Editing Trihalomethane

{{short description|Methane (CH4) derivative with 3 halogen substituents}}

In [[chemistry]], '''trihalomethanes''' ('''THM'''s) are [[chemical compound]]s in which three of the four hydrogen atoms of [[methane]] ({{chem2|CH4}}) are replaced by [[halogen]] atoms. Trihalomethanes with all the same halogen atoms are called '''haloforms'''. Many trihalomethanes find uses in industry as [[solvent]]s or [[refrigerant]]s. Some THMs are also environmental [[pollutant]]s, and a few are considered [[carcinogen]]ic.

==Table of common trihalomethanes==
{| class="wikitable"
|+'''Common trihalomethanes''' (ordered by [[molecular mass|molecular weight]])
|-
!Molecular
formula
![[IUPAC]] name
![[CAS registry number]]
!Common name
!Other names
!Molecule
|-
|CHF<sub>3</sub>
|trifluoromethane
|75-46-7
|[[fluoroform]]
|[[Freon]] 23, R-23, HFC-23
|align="center"|[[File:Fluoroform-3D-vdW.png|50px|Fluoroform]]
|-
|CHClF<sub>2</sub>
|chlorodifluoromethane
|75-45-6
|align="center"|[[chlorodifluoromethane]]
|R-22, HCFC-22
|align="center"|[[File:Chlorodifluoromethane-3D-vdW.png|50px|Chlorodifluoromethane]]
|-
|CHCl<sub>3</sub>
|trichloromethane
|67-66-3
|[[chloroform]]
|R-20, methyl trichloride
|align="center"|[[File:Chloroform-3D-vdW.png|50px|Chloroform]]
|-
|CHBrCl<sub>2</sub>
|bromodichloromethane
|75-27-4
|[[bromodichloromethane]]
|dichlorobromomethane, BDCM
|align="center"|[[File:Bromodichloromethane-3D-vdW.png|50px|Bromodichloromethane]]
|-
|CHBr<sub>2</sub>Cl
|dibromochloromethane
|124-48-1
|[[dibromochloromethane]]
|chlorodibromomethane, CDBM
|align="center"|[[File:Dibromochloromethane-3D-vdW.png|50px|Dibromochloromethane]]
|-
|CHBr<sub>3</sub>
|tribromomethane
|75-25-2
|[[bromoform]]
|methyl tribromide
|align="center"|[[File:Bromoform-3D-vdW.png|50px|Bromoform]]
|-
|CHI<sub>3</sub>
|triiodomethane
|75-47-8
|[[iodoform]]
|methyl triiodide
|align="center"|[[File:Iodoform-3D-vdW.png|50px|Iodoform]]
|}

==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]].<ref>{{cite journal |author1=Dae Jin Sung |author2=Dong Ju Moon |author3=Yong Jun Lee |author4=Suk-In Hong |title=Catalytic Pyrolysis of Difluorochloromethane to Produce Tetrafluoroethylene |journal=International Journal of Chemical Reactor Engineering |year=2004 |volume=2 |page=A6 |doi=10.2202/1542-6580.1065 |s2cid=97895482}}</ref> Chloroform is fluorinated by reaction with [[hydrogen fluoride]] to produce [[chlorodifluoromethane]] (R-22). Pyrolysis of chlorodifluoromethane (at 550-750&nbsp;°C) yields TFE, with [[difluorocarbene]] as an intermediate.
:<chem>CHCl3 + 2 HF -> CHClF2 + 2 HCl</chem>
:<chem>2 CHClF2 -> C2F4 + 2 HCl</chem>

===Refrigerants and solvents===
Trihalomethanes released to the environment break down faster than [[haloalkane|chlorofluorocarbons]] (CFCs), thereby doing much less damage to the [[ozone layer]]. [[Trifluoromethane]] and [[chlorodifluoromethane]] are both used as [[refrigerant]]s. 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 {{val|660000}} tonnes per year,<ref>{{cite journal |last1=Gribble |first1=Gordon W. |year=2004 |title=Natural Organohalogens: A New Frontier for Medicinal Agents? |journal=Journal of Chemical Education |volume=81 |issue=10 |page=1441 |doi=10.1021/ed081p1441 |bibcode=2004JChEd..81.1441G}}</ref> and about 90% of emissions are natural in origin. Many kinds of [[seaweed]] produce chloroform, and [[fungi]] are believed to produce chloroform in soil.<ref>{{cite journal |last1=Cappelletti |first1=M. |year=2012 |title=Microbial degradation of chloroform |journal=Applied Microbiology and Biotechnology |volume=96 |issue=6 |pages=1395–409 |doi=10.1007/s00253-012-4494-1 |pmid=23093177 |s2cid=12429523}}</ref>

Most of the {{nowrap|haloforms{{tsp}}{{mdash}}{{tsp}}}}specifically, [[chloroform]] ({{chem2|CHCl3}}), [[bromoform]] ({{chem2|CHBr3}}), and [[iodoform]] {{nowrap|({{chem2|CHI3}}){{tsp}}{{mdash}}{{tsp}}}}are easy to prepare through the [[haloform reaction]], although this method does not lend itself to bulk syntheses. ([[Fluoroform]] ({{chem2|CHF3}}) cannot be prepared in this manner.)

