Chlorodifluoromethane
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| Names | |||
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| IUPAC name
Chlorodifluoromethane
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| Other names
Difluoromonochloromethane, Monochlorodifliuoromethane, HCFC-22, R-22, Genetron 22, Freon 22, Arcton 4, Arcton 22, UN 1018,
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| Identifiers | |||
3D model (JSmol)
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| ChEMBL | |||
| ChemSpider | |||
| ECHA InfoCard | 100.000.793 | ||
| EC Number |
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| KEGG | |||
PubChem CID
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| RTECS number |
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CompTox Dashboard (EPA)
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| Properties | |||
| CHClF2 | |||
| Molar mass | 86.47 g/mol | ||
| Appearance | Colorless gas | ||
| Density | 3.66 kg/m3 at 15°C, gas | ||
| Melting point | −175.42 °C (−283.76 °F; 97.73 K) | ||
| Boiling point | −40.7 °C (−41.3 °F; 232.5 K) | ||
| 0.7799 vol/vol at 25 °C; 3.628 g/L | |||
| log P | 1.08 | ||
| Vapor pressure | 908 kPa at 20 °C | ||
Henry's law
constant (kH) |
0.033 mol.kg-1.bar-1 | ||
| Structure | |||
| Tetrahedral | |||
| Hazards | |||
| Occupational safety and health (OHS/OSH): | |||
Main hazards
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Dangerous for the environment (N), Central nervous system depressant, Carc. Cat. 3 | ||
| NFPA 704 (fire diamond) | |||
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Chlorodifluoromethane or difluoromonochloromethane is a hydrochlorofluorocarbon (HCFC). This colorless gas is better known as HCFC-22, R-22. It was once commonly used as a propellant and in air conditioning applications. These applications are being phased out due to ozone depletion potential and status as a potent greenhouse gas. R22 is a versatile intermediate in industrial organofluorine chemistry, e.g. as a precursor to tetrafluoroethylene.
Production and current applications
Chlorodifluoromethane is prepared from chloroform:
- HCCl3 + 2 HF → HCF2Cl + 2 HCl
The main application of R22 is as a precursor to tetrafluoroethylene. This conversion involves pyrolysis to give difluorocarbene, which dimerizes:[1]
- 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 R22 in the presence of chlorofluoromethane gives hexafluorobenzene.
Environmental effects
Chlorodifluoromethane was 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,[2] 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 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-tetrafluroethane) and R-409A.
As an additional environmental concern, chlorodifluoromethane has a global warming potential that is 1810 (1810 times that of carbon dioxide).[3] HFCs such as R-410A have high global warming potential, whereas that of propane (R-290) is only 3.
Beginning in 2010 in the U.S., the production and importing of HCFC-22 will be limited to 25% of each country's 1989 consumption level. New and imported HCFC-22 will be available only for use in equipment manufactured before 1/1/2010.
On January 1, 2010, it will be illegal to import, produce, or sell R-22 for use in new equipment or pre-charged in new equipment. In 2015, the production and importing of HCFC-22 will be limited to 10% of each country's 1989 consumption level and in 2020, production and importing of HCFC-22 will be illegal. Re-use of recovered HCFC-22 to service existing equipment will be allowed indefinitely.
Physical Properties
| Property | Value |
|---|---|
| Density (ρ) at -69 °C (liquid) | 1.49 g.cm−3 |
| Density (ρ) at -41 °C (liquid) | 1.413 g.cm−3 |
| Density (ρ) at -41 °C (gas) | 4.706 kg.m−3 |
| Density (ρ) at 15 °C (gas) | 3.66 kg.m−3 |
| Specific gravity at 21 °C (gas) | 3.08 (air = 1) |
| Specific volume (ν) at 21 °C (gas) | 0.275 m³.kg−1 |
| Density (ρ) at 15 °C (gas) | 3.66 kg.m−3 |
| Triple point temperature (Tt) | -157.39 °C (115.76 K) |
| Critical temperature (Tc) | 96.2 °C (369.3 K) |
| Critical pressure (pc) | 4.936 MPa (49.36 bar) |
| Critical density (ρc) | 6.1 mol.l−1 |
| Latent heat of vaporization (lv) at boiling point (-40.7 °C) | 233.95 kJ.kg−1 |
| Heat capacity at constant pressure (Cp) at 30 °C (86 °F) | 0.057 kJ.mol−1.K−1 |
| Heat capacity at constant volume (Cv) at 30 °C (86 °F) | 0.048 kJ.mol−1.K−1 |
| Heat capacity ratio (γ) at 30 °C (86 °F) | 1.178253 |
| Compressibility factor (Z) at 15 °C | 0.9831 |
| Acentric factor (ω) | 0.22082 |
| Dipole moment[disambiguation needed] | 1.458 D |
| Viscosity (η) at 0 °C | 12.56 µPa.s (0.1256 cP) |
| Ozone depletion potential (ODP) | 0.055 (CCl3F = 1) |
| Global warming potential (GWP) | 1810 (CO2 = 1) |
It has two allotropes: crystalline II below 59 K and crystalline I above 59 K to 115.73 K.
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)
References
- ^ Günter Siegemund, Werner Schwertfeger, Andrew Feiring, Bruce Smart, Fred Behr, Herward Vogel, Blaine McKusick "Fluorine Compounds, Organic" Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim, 2002. doi:10.1002/14356007.a11_349
- ^ The Montreal Protocol on Substances that Deplete the Ozone Layer. UNEP, 2000. ISBN 92-807-1888-6
- ^ IPCC (2007), Changes in Atmospheric Constituentsand in Radiative Forcing, http://www.ipcc.ch/pdf/assessment-report/ar4/wg1/ar4-wg1-chapter2.pdf