Tetrachloro-1,2-difluoroethane
chemical compound
Tetrachloro-1,2-difluoroethane is a chlorofluorocarbon known as Freon 112, CFC-112 or R-112. It has a symmetrical structure CCl2FCCl2F and so can be called symmetrical tetrachlorodifluoroethane. "Symmetrical" may also be abbreviated to "s-" or "sym-". In contrast an asymmetrical isomer has formula CCl3CClF2.
Production
CFC-112 can be made in a reaction of hexachloroethane or tetrachloroethane with hydrogen fluoride and extra chlorine. This reaction is catalysed by aluminium fluoride with some extra iron, nickel and chromium at 400°C. The extra metal in the catalyst yields can be 98% compared with the unsymmetrical isomer.
Mixed with perfluorooctane, it is a solvent for polydimethylsiloxane.
CFC-112 can be prepared as a mixture with other hydrochlorofluorocarbons from trichloroethylene and anhydrous hydrogen fluoride when electric current is passed through.
Another method involves addition of fluorine to the double bond in tetrachloroethylene by lead tetrafluoride:
CCl2=CCl2 + PbF4 → CCl2F−CCl2F + PbF2
When CFC-11 is packaged with alcohol in a metal container, a free radical reaction can result in production of CFC-112.
Properties
Critical properties are critical temperature 278°C, critical pressure 4.83 MPa at a density of 0.754 g/cc.
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