 

 

Indole                               Skatole


ˆ CH3

 

 

Both possess unpleasant odors and are produced during the putrefaction of protein matter. Under controlled conditions, such as exist in well-operated sludge digesters, very little indole or skatole is formed.

Other heterocyclic nitrogen compounds of interest include the explosives RDX (hexahydro-1,3,5-trinitro-1,3,5-triazine)  and  HMX  (octahydro-1,3,5,7-tetranitro-

 

 

 

۱,۳,۵,۷-tetrazocine). These compounds have been found as soil or groundwater con- taminants at a number of U.S. Department of Defense facilities. They are slightly soluble in water but are not particularly hydrophobic; they have low vapor pressures and are not very biodegradable under most conditions found in the natural environ- ment. They have been detected in a number of groundwater supplies and present en- vironmental engineers and scientists with challenging remediation problems.

 

 

NO2

 

N

 

O2N

N


NO2

N

 

 

 

 

O2N

 

N       N

 

RDX

 

NO2

 

 

O2N


N     N

 

HMX

 

 

NO2

 

(hexahydro-1,3,5-trinitro-1,3,5-triazine)


(octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine)

 

 

 

۵٫۱۸ | DYES

 

The subject of dyes is of such magnitude and complexity that a discussion of vari- ous types will not be presented here. The environmental engineer and scientist con- cerned with the treatment of textile wastes, and possibly a few others, will be con- fronted with the need to learn more about these materials. Recourse for information should be made to standard organic chemistry texts or treatises on dyes. The sulfur dyes are noted for their toxic properties.

 

 

THE COMMON FOODS AND RELATED COMPOUNDS

 

۵٫۱۹ | GENERAL

 

The term food is applied to a wide variety of organic materials that can serve as a source of energy for living organisms. In the case of bacteria, these compounds range from hydrocarbons through various oxidation products, including organic acids. In the case of higher animals and humans, the principal or common foods are restricted to carbohydrates, fats,   and proteins. Other organic compounds such  as  ethanol,  certain  aldehydes,  and  many  acids  serve  as  food  or  energy sources also. The latter are sometimes referred to as exotic foods, as they are not considered part of an essential diet but are added to increase palatability or for other reasons.

 

 

۵٫۲۰ | CARBOHYDRATES

 

The term carbohydrate is applied to a large group of compounds of carbon, hydro- gen, and oxygen in which the hydrogen and oxygen are in the same ratio as in water, i.e., two atoms of hydrogen for each atom of oxygen. The processing of car-

 

 

 

bohydrate materials occurs in the lumber, paper, and textile industries, as well as in the food industry. Wastes from these industries are major problems and tax the in- genuity of environmental engineers and scientists to find satisfactory solutions.

Carbohydrates may be grouped into three general classifications, depending upon the complexity of their structure: (1) simple sugars, or monosaccharides; (2) complex sugars, or disaccharides; (3) polysaccharides. In general, the -ose ending is used to name carbohydrates.

 

Simple Sugars, or Monosaccharides

 

The simple sugars, or monosaccharides, all contain a carbonyl group in the form of an aldehyde or a keto group. Those with aldehyde groups are known as aldoses and those with keto groups are known as ketoses. They are also glycols, as they possess several OH groups. Two series of simple sugars are of importance commercially: the pentoses are five-carbon-atom sugars and the hexoses are six-carbon-atom sugars.

 

Pentoses    Pentoses have the general formula C5H10O5. Two pentoses are of com- mercial importance, and both are aldopentoses. Xylose is formed by the hydrolysis of pentosans, which are commonly found in waste organic materials such as oat hulls, corn cobs, and cottonseed hulls. Considerable amounts of xylose are formed in the pulping of wood through the hydrolysis of hemicellulose. Arabinose is pro- duced by the hydrolysis of gum arabic or wheat bran.

 

 

H

C ¨ O

 

Hˆ Cˆ OH HO ˆ Cˆ H

H ˆ Cˆ OH

 

CH2OH


H

C ¨ O

 

HO ˆ Cˆ H

 

H ˆ Cˆ OH H ˆ Cˆ OH

CH2OH

 

D(–)-Xylose21                       D(–)-Arabinose21

 

Both xylose and arabinose are used in bacteriological work in media used to differentiate among various bacteria. Certain bacteria can ferment one but not the other, and vice versa. Mixed cultures of bacteria, such as those derived from the soil or waste, convert both sugars to carbon dioxide and water. The pentose sugars are not fermented by yeast under anaerobic conditions; therefore, they cannot be used to produce ethanol. They do serve as an energy source for yeast under aerobic con- ditions, however, and advantage is taken of this fact in one method of treating spent sulfite liquors from the pulping of wood.

 

Hexoses    There  are  four  important  hexose  sugars  with  the  general  formula

C6H12O6. Glucose, galactose, and mannose are all aldoses, and fructose is a ketose.

 

۲۱All sugars are optically active. The nomenclature is somewhat complicated, however, and details should be obtained from a standard text on organic chemistry.

 

 

 

Glucose    Glucose is the most common of the aldohexose sugars. It is found natu- rally in fruit juices and in honey. It is manufactured in great quantity by the hydrol- ysis of corn starch. It is the principal component of corn syrup. Both corn syrup and glucose are used extensively in candy manufacture. Glucose is much less sweet than ordinary sugar and replaces it for many purposes.

 

H

C ¨ O

 

Hˆ Cˆ OH HOˆ Cˆ H

H ˆ Cˆ OH H ˆ Cˆ OH

CH2OH

D-(+)-Glucose

 

Glucose is the only hexose sugar that can be prepared in relatively pure form by the hydrolysis of disaccharides or polysaccharides. All the other hexose sugars occur in combination with glucose.

 

Fructose    Fructose  is  the  only  significant ketohexose  and  occurs  naturally  in honey. When cane or beet sugar is hydrolyzed, one molecule of fructose and one molecule of glucose are formed from each molecule of sucrose.

 

Galactose and Mannose    Galactose and mannose do not occur in free form in na- ture. Galactose is produced by the hydrolysis of lactose, more commonly called milk sugar. Glucose is formed simultaneously. Mannose is produced by the hydrol- ysis of ivory nut, and glucose is formed at the same time.

 

 

 

CH2OH C ¨ O

HO ˆ Cˆ H

 

H ˆ Cˆ OH H ˆ Cˆ OH

CH2OH

D-(–)-Fructose

 

H

C ¨ O

 

H ˆ Cˆ OH HOˆ Cˆ H HOˆ Cˆ H

Hˆ Cˆ OH

 

CH2OH

D-(+)-Galactose

 

H

C ¨ O

 

HOˆ Cˆ H HOˆ Cˆ H

H ˆ Cˆ OH H ˆ Cˆ OH

CH2OH

D-(+)-Mannose

 

 

Glucose and galactose are of particular interest. Glucose is always one of the products and may be the sole product when di- or polysaccharides are hydrolyzed. It is therefore found in a wide variety of industrial wastes. Galactose is formed from the hydrolysis of lactose, or milk sugar, and is found in wastes from the dairy indus- try. Both sugars are readily oxidized by aerobic bacteria to form acids, and the oxi-

 

 

 

dation may stop at that point because of the unfavorable pH conditions produced by the acids unless precautions are taken to control the pH by means of buffers or alka- line materials. Lactic acid is an important intermediate in the oxidation of galactose. Both sugars are fermented rapidly under anaerobic conditions, with acid formation.

 

Complex Sugars, or Disaccharides

 

There are three important sugars with the general formula C12H22O11: sucrose, mal- tose, and lactose. All disaccharides may be considered as consisting of two hexose sugars hooked together in one molecule. Hydrolysis results in cleavage of the mole- cule and formation of the hexoses.

 

Sucrose    Sucrose is the common sugar of commerce. It is derived largely from sugarcane and sugar beets. The sap of such trees as the sugar maple contains con- siderable sucrose. Hydrolysis of the sucrose molecule results in the formation of one molecule of glucose and one molecule of fructose.

 

 

 

 

 

 

 

Glucose part


H ˆ C

 

 

H ˆ C ˆ OH HO ˆ Cˆ H

H ˆ Cˆ OH H ˆ C

CH2OH


CH2OH O

C O

HO ˆ Cˆ H

 

H ˆ Cˆ OH H ˆ C

CH2OH

 

 

 

 

 

Fructose

O  part

 

Sucrose (C12H22O11)

 

Maltose    Maltose is made by the hydrolysis of starch, induced by diastase, an en- zyme present in barley malt. The starch may be derived from a wide variety of sources, and its hydrolysis by diastase results in commercial maltose, which is used in infant foods and in malted milk.

 

 

H ˆ C¨ O

 

H ˆ C ˆ OH   O HO ˆ Cˆ H

H ˆ C

H ˆ Cˆ OH CH2OH


H ˆ C

 

H ˆ C ˆ OH

 

HO ˆ Cˆ H      O H ˆ Cˆ OH

H ˆ C

 

CH2OH

 

Maltose (C12H22O11)

 

Maltose is readily hydrolyzed to yield two molecules of glucose.

 

 

 

Alcohol production by fermentation processes uses starch from a wide variety of sources. The starch is converted to maltose by the enzyme from barley malt. En- zymes from the yeast hydrolyze maltose to glucose and convert the glucose to alco- hol and carbon dioxide (Sec. 5.3).

 

Lactose    Lactose, or milk sugar, occurs in the milk of all mammals. Upon hydroly- sis, the molecule is split to yield a molecule of glucose and a molecule of galactose.

 

 

 

 

 

 

 

Glucose part

 

H ˆ C¨ O

 

H ˆ C ˆ OH

O HO ˆ Cˆ H

 

H ˆ C

H ˆ Cˆ OH CH2OH

 

H C

 

Hˆ C ˆ OH

 

 

HO ˆ Cˆ H HO ˆ Cˆ H

H ˆ C

 

CH2OH

 

 

 

 

 

Galactose part

O

 

Lactose (C12H22O11)

 

Lactose is used in infant foods and in candy making. Dried skimmed-milk solids contain about 60 percent lactose.

 

Polysaccharides

 

The polysaccharides are all condensation products of hexoses or other monosaccha- rides. Glucose and xylose are the most common units involved. Three polysaccharides are of interest: starch, cellulose, and hemicellulose. None of them have the characteris- tic sweet taste of sugar because of their insolubility and complex molecular structure.

 

Starch    Starch has the general formula (C6H10O5)x. It occurs in a wide variety of products grown for food purposes (corn, wheat, potatoes, rice, etc.). It is the cheap- est foodstuff and serves mainly in human nutrition as a source of energy. Starch is used in fermentation industries to produce a wide variety of products. The structure of the starch molecule is not known definitely. Its hydrolysis yields glucose as the only monosaccharide, and its general formula may be indicated as follows:

 

 

CH2OH                      CH2OH

O                               O


CH2OH

O

 

H  H               H        H H OH            H                  OH

HO                          O


H        H  H               H H                  OH       H

O                          OH

 

H          OH


H          OH    x               H          OH

 

Starch (amylose, x = about 100 to 1000)

 

Starch consists of two major fractions. One fraction, consisting of glucose units connected in a straight chain, is termed amylose, and the other fraction, consisting

 

 

 

of glucose units attached to form branched chains, is termed amylopectin. The amy- lose molecule contains 100 to 1000 glucose units. Amylose is soluble in water and absorbs up to 20 percent of its own weight in iodine to form the blue complex used as an indicator in iodimetric analysis (Sec. 11.4). The amylopectin molecule, not shown, is much larger and contains about 500 to 5000 glucose units. It is not as sol- uble in water as amylose.

The glucose units in starch are connected by what is termed an alpha linkage. This linkage is readily hydrolyzed by enzymes common to all mammals as well as to microorganisms, and hence they are able to use starch as food.

The industrial wastes produced from the manufacture of starch, from the pro- cessing of carbohydrate foods, and from the industrial uses of starch can be readily treated by biological processes.

 

Cellulose    Cellulose forms the structural fiber of many plants. Cotton is essentially pure cellulose. High-grade cellulose can be produced from wood through the sulfite and sulfate pulping processes. Like starch, cellulose consists of glucose subunits. However, these units are connected by what is termed beta linkage, and mammals, in- cluding humans, do not have enzymes capable of promoting the hydrolysis of this linkage. Therefore, cellulose passes through the digestive tract unchanged. Certain an- imals, especially ruminants (cud-chewing animals) such as the cow, have bacteria in the digestive tract that can hydrolyze the beta link. This is a convenient arrangement, for the animal can digest the bacterial fermentation products and thus derive nourish- ment indirectly from cellulose. The beta linkage for cellulose is indicated as follows:

 

 

H          OH


CH2OH

O


H          OH


CH2OH

O

 

O        OH H

H


H  H        H  H OH

O       O


O       OH H                  H

H        H


H  H        H  H

OH       H

O       O                          H

 

CH2OH


H          OH


CH2OH


H          OH

 

Portion of cellulose molecule

 

Industrial wastes from the paper industry usually contain considerable amounts of cellulose in suspension. This is particularly true of the wastes from the manufac- ture of low-grade papers involving the reuse of waste paper. Most of the wastes from other industries processing cellulose contain very little cellulose. The principal cont- aminants are inorganic compounds, derivatives of cellulose, and other organic com- pounds. Since certain bacteria can hydrolyze cellulose, biological treatment of cellu- lose containing wastes is possible. However, treatment by aerobic processes is slow. Since most of the cellulose will settle to produce a sludge, preliminary treatment by sedimentation is practiced, and the sludges produced are disposed of by anaerobic di- gestion or by physical methods such as filtration, centrifugation, and incineration.

 

Hemicelluloses  The hemicelluloses are compounds that have characteristics somewhat like cellulose. They are composed of a mixture of hexose and pentose units, however, and upon hydrolysis yield glucose and a pentose, usually xylose.

 

 

 

 

Disaccharides


Starch                Cellulose               Hemicellulose

 

 

 

S u c

۶ r 6  ۶ o

s e


L          M a                            a c                           l

t  ۶   ۶ t o          o s          s e          e

 

 

۶             ۶ ۶ ۶ ۶ ۶ ۶

 

 

۶ ۶ ۶ ۶ ۶ ۶ ۶ ۶ ۶        ۶ ۵ ۶ ۵ ۶ ۵ ۶ ۵

 

 

 

 

 

 

 

 

۶                  ۶                 ۶                 ۶                           ۵                 ۵

 

Fructose    Galactose   Mannose    Glucose             Arabinose    Xylose

 

Hexoses


Pentoses

 

 

Figure 5.1

Summary of hydrolytic behavior of carbohydrates.

 

 

Most natural woods contain cellulose, hemicellulose, and lignin, along with resins, pitch, and so on. In the pulping process, the lignin, hemicellulose, resins, and so on, are dissolved, leaving cellulose as the product. As a result, spent pulping liquors contain considerable amounts of glucose and xylose as well as other organic sub- stances, principally derivatives of lignin. The lignin derivatives, which have highly complex aromatic structures, are very resistant to biological degradation. Glucose, xylose, and other organic substances are converted to carbon dioxide and water by yeast or bacteria under aerobic conditions. Yeast may be used to ferment the glu- cose to alcohol under anaerobic conditions, but the xylose, a pentose, is not fer- mentable to alcohol.

