Trihalomethane

Table of common trihalomethanes

Industrial uses

Only chloroform has significant applications of the haloforms. In the predominant application, chloroform is required for the production of tetrafluoroethylene (TFE), precursor to teflon. Chloroform is fluorinated by reaction with hydrogen fluoride to produce chlorodifluoromethane (R-22). Pyrolysis of chlorodifluoromethane (at 550–750 °C) yields TFE, with difluorocarbene as an intermediate. :CHCl3 + 2 HF - CHClF2 + 2 HCl :2 CHClF2 - C2F4 + 2 HCl

Refrigerants and solvents

Trihalomethanes released to the environment break down faster than chlorofluorocarbons (CFCs), thereby doing much less damage to the ozone layer. Trifluoromethane and chlorodifluoromethane are both used as refrigerants. Chlorodifluoromethane is a refrigerant HCFC, or hydrochlorofluorocarbon, while fluoroform is an HFC, or hydrofluorocarbon. Fluoroform is not ozone depleting.

Chloroform is a common solvent in organic chemistry.

Occurrence and production

The total global flux of chloroform through the environment is approximately tonnes per year, and about 90% of emissions are natural in origin. Many kinds of seaweed produce chloroform, and fungi are believed to produce chloroform in soil.

Most of the haloformsspecifically, chloroform (), bromoform (), and iodoform ()are easy to prepare through the haloform reaction, although this method does not lend itself to bulk syntheses. (Fluoroform () cannot be prepared in this manner.)

Chloroform is produced by heating mixtures of methane or methyl chloride with chlorine. Dichloromethane is a coproduct.

Bromochlorofluoromethane is one of the simplest possible stable chiral compounds, and is used for studies.

Regulation

Trihalomethanes were the subject of the first drinking water regulations issued after passage of the U.S. Safe Drinking Water Act in 1974.

The EPA limits the total concentration of the four chief constituents (chloroform, bromoform, bromodichloromethane, and dibromochloromethane), referred to as total trihalomethanes (TTHM), to 80 parts per billion in treated water.

Traces of chloroform are produced in swimming pools.

References

References

1. (2004). "Catalytic Pyrolysis of Difluorochloromethane to Produce Tetrafluoroethylene". International Journal of Chemical Reactor Engineering.
2. (2004). "Natural Organohalogens: A New Frontier for Medicinal Agents?". Journal of Chemical Education.
3. (2012). "Microbial degradation of chloroform". Applied Microbiology and Biotechnology.
4. (2006). "Ullmann's Encyclopedia of Industrial Chemistry".
5. EPA Alumni Association: Senior EPA officials discuss early implementation of the Safe Drinking Water Act of 1974, [https://web.archive.org/web/20161105133921/http://www.epaalumni.org/history/video/interview.cfm?id=13 Video], [https://www.epaalumni.org/userdata/pdf/6014106B36AE81EB.pdf#page=12 Transcript] (see pages 12–13).
6. "EPA {{!}} Envirofacts {{!}} ICR {{!}} Regulations".
7. (1997). "Alveolar breath sampling and analysis to assess trihalomethane exposures during competitive swimming training". Environmental Health Perspectives.
8. (1996). "Assessment of chlorine exposure in swimmers during training". Medicine & Science in Sports & Exercise.
9. (1994). "Swimming pool chlorination: a health hazard?". [[Toxicology Letters]].
10. (2011). "Associations between testicular hormones at adolescence and attendance at chlorinated swimming pools during childhood". International Journal of Andrology.