Chlorodifluoromethane

Overview
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.

Chlorodifluoromethane was first used as an alternative to the ozone depleting CFC-11 and CFC-12, but was later decided to be not environmentally friendly enough, although its ozone depletion potential is 0.055, among the lowest for chlorine-containing haloalkanes. It will be phased out soon under the Montreal Protocol, to be replaced by more environmentally friendly refrigerants such as Propane (R-290), and other refrigerants ( even though not having very similar properties ): R-410A (an azeotropic mixture of difluoromethane and pentafluoroethane), R-502, R-134a (1,1,1,2-tetrafluroethane) and R-409A.

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.