V V

Purine 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 primary 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 benzene nucleus condensed with a pyrrole nucleus.

Indole Skatole

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 (fie explosives RDX (hexahydro-1,3,5-trinitro-l,3,5-triazine) and HMX (octahydro-I,3,5,7-tetranitro-

1 3 5 7-tetrazocine), These compounds have been found as soil or groundwater contaminants 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 eamron-ment. They have been detected in a number of groundwater supplies and present environmental engineers and scientists with challenging remediation problems.

Chexahydro-l,3,5-trii«itro-l,3>triazine) <octahydr^l,3.5.7-tetnmili©-l,3,5;7-tetrazocine)

5.18 i dyes

The subject of dyes is of such magnitude and complexity that a discussion of various types will not be presented here. The environmental engineer and scientist concerned with the treatment of textile wastes, and possibly a few others, will be confronted 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

5.19 i 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 payability or for j other reasons.

5.20 i carbohydrates

The term carbohydrate is applied to a large group of compounds of carbon, hydrogen, 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-,

CHAPTERS Basic Concepts from Organic Chemistry

¡^hydrate materials occurs in the lumber, paper, and textile industries, as well as in lj,e food industry. Wastes from these industries are major problems and tax the ingenuity 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) corriplex sugars, or disaccharides; (3) polysaccharides. In general, the -ose ending : is used to name carbohydrates.

gjmp]e 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 CjH^Oj. Two pentoses are of commercial 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 produced by the hydrolysis of gum arabic or wheat bran.

chjoh D(-)-Xyiose2i

CH2OH

Di-O-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 conditions, 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 C6H,206. Glucose, galactose, and mannose are all aldoses, and fructose is a Icetose.

aAU 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 naturally in fruit juices and in honey. It is manufactured in great quantity by the hydrolysis of com 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.

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 nature. 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.

H

h

ch2oh

C—0 j

c—o |

c=o

h—C— oh

ho—C—h j

j ho—c—H

ho—C—h j

ho—C—H

H—C—oh

ho—C—h

H—C—OH

H—C—OH 1

I

ch2oh

ch2oh

ch2oh

D-(-)-Fructose

D-(+)-Galactose

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-

Ration may stop at that point because of the unfavorable pH conditions produced by : fye acids unless precautions are taken to control the pH by means of buffers or alkaline 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

•jftere are three important sugars with the general formula CI2H22On: sucrose, mal-fose, and lactose. All disaccharides may be considered as consisting of two hexose sugars hooked together in one molecule. Hydrolysis results in cleavage of the molecule 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.

Il C OH

CH2OH

Fructose

CH'iOH

ch2oh

Sucrose (Ci2HJ20| J

Maltose Maltose is made by the hydrolysis of starch, induced by diastase, an enzyme 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"

CH20H

Maltose (C[;HaOn)

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. Enzymes from the yeast hydroiyze maltose to glucose and convert the glucose to alco- | hoi and carbon dioxide (Sec. 5.3).

Lactose Lactose, or milk sugar, occurs in the milk of all mammals. Upon hydroly- ; sis, the molecule is spirt to yield a molecule of glucose and a molecule of galactose. 1

Glucose

HOHO-

Galactose part

CH2OB

CHoOH

Lactose (cijhjjoj i)

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- ;j rides. Glucose and xylose are the most common units involved. Three polysaccharides I are of interest: starch cellulose, and hemicellulose. None of them have the characteris- j tic sweet taste of sugar because of their insolubility and complex molecular structure.

Starch Starch has the general formula (qhka)*. It occurs in a wide variety of j products grown for food purposes (corn, wheat, potatoes, rice, etc.). It is the cheap- j 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 j only monosaccharide, and its general formula may be indicated as follows: -}

CH,OH CHoOH I CH2OH

CH,OH CHoOH I CH2OH

about 100 to 1000)

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 :

chapter 5 Basic Concepts from Organic Chemistry

of glucose units attached to form branched chains, is termed amylopectin. The amylose 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-able 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 processing 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, including humans, do not have enzymes capable of promoting the hydrolysis of this linkage. Therefore, cellulose passes through the digestive tract unchanged. Certain animals, 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 nourishment indirectly from cellulose. The beta linkage for cellulose is indicated as follows:

CH2OH

CH2OH

CH2OH

Portion of cellulose moteculc

CH2OH

Portion of cellulose moteculc

Industrial wastes from the paper industry usually contain considerable amounts of cellulose in suspension. This is particularly true of the wastes from the manufacture 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 contaminants are inorganic compounds, derivatives of cellulose, and other organic compounds. Since certain bacteria can hydrolyze cellulose, biological treatment of cellulose 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 digestion 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 M

Disaccharides Starch Cellulose Hemicellulose M

Figure 5.1

Summary of hydrolytic behavior of carbohydrates.

