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.