 

Summary of Hydrolytic Behavior of Carbohydrates

 

The hydrolytic behavior of carbohydrates is presented in a simplified graphic form in Fig. 5.1. All di- and polysaccharides yield glucose. Sucrose yields fructose, lac- tose yields galactose, and hemicellulose yields xylose in addition to glucose.

 

 

۵٫۲۱ | FATS, OILS, AND WAXES

 

Fats, oils, and waxes are all esters. Fats and oils are esters of the trihydroxy alcohol, glycerol, while waxes are esters of long-chain monohydroxy alcohols. All serve as food for humans, as well as bacteria, since they can be hydrolyzed to the corre- sponding fatty acids and alcohols.

 

 

 

Fats and Oils

 

Fats and oils are both glycerides of fatty acids. The fatty acids are generally of 16- or 18-carbon atoms, although butyric, caproic, and caprylic acids are present to a significant extent as components of the esters of butterfat. The acids may also be unsaturated. Oleic and linoleic are important acids in cottonseed oil. Linseed oil contains large amounts of linoleic and linolenic acids. The glycerides of fatty acids that are liquid at ordinary temperatures are called oils and those that are solids are called fats. Chemically they are quite similar. The oils have a predominance of short-chain fatty acids or fatty acids with a considerable degree of unsaturation, such as linoleic or linolenic.

 

 

O

 

H2Cˆ O ˆ Cˆ C3H7

O

 

H ˆ Cˆ O ˆ Cˆ C3H7

O

 

H2Cˆ O ˆ Cˆ C3H7

Glyceryl (or glycerol)

tributyrate, tributyrin

 

O

 

H2Cˆ O ˆ Cˆ C17H35

O

 

H ˆ Cˆ O ˆ Cˆ C17H35

O

 

H2Cˆ O ˆ Cˆ C17H35

Glyceryl (or glycerol)

tristearate, tristearin

 

 

The fatty acids in a given molecule of a glyceride may be all the same, as just shown, or they may all be different.

 

O                                                                      O

 

 

H2Cˆ O ˆ Cˆ C3H7

O

 

H ˆ Cˆ O ˆ CˆC15H31

O

 

H2Cˆ O ˆ C(CH2)7C¨ C(CH2)7CH3

 

H2Cˆ O ˆ Cˆ C17H35

O

 

 Hˆ Cˆ O ˆ Cˆ C15H31

O

 

H2Cˆ O ˆ C17H35

 

H   H                                    ‘

 

Glyceryl (or glycerol) oleo- butyropalmitate (found in butter fat)


 -Palmito-  ,  ‘-distearin

 

 

The principal acids composing the glycerides of fats and oils are shown in

Table 5.12.

The relative amounts of the major fatty acids contained in various fats and oils are shown in Table 5.13.

Fats and oils undergo three types of chemical reactions of interest: hydrolysis, addition, and oxidation.

 

 

 

Table 5.12 | Acids of fats and oils

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Name

Formula

Mp, C

Source

Butyric

C3H7COOH

 ۵٫۷

Butter

Caproic

C5H11COOH

 ۳

Butter, coconut oil

Caprylic

C7H15COOH

۱۶٫۳

Palm oil, butter

Capric

C9H19COOH

۳۱٫۹

Coconut oil

Lauric

C11H23COOH

۴۳٫۲

Coconut oil, spermaceti

Myristic

C13H27COOH

۵۳٫۹

Nutmeg, coconut oil

Palmitic

C15H31COOH

۶۳٫۱

Palm oil, animal fats

Stearic

C17H35COOH

۶۹٫۶

Animal and vegetable fats, oils

Arachidic

C20H40O2

۷۶٫۵

Peanut oil

Behenic

C22H44O2

۸۱٫۵

Ben oil

Oleic

C18H34O2

۱۳٫۴

Animal and vegetable fats, oils

Erucic

C22H42O2

۳۴٫۷

Rape oil, mustard oil

 

Linoleic                  C18H32O2                       ۱۲                      Cottonseed oilLinolenic                C18H30O2                       ۱۱                      Linseed oil

Source: D. R. Linde (ed.): “Handbook of Chemistry and Physics,” ۸۲nd ed., CRC Press LLC, Boca

Raton, 2001.

 

 

 

 

 

 

 

Table 5.13 | Acid content of fats and oils (percent)

 

Lino-          Lino-                                                                                   Ara- Name                      Oleic          leic             lenic            Stearic         Myristic           Palmitic          chidic

 

Buttera

۲۷٫۴

۱۱٫۴

۲۲٫۶

۲۲٫۶

Mutton tallow

۳۶٫۰

۴٫۳

۳۰٫۵

۴٫۶

۲۴٫۶

Castor oilb

۹

۳

۳

Olive oil

۸۴٫۴

۴٫۶

۲٫۳

Trace

۶٫۹

۰٫۱

Palm oil

۳۸٫۴

۱۰٫۷

۴٫۲

۱٫۱

۴۱٫۱

Coconut oilc

۵٫۰

۱٫۰

۳٫۰

۱۸٫۵

۷٫۵

Peanut oild

۶۰٫۶

۲۱٫۶

۴٫۹

۶٫۳

۳٫۳

Corn oile

۴۳٫۴

۳۹٫۱

۳٫۳

۷٫۳

۰٫۴

Cottonseed oil

۳۳٫۲

۳۹٫۴

۱٫۹

۰٫۳

۱۹٫۱

۰٫۶

Linseed oil

۵

۴۸٫۵

۳۴٫۱

Soybean oilf

۳۲٫۰

۴۹٫۳

۲٫۲

۴٫۲

۶٫۵

۰٫۷

Tung oilg

۱۴٫۹

۱٫۳

۴٫۱

aContains caproic, 1.4 percent; caprylic, 1.8 percent; capric, 1.8 percent; butyric, 3.2 percent; lauric, 6.9 percent. bContains about 85 percent of ricinoleic acid, 12-hydroxy-9-octadecenoic acid (mp, 17 ), CH3(CH2)5CHOHCH2CH¨CH(CH2)7COOH.

cContains caprylic, 9.5 percent; capric, 4.5 percent; lauric, 51 percent.

dContains 2.6 percent lignoceric acid. eContains 0.2 percent lignoceric acid. fContains 0.1 percent lignoceric acid. gContains 79.7 percent eleostearic acid.

Source: From E. Wertheim and H. Jeskey, “Introductory Organic Chemistry,” ۳rd ed., McGraw-Hill, New York, 1956. Table reproduced by permission of the authors.

 

 

 

Hydrolysis    Since fats and oils are esters, they undergo hydrolysis with more or less ease. The hydrolysis may be induced by chemical means, usually by treatment with NaOH, or by bacterial enzymes that split the molecule into glycerol plus fatty acids. Hydrolysis with the aid of NaOH is called saponification. Hydrolysis by bac- terial action may produce rancid fats or oils and renders them unpalatable. Rancid butter and margarine are notorious for their bad odor.

 

Addition    The fats and oils containing unsaturated acids add chlorine at the double bonds, as other unsaturated compounds do. This reaction is often slow because of the relative insolubility of the compounds. It may represent a significant part of the chlorine demand of some wastes, and chlorinated organics will be produced during chlorination, some of which may be of health concern.

Oils that contain significant amounts of oleic and linoleic acids may be con- verted to fats by the process of hydrogenation. In this process hydrogen is caused to add at the double bonds, and saturated acids result. Thus, low-priced oils such as soybean and cottonseed can be converted into margarine, which is acceptable as human food. Many cooking fats or shortenings are made in the same manner. The hydrogenation can be controlled to produce any degree of hardness desired in the product.

 

Oxidation    The oils with appreciable amounts of linoleic and linolenic acids or other highly unsaturated acids, such as linseed and tung oil, are known as drying oils. In contact with the air, oxygen adds at the double bonds and forms a resinlike material. The drying oils are the major component in all oil-based paints.

 

Waxes

 

Waxes, with the exception of paraffin wax, are esters of long-chain acids and alco- hols of high molecular weight. Beeswax is an ester of palmitic acid and myricyl al- cohol (C15H31COOC31H63). It also contains cerotic acid (C25H51COOH). Spermaceti is obtained from the heads of sperm whales and is principally an ester of palmitic acid and cetyl alcohol (C15H31COOC16H33). Cetyl esters of lauric and myristic acids are also present to a limited extent.

 

 

۵٫۲۲ | PROTEINS AND AMINO ACIDS

 

Proteins are complex compounds of carbon, hydrogen, oxygen, and nitrogen. Phos- phorus and sulfur are present in a few. They are among the most complex of the or- ganic compounds produced in nature and are widely distributed in plants and ani- mals. They form an essential part of protoplasm and enzymes, and are a necessary part of the diet of all higher animals, in which they serve to build and repair muscle tissue. Like polysaccharides, which may be considered to be made up of glucose units, proteins are formed by the union of   -amino acids. Since more than 20 differ- ent amino acids are normally found present in proteins, the variety of proteins is considerable.

 

 

 

Amino Acids

 

The    -amino acids are the building blocks from which proteins are constructed. Most plants and bacteria have the ability to synthesize the amino acids from which they build proteins. Animals are unable to synthesize certain of the amino acids and must depend upon plants to supply them in the form of proteins. Such amino acids are considered to be indispensable.

The amino acids that occur in proteins all have an amino group attached to the alpha carbon atom and are therefore called   -amino acids.

 

NH2

 

Rˆ C ˆ COOH H

 -Amino acid

 

Chemistry of Amino Acids    The free amino acids behave like acids and also like bases because of the amino group that they contain. Thus, they are amphoteric in character and form salts with acids or bases.

Salt formation with an acid:

 

H2NCH2COOH     HCl l Cl               H3NCH2COOH                (۵٫۴۸) Salt formation with a base:

H2NCH2COOH     NaOH l H2O     H2NCH2COO            Na                   (۵٫۴۹)

 

The amino acids having one amino and one carboxyl group are essentially neu- tral in aqueous solution. This is considered to be due to a case of self-neutralization in which the hydrogen ion of the carboxyl group migrates to the amino group and a positive-negative (dipolar) ion known as a zwitterion results.

 

 

NH2

Rˆ Cˆ COOH

H

 

 

۳

NH +

. Rˆ Cˆ COO–

H

Zwitterion

 

 

(۵٫۵۰)

 

 

In Sec. 5.9 it was shown that organic acids can react with ammonia to form amides. The amino and carboxyl groups of separate amino acid molecules can react in the same manner.

 

O                       R H

Rˆ Cˆ Cˆ OH  H Nˆ C ˆ COOH  l

H    H NH2

O           R H

 

Rˆ Cˆ CˆNˆ C ˆ COOH      H2O


(۵٫۵۱)

 

H    H NH2

A dipeptide

 

 

 

It is this ability to form linkages between the amino and carboxyl groups that al- lows the large complex molecules of proteins to be formed. In the example given in Eq. (5.51), the resulting molecule contains one free amino and one free car- boxyl group. Each can combine with another molecule of an amino acid. In turn, the resulting molecule will contain free amino and carboxyl groups, and the process can be repeated, presumably, ad infinitum. Biochemical processes, how- ever, direct the synthesis to produce the type and size of protein molecules desired.

The molecule formed by the union of two molecules of amino acids is known as a dipeptide; if there are three units, the name is tripeptide; if more than three units, the compound is called a polypeptide. The particular linkage formed when amino acids join is called the peptide link and is formed by loss of water between an amino and a carboxyl group.

 

O                                        O

H                        H

 

ˆ Cˆ OH  H ˆNˆ  l


ˆ CˆNˆ     H2O

Peptide link


(۵٫۵۲)

 

 

Classes of Amino Acids    About 20 different   -amino acids can generally be iso- lated by the hydrolysis of protein matter. The simplest have one amino group and one carboxyl group per molecule. Some have sulfur in the molecule. Some have two amino groups and one carboxyl group and consequently are basic in reaction. Some have one amino group and two carboxyl groups and are acidic in reaction. Others have aromatic or heterocyclic groups.

All the amino acids, except glycine, are optically active. In the following list, those marked with an asterisk are considered indispensable in human nutrition. The generally used abbreviation for each amino acid is noted after the name.

 

 

Monoamino monocarboxy acids

 

H2NCH2COOH CH3CHNH2COOH

 

 

Glycine (Gly) Alanine (Ala)

 

H    H CH3

 

 

 

CH3

 

C ˆ C ˆ COOH

 

NH2


*Valine (Val)

 

H           H CH3               H

 

 

CH3


C ˆ Cˆ C ˆ COOH H

NH2


*Leucine (Leu)

 

H    H CH3

 

 

 

C2H5


C ˆ C ˆ COOH NH2


*Isoleucine (Ile)

 

 

 

Monocarboxy diamino acids

 

H

N                                  H

H

 

H2Nˆ Cˆ Nˆ CH2(CH2)2 ˆ Cˆ COOH

 

NH2


Arginine (Arg)

 

O

H2Nˆ Cˆ CH2 ˆ CH ˆ COOH NH2

H2Nˆ CH2 ˆ(CH2)3ˆ CH ˆ COOH

 

NH2

 

 

Asparagine (Asn)

 

 

*Lysine (Lys)

 

O

H2Nˆ Cˆ (CH2)2 ˆ CH ˆ COOH NH2

 

 

Glutamine (Gln)

 

 

 

Aromatic homocyclic acids

 

 

H

ˆ CH2 ˆ Cˆ COOH

NH2

 

 

HO

H

ˆ CH2 ˆ Cˆ COOH

NH2

 

*Phenylalanine (Phe)

 

 

 

 

 

Tyrosine (Tyr)

 

I                      I

H    H

 

HO            ˆ Oˆ


Cˆ Cˆ COOH


Thyroxine (Thy)

 

H    NH2

I                      I

 

 

 

Monoamino monocarboxy monohydroxy acids

 

OH H

 

HCˆ Cˆ COOH

 

 

 

 

Serine (Ser)

 

 

H    NH2

 

H    H

 

 

CH3 ˆ C ˆ C ˆ COOH

 

*Threonine (Thr)

 

 

O    NH2

H

 

 

 

Sulfur-containing acids

 

H

S    H

 

HCˆ Cˆ COOH


Cysteine (Cys)

 

H    NH2

H

 

CH3 ˆSˆCH2ˆCH2 ˆ Cˆ COOH NH2

 

*Methionine (Met)

 

 

 

 

Dicarboxy monoamino acids

HOOC ˆ CH2ˆ CH ˆ COOH NH2

HOOC ˆ CH2ˆ CH2ˆ CH ˆ COOH

 

NH2


Aspartic acid (Asp) Glutamic acid (Glu)

 

 

 

 

Heterocyclic acids

 

 

 

 

 

 

 

 

H2C

 

 

H N

H

ˆ CH2 ˆ Cˆ COOH

NH2

H

N  H

C ˆ COOH

 

 

 

 

 

*Tryptophan (Trp)

 

 

 

Proline (Pro)

 

 

H2Cˆˆ CH2

 

H

 

 

H2C


N  H

C ˆ COOH

 

Hydroxyproline (Hypro)

 

 

HOCˆˆ CH2

H

 

 

H

N                     H

HC         Cˆ CH2 ˆ C ˆ COOH NH2

 

 

 

Histidine (His)

 

Nˆˆ CH

 

Proteins from different sources yield varying amounts of the different amino acids upon hydrolysis. The protein from a given source, however, normally yields the same amino acids and in the same ratio. All proteins yield more than one amino acid.