Figure 5.1

Summary of hydrolytic behavior of carbohydrates.

Most natural woods contain cellulose, hemicellulose, and lignin, along with resins, i 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- i 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 fermentable 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- V tose yields galactose, and hemicellulose yields xylose in addition to glucose.

5.211 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.

chapter s Basic Concepts from Organic Chemistry

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.

-C3H7 h2c o c cj7o35 0

0 II

0 II

Glyceryl (or glycerol) tributyrate, tribatyrin

-c cj7h35 O

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.

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

H2C O C57HUS a'

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 5.121 Acids of fats and oils

Name .

luriiiiilii

Xiji^

Butyric

CJH7COOH

-5.7

Caproic

c5h„cooh

-3

Caprylic

c7h13cooh

16.3

Capric

c9hwcooh

31.9

Laurie

CuHBCOOH

43.2

Myristic

c!3h2,cooh

53.9

Palmitic

cI5h31cooh

63.1

Stearic

C|THmCOOH

69.6

Arachidic

C^OHjoOJ

76.5

Behenic

C22H4402

81.5

Oleic

CiaH340j

13.4

Erucxc

CjlHflOj

34.7

Linoleic

C|gH3202

-12

Linolenic

CISH30O2

Butter

Butter, coconut oil Palm oil, butter Coconut oil

Coconut oil, spermaceti Nutmeg, coconut oil Palm oil, animal fats Animal and vegetable fats, oils Peanut oil Ben oil

Animal and vegetable fats, oils Rape oil, mustard oil Cottonseed oil Linseed oil

Source: D. R. Linde (ed.): "Handbook of Chemistry and Physics," 82nd ed., CRC Press LLC, Boca Raton, 2001.

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

V- Lino

Lino

V« 1"

P^ÜIIÄll

N'nme

Oleic

leic ''. rO

len«:

Stearic

Myristic

Palmitic

Butter"

27.4

11.4

22.6

22.6

Mutton tallow

36.0

4.3

30.5

4.6

24.6

Castor oiF '

9

3

3

6.9

0.1

Olive oil

84.4

4.6

2.3

Trace

Palm oil

38.4

10.7

4.2

1.1

41.1

Coconut oilc

5.0

1.0

3,0

18.5

7.5

3.3

Peanut oild

60.6

21.6

4.9

6.3

Corn oil"

43.4

39.1

3.3

7.3

0.4

Cottonseed oil

33.2

39.4

1.9

0.3

19.1

0.6

Linseed oil

5

48.5

34.1

6.5

0.7 .

Soybean oil^

32.0

49,3

2.2

4.2

Tung oil8

14.9

1.3

4.1

"Contains caproic, 1.4 percent; caprylic, 1.8 percent; capric, 1.8 percent; butyric, 3.2 percent; iauric, 6.9 percent.

'Contains about 85 percent of ricinoleic acid, 12-hydroxy-9-octadecenoic acid (mp, 17°),

CH3(CH2)5CHOHCHJCH=CH(CH2)JCOOH.

'Contains caprylic, 9.5 percent; capric, 4.5 percent; Iauric, 51 percent.

''Contains 2.6 percent lignoceric acid.

"Contains 0.2 percent lignoceric acid.

'Contains 0.1 percent lignoceric acid.

^Contains 79.7 percent eleostearic acid.

Source: From E. Wertheim and H. Jeskey, "Introductory Organic Chemistry," 3rd ed„ McGraw-Hill, New York, 1956. Table reproduced by permission of the authors.

"Contains caproic, 1.4 percent; caprylic, 1.8 percent; capric, 1.8 percent; butyric, 3.2 percent; iauric, 6.9 percent.

'Contains about 85 percent of ricinoleic acid, 12-hydroxy-9-octadecenoic acid (mp, 17°),

CH3(CH2)5CHOHCHJCH=CH(CH2)JCOOH.

'Contains caprylic, 9.5 percent; capric, 4.5 percent; Iauric, 51 percent.

''Contains 2.6 percent lignoceric acid.

"Contains 0.2 percent lignoceric acid.

'Contains 0.1 percent lignoceric acid.

^Contains 79.7 percent eleostearic acid.

