Trihalomethane Trihalomethane Roger Valley Category="Solvents"Trihalomethanes (THMs) are chemical compounds in which three of the four hydrogen atoms of Methane (CH4) are replaced by Halogen atoms. Many trihalomethanes find uses in industry as solvents or refrigerants. THMs are also environmental pollutants, and many are considered carcinogenic.

Common trihalomethanes (ordered by molecular weight)
Molecular formulaIUPAC nameCommon nameOther names
CHF3trifluoromethanefluoroformFreon 23, R-23, HFC-23
CHClF2chlorodifluoromethane-R-22, HCFC-22
CHCl3trichloromethaneChloroformmethyl trichloride
CHBrCl2bromodichloromethane--
CHBr2Cldibromochloromethane--
CHBr3tribromomethaneBromoformmethyl tribromide
CHI3triiodomethaneIodoformmethyl triiodide

Industrial uses

Refrigerants

Trifluoromethane and chlorodifluoromethane are both used as refrigerants in some applications. Trihalomethanes released to the environment break down faster than chlorofluorocarbons (CFCs), thereby doing less damage to the Ozone layer. These two compounds are examples of refrigerant HCFCs, or hydrochlorofluorocarbons.

Unfortunately, the breakdown of these compounds does still result in the creation of some free chlorine radicals in the upper atmosphere and subsequent ozone destruction. Ideally, these chemicals will be phased out entirely in favour of entirely nonchlorinated refrigerants.

Solvents

Chloroform (trichloromethane) is a very common solvent used in organic chemistry. It is a significantly less polar solvent than water, well-suited to dissolving many organic compounds.

Although still toxic and potentially carcinogenic, chloroform is significantly less harmful than Carbon tetrachloride. Because of the health and regulatory issues associated with the use of carbon tetrachloride, in modern chemistry laboratories chloroform is used a cheaper, cleaner alternative wherever possible.

Water pollutants

Trihalomethanes are formed as a byproduct when Chlorine or Bromine are used to purify water for drinking. They result from the reaction of chlorine and/or bromine with organic matter in the water being treated. The THMs produced may have adverse health effects at high concentrations, and many governments set limits on the amount permissible in drinking water. In the United States, the EPA limits the total concentration of chloroform, bromoform, bromodichloromethane, and dibromochloromethane to 80 parts per billion in treated water.