 

 

 

Proteins

 

Proteins constitute a very important part of the diet of humans, particularly in the form of meats, cheeses, eggs, and certain vegetables. The processing of these mate- rials, except for eggs, results in the production of industrial wastes that can gener- ally be treated by biological processes.

 

Properties of Proteins    Protein molecules are very large and have complex chem- ical structures. Insulin, which contains 51 amino acid units per molecule, was the first protein for which the precise order of the atoms in the molecule was discov- ered. For this significant achievement, Frederick Sanger at the University of Cam- bridge received the Nobel prize in 1958. Among the large number of proteins for which the order of atoms is now known are ribonuclease with 124 amino acids, to- bacco mosaic virus protein with 158 amino acids, and hemoglobin with 574 amino acid units. Hemoglobin has a molecular weight of 64,500 and contains 10,000 atoms of hydrogen, carbon, nitrogen, oxygen, and sulfur, plus 4 atoms of iron. The iron atoms are more important than all the rest as they give blood its ability to com- bine with oxygen. Some protein molecules are thought to be 10 to 50 times larger than that of hemoglobin.

All proteins contain carbon, hydrogen, oxygen, and nitrogen. Regardless of their source, be it animal or vegetable, the ultimate analysis of all proteins falls within a very narrow range, as shown here:

 

Percentage

Carbon                                ۵۱–۵۵

Hydrogen                          ۶٫۵–۷٫۳

Oxygen                               ۲۰–۲۴

Nitrogen                             ۱۵–۱۸

Sulfur                                ۰٫۰–۲٫۵

Phosphorus                        ۰٫۰–۱٫۰

 

The nitrogen content varies from 15 to 18 percent and averages about 16 percent. Since carbohydrates and fats do not contain nitrogen, advantage is taken of this fact in food analysis to calculate protein content. The value for nitrogen as determined by the Kjeldahl digestion procedure (Sec. 25.3), when multiplied by the factor

۱۰۰/۱۶ or 6.25, gives an estimate of the protein content. This procedure is some- times used to estimate the protein content of domestic and industrial wastes and of sludges from their organic nitrogen (Sec. 25.3) content. There are several other nitrogen-containing organics in such wastes, however, and so such estimates should be considered only as crude approximations.

 

Biological Treatment of Protein Wastes    In general, satisfactory treatment of wastes containing significant amounts of proteins requires the use of biological processes. In these processes, the first step in degradation of the protein is consid- ered to be hydrolysis, induced by hydrolytic enzymes. The hydrolysis is considered to progress in steps in reverse manner to those in which proteins are synthesized.

 

 

 

 

Hydrolysis Products of Proteins

 

Protein l polypeptides

b

 

 

 

(۵٫۵۳)

 

 – amino acids k


dipeptides

 

 

The   -amino acids are then deaminated by enzymic action, and free fatty and other acids result. The free acids serve as food for the microorganisms, and they are con- verted to carbon dioxide and water.

 

 

 

DETERGENTS

 

۵٫۲۳ | DETERGENTS

 

The term detergent is applied to a wide variety of cleansing materials used to re- move soil from clothes, dishes, and a host of other things. The basic ingredients of detergents are organic materials that have the property of being “surface ac- tive” in aqueous solution and are called surface-active agents or surfactants. All surfactants have rather large polar functional groups. One end of the molecule is particularly soluble in water and the other is readily soluble in oils. The solubil- ity in water is due to carboxyl, sulfate, hydroxyl, or sulfonate groups. The surfac- tants with carboxyl, sulfate, and sulfonate groups are all used as sodium or potas- sium salts.

 

Oil-soluble part      Water-soluble part

ˆ COO Na

 

 

Organic group


ˆ SO4 Na

 

۳

ˆ SO Na

ˆ OH

 

The nature of the organic part of the molecule varies greatly with the various surfac- tant types.

 

 

۵٫۲۴ | SOAPS

 

Ordinary soaps are derived from fats and oils by saponification with sodium hy- droxide. Saponification is a special case of hydrolysis in which an alkaline agent is present to neutralize the fatty acids as they are formed. In this way the reaction is caused to go to completion.

 

 

H2COOCC17H35

Hˆ COOCC17H35     ۳NaOH H2COOCC17H35

Stearin


H2COH

 

l Hˆ COH      ۳C17H35COONa

 

H2COH

Glycerol

 

 

(۵٫۵۴)

 

 

 

The fats and oils are split into glycerol and sodium soaps. The nature of the soap de- pends upon the type of fat or oil used. Beef fat and cottonseed oil are used to pro- duce low-grade, heavy-duty soaps. Coconut and other oils are used in the produc- tion of toilet soaps.

All sodium and potassium soaps are soluble in water. If the water is hard, the calcium, magnesium, and any other ions causing hardness precipitate the soap in the form of metallic soaps.

۲C17H35COONa(aq)     Ca2     l (C17H35COO)2Ca(s)     ۲Na                  (۵٫۵۵) Soap must be added to precipitate all the ions causing hardness before it can act as a

surfactant, usually indicated by the onset of frothing upon agitation.

 

 

 

۵٫۲۵ | SYNTHETIC DETERGENTS

 

Since 1945 a wide variety of synthetic detergents have been accepted as substitutes for soap. Their major advantage is that they do not form insoluble precipitates with the ions causing hardness. Most commercially available products contain from 20 to

۳۰ percent surfactant (active ingredient) and 70 to 80 percent builders. The builders are  usually  sodium  sulfate,  sodium  tripolyphosphate,  sodium  pyrophosphate, sodium silicate, and other materials that enhance the detergent properties of the ac- tive ingredient. The use of phosphate has been curtailed because of its role in eu- trophication. The synthetic surfactants are of three major types: anionic, nonionic, and cationic.

 

 

Anionic Detergents

 

The anionic detergents are all sodium salts and ionize to yield Na     plus a negatively charged, surface-activated ion. The common ones are all sulfates and sulfonates.

 

 

Sulfates   Long-chain alcohols when treated with sulfuric acid produce sulfates (in- organic esters) with surface-active properties. Dodecyl or lauryl alcohol is com- monly used.

 

C12H25OH     H2SO4 l C12H25ˆOˆSO3H   H2O                (۵٫۵۶)

Lauryl

alcohol

 

The sulfated alcohol is neutralized with sodium hydroxide to produce the surfactant.

 

C12H25ˆOˆSO3H   NaOH l C12H25ˆOˆSO3Na   H2O        (۵٫۵۷)

Sodium lauryl sulfate

 

The sulfated alcohols were the first surfactants to be produced commercially. The sulfated alcohols are used in combination with other synthetic detergents to produce blends with desired properties.

 

 

 

Sulfonates    The  principal  sulfonates  of  importance  are  derived  from  esters, amides, and alkylbenzenes.

 

 

O           H    H    O


H                          R

 

 

Rˆ Cˆ O ˆ C ˆ C ˆ S ˆ O ˆNa

 

Rˆ CˆR

 

Rˆ CˆR

 

 

H    H    O

Ester

 

 

O           H    H    O

 

 

O ¨ S¨O

 

 

O ¨ S¨O

 

Rˆ Cˆ N ˆ C ˆ C ˆ S ˆ O ˆNa

O                          O

 

H    H    O

N ˆ C ˆ H

 

Na

Secondary

 

Na

Tertiary

 

H

Amide


Sulfonated alkylbenzenes

 

 

The esters and amides are of organic acids with 16 or 18 carbon atoms. In the past the alkylbenzene sulfonates (ABS) were derived largely from polymers of propylene, and the alkyl group, which averaged 12 carbon atoms, was highly branched. These materials are now made largely from normal (straight-chain) paraffins, and thus the alkane chain is not branched and the benzene ring is attached primarily to secondary carbon atoms. These latter materials have been labeled LAS (linear alkyl sulfonate).

 

Nonionic Detergents

 

The nonionic detergents do not ionize and have to depend upon groups in the mole- cule to render them soluble. All depend upon polymers of ethylene oxide (C2H4O) (polyethoxylates) to give them this property.

 

 

 

O

 

Rˆ Cˆ O ˆ[C2H4O]xH


R

 

ˆ O ˆ[C2H4O]xH

 

 

Ester type                                                  Aryl type

O

 

Rˆ Cˆ N ˆ[C2H4O]xH R

 

HO[C2H4O]xH

 

Amide type                                            Ethylene oxide polymer type

 

Nonylphenol (Sec. 5.14) and octylphenol with a variable number of ethylene oxides are important members of the aryl class.

 

 

 

Cationic Detergents

 

The cationic detergents are salts of quaternary ammonium hydroxide. In quater- nary ammonium hydroxide, the hydrogens of the ammonium ion have all been replaced with alkyl groups. The surface-active properties are contained in the cation.

 

 

R

 

RˆNˆR

 

R”’


+

 

Cl–

 

A cationic detergent

 

The cationic detergents are noted for their disinfecting (bactericidal) properties. They are used as sanitizing agents for dishwashing where hot water is unavailable or undesirable. They are also useful in the washing of babies’ diapers, where steril- ity is important. If diapers are not sterilized by some means, bacterial infestations may occur that release enzymes that will hydrolyze urea to produce free ammonia [Eq. (5.43)]. The high pH resulting is harmful to the tender skin of babies, and the odor of free ammonia is unpleasant to all.

 

 

Biological Degradation of Detergents

 

Detergents vary greatly in their biochemical behavior, depending on their chemical structure.22  Common soaps and the sulfated alcohols are readily used as bacterial food. The synthetic detergents with ester or amide linkages are readily hydrolyzed. The fatty acids produced serve as sources of bacterial food. The other hydrolysis product may or may not serve as bacterial food, depending upon its chemical struc- ture. The synthetic detergents prepared from polymers of ethylene oxide appear susceptible to biological attack. However, recent evidence has demonstrated they are only partially transformed, leaving an alkyl aromatic compound that can be chlorinated or brominated during chlorine disinfection. As noted previously, the alkylphenols are suspected endocrine disruptors. The alkyl-benzene sulfonates de- rived from propene were highly resistant to biodegradation, and their persistence resulted in excessive foaming in rivers and groundwaters in the 1950s. This pre- sented some of the first evidence of the potential harmful environmental conse- quences of synthetic organic chemicals. For this reason, the detergent manufactur- ing industry changed to the production of LAS surfactants. LAS is readily degradable under aerobic conditions, and its use has helped relieve the most seri- ous problems of detergent foaming. However, unlike common soap, it is resistant

 

 

۲۲C. N. Sawyer and D. W. Ryckman, Anionic Detergents and Water Supply Problems, J. Amer. Water

Works Assoc., 49: 480 (1957).

 

 

 

to degradation under anaerobic conditions. Currently, there is a United States EPA secondary standard of 0.5 mg/L for foaming agents. Enforcement of secondary standards by states is optional.

 

 

PESTICIDES

 

۵٫۲۶ | PESTICIDES

 

Pesticides are materials used to prevent, destroy, repel, or otherwise control ob- jectionable insects, rodents, plants, weeds, or other undesirable forms of life. Common pesticides can be categorized chemically into three general groups, in- organic, natural organic, and synthetic organic. They may also be classified by their biological usefulness, viz., insecticides, herbicides, algicides, fungicides, and rodenticides.

The synthetic organic pesticides gained prominence during World War II, and since then their numbers have grown into the thousands, while the total an- nual production has increased to about 1.5 billion pounds of active ingredients. They are used mainly for agricultural purposes. The synthetic organic pesticides are best classified according to their chemical properties, since this more readily determines their persistence and behavior when introduced into the environment. The major types of synthetic pesticides are the chlorinated hydrocarbons, the or- ganic phosphorus pesticides, and the carbamate pesticides. An additional category of current interest is the s-triazine pesticides. There are many other types of syn- thetic pesticides.

 

 

۵٫۲۷ | CHLORINATED PESTICIDES

 

Chlorinated pesticides are of many types and have been widely used for a variety of purposes. DDT proved to be an extremely versatile insecticide during World War II when it was used mainly for louse and mosquito control. It is still one of the major pesticides used internationally, although use in the United States has been banned for quite some time for environmental reasons. DDT is a chlorinated aromatic com- pound with the following structure:

 

 

 

 

Clˆ

 

H

 

ˆ C ˆ

 

Clˆ C ˆ Cl

 

Cl

DDT

 

 

 

ˆ Cl

 

 

Technical grade DDT contains three isomers, the above isomer representing about 70 percent of the total. It has the long technical name 2,2-bis(p– chlorophenyl)-1,1,1-trichloroethane.

 

 

 

When benzene and chlorine react in direct sunlight, the addition product ben- zene hexachloride or BHC is formed. Several stereoisomers are produced, but the gamma isomer called lindane is by far the most effective as an insecticide.

 

Cl     Cl

 

H                H H      H

Cl     Cl

Cl               Cl

 

H      H

 -Benzene hexachloride (lindane)

 

Two other formerly widely used chlorinated insecticides are endrin and dield- rin. They are isomers, and their structural formulas appear the same:

 

Cl

 

 

Cl

 

Clˆ Cˆ Cl

 

Cl

 

 

Hˆ CˆH                O

 

 

Cl

Dieldrin or endrin

 

However, their spatial configurations are significantly different, as are their insecti- cidal properties.

Chlorinated pesticides are also used as herbicides. Two of the most common are 2,4-D and 2,4,5-T.

 

Cl                                                Cl

 

 

ˆ O ˆCH2COOH


ˆ O ˆCH2COOH

 

 

Cl                                                Cl

Cl

 

۲,۴-Dichlorophenoxyacetic acid

(۲,۴-D)

 

۲,۴,۵-Trichlorophenoxyacetic acid

(۲,۴,۵-T)

 

 

 

These two herbicides are effective in destroying certain broad-leaf plants while not killing grasses. They have also been used for aquatic-plant control in lakes, ponds, and reservoirs. Dioxin, an extremely toxic organic to humans, is a side product con- taminant in 2,4,5-T, which has led to restrictions in its use. Dioxins are also formed

 

 

 

during the combustion of chlorinated organic compounds. The most toxic dioxin is

۲,۳,۷,۸-tetrachlorodibenzo-p-dioxin (TCDD):

 

Cl                 O                 Cl

 

 

Cl                 O                 Cl

۲,۳,۷,۸-Tetrachlorodibenzo-p-dioxin (TCDD)

 

Because of its extreme toxicity, a very low drinking water MCL of 3     ۱۰   ۵   g/L

has been established for this dioxin.

The family of compounds called the chloroacetamides are also commonly used as herbicides for control of broad-leaf weeds. Two of the most common examples are  alachlor  [۲-chloro-2 ,6 -diethyl-N-(methoxymethyl)-acetanilide)  and  meto- lachlor   [۲-chloro-6 -ethyl-N-(2-methoxy-1-methyl-ethyl)acet-o-toluidine].   These herbicides are used primarily for weed control in the production of corn and soy- beans.