Source: From E. Wertheim and H. Jeskey, "Introductory Organic Chemistry," 3rd ed„ McGraw-Hill, New York, 1956. Table reproduced by permission of the authors.

chapter S Basic Concepts from Organic Chemistry

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 bacterial 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. ït 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 converted to fats by the process of hydrogénation. 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 hydrogénation 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 alcohols of high molecular weight. Beeswax is an ester of palmitic acid and myricyl alcohol (Cî5H3lCOOC3!H63). It also contains cerotic acid (C25HsiCOOH). Spermaceti is obtained from the heads of sperm whales and is principally an ester of palmitic acid and cetyl alcohol (cdhjicooci^hjj). Cetyl esters of lauric and myristic acids are also present to a limited extent.

5.22 i proteins and amino acids

Proteins are complex compounds of carbon, hydrogen, oxygen, and nitrogen. Phosphorus and sulfur are present in a few. They are among the most complex of the organic compounds produced in nature and are widely distributed in plants and animals. 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 ce-amino acids. Since more than 20 different amino acids are normally found present in proteins, the variety of proteins is considerable.

Amino Acids |

The a-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 S

they build proteins. Animals are unable to synthesize certain of the amino acids and -3

must depend upon plants to supply them in the form of proteins. Such amino acids i 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 a-amino acids. q

Chemistry of Amino Acids The free amino acids behave like acids and also like I 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 + HC1 —> CI" + +H3NCH2COOH (5.48) |

Salt formation with a base:.

The amino acids having one amino and one carboxyl group are essentially neutral 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 NBi

Zwitterion

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.

A dipeptide j chapter s Basic Concepts from Organic Chemistry

It is this ability to form linkages between the amino and carboxyl groups that allows 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 carboxyl 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, however, 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.

II h

Classes of Amino Acids About 20 different «-amino acids can generally be isolated 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, (hose marked with an asterisk are considered indispensable in human nutrition. The generally used abbreviation for each amino acid is noted after the na'mp.

Monoamino monocarboxy acids h2nch2cooh ch3chnh2c00h ch3 f f

CH3x|

c2h5

"Leucine (Leu)

Monocarboxy diamino acids h n h h h2N—c—N—ch2(ch2)2—ç—cooh Arginine (Arg)

Aromatic homocyclic acids h ach2—c—cooh nh,

«Phenylalanine (Phe)

Tyrosine (Tyr)

Monoamino monocarboxy monohydroxy acids oh h

hc—c—cooh Serine (Ser) h nhî h h ch, —c —c—cooh »Threonine (Thr)

o nh2

Sulfur-containing acids h s h hc—c—cooh h nh2

Cysteine (Cys)

ch3—s—-ch2—ch2—c~ cooh "Methionine (Met)

Dicarboxy monoamino acids hooc—ch2— ch— cooh Aspartic acid (Asp)

hooc—ch2—ch2—ch—cooh Glutamic acid (Glu) nh2

Heterocyclic acids

-cooh

Proline (Pro)

Hydroxyproline (Hypro)

Histidine (His)

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- i 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 discovered 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 ammo 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 combine 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 protems falls : within a very narrow range, as shown here:

Carbon

51-55

Hydrogen

6.5-7.3

Oxygen

20-24

Nitrogen

15-18

Sulfur

0.0-2.5

Phosphorus

0.0-1.0

The nitrogen content varies from 15 to 18 percent and averages about 16 percent, j Since carbohydrates and fats do not contain nitrogen, advantage is taken of this fact j 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 > 100/16 or 6.25, gives an estimate of the protein content. This procedure is sometimes 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 considered 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.

I Hydrolysis Products of Proteins

Protein polypeptides i (5.53)

a-amino acids <— dipeptides

The a-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 converted to carbon dioxide and water.

detergents

5.23 i detergents

The term detergent is applied to a wide variety of cleansing materials used to remove 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 active" 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 solubility in water is due to carboxyl, sulfate, hydroxyl, or sulfonate groups. The surfactants with carboxyl, sulfate, and sulfonate groups are all used as sodium or potassium salts.

Oil-soluble part Water-soluble part —COO~Na+

Organic group

The nature of the organic part of the molecule varies greatly with the various surfactant types.

5.24 i soaps

Ordinary soaps are derived from fats and oils by saponification with sodium hydroxide. 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.

H2COOCC!7H35 H2COH

H COOCC17H35 + 3NaOH H—COH + 3C17H35COONa (5 54)

H2COOCC17H35 H2COH

Stearin Glycerol

The fats and oils are split into glycerol and sodium soaps. The nature of the soap de- 3 pends upon the type of fat or oil used. Beef fat and cottonseed oil are used to produce low-grade, heavy-duty soaps. Coconut and other oils are used in the produc- i 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.

