Trihalomethanes

Trihalomethanes (THM) are organic compounds in which exactly three hydrogen atoms in methane have been replaced by halogens . Trihalomethanes belong to the haloalkanes or the subgroup of halomethanes .

According to the IUPAC nomenclature recommendations , the systematically correct name is trihalomethane . Haloforme is a common name for the simple CHX ₃ representatives with three identical halogen atoms.

Representative

Structural formula
Surname	Fluoroform	chloroform	Bromoform	Iodoform
Melting point	−155.2 ° C	−63 ° C	9.2 ° C	119 ° C
boiling point	−82.2 ° C	61 ° C	149.5 ° C	218 ° C
Dome model

The corresponding trihalomethanes of all halogens are known: trifluoromethane ( fluoroform ), trichloromethane ( chloroform ), tribromomethane ( bromoform ), triiodomethane ( iodoform ).

There are also two groups of mixed trihalomethanes:

of the CHXY ₂ type , for example bromodichloromethane or dibromochloromethane .
of the CHXYZ type, for example bromochlorofluoromethane .

Extraction

Chloroform can be obtained by radical substitution of methane. A known method for the production of chloroform, bromoform and iodoform is the haloform reaction .

Occurrence in water treatment

Trihalomethanes are formed as a by-product of the disinfection of drinking water or of water treatment in swimming pools with chlorine or sodium hypochlorite. Trichloromethane, bromodichloromethane, dibromochloromethane and tribromomethane are of health importance. For these substances limit values are specified as sum parameters ( THM content), compliance with which must be monitored analytically.

The limit value for drinking water is a value of 0.05 mg / L in the distribution network and 0.01 mg / L at the outlet of the waterworks. If the limit value for THM is exceeded, disinfection with chlorine dioxide is recommended , with which virtually no halogenation occurs.

Web links

Commons : Trihalomethanes - collection of images, videos and audio files

Individual evidence

↑ ^a ^b Entry on trifluoromethane in the GESTIS substance database of the IFA , accessed on February 29, 2020(JavaScript required) .
↑ ^a ^b Entry on trichloromethane in the GESTIS substance database of the IFA , accessed on February 29, 2020(JavaScript required) .
↑ ^a ^b Entry on tribromomethane in the GESTIS substance database of the IFA , accessed on February 29, 2020(JavaScript required) .
↑ ^a ^b Entry on triiodomethane in the GESTIS substance database of the IFA , accessed on February 29, 2020(JavaScript required) .
↑ Water quality of the swimming and bathing pools. Federal Environment Agency , November 13, 2013, accessed on December 27, 2017 .
↑ Wolfgang Roeske: Drinking water disinfection , p. 35 ( limited preview in the Google book search).
↑ Fritz Baum: Environmental Protection in Practice , p. 170 ( limited preview in the Google book search).

[GESTIS_F-1] Entry on trifluoromethane in the GESTIS substance database of the IFA , accessed on February 29, 2020(JavaScript required) .

[GESTIS_CL-2] Entry on trichloromethane in the GESTIS substance database of the IFA , accessed on February 29, 2020(JavaScript required) .

[GESTIS_BR-3] Entry on tribromomethane in the GESTIS substance database of the IFA , accessed on February 29, 2020(JavaScript required) .

[GESTIS_I-4] Entry on triiodomethane in the GESTIS substance database of the IFA , accessed on February 29, 2020(JavaScript required) .

[5] Water quality of the swimming and bathing pools. Federal Environment Agency , November 13, 2013, accessed on December 27, 2017 .

[6] Wolfgang Roeske: Drinking water disinfection , p. 35 ( limited preview in the Google book search).

[7] Fritz Baum: Environmental Protection in Practice , p. 170 ( limited preview in the Google book search).