• Source: Tetrachloro-1,1-difluoroethane

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.




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.
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.




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




= Reactions

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




Use


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




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.
In 2000 Earth's atmosphere contained 0.08 parts per trillion of Freon 112a. Level slightly declined to 0.07 ppt by 2012. Estimated lifetime in the stratosphere is 44 years. By 2014 3,600 tons of Freon 112a had been put into the atmosphere.
As of 2023, levels have been rising in the Earth's atmosphere.
As a greenhouse gas its radiative efficiency is 0.25 Wm−2ppb−1.




References






Extra reading


Sládek, Petr; Navrátil, Oldřich; Linhart, Petr (1992). "Extraction of Selected Lanthanoids and Scandium with Bis(2-ethylhexyl)hydrogenphosphate in 1,1,2,2-Tetrachlorodifluoroethane". Collection of Czechoslovak Chemical Communications. 57 (8): 1647–1654. doi:10.1135/cccc19921647.
Sládek, Petr; Navrátil, Oldřich; Linhart, Petr (1992). "Extraction of Ce, Pm, Eu, Tm and Sc Using Di-n-butylhydrogenphosphate in 1,1,2,2-Tetrachlorodifluoroethane". Collection of Czechoslovak Chemical Communications. 57 (8): 1639–1646. doi:10.1135/cccc19921639.
Kakáč, B.; Hudlický, M. (1965). "Organic compounds of fluorine. VII. Spectrophotometric study in the series of halofluoroethanes". Collection of Czechoslovak Chemical Communications. 30 (3): 745–751. doi:10.1135/cccc19650745.

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