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Jai Ganesh

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Registered: 2005-06-28

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Chloroform

Chloroform

Gist

Chloroform is a dense, colorless liquid with the formula CHCl3, also known as trichloromethane. While once used as an anesthetic, it is now primarily a chemical intermediate for making refrigerants and plastics, an industrial solvent, and a common laboratory solvent. Chloroform is a toxic substance that can cause liver and kidney damage from chronic exposure, central nervous system depression, and is considered a probable human carcinogen by the EPA.

Chloroform has declined significantly in medical use due to toxicity but remains in demand as a chemical intermediate for producing refrigerants and other chemicals. Its uses as a solvent include extracting fats, oils, and alkaloids, though less toxic alternatives are replacing it. Chloroform also serves as a laboratory solvent, in some pest control, and historically in dry cleaning and dentistry. 

Summary

Chloroform, or trichloromethane (often abbreviated as TCM), is an organochloride with the formula CHCl3 and a common solvent. It is a volatile, colorless, sweet-smelling, dense liquid produced on a large scale as a precursor to refrigerants and polytetrafluoroethylene (PTFE). Chloroform was once used as an inhalational anesthetic between the 19th century and the first half of the 20th century. It is miscible with many solvents but it is only very slightly soluble in water (only 8 g/L at 20°C).

Structure and name

The molecule adopts a tetrahedral molecular geometry with C3v symmetry. The chloroform molecule can be viewed as a methane molecule with three hydrogen atoms replaced with three chlorine atoms, leaving a single hydrogen atom.

The name "chloroform" is a portmanteau of terchloride (tertiary chloride, a trichloride) and formyle, an obsolete name for the methylylidene radical (CH) derived from formic acid.

Natural occurrence

Many kinds of seaweed produce chloroform, and fungi are believed to produce chloroform in soil. Abiotic processes are also believed to contribute to natural chloroform productions in soils, although the mechanism is still unclear.

Details

Cloroform (CHCl3) is a nonflammable, clear, colourless liquid that is denser than water and has a pleasant etherlike odour. It was first prepared in 1831. The Scottish physician Sir James Simpson of the University of Edinburgh was the first to use it as an anesthetic in 1847. It later captured public notice in 1853 when English physician John Snow administered it to Queen Victoria during the birth of Prince Leopold, her eighth child.

Chloroform has a relatively narrow margin of safety and has been replaced by better inhalation anesthetics. In addition, it is believed to be toxic to the liver and kidneys and may cause liver cancer. Chloroform was once widely used as a solvent, but safety and environmental concerns have reduced this use as well. Nevertheless, chloroform has remained an important industrial chemical.

Chloroform is prepared by the chlorination of methane. The major use of chloroform is in the preparation of chlorodifluoromethane (HCFC-22). HCFC-22 contributes to depletion of the ozone layer, and its production is scheduled to halt by 2020 in the United States. As HCFC-22 production is phased out, chloroform production is expected to decrease significantly.

Chloroform is formed by the reaction of chlorine with organic substances present in water and thus can occur in drinking water that has been chlorinated. The limit set by the U.S. Environmental Protection Agency for chloroform contamination is 80 parts per billion (ppb); a typical municipal water supply contains roughly 50 ppb.

Additional Information

Chloroform (CHCl3) is a solvent, reagent, refrigerant, and anesthetic with a chemical history that dates back to the 1830s. During that period, at least five scientists synthesized it; but there was much confusion about its chemical formula. Proposed formulas ranged from CH2ClCH2Cl (“chloric ether” or 1,2-dichloroethane) to C2Cl5 (an impossibility) to C2H2Cl6 (double the actual formula).

By the 1840s, chloroform began to be used as an anesthetic; and by the next decade, it was manufactured on a large scale via the reaction between chloral1 and sodium hydroxide. Chloroform was produced by this process for more than a century; after which, it was replaced by heating methane and/or chloromethane with chlorine. This method produces dichloromethane as well.

An early use of chloroform as a solvent appeared in an 1882 article by Arthur H. Elliott at Columbia College (now Columbia University, New York City). Elliott assessed the solubility of then-new “nitrosaccharose” (nitrocellulose2) in about 40 solvents available to him and found that chloroform dissolved the substance at ambient temperature. Chloroform eventually became a widely used industrial and laboratory solvent until recent decades when its hazardous properties (see hazard information table) caused regulatory agencies to restrict its use.

Chloroform alone has little use as a refrigerant; but large quantities of it were used to synthesize chlorodifluoromethane3 (CHClF2), a widely used refrigerant until it was phased out because of its high ozone-depleting and global-warming potentials. Besides CHClF2 synthesis, chloroform, when treated with sodium hydroxide, is used to generate dichlorocarbene4 (:CCl2), which reacts with alkenes in situ to produce dichlorocyclopropane derivatives.

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