Significations et usages de Chlorodifluoromethane

Chlorodifluoromethane
IUPAC name Chlorodifluoromethane
Other names Difluoromonochloromethane, Monochlorodifliuoromethane, HCFC-22, R-22, Genetron 22, Freon 22, Arcton 4, Arcton 22, UN 1018,
Identifiers
CAS number	75-45-6 Y
PubChem	6372
ChemSpider	6132 Y
EC number	200-871-9
KEGG	C19361 N
ChEMBL	CHEMBL116155 Y
RTECS number	PA6390000
Jmol-3D images	Image 1
SMILES ClC(F)F
InChI InChI=1S/CHClF2/c2-1(3)4/h1H Y Key: VOPWNXZWBYDODV-UHFFFAOYSA-N Y InChI=1/CHClF2/c2-1(3)4/h1H Key: VOPWNXZWBYDODV-UHFFFAOYAQ
Properties
Molecular formula	CHClF2
Molar mass	86.47 g/mol
Appearance	Colorless gas
Density	3.66 kg/m3 at 15°C, gas
Melting point	-175.42 °C, 98 K, -284 °F
Boiling point	-40.7 °C, 232 K, -41 °F
Solubility in water	0.7799 vol/vol at 25 °C; 3.628 g/L
log P	1.08
Vapor pressure	908 kPa at 20 °C
kH	0.033 mol.kg-1.bar-1
Structure
Molecular shape	Tetrahedral
Hazards
R-phrases	R59
S-phrases	S23 S24 S25 S59
Main hazards	Dangerous for the environment (N), Central nervous system depressant, Carc. Cat. 3
NFPA 704	0 1 1
Autoignition temperature	632 °C
N (verify) (what is: Y/N?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Chlorodifluoromethane or difluoromonochloromethane is a hydrochlorofluorocarbon (HCFC). This colorless gas is better known as HCFC-22, or R-22. It is commonly used as a propellant and refrigerant. These applications are being phased out in developed countries due to the compound's ozone depletion potential (ODP) and high global warming potential (GWP), although global use of R-22 continues to increase because of high demand in developing countries.^[1] R-22 is a versatile intermediate in industrial organofluorine chemistry, e.g. as a precursor to tetrafluoroethylene.

  Production and current applications

Worldwide production of R-22 in 2008 was about 800 Gg per year, up from about 450 Gg per year in 1998, with most production in developing countries.^[1] R-22 use is increasing in developing countries, largely for air conditioning applications. Air conditioning sales are growing 20% annually in India and China.

R-22 is prepared from chloroform:

HCCl₃ + 2 HF → HCF₂Cl + 2 HCl

An important application of R-22 is as a precursor to tetrafluoroethylene. This conversion involves pyrolysis to give difluorocarbene, which dimerizes:^[2]

2 CHClF₂ → C₂F₄ + 2 HCl

The compound also yields difluorocarbene upon treatment with strong base and is used in the laboratory as a source of this reactive intermediate.

The pyrolysis of R-22 in the presence of chlorofluoromethane gives hexafluorobenzene.

  Environmental effects

R-22 is often 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,^[3] among the lowest for chlorine-containing haloalkanes. However, even this lower ozone depletion potential is no longer considered acceptable.

As an additional environmental concern, R-22 is a powerful greenhouse gas with a global warming potential that is 1810 (which indicates 1810 times as powerful as carbon dioxide).^[4] Hydrofluorocarbons (HFCs) are often substituted for R-22 because of their lower ODP, but these refrigerants also have high global warming potential. R-410A, for example, is often substituted, but has a GWP of 1725. Other substitute refrigerants are available with low GWP. Propane (R-290), for example, has a GWP of 3, although it is rarely used in refrigeration systems because of its flammability and potential for explosion.

  United States phaseout

R-22 has been mostly phased out in new equipment in the United States under the Montreal Protocol, and has been replaced by other refrigerants with lower ozone depletion potential such as propane (R-290), R-410A (an azeotropic mixture of difluoromethane and pentafluoroethane), R-507A, R-134a (1,1,1,2-tetrafluoroethane) and R-409A. ^[5]

• Beginning January 1, 2004: The Montreal Protocol required the U.S. to reduce its consumption of HCFCs by 35% below the U.S. baseline cap. As of January 1, 2003, the United States Environmental Protection Agency banned production and import of HCFC-141b, the most ozone-destructive HCFC. This action allowed the United States to meet its obligations under the Montreal Protocol. EPA was able to issue 100% of company baseline allowances for production and import of HCFC-22 and HCFC-142b.

• Beginning January 1, 2010: The Montreal Protocol required the U.S. to reduce its consumption of HCFCs by 75% below the U.S. baseline. Allowance holders may only produce or import HCFC-22 to service existing equipment. Virgin R-22 may not be used in new equipment. As a result, heating, ventilation and air-conditioning (HVAC) system manufacturers may not produce new air conditioners and heat pumps containing R-22.

• Beginning January 1, 2015: The Montreal Protocol requires the U.S. to reduce its consumption of HCFCs by 90% below the U.S. baseline.

• Beginning January 1, 2020: The Montreal Protocol requires the U.S. to reduce its consumption of HCFCs by 99.5% below the U.S. baseline. Refrigerant that has been recovered and recycled/reclaimed will be allowed beyond 2020 to service existing systems, but chemical manufacturers will no longer be able to produce R-22 to service existing air conditioners and heat pumps.

  Physical properties

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

  References

  External links

• MSDS at Oxford University
• International Chemical Safety Card 0049
• Data at Integrated Risk Information System: IRIS 0657
• Phase change data at webbook.nist.gov
• IR absorption spectra
• IARC Summaries & Evaluations: Vol. 41 (1986), Suppl. 7 (1987), Vol. 71 (1999)