 

 

H    O           H           H


H    O       H3C    H           H

 

 

Clˆ C ˆ C

 

C ˆ Oˆ C ˆ H N

 

Clˆ C ˆ C

 

C ˆ C ˆ Oˆ C ˆ H N

 

H                  H           H

H    H                  H    H


H                  H    H           H

H                  H    H

 

 

Hˆ C ˆ C ˆ

 

ˆ C ˆ C ˆ H

 

Hˆ C ˆ

 

ˆ C ˆ C ˆ H

 

 

H    H                  H    H

Alachlor

 

H                  H    H

Metolachlor

 

 

Other chlorinated or halogenated pesticides of significance are aldrin, chlor- dane, toxaphene, heptachlor, methoxychlor, DDD, EDB, DBCP, and 1,2- dichloropropane; all have been used as insecticides, fungicides, or nematocides. All halogenated pesticides are considered to be of significant concern because of their persistence and high potential for creating harm to humans and the environ- ment. For this reason aldrin and dieldrin are now banned from use in the United States, and many of the other chlorinated pesticides have been greatly restricted in usage.

 

 

۵٫۲۸ | ORGANIC PHOSPHORUS PESTICIDES

 

The organic phosphorus pesticides became important as insecticides after World War II. These compounds were developed in the course of chemical warfare re- search in Germany and in general are quite toxic to humans as well as to pests. Parathion is an important pesticide, which was introduced into the United States

 

 

 

from Germany in 1946. It is an aromatic compound and contains sulfur and nitro- gen as well as phosphorus in its structure, so do many of the organic phosphorus pesticides.

 

 

OC2H5

 

S¨ P ˆ O ˆ

 

OC2H5

 

 

 

ˆNO2

 

O,O-Diethyl-Op-nitrophenylthiophosphate

(parathion)

 

Parathion has been particularly effective against certain pests such as the fruit fly. However, it is also quite toxic to humans and extreme caution must be exercised in its use.

Malathion is highly toxic to a variety of insects, but unlike many organic phos- phorus pesticides, it has low toxicity to mammals. This has made it particularly suc- cessful and it is widely used.

 

CH3O   S                     O

 

 

 

CH3O


P ˆSˆ CH ˆ Cˆ OC2H5

 

CH2ˆ Cˆ OC2H5

 

O

 

S-(1,2)-Dicarbethoxyethyl)-O,O-dimethyldithiophosphate

(malathion)

 

Other organic phosphorus pesticides of significance are methyl parathion, glyphosate, demeton, guthion, systox, metasystox, chlorthion, disyston, and dicapthon.

 

 

۵٫۲۹ | CARBAMATE PESTICIDES

 

Carbamate pesticides are amides having the general formula RHNCOOR . One that has received wide usage is isopropyl N-phenylcarbamate (IPC).

 

H                   CH3

 

ˆN ˆC ˆO ˆCH

 

O           CH3

Isopropyl N-phenylcarbamate

(IPC)

 

IPC is a herbicide that is effective for the control of grasses, without affecting broad-leaf crops. Other carbamates of importance are aldicarb, carbaryl (Sevin  ), carbofuran, ferbam, and captan. Carbamates in general appear to have low toxicity to mammals.

 

 

 

۵٫۳۰ | s-TRIAZINES

 

The class of compounds called the s-triazines are primarily used as herbicides in

agricultural  regions  and  are  of  three  general  types:

(۱)

chloro  s-triazines,  (۲)

methylthio s-triazines, and (3) methoxy s-triazines:

Cl                                         SCH3

OCH3

N       N                               N       N                             N       N

 

 

RHN


N       NHR


RHN


N       NHR


RHN       N


NHR

 

Chloro-s-triazine


Methylthio-s-triazine


Methoxy-s-triazine

 

 

Two of the most commonly used s-triazines are atrazine (2-chloro-4-ethyl- amino-6-isopropylamino-s-triazine) and cyanazine [2-chloro-4-ethylamino-6-(1- cyano-1-methylethylamino)-s-triazine].

 

 

 

 

 

 

H5C2HN

 

Cl

 

N       N

 

N       NHCH(CH3)2

 

 

 

 

 

H5C2HN

 

Cl

 

N       N        CH3

N         NHC    CN CH3

 

Atrazine


Cyanazine

 

 

Atrazine is currently one of the most widely used herbicides, is difficult to degrade biologically, and is a commonly detected groundwater and surface water contami- nant in agricultural areas.

 

 

۵٫۳۱ | BIOLOGICAL PROPERTIES OF PESTICIDES

 

Pesticides may gain access to groundwater and surface water supplies through di- rect application or through percolation and runoff from treated areas. Several recent surveys have shown that pesticides are present in many groundwater and surface water supplies. For example, one report indicated that 46 different pesticides were found in groundwaters in 26 states.23 Concentrations are typically higher in surface waters than in groundwaters. Some pesticides are toxic to fish and other aquatic life at only a small fraction of a milligram per liter. They also tend to concentrate in aquatic plants and animals to values several thousand times that occurring in the water in which they live. Also, some pesticides are quite resistant to biological degradation and persist in soils and water for long periods of time. A major concern with all pesticides is the potential for incomplete transformation of the parent com- pound into metabolites that may be more or less toxic.

 

 

۲۳D. J. Munch et al., Methods Development and Implementation for the National Pesticide Survey. Env. Sci. Tech., 24: 1445–۱۴۵۱ (۱۹۹۰).

 

 

 

In general, the chlorinated pesticides are the most resistant to biological degra- dation and may persist for months or years following application. Many are also highly toxic to aquatic life or to birds that feed on aquatic life. This persistence and great potential for harm has led to restrictions on chlorinated pesticide usage. Sev- eral chlorinated pesticides (e.g., DDT, dieldrin, methoxychlor, toxaphene) are sus- pected endocrine disruptors. As a group, the organic phosphorus pesticides are not too toxic to fish life and have not caused much concern in this respect, except when large accidental spills have occurred. Also, they tend to hydrolyze rather quickly at pH values above neutral, thus losing their toxic properties. Under proper conditions such as dryness, however, some have been observed to persist for many months. Their main potential for harm is to farm workers who become exposed both from contact with previously sprayed foliage as well as from direct contact during or- ganic phosphorus pesticide application. Some of these pesticides are readily ab- sorbed through the skin and affect the nervous system by inhibiting the enzyme cholinesterase, which is important in the transmission of nerve impulses. The carba- mates are noted for their low toxicity and high susceptibility to degradation. The s-triazines  are  in  general  quite  resistant  to  environmental  degradation  and  are known endocrine disruptors.

Because of the several potential health problems that have been associated with pesticides, drinking water MCLs have been established for several pesticides that are still in somewhat common usage. These are listed in Table 34.1.

 

 

 

۵٫۳۲ | PHARMACEUTICALLY ACTIVE AND

ENDOCRINE-DISRUPTING CHEMICALS

 

Two groups of chemicals of emerging concern are pharmaceutically active chemi- cals (PhACs) and endocrine-disrupting chemicals (EDCs). These compounds are being found in surface waters and groundwaters and in wastewater treatment plant effluents in the ng/L (parts per trillion) to   g/L concentration range. Understanding the fate and effects of these chemicals in the environment and removing them from drinking water supplies and wastewaters present difficult challenges for environ- mental engineers and scientists.

 

 

Pharmaceutically Active Chemicals (PhACs)

 

Pharmaceuticals are generally defined as chemicals used for the treatment or pre- vention of illness. As such, they can range from compounds used for cancer treat- ment (chemotherapy) and birth control to antibiotics used to combat infection to compounds used to relieve pain (e.g., aspirin and ibuprofen). They are found in per- sonal care products such as fragrances, disinfectants and antiseptics, sunscreen agents, and preservatives. Pharmaceuticals are also used in veterinary health care (e.g., antibiotics and growth hormones). Very little is known with respect to the ef-

 

 

 

fect of PhAC on human and wildlife health. However, there is potential for adverse effects and the reasoning goes like this. Most of these compounds are lipophilic (“fat-loving”; synonymous with hydrophobic) and their activity is slow to decay (that is, they remain pharmaceutically active for an extended time). Thus, bioconcen- tration is possible. While the concentration of individual PhACs in water supplies is low (generally less than 0.5   g/L with many in the ng/L range), the presence of numerous drugs with similar modes of action could lead to measurable effects. Finally, exposure can be chronic because PhACs are continually introduced into the environment via human wastewater treatment, livestock production, and similar ac- tivities. One special concern with antibiotics is the development of antibiotic- resistant strains of pathogenic bacteria due to overuse of these compounds. In gen- eral this is because a large portion of the administered antibiotic leaves the body (humans and animals) via urine and feces as a mixture of parent compound and metabolites.

PhACs come from a wide variety of organic chemical classes. Examples of PhACs that have been found in surface waters and wastewater treatment effluents include pain killers such as ibuprofen (a chiral compound), acetaminophen, acetyl- salicylic acid (aspirin), and codeine; antibiotics in the sulfonamide, tetracycline, flu- oroquinolone, and macrolide classes; chlofibric acid [environmental metabolic of the lipid regulator clofibrate (helps lower cholesterol)], and caffeine. Some chemi- cal structures are given here.

 

O

O        OH HN

O       O

 

 

 

O               OH

 

OH

Ibuprofen               Acetaminophen              Acetylsalicylic acid

(aspirin)

 

 

O                                               NH2

 

H3C


H2  H2


O    S    O

 

C   C

 

 

O

Hˆ   H       H HO

 

N CH3

 

 

 

 

NH2

 

Codeine                               Sulfanilamide

 

 

 

H3C        CH3                                 HN

 

HO     CH3


N

OH                           N                 N

OH              NH2                                                                                                 OH F

 

OH    O


OH    O       O                                                    O       O

 

Tetracycline                                                           Fluoroquinolone

 

 

 

H3C HO


O

CH3

 

OH OH

 

 

H3C HO         N

 

 

 

 

CH3

 

H3C         H C


CH3

 

H2C        O 3

CH3

 

O

H3C      O

 

O                O               O


CH3

 

CH3                                       CH3

O

OH

CH3

 

Erythromycin (a macrolide antibiotic)

 

Cl                                                        O

 

 

CH3

 

 

 

 

 

H3C

 

 

O

OH

 

C

H3 O


H3C

 

 

O


N              N N        N

CH3

 

Clofibric acid                                    Caffeine

 

Endocrine-Disrupting Chemicals (EDCs)

 

The human endocrine system, which includes a variety of glands (e.g., thyroid, pitu- itary, pineal, ovaries, and testes) and the hormones they produce (e.g., adrenaline, es- trogens, and testosterone), regulates growth, development, reproduction, and behav- ior. Chemical structures for testosterone and estradiol, an estrogen, are given here.

 

 

CH3 OH

 

CH3 OH

 

 

H3C       H                                                   H

 

H       H                                         H       H

O                                                HO

Testosterone                                     Estradiol (an estrogen)

 

 

 

There is concern that some synthetic organic chemicals released into the environ- ment can interfere with or disrupt this system. In general, it is thought that such compounds mimic the body’s natural hormones, binding with receptor molecules in the body, and thus interfering with the regulation of the endocrine system. An ex- cellent review of how EDCs can interfere with the endocrine system is given by Trussell.24  There is still some controversy as to whether observed effects of EDCs are due to their hormonal properties or some other toxicological mechanism.25  For this and other reasons, a National Research Council committee recommends use of the term hormonally active agent (HAA) instead of EDC.26  It should be noted that some naturally produced organic compounds (e.g., phytoestrogens produced by plants such as soybeans) and inorganic chemicals (e.g., lead, mercury) can also act as EDCs. Some PhACs are also EDCs (for example, growth hormones used in live- stock production).

EDCs have been reported to have a variety of effects on humans and wildlife; most are developmental abnormalities, although some neurological and immuno- logical effects have been reported. A widely reported example is the effect of di- ethylstilbestrol (DES), a synthetic estrogen used in the 1950s to prevent miscar- riages. Children of mothers taking DES during pregnancy experienced a wide variety of problems including cancers of the vagina and cervix, malformed repro- ductive organs, undescended testicles, and abnormal sperm. These effects were as- sociated with high exposure to DES. Recent reports indicate effects in wildlife as- sociated with exposure to lower levels of EDCs. For example, developmental abnormalities in alligators in Florida and male fish living near outfalls from waste- water treatment plants, and declines in fish and bird populations in the Great Lakes have been associated with EDC exposure. It must be stressed that much more needs to be learned about the effects of EDCs on adverse health outcomes in hu- mans and wildlife.

A wide variety of chemicals have been implicated as EDCs. These include several pesticides, organochlorine compounds including PCBs, phenolic com- pounds, phthalates, PAHs, synthetic steroids, and triazines. Specific examples in- clude  malathion,  dieldrin,  methoxychlor,  DDT  and  its  metabolites,  dioxin (TCDD), pentachlorophenol, bisphenol A, nonylphenol, butyl benzyl phthalate, and atrazine. Phytoestrogens include a variety of flavones and isoflavones. Chemi- cal structures for PCBs, malathion, dieldrin, DDT, dioxin, pentachlorophenol, bisphenol A, nonylphenol, and atrazine were given in Secs. 5.13 to 5.30. Structures

 

 

 

 

۲۴R. R. Trussell, Endocrine Disrupters and the Water Industry, J. American Water Works Assoc., 93(2):

۵۸–۶۵, ۲۰۰۱٫

۲۵National Research Council, “Hormonally Active Agents in the Environment,” National Academy

Press, Washington, D.C., 1999.

۲۶Use of the acronym HAA for hormonally active agent may cause confusion. As noted in Sec. 5.8,

HAA is also used by environmental engineers and scientists to describe the haloacetic acids produced as disinfection by-products and regulated as drinking water contaminants.

 

 

 

for methoxychlor, butyl benzyl phthalate, and genistein, an isoflavone in soybeans are given here.

 

 

 

O                                      O

H3C                                                    CH3

 

 

Clˆˆ Cl

Cl

 

O

O O

H2

O       C

C       C

H2          H2

 

 

 

 

 

 

CH3

 

Methoxychlor


Butyl benzyl phthalate

 

 

O                 OH

 

 

 

O       OH HO

Genistein

 

 

BEHAVIOR OF ORGANICS IN THE ENVIRONMENT AND IN ENGINEERED SYSTEMS

 

۵٫۳۳ | INTRODUCTION

 

It is important for the environmental engineer and scientist to have knowledge of the  properties,  both  physicochemical  and  structural,  of  the  different  types  and classes of organic compounds to aid in understanding and predicting the fate, ef- fects, and potential of engineered processes for removal or control of these com- pounds. In the previous sections classes of organic compounds were described with respect to the functional group or groups characteristic of each class of compound. These characteristic functional groups also manifest themselves in other important properties that aid in understanding the behavior of organics in the environment and in engineered reactors. Physicochemical properties include, but are not limited to, solubility, hydrophobicity, polarity, volatility, density, and energy content. Solubil- ity, hydrophobicity, and polarity are somewhat related and are useful in understand- ing the tendency of organics to partition between phases (i.e., solid-liquid or liquid- gas partitioning). Volatility, which can be quantified using Henry’s constant or vapor pressure (Chap. 2), is useful in understanding partitioning between the gas and liquid phases. Density is useful in understanding physical separation potential and  transport  behavior.  Energy  content  is  useful  in  predicting  bacterial  yields (Chap. 6). Structural characteristics such as molecular connectivity and molecular surface area can be related through structure- and property-activity relationships (SARs and PARs) that can be used to predict compound behavior and fate. Detailed discussion of these and other properties is beyond the scope of this text; additional material can be found in the references listed at the end of the chapter.

