cis- 1,2-Dichloroethene trans-1,2-Dichloroethene
It is important to note that the physical properties can be different for geometric isomers 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):
Boiling point, °C Density, g/cm3 Vapor pressure, aim Henry's constant, atm/M Water solubility, mg/L
60.3 1.2837 0.24 7.4 3500
47.5 1.2565 0.37 6.7 6300
Both cis- and trans-1,2-dichloroethene have been found in the environment as biological transformation products of TCE. Drinking water MCLs have been established for both (70 and 100 ptg/L, respectively).
Tetrachloroethene (CClr=CCl2), also called perchloroethene (PCE), is a widely used industrial solvent and is a commonly found groundwater pollutant. It is a regulated drinking water contaminan!: with an MCL of 5 /xg/L.
Dibromochloropropane (DBCP) Although there are nine possible isomers of di-bromochloropropane (C3H5Br2Cl), it is l,2-dibromo-3-chloropropane (CHJBrCH BrCHjCl) 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 ftg/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 CC13F (CFC-11), CC12F2 (CFC-12), CC12FCC1F2 (CFC-113), CC1F2CC1F2 (CFC-114), and CC1F2CF3 (CFC-115). Recently, CFCs have been shown to be involved in the destruction of the stratos-
ch apter 5 Basic Concepts from Organic Chemistry
"ozone hole" effect, via the following reactions with ul-CFjClj + hy —» CI* + CFjCl*
(ozone) (free radical chlorine oxide) CIO- + O -> CI- + 02 (0 atom) O + 03 02+ 02 fi f chlorofluorocarbons are also known to be greenhouse gases. Because of their role |i in ozone destruction and the greenhouse effect, manufacture and use of chlorofluo-' rocarbons is being eliminated worldwide.
iiv f . Haloacetic Acids (HAA) Another important group of halogenated aliphatic compounds 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-fi . lished for the sum of five haloacetic acids (HAA5), mono-, di-, and trichloroacetic f acids and mono- and dibromoacetic acids.
I Periluorinated Compounds Another class of halogenated compounds of emerging concern are the perfluorinated compounds. Here, all C—H bonds are replaced by C—F 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 |7 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 I down to this compound.
' Perfluoro-octane-sulfonate (PFOS)
| These compounds are known to bioaccumulate and are being found in blood sam-pies from humans and animals far from their known sources.7 Laboratory toxicity
W. I. P. Giesy and K. Kannan, Global Distribution of Perfiuorooctane Sulfonate in Wildlife, Env. Sci. | Tech., 35: 1339-1342 (2001).
s ft: pheric ozone layer, the I traviolet radiation.
Monochloroacetic acid Dichloroacetic acid studies are showing that these compounds are toxic, causing a variety of effects in the livers of test animals, and perhaps carcinogenic.9,9
5.9 ! simple compounds containing nitrogen
The simple aliphatic compounds containing nitrogen are of three types: amines, amides, and nitriles (cyanides). Other nitrogen-containing compounds of environmental significance include nitrosamines and isocyanates.
The amines are alkyl derivatives of ammonia. They are of three types: primary, secondary, and tertiary.
Primary Secondary10 Tertiary10 amine amine amine
In primary amines, one hydrogen atom of ammonia is replaced by an alky] group such as CH3—, C2H5—, 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 increases 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 easily with secondary amines.
Tertiary amines combine with alkyl halides to form quaternary ammonium salts as follows:
The compounds formed are actually chloride salts and ionize to form a quaternary ammonium ion and a chloride ion. The quaternary ammonium salts have bactericidal properties that can be enhanced by the proper choice of the R groups. They
«R. Renner, Growing Concern Over Perfluorinated Chemicals, Env. Sei. Tech., 35: 154A-160A (2001). ®R. Renner, Perfluorinated Compounds Linked lo Carcinogenicity in Vitro," Env. Sei. Tech., 35: 180A (2001).
I0R, R', R" represent alkyi groups. They may ail 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 quaternary ammonium salts are sold for disinfecting purposes under a variety of trade names.
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.
Under special conditions, an amide results.
R—C—[OH_+_Hj—NH2 -»• R—C—NH2 + H20 (5.41)
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 + 4NaOH 2NaBr + Na2C03 + 2H20 + CH3NH2 (5.42)
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 \ C NH2/ is related to an important group of compounds conO
taming the peptide linkage \—C—N—/ , as discussed in Sec. 5.22. Urea,
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 accidental production from ammonium cyanate by Wôhler 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. if
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, 3 control odors.
Nitriles, or organic cyanides, are important compounds of industry. They have the general'formula R— CN, 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, or jV-nitroso compounds, have the general formula R2 N N=0 ; 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 W-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
, Name as'nitrile*v
Acetonltrile Propionitrile Succmooltrile Acrylonitrile
Methyl cyanide Ethyl cyanide
; }„ 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 have the general formula R—N=C—O and are widely used industrial chemicals. Methyl isocyanate (CH3—N=C=0) 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 compounds makes them potent potential air pollutants.
5.10 i cyclic aliphatic compounds
A number of cyclic aliphatic hydrocarbons are known. Many of these occur in petroleum and are known as naphthenes.
CH2 CH2 CH2 CH2
ch2-ch2 ch2—ch2 ch2 ch2
Cyclopropane Cyclopentane 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 choh ch2 c=o
ch2 ch2 ch2 ch2
Mercaptans or thioalcohols are aliphatic compounds that contain sulfur. They have a structure similar to alcohols, except that oxygen is replaced by sulfur.
"M. Alexander, "Biodégradation and Bioremediation," 2nd éd., Academic Press, San Diego, 1999.
I2Ï. Najm and R. R. Trussell, NDMA Formation in Water and Wastewater, J. American Water Works Assoc., 93(2): 92-99 (2001).
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, j They are considered to be quite toxic to fish. The odor of skunks is largely due to i butyl mercaptan.
aromatic compounds 5.12 ! 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.
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