1,1-Dichlorotetrafluoroethane

1,1-Dichlorotetrafluoroethane is a chlorofluorocarbon also known as CFC-114a or R114a by American Society of Heating, Refrigerating, and Air Conditioning Engineers. It has two chlorine atoms on one carbon atom and none on the other. It is one of two isomers of dichlorotetrafluoroethane, the other being 1,2-dichlorotetrafluoroethane, also known as CFC-114.

Formation
1,1-Dichlorotetrafluoroethane can be made free from other isomers by reacting trichlorotrifluoroethane (CFC-113 or CFC-113a) with antimony pentachloride. Trichlorotrifluoroethane can also be reacted with sulfur tetrafluoride or dichlorodifluoromethane with aluminium fluoride catalyst to yield 1,1-dichlorotetrafluoroethane. The use of aluminium in the catalyst favours the asymmetric molecules.

It can also be made in a reaction of tetrachloroethylene with hydrogen fluoride and chlorine, but this results in a mixture.

Fluorinating 1,2-dichlorodifluoroethylene with fluorine produces a small amount of 1,1-dichlorotetrafluoroethane, but mostly tetrachlorotetrafluorobutene and some other chloroflurocarbons, so is not a good way.

Properties
1,1-Dichlorotetrafluoroethane has a close boiling point (3.6°C) to the isomer 1,2-dichlorotetrafluoroethane (3.8°C), and so is difficult to separate by distillation. Also in a gas chromatograph, it is hard to distinguish from the symmetric 1,2 isomer.

Critical properties include critical temperature 145.7°C, critical pressure 4.92 Mpa and critical density of 0.82 g/ml.

1,1-Dichlorotetrafluoroethane does not ignite in air.

Reactions
1,1-Dichlorotetrafluoroethane reacts with hydrogen when heated at 300 to 600°C with a palladium catalyst in a hydrodechlorination. The main reaction product is 1,1,1,2-tetrafluoroethane, but also 1-chloro-1,2,2,2-tetrafluoroethane (CF3CHClF) and 1,1,1-trifluoroethane are formed.

1,1-Dichlorotetrafluoroethane reacts with alkali metals, alkaline earths and aluminium.

When heated with hydrogen over a nickel catalyst, 1,1-dichlorotetrafluoroethane is dechlorinated with replacement by hydrogen to yield a mixture of CF3CHClF and the dimer CF3CClFCClFCF3.

Use
CFC-114a was used in aerosol propellants, blowing agents, and in polyolefin foams. There was also use in refrigerants. Production was banned in by the Montreal Protocol.

CFC-114a is a possible intermediate in the production of HFC-134a which can be produced by hydrogenation.

Atmosphere
The ozone depletion potential of 1,1-dichlorotetrafluoroethane is 0.72. The estimated lifetime in the atmosphere is about 100 years. The radiative efficiency is 0.28 Wm−2ppb−1. Global warming potential in 20 years is 6750. The atmospheric concentration of CFC-114a is not usually measured separately from CFC-114 due to difficulties in distinguishing them apart.

In 1978 atmospheric levels of CFC-114a were 0.35 ppt. By 2020 the level was up to 1.13 ppt. CFC-114a appears to be emitted into the atmosphere is South East Asia.

The atmospheric natural destruction of CFC-114a is by reaction with atomic oxygen, or breakup by ultraviolet light. As of 2014 about 250 tons per year of CFC-114a were being put into the atmosphere.