Английская Википедия: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.[1] 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
Given the ban on producing chlorofluorocarbons, it is actually important not to produce 1,1-dichlorotetrafluoroethane intentionally or unintentionally.
1,1-Dichlorotetrafluoroethane can be made free from other isomers by reacting trichlorotrifluoroethane (CFC-113 or CFC-113a) with antimony pentachloride.[2] 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.[3]
It can also be made in a reaction of tetrachloroethylene with hydrogen fluoride and chlorine, but this results in a mixture.[2]
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.[4]
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.[5] Also in a gas chromatograph, it is hard to distinguish from the symmetric 1,2 isomer.[5]
Critical properties include critical temperature 145.7°C, critical pressure 4.92 Mpa and critical density of 0.82 g/ml.[6]
1,1-Dichlorotetrafluoroethane does not ignite in air.[6]
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.[7]
1,1-Dichlorotetrafluoroethane reacts with alkali metals, alkaline earths and aluminium.[6]
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.[8]
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.[9]
CFC-114a is a possible intermediate in the production of HFC-134a[9] which can be produced by hydrogenation.[10]
Atmosphere
The ozone depletion potential of 1,1-dichlorotetrafluoroethane is 0.72.[11] The estimated lifetime in the atmosphere is about 100 years.[11] The radiative efficiency is 0.28 Wm−2ppb−1.[11] Global warming potential in 20 years is 6750.[11] The atmospheric concentration of CFC-114a is not usually measured separately from CFC-114 due to difficulties in distinguishing them apart.[11]
In 1978 atmospheric levels of CFC-114a were 0.35 ppt. By 2020 the level was up to 1.13 ppt.[12] CFC-114a appears to be emitted into the atmosphere is South East Asia.[9]
The atmospheric natural destruction of CFC-114a is by reaction with atomic oxygen, or breakup by ultraviolet light.[9] As of 2014 about 250 tons per year of CFC-114a were being put into the atmosphere.[9]
References
- ↑ Шаблон:Cite journal
- ↑ 2,0 2,1 Шаблон:Cite web
- ↑ Шаблон:Cite journal
- ↑ Шаблон:Cite journal
- ↑ 5,0 5,1 Шаблон:Cite journal
- ↑ 6,0 6,1 6,2 Шаблон:Cite book
- ↑ Шаблон:Cite journal
- ↑ Шаблон:Cite journal
- ↑ 9,0 9,1 9,2 9,3 9,4 Шаблон:Cite journal
- ↑ Шаблон:Cite journal
- ↑ 11,0 11,1 11,2 11,3 11,4 Шаблон:Cite journal
- ↑ Шаблон:Cite journal