 

 

 

۵٫۳۴ | FATE OF ORGANICS

 

Important processes involved in the movement and fate of organics in the environment and in engineered systems are listed in Table 5.14. Processes especially important in understanding the fate and removal of organics found at contaminated sites and in in- dustrial wastes and leachates are volatilization, sorption, and transformation reactions.

 

Volatilization

 

The concepts relevant to volatilization were introduced in Sec. 2.9 and are reviewed here. The equation for Henry’s law constants (KH) for chemical equilibrium be- tween gaseous and aqueous phases is repeated here:

 

 

concentration in gas


Pgas

 

KH     concentration in water     C

 

equil


(۲٫۱۵)

 

 

KH can be thought of as a partition coefficient between water and the atmosphere. It can take several forms. The most common units are partial pressure (atm)/molar concentration (mol/L) or atm/M. The so-called unitless Henry’s constant H results when the concentrations in both water and gas are expressed in mol/vol. Conversion can be made using the following:

 

H      KH

RT

 

(۵٫۵۸)

 

 

where R is 0.08206 atm/M-K and T is the temperature (K). Henry’s constant has a strong temperature dependence; organic compounds are less volatile at lower tem- peratures. Values of Henry’s constant for some environmentally significant organic compounds are given in Table 5.15. The higher the value of KH, the more likely the compound is to partition to the atmosphere.

 

 

 

Table 5.14 | Processes involved in the fate of organics

 

Process

Air

Water

Soil

Meteorological transport

X

Condensation

X

Settling

X

X

Volatilization

X

X

Runoff (erosion)

X

Filtration

X

Sorption

X

X

X

Desorption

X

X

X

Precipitation

X

X

X

Chemical transformation

Photolysis

X

X

Hydrolysis

X

X

X

Oxidation

X

X

X

Reduction

X

X

X

Bio-uptake (bioconcentration)

X

X

Biodegradation (biotransformation)

X

X

 

 

 

Table 5.15 | Values of Kow, water solubilities and Henry’s law constants for selected organic compounds

 

Water solubility,

KH,

Compound

log Kow

mg/L

atm/M

Data from Yaws for 25 C

Halogenated aliphatic compounds

Methanes

Chloromethane

۰٫۹۱

۵,۹۰۰

۸٫۲

Dichloromethane

۱٫۲۵

۱۹,۴۰۰

۲٫۵

Chloroform

۱٫۹۷

۷,۵۰۰

۴٫۱

Bromoform

۲٫۴

۳,۱۰۰

۰٫۵۹

Carbon tetrachloride

۲٫۸۳

۷۹۰

۲۹

Dichlorodifluoromethane

۲٫۱۶

۱۸,۸۰۰

۳۹۰

Ethanes

Chloroethane

۱٫۴۳

۹,۰۰۰

۶٫۹

۱,۱-Dichloroethane

۱٫۷۹

۵,۰۰۰

۵٫۸

۱,۲-Dichloroethane

۱٫۴۸

۸,۷۰۰

۱٫۱۸

۱,۱,۱-Trichloroethane

۲٫۴۹

۱,۰۰۰

۲۲

۱,۱,۲-Trichloroethane

۱٫۸۹

۴,۴۰۰

۰٫۹۲

Hexachloroethane

۳٫۹۱

۸

۲۵

Ethenes

Vinyl chloride

۱٫۶۲

۲,۷۰۰

۲۲

۱,۱-Dichloroethene

۲٫۱۳

۳,۴۰۰

۲۳

۱,۲-cis-Dichloroethene

۱٫۸۶

۳,۵۰۰

۷٫۴

۱,۲-trans-Dichloroethene

۲٫۰۹

۶,۳۰۰

۶٫۷

Trichloroethene

۲٫۴۲

۱,۱۰۰

۱۱٫۶

Tetrachloroethene

۳٫۴

۱۵۰

۲۶٫۹

Aromatic compounds

Hydrocarbons

Benzene                                                     ۲٫۱۳                   ۱,۷۶۰                    ۵٫۶

Toluene                                                      ۲٫۷۳                      ۵۴۰                    ۶٫۴

Ethylbenzene                                             ۳٫۱۵                      ۱۶۵                    ۸٫۱

Styrene                                                      ۲٫۹۵                      ۳۲۲                    ۲٫۶ o-Xylene                                                    ۳٫۱۲                      ۲۲۱                    ۴٫۲ m-Xylene                                                   ۳٫۲                        ۱۷۴                    ۶٫۸ p-Xylene                                                    ۳٫۱۵                      ۲۰۰                    ۶٫۲

۱,۲,۳-Trimethylbenzene                            ۳٫۶۶                        ۳۶                    ۷٫۴

۱,۲,۴-Trimethylbenzene                            ۴٫۰۲                        ۳۵

Napthalene                                                ۳٫۳                          ۳۲                    ۰٫۴۶ (۲۰ C) Phenanthrene                                             ۴٫۴۶                     ۱٫۱۸

Anthracene                                                ۴٫۴۵                   ۰٫۰۵۳

Fluorene                                                    ۴٫۱۸                     ۱٫۸۹

 

Chlorobenzene

۲٫۸۴

۳۹۰

۴٫۵

۱,۲-Dichlorobenzene

۳٫۴۳

۹۲

۲٫۸

۱,۳-Dichlorobenzene

۳٫۵۳

۱۲۳

۳٫۴

۱,۴-Dichlorobenzene

۳٫۴۴

۸۰

۱,۲,۴-Trichlorobenzene

۳٫۰

Hexachlorobenzene

۵٫۷۳

۰٫۰۰۴۷

 

Other aromatic compounds

 

 

Table 5.15 | (continued)

Water

Compound

log Kow

solubility,

mg/L

KH, atm/M

Data from Yaws for 25 C

Other aromatic compounds

Nitrobenzene

۱٫۸۵

۱,۹۴۰

۰٫۰۲۱

۳-Nitrotoluene

۲٫۴۵

۵۰۰

۰٫۰۷۵

Phenol

۱٫۴۶

۸۰,۰۰۰

۰٫۰۰۰۷۶

Diethyl phthalate

۲٫۴۷

۱,۰۰۰

۰٫۰۰۰۱۴

۲-Chlorophenol

۲٫۱۵

۲۵,۰۰۰

۰٫۰۳۷

۳-Chlorophenol

۲٫۵

۲۵,۰۰۰

۰٫۰۰۲۰۴

Dibenzofuran

۴٫۱۲

Other aliphatic compounds

Methyl t-butyl ether

۰٫۹۴

۵۱,۰۰۰

۰٫۵۴

Methyl ethyl ketone

۰٫۲۹

۲۵۰,۰۰۰

۰٫۰۳۰

Data from Schnoor et al. for 20 C

۲-Nitrophenol

۱٫۷۵

۲,۱۰۰

Benzo(a)pyrene

۶٫۰۶

۰٫۰۰۳۸

۰٫۰۰۰۴۹

Acrolein

۰٫۰۱

۲۱۰,۰۰۰

۰٫۰۰۳۸

Alachlor

۲٫۹۲

۲۴۰

Atrazine

۲٫۶۹

۳۳

Pentachlorophenol

۵٫۰۴

۱۴

DDT

۶٫۹۱

۰٫۰۰۵۵

۰٫۰۳۸

Lindane

۳٫۷۲

۷٫۵۲

۰٫۰۰۴۸

Dieldrin

۳٫۵۴

۰٫۲

۰٫۰۰۰۲

۲,۴-D

۱٫۷۸

۹۰۰

۰٫۰۰۰۰۰۱۷۲

Sources: C. L. Yaws, “Chemical Properties Handbook.” McGraw-Hill, New York, 1999. Schnoor et al., “Processes, Coefficients, and Models for Simulating Toxic Organics and Heavy Metals in Surface Waters,” U.S. Environmental Protection Agency, EPA/600/3-87/015, June 1987.

 

 

In general, it is considered that if Kis less than 0.2 atm/M or H is less than about 0.01, the compound will not be efficiently removed from water by air strip- ping in an engineered reactor (e.g., stripping tower, aeration pond). The larger the value of K(and H), the easier the compound can be removed by air stripping. It should be noted that values of KH  reported in the literature should be used with some caution, since methods and conditions used in determining KH vary widely.

When designing an engineered system to remove organics by volatilization, the following relationship from Sec. 3.10 is often used:

 

dC

dt      KLa(Cequil    C)                                        (۳٫۵۲)

 

where           C     concentration in water (mass/vol)

Cequil     concentration in water that would be in equilibrium with the concentration in air (mass/vol)

KLa     overall mass-transfer rate coefficient (time   ۱)

 

 

 

Often the air concentration is near zero, so Cequil  becomes zero. Different engineered systems will give different values for KLa, and this rate coefficient will be different for different organics as well. It is also a strong function of temperature, increasing with an increase in temperature.

 

 

 

EXAMPLE 5.1

Gossett27  developed relationships describing the effect of temperature on Henry’s con- stant for a variety of chlorinated aliphatic compounds. The relationship between KH (atm- m3/mol) and T for trichloroethene (CHCl2¨CCl2) is given here.

ln K       ۱۱٫۳۷      ۴۷۸۰

H                                    T

Calculate the value for K(atm/M) for temperatures of 10 C (283 K) and 25 C (298 K), which might represent the extremes in groundwater temperatures in the midwest.

For 10 C:     ln K      ۱۱٫۳۷      ۴۷۸۰        ۵٫۵۲        K       ۰٫۰۰۴۰ atm-m3/mol or 4 atm/M

H                                  ۲۸۳                           H

For 25 C:     ln K      ۱۱٫۳۷      ۴۷۸۰        ۴٫۶۷       K       ۰٫۰۰۹۴ atm-m3/mol or 9.4 atm/M

H                                 ۲۹۸                           H

For TCE, KH more than doubled due to the 15 C temperature increase. This means it will be much easier to remove TCE from contaminated groundwater by air stripping in the summer months. It may be noted that the 25 C Kvalue of 9.4 atm/M is somewhat less than the 11.6 atm/M value in Table 5.15, reflecting the different sources of the data.

 

 

 

EXAMPLE 5.2

Removing organics from water by volatilization can be thought of as forcing the organic to partition into the air. An important parameter is the air-to-water ratio, the volume of air exposed to a given volume of contaminated water. An easy way to view the importance of this ratio and of KH is by using a simple equilibrium model in which a given volume of air is mixed with a given volume of water. A mass balance yields the following expression:

 C               ۱            

C0                          Va         KH

۱    V    RT

w

where            C     equilibrium concentration in water

C0     initial concentration in water

Va /Vw     volume of air divided by volume of water (the air-to-water ratio)

T     temperature (absolute)

R     universal gas constant

 

 

 

۲۷J. J. Gossett, Measurements of Henry’s Law Constants for C1 and C2 Chlorinated Hydrocarbons, Env. Sci. Tech., 21: 202–۲۰۸, ۱۹۸۷٫

 

 

 

Consider the two chlorinated solvents carbon tetrachloride and trichlorothene. What air- to-water ratio is required to remove 95 percent of each from water? For an air-to-water ratio of 100 (typical values for air stripping towers are 10 to 100), what is the percent re- moval of each compound? Assume a temperature of 25 C.

 

For 25 C, RT is 24.5 atm/M. From Table 5.15, KH is 29 atm/M for carbon tetrachlo- ride and 11.6 atm/M for trichloroethene.

For 95 percent removal, C/C0 is 0.05. Solving the given expression for Va /Vw yields

Va        C0     ۱   RT

 

 

Vw             C

 

KH 

 

 

Substituting the proper KH   yields a Va/Vw   of 16 for carbon tetrachloride and 40 for trichloroethene.

A Va/Vw  of 100 yields a C/C0 of 0.0084 (99.2 percent removal) for carbon tetrachlo- ride and 0.0207 (97.9 percent removal) for trichloroethene.

 

 

 

 

Solubility

 

Water solubility of an organic compound is generally defined as the concentration (mass/vol or mol/vol) resulting when the water is in equilibrium with the pure compound [gas (1 atm), liquid, or solid]. There are many factors affecting com- pound solubility. They include, but are not limited to, size of the molecule; the nature, number, and location of functional groups in the molecule; temperature; pH; dissolved salt concentration; and the presence of other phases (i.e., organic liquids, solids, gases). In general, as molecular size increases, solubility de- creases. Polar functional groups (e.g., ˆOH) tend to increase solubility. Addition of Cl atoms or NO2  groups in general decreases solubility. As temperature in- creases, the solubility of solids generally increases as does volatility (vapor pres- sure and KH). A detailed discussion of the thermodynamics of solubility is beyond the scope of this text. The interested reader is referred to the Schwarzenbach et al. text listed at the end of this chapter. Values of solubility for some environmen- tally significant compounds are given in Table 5.15. Caution should be exercised when using literature values for solubility, since methods and conditions used to determine them vary widely.

A word about the term hydrophobicity is warranted. The octanol-water parti- tion coefficient (Kow—described in Sorption/Partitioning) is often used to describe hydrophobicity. However, since the term hydrophobic refers to “water hating,” aqueous solubility is a truer measure of the hydrophobicity of a compound (how much it “hates” water). In general, compounds with high Kow have low aqueous sol-

ubility. For example, DDT has a Kow of 106.91 and an aqueous solubility of 0.0055

mg/L (at 20 C). In some cases, however, compounds with low solubility do not

have particularly high values of Kow. For example, the explosive HMX (Sec. 5.17)

has a solubility of 5 mg/L at 20 C and its Kow is 100.20.

 

 

 

Sorption/Partitioning

 

Adsorption was discussed in Sec. 3.12 with a primary emphasis on its use in engi- neered reactors. Adsorption of metals on surfaces was discussed in Sec. 4.9. Sorp- tion is also an important process affecting the fate and transport of organic com- pounds in surface waters and groundwaters. The general term sorption is often used for the natural process rather than adsorption or absorption because the exact man- ner in which partitioning to solids occurs is often not known. Partitioning of an or- ganic compound between solids and water (e.g., aquifer solids in groundwater, par- ticulates and sediments in surface water systems) can be understood and predicted to some degree using physicochemical properties of organic compounds such as the relative partitioning between the liquid solvent n-octanol and water (octanol-water partition coefficient—Kow) and water solubility. Kow  has long been used as a surro- gate for living tissue and natural organic matter. For example, in the pharmaceutical industry, the Kow  of a drug is often correlated to its activity (higher Kow, higher ac- tivity). Bioconcentration of organic compounds in fatty tissues of living organisms has been correlated to Kow  (Sec. 5.35). Values of Kow  for some environmentally sig- nificant compounds are given in Table 5.15. As with KH  and solubility, values of Kow  should be used with some caution, since methods and conditions used in deter- mining them vary widely.

Sorption in most surface water and groundwater systems can be described by the Freundlich equation (Sec. 3.12). In some situations, concentration of the organic is low and the number of surface sites is quite high, so the value of n approaches 1 and a linear isotherm results (Fig. 5.2). In this case, K [Eq. (3.84)] is commonly called  the  partition  coefficient  Kp.  The  units  of  Kp   are  typically  mg  organic sorbed/kg of solid divided by mg organic/liter of water, or liter of water/kg of solid.

 

 

 

 

 

 

 

Linear range

 

 

 

 

 

 

Slope = Kp

 

 

Aqueous concentration, C

 

Figure 5.2

Linear isotherm for sorption of organics.