Chloroform is produced by heating mixtures of [[methane]] or [[methyl chloride]] with [[chlorine]]. Dichloromethane is a coproduct.<ref>{{cite book |doi=10.1002/14356007.a06_233.pub2 |chapter=Chlorinated Hydrocarbons |title=Ullmann's Encyclopedia of Industrial Chemistry |year=2006 |last1=Rossberg |first1=Manfred |last2=Lendle |first2=Wilhelm |last3=Pfleiderer |first3=Gerhard |last4=Tögel |first4=Adolf |last5=Dreher |first5=Eberhard-Ludwig |last6=Langer |first6=Ernst |last7=Rassaerts |first7=Heinz |last8=Kleinschmidt |first8=Peter |last9=Strack |first9=Heinz |last10=Cook |first10=Richard |last11=Beck |first11=Uwe |last12=Lipper |first12=Karl-August |last13=Torkelson |first13=Theodore R. |last14=Löser |first14=Eckhard |last15=Beutel |first15=Klaus K. |last16=Mann |first16=Trevor |isbn=3527306730}}</ref>

[[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.<ref>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).</ref>

The [[United States Environmental Protection Agency|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.<ref>{{cite web |title=EPA {{!}} Envirofacts {{!}} ICR {{!}} Regulations|url=https://archive.epa.gov/enviro/html/icr/web/html/regulations.html|access-date=2021-10-11|website=archive.epa.gov}}</ref>

Traces of [[chloroform]] are produced in swimming pools.<ref name="Lindstrom1997">{{cite journal |last1=Lindstrom |first1=A B |last2=Pleil |first2=J.D. |last3=Berkoff |first3=D.C. |year=1997 |title=Alveolar breath sampling and analysis to assess trihalomethane exposures during competitive swimming training |journal=Environmental Health Perspectives |volume=105 |issue=6 |pages=636–642 |issn=0091-6765 |doi=10.1289/ehp.97105636 |pmid=9288498 |pmc=1470079}}</ref><ref name="Drobnic1996">{{cite journal |last1=Drobnic |first1=Franchek |last2=Freixa |first2=Assumpci?? |last3=Casan |first3=Pere |last4=Sanchis |first4=Joaqu??N |last5=Guardino |first5=Xavier |year=1996 |title=Assessment of chlorine exposure in swimmers during training |journal=Medicine & Science in Sports & Exercise |volume=28 |issue=2 |pages=271–274 |issn=0195-9131 |doi=10.1097/00005768-199602000-00018 |pmid=8775165 |doi-access=free}}</ref><ref name="Aiking1994">{{cite journal |last1=Aiking |first1=Harry |last2=van Ackert |first2=Manila B. |last3=Schölten |first3=Rob J.P.M. |last4=Feenstra |first4=Jan F. |last5=Valkenburg |first5=Hans A. |year=1994 |title=Swimming pool chlorination: a health hazard? |journal=[[Toxicology Letters]] |volume=72 |issue=1–3 |pages=375–380 |issn=0378-4274 |doi=10.1016/0378-4274(94)90051-5 |pmid=7911264 |url=https://www.researchgate.net/publication/222136311}}</ref><ref name="Nickmilder2011">{{cite journal |last1=Nickmilder |first1=M. |last2=Bernard |first2=A. |year=2011 |title=Associations between testicular hormones at adolescence and attendance at chlorinated swimming pools during childhood |journal=International Journal of Andrology |volume=34 |issue=5pt2 |pages=e446–e458 |issn=0105-6263 |doi=10.1111/j.1365-2605.2011.01174.x |pmid=21631527 |pmc=3229674}}</ref>

==References==
{{Reflist}}

==External links==
* [https://web.archive.org/web/20060302162424/http://www.npi.gov.au/database/substance-info/profiles/23.html National Pollutant Inventory - Chloroform and trichloromethane]
* [https://web.archive.org/web/20060206224406/http://www.biozone.com:80/trihalomethanes.html How Ozone Technology Reduces Disinfection Byproducts]
* [https://nepis.epa.gov/Exe/ZyPDF.cgi/9100OQFI.PDF?Dockey=9100OQFI.PDF EPA - Trihalomethanes in Drinking Water: Sampling, Analysis, Monitoring and Compliance (August 1983)]

{{Halomethanes}}
{{Authority control}}

[[Category:Halomethanes| ]]
[[Category:Halogenated solvents]]
[[Category:Refrigerants]]