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Chlorinated hy drocarbons are organic compounds containing carbon, hydrogen, and chlorine. They are also called chlorocarbons, chlorinated organics, chlorinated insecticides, chlorinated synthetics, and organochlorides. There are thousands of chlorinated hydrocarbon compounds. Some occur naturally, and some are toxic to humans or to the environment. Chlorinated hydrocarbons are formed by the replacement of one or more hydrogen atoms with one or more chlorine molecules. Some chlorinated hydrocarbons are part of a class of chemical compounds called alkyl halides, in which a bromine, chlorine, fluorine, or iodine atom has been substituted for a hydrogen atom. Many chlorinated hydrocarbons have industrial, agricultural, and commercial uses. The simplest chlorinated hydrocarbons are chlorinated forms of methane or ethane. Tetrachloromethane (CCl4 ), commonly known as carbon tetrachloride, is a colorless, volatile, and nonflammable liquid. It is made commercially from methane (CH4) and chlorines. It is poisonous if brwathed in excessive quantities. It has been frequently used in dry cleaning, metal cleaning, and forextracting oils from seeds.
Trichloromethane (CC3H) is commonly known as chloroform. Used in medicine as an anesthetic, it is a sweet-smelling, colorless liquid. It use has been restricted because it is a possible carcinogen. Dichloromethane (CCl2H2) or methylene chloride is used in many industrial processes. These include paint stripping, paint remover manufacturing, metal cleansing and degreasing, and in the making of pharmaceuticals. Dichlorodifluoromethane (CCl2 F2) is the most important of the Freon group of compounds. Freon was used for many years in refrigerators and air conditioners. Freon is odorless, nontoxic, nonflammable, and easily liquefied from the gaseous state. It is manufactured from carbontetrachloride and hydrofloric acid (HF). The use of Freon has been banned because when it is released it rises in the atmosphere to the stratosphere. Ultraviolet light from the sun decomposes the Freon gas, in the process freeing the two fluoride atoms. These then react with ozone molecules in the ozone layer causing increases in environmental damage, eye damage, and skin cancers.
Ethylene dichloride is the older name of 1,2-dichloroethane (C2H4Cl2). It has also been called eth ane dichloride, Dutch liquid, and Dutch oil. It is used to make vinyl chloride, which is a precursor of PVC plastics. Tetrachloroethane (C2H2Cl4) was used for a while in large amounts as a solvent and as a metal degreaser. It was also used in pesticides and paints. It is no longer used for these purposes. Breathing tetrachloroethane is very noxious. Today it is used in the United States and in a number of other countries as a chemical intermediate in the manufacturing of other chemicals. Trichloroethylene (Cl2C=CHCl) has been used as an industrial solvent and for extracting oils from plants. It also supplanted chloroform for a while as a general anesthetic.
Many chlorine hydrocarbons have been used in the production of pesticides. Many organochlorides are powerful insecticides. These include chlordane (clorinated cyclodiene); DDT (C14H9Cl5); dicofol (which is made from DDT); dioxin (2,3,7,8-tetra-chlorodibenzo-p-dioxin); endosulfan (C9H6Cl6O3S), which is also used under the names thiodan and benzoepin; heptachlor (C10H5Cl7); and pentachlorophenol (C6HCl5O), which is a synthetic fungicide. Still in use (banned in California) is lindane (gamma-Hexachlorocyclohexane). Among other uses, lindane is a treatment for lice and scabies. The bond between chlorine and carbon atoms is strong. This means that they do not degrade rapidly and continue to persist in the environment. When released into the environment they can create a long-term pollution problem that is not rapidly weathered or biodegraded. Some of them have entered the food chain with negative consequences for many species that were not the target of pesticide spraying, and for humans.
- Bruce Alleman and Andrea Leeson, eds., Natural Attenuation of Chlorinated Solvents, Petroleum Hydrocarbons and Other Organic Compounds (Battelle Press, 1999);
- Kenne and Ulf G. Ahlborg, Chlorinated Paraffins (World Health Organization, 1996);
- Sita Ramamoorthy, Chlorinated Organic Compounds in the Environment, Regulatory and Monitoring Assessment (CRC Press, 1997).