 

 

 

It has been found that sorption of hydrophobic organic compounds is often related to the organic content of the solids, indicating that the process is an organic-organic partitioning, or absorption, rather than true adsorption.28  Thus, partitioning would be expected to be a function of the nature of the natural organic matter present. An organic-carbon-normalized partition coefficient Koc  is sometimes calculated by di- viding Kp  by the mass fraction of organic carbon in the solids. It should be noted that in some cases, equilibrium between solute and sorbent may take days, months, or even years, and may be more complicated than the linear isotherm given here.29,30

Desorption (partitioning back into the water) can be a very slow process. For hy- drophobic compounds in contact with environmental solids for extended periods of time (sometimes called “aging”), sorption may be for all intents and purposes, irre- versible. This behavior significantly affects our ability to remediate such soils.

Values for Koc  have been estimated from Kow  using the following relationship developed for a series of polycyclic aromatics and chlorinated hydrocarbons.31

 

Koc     ۰٫۶۳(Kow)                                            (۵٫۵۹)

 

where Koc  is the organic-carbon-normalized partition coefficient in liters per kilo- gram of organic carbon. Here Kow  serves as a surrogate for natural organic matter. Values for Koc have also been related to water solubility.32

 

log Koc        ۰٫۵۴ log S     ۰٫۴۴                                 (۵٫۶۰)

 

where S is the water solubility of the compound expressed as mole fraction. For the compounds tested, use of Kow provided a better estimate of Koc than S.

One of the convenient uses of these concepts is in the understanding of retarda-

tion of groundwater contaminants (movement of compounds relative to movement of water) due to sorption. The following equation has been used.33

 

tr     ۱       Kp/e                                             (۵٫۶۱)

 

where           tr     retardation factor or ratio of water movement rate to chemical movement rate

p     bulk density of soil, kg/L

Kp     partition coefficient, L/kg

e     void fraction or porosity of soil

 

 

۲۸S. W. Karickhoff, D. S. Brown, and T. A. Scott, Sorption of Hydrophobic Pollutants on Natural

Sediments, Water Research, 13: 241–۲۴۸ (۱۹۷۹).

۲۹W. J. Weber, Jr., P. M. McGinley, and L. E. Katz, A Distributed Reactivity Model for Sorption by Soils and Sediments. 1. Conceptual Basis and Equilibrium Assessments, Env. Sci. Tech., 26: 1955–۱۹۶۲ (۱۹۹۲).

۳۰R. P. Schwarzenbach, P. M. Gschwend, and D. M. Imboden, “Environmental Organic Chemistry,”

Wiley-Interscience, New York, 1993.

۳۱Karickhoff et al., Sorption of Hydrophobic Pollutants on Natural Sediments.

۳۲Ibid.

۳۳P. V. Roberts, M. Reinhard, and P. L. McCarty, Organic Contaminant Behavior During Groundwater

Recharge, J. Water Pollution Control Fed., 52: 161–۱۷۲ (۱۹۸۰).

 

 

 

EXAMPLE 5.3                   Compare  the  retardation  of  chloroform,  chlorobenzene,  and  DDT  for  the  following groundwater conditions:

 

    ۲ kg/L

foc     fraction organic carbon     ۰٫۰۱ (soil contains 1 percent organic carbon)

e     ۰٫۲۰

 

The following equations are used to solve this problem:

 

Kp     Koc foc

Koc     ۰٫۶۳(Kow)

tr     ۱       Kp /e

 

Using the data from Table 5.15:

 

 

Compound

log Kow

Kow

Koc

Kp

tr

Chloroform

۱٫۹۷

۹۳٫۳

۵۸٫۸

۰٫۵۸۸

۶٫۸۸

Chlorobenzene

۲٫۸۴

۶۹۲

۴۳۶

۴٫۳۶

۴۴٫۶

DDT

۶٫۹۱

۸٫۱۳     ۱۰۶

۵٫۱۲     ۱۰۶

۵٫۱۲     ۱۰۴

۵٫۱۲     ۱۰۵

 

These calculations indicate that chloroform will move slower than water by a factor of 7, chlorobenzene by a factor of 45, and DDT by a factor of about 500,000. Of these three compounds, chloroform is thus expected to move much more rapidly with groundwater flow whereas DDT is not likely to move far from its source.

 

 

Transformation Reactions

 

Transformation reactions important in the fate and removal of organics are listed in Table 5.14 and include photolysis, hydrolysis, oxidation, reduction, and biotransfor- mation. Hydrolysis, oxidation, and reduction can be chemical (abiotic) or mediated by microorganisms (biotic). An additional transformation reaction important with halogenated organics is elimination (dehydrohalogenation). In many cases, micro- bially mediated transformation reactions are much more rapid than abiotic reac- tions. Photochemical transformations are sometimes quite rapid. Biotransformation reactions are discussed in more detail in Chap. 6.

 

Photochemical  Transformations   Photochemical  transformations  are  important fate processes for organics in the near-surface aquatic environment as well as in the upper atmosphere. Enhanced photochemical processes are also being used for the treatment of some hazardous wastes. Inorganic pollutants can also be transformed by photochemical reactions; the best known such case is the production of photochemi- cal smog. There are four major photochemical reactions of environmental signifi- cance: direct photolysis, indirect photolysis, oxidation, and free-radical oxidation.

In direct photolysis, the organic absorbs light energy (photons) and is converted into an excited state which then releases this energy in conjunction with conversion into a product (different) compound. In indirect photolysis, a nontarget compound (for example, dissolved organic material such as humic substances) absorbs the

 

 

 

photons and becomes excited. This energized molecule then transmits its energy to the pollutant (target organic) causing it to be transformed.

In oxidation and free-radical oxidation, light energy is typically absorbed by an intermediate compound such as dissolved organic matter, nitrate, or Fe(III), with the resultant production of oxidants such as H2O2  and O3, free radicals such as hy- droxyl ( OH) and peroxy ( OOR), and/or other reactive species such as singlet oxy- gen 1O2. These oxidants are then available to oxidize a wide variety of organics. Chlorinated compounds are particularly susceptible to oxidation by these species. Mixtures of ultraviolet light and ozone or hydrogen peroxide are used in engineered systems for treatment of trace levels of organics in gases and water, and rely on pro- duction of these activated chemical species. As described in Sec. 5.8, free-radical reactions are involved in the depletion of the ozone layer.

 

Hydrolysis and Other Nucleophilic Substitutions    Hydrolysis reactions are nu- cleophilic substitution reactions where water acts as a nucleophile and attacks an or- ganic bond. Nucleophiles are electron-rich ions (H2O is an exception) that are often called “nucleus-liking, positive-charge-liking” species. They typically like to attack

 

 

۳

۴

saturated  bonds.  Other  common  nucleophiles  include  OH   ,
NO   ,


SO2   ,


HS   ,

 

HCO   , and HPO2   . There is no change in oxidation state of the organic compound

۳                             ۴

during these transformations. In aquatic systems, the most common reactions are

those in which water is added, and these reactions may be abiotic or biotic. Abiotic reactions are a strong function of pH. Organic compounds susceptible to hydrolysis and nucleophilic substitution include alkyl halides (halogenated aliphatics), amides, amines, carbamates, epoxides, esters, nitriles, and phosphoric acid esters. A few ex- amples, mostly with H2O serving as the nucleophile, are given here.

۱٫    Alkyl halides (X     halogen)

 

RˆCH2X   H2O l RˆCH2OH   H     X

RˆCH2X   HS   l RˆCH2SH   X

 

Iron sulfide minerals [e.g., mackinawite, typically abbreviated FeS(s)] can also facilitate nucleophilic substitution reactions for halogenated organic compounds. They can also bring about reductive dehalogenation and other electron-transferring processes. Halogenated aromatics (aryl halides) may also undergo hydrolysis. For example,

 

Cl                            OH

 

 

 

   H2O  l


   HCl

 

 

 

 

 

۲٫    Esters


Chlorobenzene                       Phenol

 

 

O                                               O

 

 

H3Cˆ Cˆ OCH3     H2O

 

l  H3Cˆ C ˆ OH

 

OH ˆ CH3

 

Methyl acetate                                       Acetic acid                  Methanol

 

 

 

 

۳٫    Amides

 

 

O

 

Rˆ CˆNHR

 

 

 

 

H2O

 

 

O

 

l Rˆ C ˆ OH      H2NR

 

Amide                                               Acid                    Amine

 

۴٫     Carbamates are converted into CO2, an amine, and other compounds (for example, alcohols).

 

 

 

H3C

H3C       O


   H2O  l

H


CO2      H2NCH3     H3C

H3C       O

 

O ˆ Cˆ N ˆ CH3                                                                                                                        OH

 

O

Furadan, a pesticide                                                   Amine

 

 

۵٫    Phosphoric esters

 

O ˆ C2H5

 

S¨ P ˆ O ˆ

 

O ˆ C2H5

Parathion

 

 

 

 

ˆ NO2     H2O

 

 

O ˆ C2H5

 

l S¨P ˆ OH     HO ˆ

 

O ˆ C2H5

 

 

 

 

ˆ NO2

 

 

Nucleophilic substitution reactions are typically expressed as second-order or pseudo-first-order reactions:

 

Rate        kh[C][N]                                          (۵٫۶۲)

 

where          kh     hydrolysis rate coefficient

[C]     concentration of organic

[N]     concentration of nucleophile

 

The minus sign represents the disappearance of the organic compound. When water is the nucleophile, or when the concentration of the nucleophile is constant or un- known, a pseudo-first-order expression may be used:

Rate        kh[C]                                             (۵٫۶۳) Hydrolysis reactions can be acid or base catalyzed, in which case the rate expres-

sions can be a bit more complicated:

 

Rate        (ka[H   ]     kn     kb[OH   ])[C]

(۵٫۶۴)

where

ka     acid-catalyzed rate coefficient

kn     neutral rate coefficient

kb     base-catalyzed rate coefficient

 

 

 

The overall hydrolysis rate coefficient can then be expressed as

kh     ka[H   ]     kn     kb[OH   ]                                  (۵٫۶۵) Care must be taken to ensure that the units used in these rate expressions are

consistent.

The concept of half-life is often used to describe the persistence of an organic in the environment. Half-life (t1/2) was defined in Sec. 3.10 as 0.693/k, where k is a first-order rate coefficient. With hydrolysis, k is represented by kh or kh[N]. Hydroly- sis reactions may be quite slow (half-lives of years) or quite rapid (half-lives of sec- onds) depending on the organic and the environmental conditions.

 

 

 

 

The following are hydrolysis rate coefficients reported by Jeffers and co-workers.34


EXAMPLE 5.4

 

 

 

Compound

kh, min   ۱

Chloroform

۷٫۱۳     ۱۰   ۱۰

Carbon tetrachloride

۳٫۲۶     ۱۰   ۸

۱,۱,۱-Trichloroethane

۱٫۲۴     ۱۰   ۶

Pentachloroethane

۱٫۳۱     ۱۰   ۴

Trichloroethene

۱٫۰۷     ۱۰   ۱۲

Tetrachloroethene

۱٫۳۷     ۱۰   ۱۵

 

From these data, calculate the half-lives, in years, of these compounds in the environment assuming that no other transformation reactions occur.

 

 

Half-life   t1/2

 

ln 2

kh

 

         ۰٫۶۹۳          (kh)(60)(24)(365)

 

 

Compound                              t1/2, years

Chloroform                         ۱۸۴۹

Carbon tetrachloride           ۴۰

۱,۱,۱-Trichloroethane         ۱٫۱

Pentachloroethane              ۰٫۰۱۰ (۳٫۷ days) Trichloroethene                  ۱٫۲۳     ۱۰۶

Tetrachloroethene               ۹٫۶۲     ۱۰۸

 

 

These data indicate that chlorinated aliphatics are in general very slowly hydrolyzed. Other data indicate that the environmental half-lives of these compounds are sometimes much shorter, indicating that other transformation processes, perhaps biotic, are more im- portant in controlling their fate.

 

 

 

۳۴P. Jeffers, L. Ward, L. Woytowitch, and L. Wolfe, Homogeneous Hydrolysis Rate Constants for

Selected Chlorinated Methanes, Ethanes, Ethenes, and Propanes. Env. Sci. Techn., 23: 965–۹۶۹ (۱۹۸۹).

 

 

 

Elimination  (Dehydrohalogenation)    Elimination  reactions  may  occur  abioti- cally or be microbially mediated. Although these reactions have been shown to occur with many organics, the ones of most importance to environmental engineers and scientists are those with halogenated organics. The most common of these reac- tions are characterized by the release of HX (dehydrohalogenation) and the forma- tion of a double bond.

 

 

Cl   H

 

Cl  H

 

 

Clˆ Cˆ C ˆ H  l

 

Clˆ C¨ C ˆ H     HCl

 

 

Cl   H

 

۱,۱,۱-Trichloroethane


۱,۱-Dichloroethene

 

 

H

Clˆ

ˆ C ˆ

ˆ Cl

l

Clˆ

ˆ Cˆ

ˆ Cl      HCl

Clˆ C ˆ Cl

Clˆ C ˆ Cl

Cl

DDT

DDE

 

 

۴

Oxidation    Oxidation occurs when an organic loses (donates) one or more elec- trons to an oxidizing agent (electron acceptor). Abiotic oxidation reactions are typi- cally very slow or nonexistent under environmental conditions. The most common natural oxidants are molecular oxygen, Fe(III), and Mn(III/IV). These are to be con- trasted with the potentially rapid oxidations that occur with photochemically pro- duced oxidants such as H2O2, O3, the free radicals such as hydroxyl ( OH) and per- oxy ( OOR), and other reactive species such as singlet oxygen 1O2. Strong oxidizing agents such as H2O2, O3, MnO     (permanganate), and various chlorine species (e.g., Cl2, ClO2) can oxidize organics during water and wastewater treatment. Biological oxidations will be covered in more detail in Chap. 6.Rates of abiotic oxidation reactions are often described using a second-order rate expression:

 

Rate        ko[C][Ox]                                         (۵٫۶۶)

 

where             ko     oxidation rate coefficient [C]     concentration of organic [Ox]     concentration of oxidant

Reduction    Reduction occurs when an organic gains (accepts) one or more elec- trons from a reducing agent (electron donor). Highly oxidized organics (e.g., highly chlorinated organics and nitroaromatics) are susceptible to reduction. Abiotic reduc- tion reactions are quite common, especially under reducing conditions (absence of oxygen). In many cases it is difficult to distinguish between truly abiotic reductions and those mediated by microorganisms. For example, HS     can take part in nucle- ophilic substitution reactions (see Hydrolysis and Other Nucleophilic Substitutions) and can be involved in reduction reactions where it is oxidized to elemental sulfur

 

 

(S(s)) with the reduction of the organic. In anaerobic environments HS     is present primarily due to microbial reduction of sulfate; without the microorganisms, the re- duction would not take place. Reducing agents found in the environment include HS   ; Fe(II) compounds such as iron sulfides, iron carbonates; iron oxides; iron and other porphyrins; and other reduced organic compounds (natural organic matter).

Rates of abiotic reduction reactions are often described using a second-order rate expression:

 

Rate        kr[C][Red]                                         (۵٫۶۷)

 

where             kr     reduction rate coefficient

[C]     concentration of organic

[Red]     concentration of reductant.