2C 17H33COONa(iig) + Ca2+ -> (CnH33COO)2Ca(s) + 2Na+ (5.55)

Soap must be added to precipitate all the ions causing hardness before it can act as a J surfactant, usually indicated by the onset of frothing upon agitation.

5.25 i 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 30 percent surfactant (active ingredient) and 70 to 80 percent builders. The builders are usually sodium sulfate, sodium ^polyphosphate, sodium pyrophosphate, sodium silicate, and other materials that enhance the detergent properties of the active ingredient. The use of phosphate has been curtailed because of its role in eu- j 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 j charged, surface-activated ion. The common ones are all sulfates and sulfonates. j

Sulfates Long-chain alcohols when treated with 'sulfuric acid produce sulfates (in-1 organic esters) with surface-active properties. Dodecyl or lauryl alcohol is com-'! monly used. I

Lauryi alcohol

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

Ci2H25—O—S03H + NaOH C12H23—0-S03Na + H20 (5.57) !

Sodium tauryl 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.

it

H H i i

H

H

R'

R-

-c—

-o-

-C—C-[ i

II

-o-

-Na

R—C—R' l

R—C—R'

1 1 H H

II 0

Ai

ifl

Ester

U

0

H H

0

T

II

1 1

1!

o=s==o

0=s=0

R~

-c-

-N-

-c—c—

-s-

-o-

-Na

1

• 1

1 1

II

0

o

H H

0

1

1

N-

-c-

-H

Na

Na

1

Secondary

Sulfonated alkylbenzenes

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 molecule to render them soluble. All depend upon polymers of ethylene oxide (C2H40) (polyethoxylates) to give them this property.

Ester type

Amide type

Aryl type

HO[C2H4OLH

Ethylene oxide polymer type

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

part 1 Fundamentals of Chemistry for Environmental Engineering and Science Cationic Detergents

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

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- j ity is important. If diapers axe not sterilized by some means, bacterial infestations j may occur that release enzymes that will hydrolyze urea to produce free ammonia I [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 j structure.25 Common soaps and the sulfated alcohols are readily used as bacterial j 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 structure. 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 brorninated during chlorine disinfection. As noted previously, the . alkyiphenols are suspected endocrine disrupters. The alkyl-benzene sulfonates de- : rived from propene were highly resistant to biodégradation, and their persistence : resulted in excessive foaming in rivers and groundwaters in the 1950s. This presented some of the first evidence of the potential harmful environmental consequences of synthetic organic chemicals. For this reason, the detergent manufacturing industry changed to the production of LAS surfactants. LAS is readily degradable under aerobic conditions, and its use has helped relieve the most serious problems of detergent foaming. However, unlike common soap, it is resistant aC. N. Sawyer and D. W. Ryckman, Anionic Detergents and Water Supply Problems, J. Amer. Water Works Assoc., 49: 480 (1957).

chapter 5 Basic Concepts from Organic Chemistry

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 are materials used to prevent, destroy, repel, or otherwise control objectionable insects, rodents, plants, weeds, or other undesirable forms of life. Common pesticides can be categorized chemically into three general groups, inorganic, 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 annual 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 organic phosphorus pesticides, and the carbamate pesticides. An additional category of current interest is the s-triazine pesticides. There are many other types of synthetic 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 compound with the following structure:

pesticides 5.26 i pesticides

5.27 i chlorinated pesticides

Cl DDT

Cl DDT

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 benzene hexachloride or BHC is formed. Several stereoisomers are produced, but the gamma isomer called lindane is by far the most effective as an insecticide.

CI CI

H Cl

H H .j y-Benzene hexachloride (lindane)

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

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.

O—CH2COOH

O—CH2COOH

2,4-Dichiorophenoxyacetic acid (2,4-D)

o—cacooH

2,4,5 -Trichlorophenoxyacetic acid (2,4,5-T)

These two herbicides are effective in destroying certain broad-leaf plants while no 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 formée the combustion of chlorinated organic compounds. The most toxic dioxin is ig:|^tetrachlorodibenzo-p-dioxin(TCDD):

2,3,7,8-Tetrachiorodibenzo-p-dioxin(TCDD)

2,3,7,8-Tetrachiorodibenzo-p-dioxin(TCDD)

Because of its extreme toxicity, a very low drinking water MCL of 3 X 1Q~S ¡ig!L "¿s beer, established for this dioxin.

| Tbe family of compounds called the chloroacetamides are also commonly used ^herbicides for control of broad-leaf weeds. Two of the most common examples aiachlor [2-chloro-2',6'-diethyl-N-(metlioxymethyl)-acetanilide) and meto-iBhior :[2-chloro-6'-ethyl-N-(2-methoxy-l-methyl-ethyl)acet-o-toluidine]. These "erfcicides are used primarily for weed control in the production of corn and soybeans.

