Tetrachloro-1,1-difluoroethane explained

Tetrachloro-1,1-difluoroethane or 1,1,1,2-tetrachloro-2,2-difluoroethane, Freon 112a, R-112a, or CFC-112a is an asymmetric chlorofluorocarbon isomer of tetrachloro-1,1-difluoroethane with formula CClF2CCl3. It contains ethane substituted by four chlorine atoms and two fluorine atoms. With a boiling point of 91.5°C it is the freon with second highest boiling point.

Tetrachlorodifluoroethane as made is a mixture of the symmetrical and asymmetric isomers.[1]

Preparation

Tetrachloro-1,1-difluoroethane can be prepared in 40% yield by reacting 1,1,2-trichloro-1,2,2-trifluoroethane (freon 113) with aluminium chloride at 60°C.[2]

It can also be made in a reaction with hydrogen fluoride with hexachloroethane or tetrachloroethane with extra chlorine. This reaction occurs with an aluminium fluoride catalyst at 400°C. unsymmetrical trichlorotrifluoroethane (CCl2FCClF2) is also produced along with other chlorofluorocarbons. Separation of the symmetrical and unsymmetrical isomer is difficult.[3]

Properties

Tetrachloro-1,1-difluoroethane is non-combustible.

It has a critical pressure of 4.83 MPa and a critical temperature of 279.2°. At the critical point the density is 0.754 g/cc.[4]

Tetrachloro-1,1-difluoroethane in liquid form is miscible with perfluorocarbons.[5]

Reactions

Tetrachloro-1,1-difluoroethane reacts with zinc in ethanol at 60°C to yield unsymmetrical dichlorodifluoroethylene (CCl2=CF2).[6]

Use

Tetrachlorodifluoroethane (mixture of isomers) has been used as a veterinary medicine to treat parasites (Fasciola hepatica).[7]

Atmosphere

Tetrachloro-1,1-difluoroethane was first detected in air collected from Cape Grim, Tasmania in the Cape Grim Air Archive, and later from air bubbles in snow from Greenland. The substance made its first appearance around 1965, and increased in level until around 2000.[8] In 2000 Earth's atmosphere contained 0.08 parts per trillion of Freon 112a. Level slightly declined to 0.07 ppt by 2012.[8] Estimated lifetime in the stratosphere is 44 years.[9] By 2014 3,600 tons of Freon 112a had been put into the atmosphere.[8] As of 2023, levels have been rising in the Earth's atmosphere.[10]

As a greenhouse gas its radiative efficiency is 0.25 Wm−2ppb−1.[9]

Extra reading

Notes and References

  1. Gallagher . C. H. . Boray . J. C. . Koch . J. H. . Toxicity of Samples of Tetrachlorodifluoroethane . Australian Veterinary Journal . June 1965 . 41 . 6 . 167–172 . 10.1111/j.1751-0813.1965.tb01814.x. 14337687 .
  2. Miller . William T. . Fager . Edward W. . Griswald . Paul H. . The Rearrangement of Chlorofluorocarbons by Aluminum Chloride 1 . Journal of the American Chemical Society . February 1950 . 72 . 2 . 705–707 . 10.1021/ja01158a013.
  3. Vecchio . M . Groppelli . G . Tatlow . J. C. . Studies on a vapour-phase process for the manufacture of chlorofluoroethanes . Journal of Fluorine Chemistry . 1 July 1974 . 4 . 2 . 117–139 . 10.1016/S0022-1139(00)82507-5.
  4. Book: Bruno . Thomas J. . Spectroscopic Library for Alternative Refrigerant Analysis . 1990 . U.S. Department of Commerce, National Institute of Standards and Technology . 9 . en.
  5. Fowler . R. . Buford III . W. . Hamilton, Jr. . J. . Sweet . R. . Weber . C. . Kasper . J. . Litant . I. . Synthesis of Fluorocarbons . Industrial & Engineering Chemistry . March 1947 . 39 . 3 . 292–298 . 10.1021/ie50447a612.
  6. Book: Barr (Jr.) . John T. . Gibson . J. D. . The Preparation and Reactions of Substituted Polychloro 1,1-difluoroethanes . 1950 . Carbide and Carbon Chemicals Division, Union Carbide and Carbon Corporation, K-25 Laboratory Division . 19 . en.
  7. McKellar . Quintin A. . Kinabo . Ludovick D. B. . The pharmacology of flukicidal drugs . British Veterinary Journal . 1 July 1991 . 147 . 4 . 306–321 . 10.1016/0007-1935(91)90003-6 . 1913127 . en . 0007-1935.
  8. Laube . Johannes C. . Newland . Mike J. . Hogan . Christopher . Brenninkmeijer . Carl A. M. . Fraser . Paul J. . Martinerie . Patricia . Oram . David E. . Reeves . Claire E. . Röckmann . Thomas . Schwander . Jakob . Witrant . Emmanuel . Sturges . William T. . Newly detected ozone-depleting substances in the atmosphere . Nature Geoscience . April 2014 . 7 . 4 . 266–269 . 10.1038/ngeo2109. 2014NatGe...7..266L . 140544959 .
  9. Davis . Maxine E. . Bernard . François . McGillen . Max R. . Fleming . Eric L. . Burkholder . James B. . UV and infrared absorption spectra, atmospheric lifetimes, and ozone depletion and global warming potentials for CCl2FCCl2F (CFC-112), CCl3CClF2 (CFC-112a), CCl3CF3 (CFC-113a), and CCl2FCF3; (CFC-114a) . Atmospheric Chemistry and Physics . 1 July 2016 . 16 . 12 . 8043–8052 . 10.5194/acp-16-8043-2016. 2016ACP....16.8043D . 102078043 . free . 1983/df193a7b-14de-427c-a539-238701f9e3b3 . free .
  10. Western . Luke M. . Vollmer . Martin K. . Global increase of ozone-depleting chlorofluorocarbons from 2010 to 2020 . Nature Geoscience . 3 April 2023 . 309–313 . 16 . 4 . 10.1038/s41561-023-01147-w . 2023NatGe..16..309W . 257941769 . 1. 1983/9e103fef-e61c-49c7-a1a3-902540ec1d7c . free .

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