 

Many types of organics are susceptible to abiotic or biotic reduction. A few ex- amples are given here.

 

۱٫    Reductive dehalogenation.

 

H

H

Clˆ

ˆ C ˆ   ˆ C

l      ۲e_      H+

l

Clˆ

ˆ C ˆ

ˆ Cl      Cl–

Clˆ Cˆ Cl

Clˆ C ˆ Cl

Cl

DDT

H

DDD

The biological reductive dehalogenation of tetrachloroethene (PCE) and trichloroethene (TCE) illustrate the potential for transformation reactions to result in more problematic products (vinyl chloride in this case). These reductions proceed with an overall transfer of 2e     per molecule and replacement of one Cl atom with a H atom:

 

 

Cl  Cl

 

Cl  Cl

_

 

Clˆ C¨ C ˆ Cl      H+      ۲e_


l Clˆ C¨ Cˆ H      Cl

 

Tetrachloroethene                                           Trichloroethene

 

 

Cl  Cl


Cl  Cl

_

 

Clˆ C¨ C ˆ H     H+      ۲e_

Trichloroethene

 

l Hˆ C¨ Cˆ H      Cl

cis-1,2-Dichloroethene

 

 

 

Cl  Cl


H   Cl

_

 

H ˆ C¨ C ˆ H     H+      ۲e_


l H ˆ C¨ Cˆ H      Cl

 

cis-1,2-Dichloroethene


Chloroethene (vinyl chloride)

 

 

H  Cl                                            H   H

 

H ˆ C¨ C ˆ H     H+      ۲e_ l

Vinyl chloride

 

_

H ˆ C¨ C ˆ H     Cl

Ethene

 

 

 

۲٫    Reductive elimination

 

 

Cl  Cl

 

Cl  Cl

_                                                                            _

 

Clˆ C¨ C ˆ Cl      ۲e


l Clˆ C¨ C ˆ Cl      ۲Cl

 

 

Cl  Cl

Hexachloroethane                           Tetrachloroethene

 

Treatment of contaminated groundwaters using permeable reactive barriers (PRB) containing iron metal (Fe(0)) is based on reduction. As Fe(0) is oxidized (corrodes), e     are released which can be used to reduce highly oxidized pollutants:

 

Fe0  l Fe2     ۲e

 

 

۴

These Fe(0)-PRB have been used to treat groundwaters contaminated with chlorinated aliphatics such as perchloroethene and trichloroethene and highly oxidized metals such as Cr(VI). In the case of Cr(VI), the less mobile and less toxic trivalent form is produced. Example stoichiometries are given here for trichloroethene (CCl2     CHCl) reduction to ethene (CH2     CH2) and chromate (HCrO   ) reduction to trivalent Cr (Cr(OH)3(s)):

۳Fe0  l 3Fe2     ۶e

CCl2    CHCl   ۳H     ۶e   l CH2    CH2    ۳Cl

 

۳Fe0    CCl2    CHCl   ۳H   l 3Fe2     CH2    CH2    ۳Cl

 

۱٫۵Fe0  l 1.5Fe2     ۳e

 

۴

HCrO           ۴H           ۳e     l Cr(OH)3(s)     H2O

 

۴

۱٫۵Fe0     HCrO           ۴H    l 1.5Fe2           Cr(OH)3(s)     H2O

As discussed in Chap. 6, the electrons necessary for accomplishing reduction can also be provided by microbial oxidation of a wide variety of electron donors.

۳٫    Reduction of nitro groups to the corresponding amino groups.

 

 

NO2


NH2

 

 

 

   ۶e_


   ۶H+   l


   ۲H2O

 

 

 

 

Nitrobenzene


Aniline

 

 

۴٫    Reduction of disulfides to mercaptans.

 

R ˆSˆSˆR    ۲e           ۲H    ¶l R ˆSH   R ˆSH

 

 

 

۵٫۳۵ | STRUCTURE- AND PROPERTY-ACTIVITY RELATIONSHIPS

 

There is considerable interest in developing methods for predicting the properties (e.g., solubility) and activities (e.g., fate, toxicity) of chemicals, especially organ- ics, in the environment and in engineered systems. Physical, chemical, and struc- tural (molecular) characteristics of organic compounds are used in this regard, and correlations have been developed for a wide variety of structures, properties, and activities. For the purposes of this discussion, structure refers to molecular charac- teristics. Activity refers to a biological effect such as toxicity, biotransformation, or bioconcentration (to be distinguished from the definition of activity given in Sec.

۲٫۱۲). It may also refer to the potential for transformation of organic compounds via abiotic reactions. Property is a more all-encompassing term that includes such environmentally significant characteristics as solubility, volatility, and liquid-liq- uid or solid-liquid partitioning. It is the purpose of this section to introduce the stu- dent to the nature and usefulness of these relationships for understanding and pre- dicting the behavior of organic compounds. The reader should be aware that the definition of the terms used herein may differ slightly with those used by others in this evolving field.

Relationships that have been developed include structure-activity, property- activity, structure-property, and property-property relationships. All are commonly referred to in the literature as quantitative structure-activity relationships (QSAR). The general goal of any QSAR is to quantitatively relate, using a variety of statisti- cal correlation techniques, a property or activity of a given set of chemicals to char- acteristics (structure or property), sometimes called descriptors, of these chemicals, QSARs were initially used in drug design and formulation of pesticides, and later were extended for use in environmental toxicology. QSARs are of current interest because they can help understand and predict the impact of organic chemicals for which there is very little environmental data. It has been estimated that there are about 70,000 synthetic chemicals currently being used, with 500–۱۰۰۰ new ones being added each year. Data about environmental fate and effects exist for only about 20% of these chemicals.35 Although QSARs are empirical relationships, they do provide important information that can help interpret causes and mechanisms in- volved. Some caution must be exercised when attempting to use QSARs for com- pounds with properties (e.g., chemical structure) that are significantly different from the compounds used to develop the QSAR.

Relationships that are developed using basic structural (molecular) charac- teristics such as molecular connectivity, molar surface area, intrinsic molar vol- ume, atomic charge, and others have some advantages in that they can be deter- mined without need for experimental data. However, the environmental engineer or scientist must have access to the structural characteristics and calculation methods necessary to determine values for these parameters. Some of this infor-

 

 

۳۵S. Postel, in “State of the World 1987,” L. R. Brown, et al., eds., Worldwatch Institute Report, W. W. Norton, New York, 1987.

 

 

 

mation is currently available in the literature, and more is becoming increasingly available in software packages that can be purchased.36  Detailed discussion of these parameters and the methods used to determine them is beyond the scope of this text.

 

Prediction of Properties of Organic Chemicals

 

Relationships have been developed that allow for prediction of environmentally sig- nificant properties such as solubility, KH, Kow, and Koc. An example of a structure- property relationship for solubility is37

 

 

log S   ۱٫۵۴۳   ۱٫۶۳۸o    ۱٫۳۷۴o v    ۱٫۰۰۳

 

where          S     aqueous solubility, mol/L

o       zero-order, simple molecular connectivity index

o  v     valence molecular connectivity index

modified polarizability parameter.

 

(۵٫۶۸)

 

 

Values for o  , o  v, and      can be calculated from molecular structure without need for experimental data. Table 5.16 contains a sample of the type of data used to calculate solubility using this relationship. The relationship in Eq. (5.68) was devel- oped from a data set of 145 different organic chemicals, including alcohols, halo- genated aliphatics, and aromatics.

Many property-property relationships have been developed. Equation (5.59), relating Koc to Kow, and Eq. (5.60), relating Koc to S, are examples. An additional ex- ample relates Kow to S (mol/L) for a set of 36 different organic compounds.38

 

log Kow        ۰٫۸۶۲ log S     ۰٫۷۱۰                               (۵٫۶۹)

 

 

Table 5.16 | o  , o  v, and      values for selected organic compounds

 

Compound

o

o  v

Phenol

۴٫۳۸

۳٫۸۳

 ۴٫۱۱

۲-Chlorophenol

۵٫۳۰

۴٫۸۹

 ۴٫۷۱

Pentachlorophenol

۹٫۰۰

۹٫۴۶

 ۷٫۱۲

Naphthalene

۵٫۶۱

۵٫۶۱

 ۶٫۷۲

Benzo(a)pyrene

۱۰٫۹۲

۱۰٫۹۲

 ۱۲٫۰۰

Source: Data taken from N. N. Nirmalakhandan and R. E. Speece, Prediction of Aqueous Solubility of Organic Chemicals Based on Molecular Structure. 2. Application to PNAs, PCBs, PCDDs, etc., Env. Sci. Tech., 23: 708–۷۱۳ (۱۹۸۹).

 

 

 

۳۶M. Reinhard and A. Drefahl, “Handbook for Estimating Physiochemical Properties of Organic

Compounds,” John Wiley & Sons, Inc., New York, 1999.

۳۷N. N. Nirmalakhandan and R. E. Speece, Prediction of Aqueous Solubility of Organic Chemicals

Based on Molecular Structure. 2. Application to PNAs, PCBs, PCDDs, etc., Env. Sci. Tech., 23:

۷۰۸–۷۱۳ (۱۹۸۹).

۳۸C. T. Chiou, Partition Coefficient and Water Solubility in Environmental Chemistry, in “Assessment of

Chemicals,” vol. 1, Academic Press, pp. 117–۱۵۳, ۱۹۸۱٫

 

 

 

Prediction of Activities of Organic Chemicals

 

Activity in the context of QSARs usually refers to a biological effect such as toxic- ity, biotransformation, or bioconcentration. Many such relationships have been de- veloped;39 a few are described here.

It has long been recognized that bioaccumulation or bioconcentration (roughly defined as the ratio of the concentration of the organic compound in a target organ- ism to the concentration of chemical in water) can be related to Kow. This is ex- pected since bioaccumulation is thought to be a partitioning process. An example of such a property-activity relationship is40

 

log BF     log Kow     ۱٫۳۲                                     (۵٫۷۰)

where BF is the bioconcentration factor. Equation (5.70) was developed from a variety of aquatic organisms (fish, algae, and mussels) and a data set of 51 organic chemicals.

Attempts have been made to develop structure-activity relationships, such as biodegradability versus chemical structure. An example is41

 

BOD     ۱۰۱۵(      x   y)     ۱٫۱۹۳                                (۵٫۷۱)

where BOD is the percentage of theoretical BOD achieved in 5 days and       x   y  is the modulus of atomic charge differences across common bonds (e.g., CˆO). This relationship was developed from 79 organic compounds, including amines, phenols, aldehydes, carboxylic acids, halogenated hydrocarbons, and amino acids.

One of the most promising uses of QSARs is in the understanding and predic- tion of toxicity of organic chemicals to organisms of environmental significance. Recent studies have related the toxicity of 50 to 130 organic chemicals to a variety of bacteria. Examples of structure-activity and property-activity relationships, re- spectively, for aerobic, heterotrophic bacteria are given here.42

 

log IC50     ۵٫۲۴     ۴٫۱۵(Vi /100)     ۳٫۷۱  m     ۰٫۴۱  m                         (۵٫۷۲)

log IC50     ۵٫۱۲     ۰٫۷۶ log Kow                                                                           (۵٫۷۳)

where                  IC50     concentration (mg/L) at which the biological reaction rate is reduced by 50 percent

Vi     intrinsic molar volume

 m and   m     measures of ability to participate in hydrogen bonding as a hydrogen donor or acceptor, respectively

Vi,   m, and   m  are commonly termed linear solvation energy relationship (LSER) parameters. Table 5.17 contains a sample of values of these parameters needed to use Eq. (5.72).

 

 

۳۹Reinhard and Drefahl, “Handbook for Estimating Physiochemical Properties of Organic Compounds.”

۴۰D. Mackay, Correlation of Bioconcentration Factors, Env. Sci. Tech., 16: 274–۲۷۸ (۱۹۸۲).

۴۱J. C. Dearden, and R. M. Nicholson, The Prediction of Biodegradability by the Use of Quantitative Structure-Activity Relationships: Correlation of Biological Oxygen Demand with Atomic Charge Difference, Pesticide Science, 17: 305–۳۱۰ (۱۹۸۶).

۴۲D. J. W. Blum and R. E. Speece, Determining Chemical Toxicity to Aquatic Species. Env. Sci. Tech.,

۲۴: ۲۸۴–۲۹۳ (۱۹۹۰).

 

 

 

Table 5.17 | Values of Vi /۱۰۰,   m, and   m for selected organic compounds

 

Compound

Vi /۱۰۰

 m

 m

Dichloromethane

۰٫۳۳۶

۰٫۰۵

۰٫۱۳

Chloroform

۰٫۴۲۷

۰

۰٫۲۰

۱,۱,۱-Trichloroethane

۰٫۵۱۹

۰

۰

Trichloroethene

۰٫۴۹۲

۰٫۰۳

۰٫۱۲

Benzene

۰٫۴۹۱

۰٫۱۴

۰

Toluene

۰٫۵۹۲

۰٫۱۴

۰

Chlorobenzene

۰٫۵۸۱

۰٫۰۹

۰

Phenol

۰٫۵۳۶

۰٫۳۳

۰٫۶۰

Source: Data taken from D. J. W. Blum, Chemical Toxicity to Environmental Bacteria: Quantitative Structure Activity Relationships and Interspecies Correlations and Comparisons, Ph.D. Dissertation, Drexel University, Philadelphia (1989).

 

One of the best-known property-activity relationships is commonly termed a linear free-energy relationship (LFER) and correlates reaction rates with equilib- rium constants. This is an attempt to relate the kinetics of a chemical reaction to its thermodynamics. An example is given here for the base-catalyzed hydrolysis of a series of 16 N-phenylcarbamates.43

 

log kb        ۱٫۱۵pKA     ۱۳٫۶                                   (۵٫۷۴)

 

where kb  is the first-order hydrolysis rate (M   ۱s   ۱) and pKA  is the pKA  of the alco- hol, or leaving group. Recall that hydrolysis of carbamates yields an amine, an alco- hol, and CO2. Leaving groups included nitrophenolates, chlorophenolates, and halo- genated  aliphatic  compounds,  among  others.  An  example  is  given  here  for

۴-nitrophenyl-N-phenylcarbamate (kb     ۲٫۷     ۱۰۵ M   ۱s   ۱):

Leaving group:

p-nitrophenylate

H    O

 

ˆN ˆC ˆO ˆ   ˆ NO2

 

 

۴-Nitrophenyl-N-phenylcarbamate

 

OH                  O–

 

H        pKA = 7.1

 

 

 

NO2


NO2

 

 

p-nitrophenol     p-nitrophenylate

 

 

۴۳R. P. Schwarzenbach and P. M. Gschwend, Chemical Transformations of Organic Pollutants in the

Aquatic Environment, in “Aquatic Chemical Kinetics,” W. Stumm, ed., Wiley-Interscience, New York,

۱۹۹۰٫

 

 

 

Another example of a LFER relates the surface-area normalized rate coefficient (kSA, L/m2-h) for reduction of 48 chlorinated alkanes and alkenes by Fe(0) to calcu- lated estimates of the lowest unoccupied molecular orbital energies (ELUMO, eV) for these compounds.44

log kSA        ۵٫۶۰۳     ۱٫۴۹ELUMO                                                      (۵٫۷۵) For example, ELUMO  for tetrachloroethene is estimated to be    ۱٫۶۸۹ eV. Using Eq.

