Trihalomethane

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In chemistry, trihalomethanes (THMs) are chemical compounds in which three of the four hydrogen atoms of methane (CH4) are replaced by halogen atoms. Trihalomethanes with all the same halogen atoms are called haloforms. Many trihalomethanes find uses in industry as solvents or refrigerants. Some THMs are also environmental pollutants, and few are considered carcinogenic.

Table of common trihalomethanes

Common trihalomethanes (ordered by molecular weight)
Molecular

formula

IUPAC
name
CAS registry number
 Common name Other names Molecule
CHF3 trifluoromethane 75-46-7 fluoroform Freon 23, R-23, HFC-23 Fluoroform
CHClF2 chlorodifluoromethane 75-45-6 chlorodifluoromethane R-22, HCFC-22 Chlorodifluoromethane
CHCl3 trichloromethane 67-66-3 chloroform R-20, methyl trichloride Chloroform
CHBrCl2 bromodichloromethane 75-27-4 bromodichloromethane dichlorobromomethane, BDCM Bromodichloromethane
CHBr2Cl dibromochloromethane 124-48-1 dibromochloromethane chlorodibromomethane, CDBM Dibromochloromethane
CHBr3 tribromomethane 75-25-2 bromoform methyl tribromide Bromoform
CHI3 triiodomethane 75-47-8 iodoform methyl triiodide Iodoform

Industrial uses

Only chloroform has significant applications of the haloforms. In the predominant application, chloroform is required for the production of

teflon.[1] 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.

Refrigerants and solvents

Trihalomethanes released to the environment break down faster than

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 660000 tonnes per year,

fungi are believed to produce chloroform in soil.[3]

Most of the haloforms — specifically, chloroform (CHCl3), bromoform (CHBr3), and iodoform (CHI3) — are easy to prepare through the haloform reaction, although this method does not lend itself to bulk syntheses. (Fluoroform (CHF3) cannot be prepared in this manner.)

Chloroform is produced by heating mixtures of

methyl chloride with chlorine. Dichloromethane is a coproduct.[4]

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.[5]

The

parts per billion in treated water.[6]

Traces of chloroform are produced in swimming pools.[7][8][9][10]

References

  1. S2CID 97895482
    .
  2. doi:10.1021/ed081p1441
    .
  3. S2CID 12429523
    .
  4. ISBN 3527306730
    .
  5. ^ EPA Alumni Association: Senior EPA officials discuss early implementation of the Safe Drinking Water Act of 1974, Video, Transcript (see pages 12-13).
  6. ^ "EPA | Envirofacts | ICR | Regulations". archive.epa.gov. Retrieved 2021-10-11.
  7. PMID 9288498
    .
  8. PMID 8775165
    .
  9. PMID 7911264
    .
  10. PMID 21631527
    .

External links
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