Alachlor

H3C H H

Alachlor h H

Metoiachior

" Other chlorinated or halogenated pesticides of significance are aldrin, chlor-.dane. toxaphene, heptachlor, methoxychlor, DDD, EDB, DBCP, and 1,2-¿¿icliloropropane; all have been used as insecticides, fungicides, or nematocides. fP halogenated pesticides are considered to be of significant concern because of iheir persistence and high potential for creating harm to humans and the environment. 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 oiiisage.

jf 28 i organic phosphorus pesticides

¿The organic phosphorus pesticides became important as insecticides after World #ar II. These compounds were developed in the course of chemical warfare research in Germany and in general are quite toxic to humans as well as to pests. Paraihion is an important pesticide, which was introduced into the United States from Germany in 1946. It is an aromatic compound and contains sulfur and nitron gen as well as phosphorus in its structure, so do many of the organic phosphorus pesticides.

OC2H5 __ 0C2H5

0,O-Diethyl-O-p-mtrophenylthiophosphate (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 US6.

Malaihion is highly toxic to a variety of insects, but unlike many organic phosphorus pesticides, it has low toxicity to mammals. This has made it particularly successful and it is widely used.

S-(l,2)-Dicarbethoxyethyt)-0,0-dimethyidithiophosphate

(malathion)

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

5.29 i carbamate pesticides

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

H CH3

o ch3

Isopropyl W-phenylcarbamate

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 générai appear to have low toxicity to mammals.

5.30 I s-TRIAZINES

The class of compounds called the s-triazines are primarily used as herbicides in agricultural regions and are of three general types: (1) chloro s-triazines, (2) niethylthio s-triazines, and (3) methoxy s-triazines:

ci sch3 och3

JL JL L Jl L Ji r'hn^n nhk1 r'hn n/nhr" r'hn n^^nhr" Chioro-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-ethyIamino-6-(l-cyano-1 -methy lethylamino)-s-triazine].

CI CI

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 contaminant in agricultural areas.

5.311 BIOLOGICAL PROPERTIES OF PESTICIDES

Pesticides may gain access to groundwater and surface water supplies through direct 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 compound into metabolites that may be more or less toxic.

aD. J, Manch et al., Methods Development and Implementation for the National Pesticide Survey. Env. Sci. Tech., 24: 1445-1451 (1990).

In general, the chlorinated pesticides are the most resistant to biological degra-.v 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. Several 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 carbamates are noted for their low toxicity and high susceptibility to degradation. The j s-tria2ines are in general quite resistant to environmental degradation and are I known endocrine disruptors. i

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

5.32 I PHARMACEUTICALLY ACTIVE AND ENDOCRINE-DISRUPTING CHEMICALS

Two groups of chemicals of emerging concern are pharmaceutically active chemicals (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 ¿tg/JL 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 environmental engineers and scientists.

Pharmaceutically Active Chemicals (PhACs)

Pharmaceuticals axe generally defined as chemicals used for the treatment or prevention of illness. As such, they can range from compounds used for cancer treatment (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 personal 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-

..„. 0f phAC on human and wildlife health. However, there is potential for adverse : and the reasoning goes like this. Most of these compounds are lipophilic ^L-ioving"; synonymous with hydrophobic) and their activity is slow to decay at is- they remain pharmaceutical^ active for an extended time). Thus, bioconcen-tlon is possible. While the concentration of individual PhACs in water supplies low (generally less than 0.5 ¡xgfh with many in the ng/L range), the presence of yperous drugs with similar modes of action could lead to measurable effects. ioally> exposure can be chronic because PhACs are continually introduced into the Environment via human wastewater treatment, livestock production, and similar ac-"vities- one special concern with antibiotics is the development of antibiotic-cjstant strains of pathogenic bacteria due to overuse of these compounds. In gen-¡jjjs is because a large portion of the administered antibiotic leaves the body iimans and animals) via urine and feces as a mixture of parent compound and ctabolites.

PhACs come from a wide variety of organic chemical classes. Examples of pil :\Cs 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 su

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