(۵٫۷۵) gives a rate coefficient of 8.2     ۱۰   ۴ L/m2-h. If the surface-area concentra-

tion in a Fe(0) permeable reactive barrier were 2 m2/mL (2000 m2/L), then the pseudo-first-order rate coefficient would be 1.64 h   ۱٫

 

 

PROBLEMS

 

۵٫۱      Why is it possible to have so many compounds of carbon?

۵٫۲      Define homologous series, homolog, hydrocarbon, and alkyl radical.

۵٫۳      Define isomerism and illustrate with structural formulas of compounds with the molecular formula C6H14.

۵٫۴      In general, how do organic compounds differ from inorganic compounds?

۵٫۵      How many grams of oxygen are required to furnish just enough oxygen for the complete oxidation of 20 g of butane?

۵٫۶      What is the difference between an aliphatic and an aromatic compound?

۵٫۷      Define with suitable illustrations the terms primary alcohol, secondary alcohol, and tertiary alcohol, and indicate their relative ease of biodegradation.

۵٫۸      Show the structures and names of the intermediate compounds formed in the biological oxidation of n-butane to butyric acid.

۵٫۹      Why are oxidation reactions of organic compounds important to environmental engineers and scientists?

۵٫۱۰    What might be formed from CH3ˆCH2ˆCH¨CHˆCH3  in the atmosphere in the presence of sunlight, oxides of nitrogen, and water droplets?

۵٫۱۱    Which of the following compounds have optical isomers?

 

 

CH2OH ˆ CH ˆ CHO


CH3ˆ C ¨ C ˆ H


CH3ˆ CH2ˆ CHˆ CH3

 

 

OH                                  H

 

CH3                                                           OH

 

 

 

CHO ˆ CH ˆ CH ˆ CH2OH


CH3 ˆ CH ˆ COOH


CH3 ˆ C ¨ CHˆ CH3

 

 

OH    OH

 

CH3

 

H  CH3

 

 

۵٫۱۲    Show a general formula for fats and oils. What is the difference between a fat and an oil?

۵٫۱۳    What is the difference between a fat and a wax?

۵٫۱۴    How many asymmetric carbon atoms are there in glucose?

 

 

۴۴M. M. Scherer, B. A. Balko, D. A. Gallagher, and P. G. Tratnyek, Correlation Analysis of Rate

Constants for Dechlorination by Zero-Valent Iron, Env. Sci. Tech., 32: 3026–۳۰۳۳ (۱۹۹۸).

 

 

 

۵٫۱۵    Write a possible structural formula for a ketopentose and for an aldopentose.

۵٫۱۶    What is the major factor contributing to the difference in biodegradability between starch and cellulose?

۵٫۱۷    Show a general formula for the building blocks of proteins and illustrate how these building blocks are connected to form proteins.

۵٫۱۸    If a sample of food waste contains 2.5 percent of organic nitrogen, what approximate percentage of the sample is protein?

۵٫۱۹    What functional group is characteristic of each of the following: alkenes, alcohols, aldehydes, ketones, acids, amines, amides, ethers, esters, and aromatic compounds?

۵٫۲۰    What monosaccharides are formed upon hydrolysis of the following: cellulose, starch, and hemicellulose?

۵٫۲۱    Name the three general classes of synthetic detergents, and give an example of each.

۵٫۲۲    Name the four general classes of synthetic pesticides, and describe how the pesticides in each class differ in degree of biodegradability.

۵٫۲۳    Explain why pharmaceutically active chemicals (PhACs) are of concern to environmental engineers and scientists. Give two examples of PhACs.

۵٫۲۴    Explain why endocrine-disrupting chemicals (EDCs) are of concern to environmental engineers and scientists. Give two examples of EDCs.

۵٫۲۵    Give the structural formula for each of the following: (a)    ۳-Nonene

(b)    n-Octyl phenol

(c)    Dimethyl ether

(d)    ۱,۱,۲-Trichloroethane

(e)    Any PCB

(f )    n-Pentanoic acid

(g)    Isopropanol

(h)    ۲,۴,۶-Trinitrotoluene (TNT)

۵٫۲۶    Give the structural formula for the following: (a)    ۱,۲-Dichloroethene

(b)    Diethyl ketone

(c)    Pentachlorophenol

(d)    Butyric acid

(e)    m-Chlorophenol

(f )    A poly-cyclic aromatic hydrocarbon (PAH) (g)    ۳-Pentanol

(h)    l-Octene

۵٫۲۷    Given the following structural formulas, name (IUPAC or common) the compound. (a)    CH3CHOH CH2CH3

(b)         Cl

 

 

 

Cl

 

 

 

(c)    CHCl2CH2Br (d)    CH3OCH2CH3 (e)    CH3CHO

(f )    CCl2CHCl

(g)    CH3CH2CH2COCH2CH3

 

(h)


CH3

 

 

 

 

Cl

 

(i)                   Cl

 

 

 

NO2

 

 

۵٫۲۸    Name the following: CH3CH2CH ˆ CH2CH3

CH3

 

CH3CH2CH2CH ˆ CH2CH2OH CH2CH3

 

 

 

CH2 ¨ CHˆ CH ˆ CH3

 

CH3


CH3CH2CH2COOH

 

 

 

 

CH3

 

 

Cl         OH ˆ


NH2

 

 

 

Cl

 

۵٫۲۹    A contaminated groundwater contains 50   g/L chlorobenzene, 25   g/L dichloromethane, and 85   g/L ethylbenzene. Using the simplified equilibrium model developed in Sec. 5.34, estimate the air-to-water ratio required to reduce the concentration of each of these compounds below 5   g/L. Assume a temperature of

۲۵ C. If you were to design a stripping tower to remove these contaminants, would you expect your design air-to-water ratio to be larger, smaller, or the same? Why?

Answer: 48.9; 39.1; 48.3

۵٫۳۰    Regarding air stripping for the removal of volatile organic compounds, what impact on removal efficiency would an increase in the following parameters have?

(a)    H

(b)    Va /Vw

(c)    KLa

(d)    Temperature

 

 

 

۵٫۳۱    Rank the following compounds from most volatile (most likely to partition into the atmosphere) to least volatile. Include appropriate data and reference the data to substantiate your ranking.

(a)    Benzene

(b)    Phenol

(c)    Chloroform

(d)    Bromoform

(e)    Trichloroethene

(f )    ۱,۱,۱-Trichloroethane

(g)    Tetrachloroethene (also called perchloroethene)

۵٫۳۲    An industry has dumped a total of 100 pounds of trichloroethene (TCE) into a well- capped landfill (that is, assume the landfill is closed to the atmosphere). This chemical landfill is 100 feet long by 100 feet wide and 10 feet deep. The void volume is 30 percent and 70 percent of the voids are filled with water. Assuming that aqueous solubility is not exceeded and that there is no transformation or sorptive removal, estimate the concentration of TCE in the aqueous phase. Assume a temperature of

۲۵ C. [Think about how complex this problem would be if biodegradation (vinyl chloride can be produced under anaerobic conditions!) and sorption occurred, and if the landfill were not capped and/or a substantial amount of methane were produced and vented to the atmosphere.]

Answer: 63 mg/L

۵٫۳۳    A wastewater is saturated with trichloroethene giving a concentration of 1100 mg/L.

One million liters of this waste is put into a closed holding tank (total tank volume

۲ million liters). What percent removal of TCE from the liquid would occur from this action? Assume a temperature of 25 C.

Answer: 32 percent

۵٫۳۴    Using values from Table 5.15, estimate Koc using octanol-water partition coefficients and water solubilities for the following compounds:

(a)    Chloroform

(b)    ۱,۱,۱-Trichloroethane

(c)    Benzene

(d)    Chlorobenzene

(e)    Phenol

(f )    Pentachlorophenol

(g)    Benzo(a)pyrene

(h)    Atrazine

۵٫۳۵    Using data from Table 5.15, determine which of the following will move faster with groundwater. By what degree? Show all calculations necessary to justify your answer. Assume the aquifer has a void fraction of 0.20, a bulk density of 2 kg/L, and contains

۱ percent organic carbon. (a)    Benzene

(b)    Toluene

(c)    Trichloroethene

(d)    ۱,۱,۱-Trichloroethane

 

 

 

(e)    Acrolein

(f )    Naphthalene

Answer: acrolein is fastest; naphthalene slowest

۵٫۳۶    Assuming a temperature of 25 C, estimate the degree to which tetrachloroethene

(PCE) will be retarded in a groundwater aquifer with

(a)    A void fraction of 0.30, a bulk density of 2000 kg/m3, and an organic carbon content of 0.25 percent.

(b)    A void fraction of 0.30, a bulk density of 2000 kg/m3, and an organic carbon content of 1.0 percent.

۵٫۳۷    Which parameter, H, water solubility, or Kow, would you expect to be a better predictor for whether a compound will sorb strongly to particulate material in soils and sediments? Why?

۵٫۳۸    The organic compounds listed here are contained in a combined domestic-industrial wastewater. Rank the compounds in increasing order of susceptibility to removal by settling of wastewater suspended solids during primary sedimentation. Provide suitable justification for your rankings.

(a)    Alachlor

(b)    Phenol

(c)    Pentachlorophenol

(d)    Acrolein

(e)    Carbon tetrachloride

(f )    Nitrobenzene

(g)    Ethanol

Answer: pentachlorophenol most susceptible

۵٫۳۹    Groundwater contamination problems have been caused because of underground storage tanks leaking gasoline. In most situations the compounds causing the most concern are MTBE and the BTEX compounds. Using data contained in Table 5.15, answer the following.

(a)    Which compound would you expect to move fastest in the groundwater?

Why?

(b)    Which compound would be easiest to remove by air stripping? Why? (c)    Which compound would be easiest to remove by adsorption? Why?

۵٫۴۰    The following are types of transformation reactions. Give an adequate definition of each by writing an example reaction with a specific organic for each. Do not use the example reactions listed in the text, generate your own.

(a)    Hydrolysis (b)    Elimination (c)    Oxidation (d)    Reduction

(e)    Nucleophilic substitution

۵٫۴۱    Using example reactions, explain the difference between dehydrohalogenation, reductive dehalogenation, and reductive elimination.

۵٫۴۲    The pesticides shown here are subject to transformation in the environment. Give the class of pesticide and suggest a transformation reaction that it may possibly undergo

 

 

 

in the environment. Balance the reaction as best you can and tell under what conditions it might occur (i.e., aerobic, anaerobic).

 

(a)

 

 

N Clˆ


H

 

ˆ N ˆ CH(CH3)2

 

N        N

 

 

 

 

(b)


CH2CH3

 

H    O

 

ˆ N ˆ C ˆ O ˆ CH(CH3)2

 

 

 

 

 

(c)

 

 

Clˆ

 

H

 

ˆ Cˆ

 

Cl ˆ Cˆ Cl

 

Cl

 

 

ˆ Cl

 

 

(d)

 

S              H    O

 

 

H3C ˆ O ˆ P ˆS

 

C ˆ C ˆ O ˆ CH2CH3

 

 

O ˆ CH3   CH2 ˆ Cˆ O ˆ CH2CH3

 

O

 

۵٫۴۳    The following are pseudo-first-order rate coefficients for the pesticide parathion:

 

kp     ۰٫۱۰ day   ۱                photolysis kh     ۰٫۰۲۸ day   ۱            hydrolysis ko     ۰٫۰۰۵ day   ۱            oxidation

Calculate the environmental half-life for each of the transformation reaction types and the overall half-life of parathion. (Note: Rate coefficients for this problem were provided by Prof. J. L. Schnoor of the University of Iowa.)

Answer: 6.9 d; 24.8 d; 139 d; 5.2 d

۵٫۴۴    A groundwater plume contains trichloroethene (TCE). TCE is reduced by iron metal (Fe(0)) following first-order kinetics with respect to TCE concentration. A permeable reactive barrier (PRB) containing Fe(0) is proposed to intercept and treat the contaminated groundwater. The following information is to be used to solve this problem.

 

 

 

 

For the PRB,

 

TCE concentration entering the PRB     ۱۰۰   g/L

kTCE     ۰٫۰۰۲ h   ۱

 

 

foc     ۰٫۰۱               ۲٫۸ kg/L        porosity     ۰٫۴۵

 

Linear groundwater velocity     ۰٫۳ ft/d

 

 

 

Since the PRB contains organic carbon, TCE will be retarded as it passes through the PRB as well as reduced by the Fe(0). Will a 3-foot-wide PRB be adequate to reduce the concentration of TCE below its drinking water MCL (5   g/L)? Assume a temperature of 25 C. Hint: Calculate the “retarded” velocity of TCE and note that TCE removal by reduction is described by first-order kinetics. (Note: This problem is courtesy of Prof. Michelle Scherer of the University of Iowa.)

۵٫۴۵    Using Eq. (5.68), and assuming a temperature of 25 C, estimate the solubility of the compounds listed in Table 5.16. Compare these values with those given in Table 5.15.

۵٫۴۶    Using Eq. (5.69) and Kow data in Table 5.15, estimate the solubility of the compounds listed in Table 5.16. Compare these values with your answers for Prob. 5.45.

۵٫۴۷    Using Kow data from Table 5.15, rank the following compounds on the basis of lowest to highest degree of bioconcentration by estimating the bioconcentration factor for each.

(a)    Chloroform

(b)    Trichloroethene

(c) Benzene (d) Toluene (e)    Phenol

(f)    Benzo(a)pyrene

(g)    Acrolein

(h)    DDT

۵٫۴۸    Using Kow data from Table 5.15, rank the following compounds on the basis of least

to most toxic to aerobic heterotrophic bacteria by estimating the IC50 using Eqs. (5.72)

and (5.73).

(a)    Dichloromethane

(b)    Chloroform

(c)    ۱,۱,۱-Trichloroethane

(d)    Trichloroethene

(e)    Benzene

(f)    Toluene

(g)    Chlorobenzene

(h)    Phenol

Answer: least, phenol or dichloromethane

 

 

REFERENCES

 

Brezonik, P. L.: Principles of Linear Free-Energy and Structure-Activity Relationships and Their Applications to the Fate of Chemicals in Aquatic Systems, in “Aquatic Chemical Kinetics,” W. Stumm, ed., Wiley-Interscience, New York, 1990.

Carey, F. A.: “Organic Chemistry,” ۴th ed., McGraw-Hill, New York, 2000.

Loudon, G. C.: “Organic Chemistry,” ۳rd ed., Benjamin/Cummings, Menlo Park, CA, 1995. Manahan, S. E.: “Environmental Chemistry,” ۵th ed., Lewis, Chelsea, MI, 1991.

Morrison, R. T., and R. N. Boyd: “Organic Chemistry,” ۴th ed., Allyn and Bacon, Boston,

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Reinhard, M., and A. Drefahl, “Handbook for Estimating Physiochemical Properties of

Organic Compounds,” John Wiley & Sons, Inc., New York, 1999. Schwarzenbach, R. P., P. M. Gschwend, and D. M. Imboden: “Environmental Organic

Chemistry,” Wiley-Interscience, New York, 1993.

Schwarzenbach, R. P. and P. M. Gschwend: Chemical Transformations of Organic Pollutants in the Aquatic Environment, in “Aquatic Chemical Kinetics,” W. Stumm, ed., Wiley-Interscience, New York, 1990

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