Dichlorodifluoromethane

Dichlorodifluoromethane
Names
IUPAC name
Dichlorodifluoromethane
Other names
Carbon dichloride difluoride, Dichloro-difluoro-methane, Difluorodichloromethane, Freon 12, R-12, CFC-12, P-12, Propellant 12, Halon 122, Arcton 6, Arcton 12, E940, Fluorocarbon 12, Genetron 12, Refrigerant 12
Identifiers
75-71-8 Yes
ChEMBL ChEMBL2106634 
ChemSpider 6151 Yes
EC number 200-893-9
Jmol-3D images Image
KEGG D03789 Yes
PubChem 6391
RTECS number PA8200000
UNII OFM06SG1KO Yes
UN number 1028
Properties
Molecular formula
 CCl2F2
Molar mass 120.91 g·mol−1
Appearance Colorless gas with ether-like odor
Odor ether-like at very high concentrations
Density 1.486 g/cm³ (−29.8 °C (−21.6 °F))
Melting point −157.7 °C (−251.9 °F; 115.5 K)
Boiling point −29.8 °C (−21.6 °F; 243.3 K)
0.286 g/l at 20 °C (68 °F)
Solubility in alcohol, ether, benzene, acetic acid Soluble
log P 2.16
Vapor pressure 568 kPa (20 °C (68 °F))
0.0025 mol kg−1 bar−1
Hazards
MSDS External MSDS
Main hazards Damaging to Earth's protective ozone
EU Index Not listed
R-phrases R44 R59[1]
S-phrases S9 S38[1]
Flash point Non-flammable [2]
US health exposure limits (NIOSH):
TWA 1000 ppm (4950 mg/m3)[2]
TWA 1000 ppm (4950 mg/m3)[2]
15000 ppm[2]
Supplementary data page
Refractive index (n),
Dielectric constant (εr), etc.
Thermodynamic
data
 Phase behaviour
solid–liquid–gas
UV, IR, NMR, MS
Except where noted otherwise, data is given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
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Infobox references

Dichlorodifluoromethane (R-12) is a colorless gas usually sold under the brand name Freon-12, and a chlorofluorocarbon halomethane (CFC) used as a refrigerant and aerosol spray propellant. Complying with the Montreal Protocol, its manufacture was banned in the United States along with many other countries in 1996 due to concerns about its damaging impact to the ozone layer.[3] It is soluble in many organic solvents. Dichlorodifluoromethane was one of the original propellants for Silly String. R-12 cylinders are colored white.

Preparation

It can be prepared by reacting carbon tetrachloride with hydrogen fluoride in the presence of a catalytic amount of antimony pentachloride:

CCl4 + 2HF → CCl2F2 + 2HCl

This reaction can also produce trichlorofluoromethane (CCl3F), chlorotrifluoromethane (CClF3) and tetrafluoromethane (CF4).[4]

Use as an aerosol

The use of chlorofluorocarbons as aerosols in medicine, such as USP-approved salbutamol, has been phased out by the U.S. Food and Drug Administration. A different propellant known as hydrofluoroalkane, or HFA, which is not known to harm the environment, was chosen to replace it.[5]

Retrofitting

R-12 was used in most refrigeration and vehicle air conditioning applications prior to 1994 before being replaced by 1,1,1,2-tetrafluoroethane (R-134a), which has an insignificant ozone depletion potential. 1992–1994 was the time period in which automobile manufacturers started using R-134a instead of R-12. When older units leak, retrofits to R-134a are recommended. Retrofit to R-134a requires complete flushing and filter/dryer replacement to remove the mineral oil. Mineral oil used for R12 is not compatible with R-134a. Some oils designed for conversion to R-134a are advertised as compatible with residual R-12. New rubber hoses which are R-134a compatible may be needed for the same reason.

In systems where R-134a is not practical, an R-409A blend (60% R-22; 25% R-124; 15% R-142b) may be directly added to an R-12 system without changing the oil, although a filter change is always recommended. R-409A usually runs on the low-pressure side of the system at 12 pounds per square inch (psi), while R-12 usually runs on the low side at 10 psi. R-409A runs at higher pressures and is less efficient but works quite well. Manufacturers recommend that the existing R-12 charge be recovered. However, as the two refrigerants are soluble in the same mineral oil, there are no complications associated with mixing them. Note that the instructions for R-409A recommend charging a system with liquid to keep the mixture ratios constant. The constituents have varying vapor pressures.

Gallery

References

  1. ↑ 1.0 1.1 "Dichlorodifluoromethane MSDS" (PDF). Synquest Labs.
  2. ↑ 2.0 2.1 2.2 2.3 "NIOSH Pocket Guide to Chemical Hazards #0192". National Institute for Occupational Safety and Health (NIOSH).
  3. ↑ Dichlorodifluoromethane at LearnChemistry (Royal Society of Chemistry)
  4. ↑ Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. p. 304. ISBN 0080379419.
  5. ↑ 'Rescue' asthma inhaler replacements coming to Pa.

External links