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Two representations of the organochloride chloroform.

An organochloride, organochlorine, chlorocarbon, or chlorinated solvent is an organic compound containing at least one covalently bonded chlorine atom. Their wide structural variety and divergent chemical properties lead to a broad range of uses. These chemicals are typically nonaqueous and are usually denser than water due to the presence of heavy chlorine atoms.

Applications

The simplest form of organochlorides are chlorinated hydrocarbons. These consist of simple hydrocarbons in which one or more hydrogen atoms have been replaced with chlorine. Most low molecular weight chlorinated hydrocarbons such as chloroform, dichloromethane, dichloroethene, and trichloroethane are useful as solvents. These solvents tend to be relatively non-polar; they are therefore immiscible with water and effective in cleaning applications such as degreasing and dry cleaning.

Many pesticides widely used in agriculture are organochlorides. These include DDT, dicofol, heptachlor, endosulfan, chlordane, mirex, and pentachlorophenol. These can be either hydrophilic or hydrophobic depending on their molecular structure.

Polychlorinated biphenyls (PCBs) were once commonly used electrical insulators and heat transfer agents. Their use has generally been phased out due to health concerns.

Chlorinated alkenes are useful monomers used in the preparation of a variety of materials. For example, vinyl chloride is polymerized to form the plastic polyvinyl chloride (PVC).

Natural presence

Although halogenated organic compounds are relatively rare in nature compared to non-halogenated organic compounds, many organochlorides have been isolated from natural sources ranging from bacteria to humans.^[1][2] There are examples of natural chlorine-containing compounds found in nearly every class of biomolecules including alkaloids, terpenes, amino acids, flavonoids, steroids, and fatty acids.^[1][3] Organochlorides, including dioxins, are produced in the high temperature environment of forest fires, and dioxins have been found in the preserved ashes of lightning-ignited fires that predate synthetic dioxins.^[4] In addition, a variety of a simple chlorinated hydrocarbons including dichloromethane, chloroform, and carbon tetrachloride have been isolated from marine algae.^[5] A majority of the chloromethane in the environement is produced naturally by biological decomposition, forest fires, and volcanoes.^[6] The natural organochloride epibatidine, an alkaloid isolated from tree frogs, has potent analgesic effects and has stimulated research into new pain medication.

Toxicity

Some types of organochlorides have significant toxicity to plants or animals, including humans. Dioxins, produced when organic matter is burned in the presence of chlorine, and some insecticides such as DDT are persistent organic pollutants which pose dangers when they are released into the environment. For example, DDT ,which was widely used to control insects in the mid 20th century, also accumulates in aquatic food chains. Because the body is not able to break down or dispose of it, and it interferes with calcium metabolism in birds, there were severe declines in some bird predator populations.

When chlorinated solvents, such as carbon tetrachloride, are not disposed of properly, they accumulate in groundwater. Some highly reactive organochlorides such as phosgene have even been used as chemical warfare agents.

However, the presence of chlorine in an organic compound does not ensure toxicity. Many organochlorides are safe enough for consumption in foods and medicines. For example, peas and broad beans contain the natural chlorinated plant hormone 4-chloroindole-3-acetic acid (4-Cl-IAA);^[7][8] and the sweetener sucralose (Splenda) is widely used in diet products. As of 2004, there were at least 165 organochlorides approved worldwide for use as pharmaceutical drugs, including the antihistamine loratadine (Claritin), the antidepressant sertraline (Zoloft), the anti-epileptic lamotrigine (Lamictal), and the inhalation anesthetic isoflurane.^[9]

Rachel Carson brought the issue of DDT pesticide toxicity to public awareness with her 1962 book Silent Spring, . While many countries have phased out the use of some types of organochlorides (such as the US ban on DDT as a result of Carson's work), persistent DDT, PCB, and other organochloride residues continue to be found in humans and mammals across the planet many years after production and use have been limited. In Arctic areas, particularly high levels are found in marine mammals. These chemicals concentrate in mammals, and are even found in human breast milk. Males typically have far higher levels, as females reduce their concentration by transfer to their offspring through breast feeding.^[10]

See also

• Haloalkane
• Organic halide
• Dichloromethane

References

1. ^ ^{a b} Gordon W. Gribble (1998). "Naturally Occurring Organohalogen Compounds". Acc. Chem. Res. 31 (3): 141–152. doi:10.1021/ar9701777. 
2. ^ Gordon W. Gribble (1999). "The diversity of naturally occurring organobromine compounds". Chemical Society Reviews 28 (5): 335. doi:10.1039/a900201d. 
3. ^ Kjeld C. Engvild, "Chlorine-Containing Natural Compounds in Higher Plants", Phytochemistry, Vol. 25, No. 4, 7891-791, 1986.
4. ^ Gribble, G.W. (1994). "The Natural production of chlorinated compounds". Environmental Science and Technology 28: 310A–319A. doi:10.1021/es00056a001. 
5. ^ Gribble, G. W. , "Naturally occurring organohalogen compounds - A comprehensive survey", Progress in the Chemistry of Organic Natural Products (1996), 68, 1-423.
6. ^ Public Health Statement - Chloromethane, Centers for Disease Control, Agency for Toxic Substances and Disease Registry
7. ^ Pless, Tanja; Boettger, Michael; Hedden, Peter; Graebe, Jan (1984). "Occurrence of 4-Cl-indoleacetic acid in broad beans and correlation of its levels with seed development". Plant Physiology 74 (2): 320–3. 
8. ^ Magnus, Volker; Ozga, Jocelyn A.; Reinecke, Dennis M.; Pierson, Gerald L.; Larue, Thomas A.; Cohen, Jerry D.; Brenner, Mark L. (1997). "4-chloroindole-3-acetic and indole-3-acetic acids in Pisum sativum". Phytochemistry 46 (4): 675–681. doi:10.1016/S0031-9422(97)00229-X. 
9. ^ MDL Drug Data Report (MDDR), Elsevier MDL, version 2004.2
10. ^ Marine Mammal Medicine, 2001, Dierauf & Gulland

External links

• "Formation of Chlorinated Hydrocarbons in Weathering Plant Material" article at SLAC website
• "The oxidation of chlorinated hydrocarbons" article from The Institute for Green Oxidation Chemistry at the Carnegie Mellon University website

Wikipedia content modification information:

• This page was last modified on 28 September 2008, at 21:29.

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