Help
Add this page to your book
Show book (0 pages)
Suggest pagesChlorodifluoromethane
| Chlorodifluoromethane | |
|---|---|
 |
 |
|
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  |
| PubChem | 6372 |
| ChemSpider | 6132 |
| EC number | 200-871-9 |
| KEGG | D03789  |
| ChEMBL | CHEMBL116155 |
| RTECS number | PA6390000 |
| Jmol-3D images | Image 1 |
|
|
|
|
| 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 |
 (verify) (what is:  / ?)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 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, with a high global warming potential. R22 is a versatile intermediate in industrial organofluorine chemistry, e.g. as a precursor to tetrafluoroethylene.
Contents |
[edit] 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.
[edit] 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.
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, but has an ODP (or ozone depletion potential) of 0. The GWP of propane (R-290), for example, is only 3.
[edit] EPA Phaseout
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-tetrafluoroethane) and R-409A. [4]
- 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, EPA 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 requires 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.
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 became 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.
[edit] 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 |
| Molecular dipole moment | 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.
[edit] 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)
[edit] 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
- ^ http://www.epa.gov/ozone/title6/phaseout/22phaseout.html EPA Phase-out
|
|||||||||||||||||
