Chlorodifluoromethane

For the Robinson R22 helicopter, see Robinson R22.

Chlorodifluoromethane or difluoromonochloromethane is a hydrochlorofluorocarbon (HCFC). It is better known under its code names of HCFC-22, R-22, Genetron 22 or Freon 22, and is commonly used in air conditioning applications, such as residential split systems in the US, rooftop units and window air conditioners.

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Chlorodifluoromethane was first used as an alternative to the highly ozone depleting CFC-11 and CFC-12 because of its relatively low ozone depletion potential of 0.055,^[1] among the lowest for chlorine-containing haloalkanes. However, even this lower ozone depletion potential is no longer considered acceptable it will be phased out soon under the Montreal Protocol, to be replaced by refrigerants with zero ozone depletion potential such as Propane (R-290), and other refrigerants (even though they don't have very similar properties): R-410A (an azeotropic mixture of difluoromethane and pentafluoroethane), R-502, R-134a (1,1,1,2-tetrafluroethane) and R-409A.

An additional environmental concern regarding Chlorodifluoromethane, as well as some of the proposed replacements, is their global warming potential. The global warming potential of Chlorodifluoromethane is 1700 (1700 times that of carbon dioxide)^[2]. HFCs such as R-410A have high global warming potential, whereas that of propane (R-290) is only 3.

It is an intermediate in the synthesis of tetrafluoroethylene, into which it is converted by pyrolysis. Difluorocarbene is an intermediate in this reaction. The compound also yields difluorocarbene upon treatment with strong base and is used in the laboratory as a source of this reactive intermediate.

The US EPA has enacted regulation which will phase out the use of HCFC-22 in the near future. Air conditioning manufacturers will no longer be allowed to sell R22 equipment as of January 1, 2010. In the aftermarket service business, the allocation rights for producers who manufacture R22 will be cut each year making the remaining R22 supply potentially smaller than the service demand for the product. This could make R22 scarce in the future, and drive prices to consumers higher.

Physical Properties

It has two allotropes: crystaline II below 59 K and crystaline I above 59 K to 115.73 K.

See also

• Haloalkane
• Halomethane
• Trihalomethane
• Hydrochlorofluorocarbon
• Chlorofluoromethane
• Difluoromethane
• Dichlorodifluoromethane
• Chlorotrifluoromethane

References

1. ^ The Montreal Protocol on Substances that Deplete the Ozone Layer. UNEP, 2000. ISBN 92-807-1888-6
2. ^ Comfort Air Conditioning list of Refrigerants, http://www.comfort.uk.com/refrigerants.htm