Carbene chemistry. Part VII. The preparation and pyrolysis of 2-chloro-1,1-difluoroethyl-, 1-chloro-1,2,2-trifluoroethyl-, and 1,2-dichloro-1,2-difluoroethyl-trichlorosilanes

Abstract

Pyrolysis of 2-chloro-1,1-difluoroethyltrichlorosilane at 225 °C mainly involves α-elimination and halogen-exchange followed by α-elimination to give a mixture of fluorochlorosilanes, 1-chloro-1-fluoroethylene, and 1,1-dichloroethylene as major products. At 140 °C only halogen-exchange takes place and 1,1,2-trichloroethylchlorodifluorosilane is formed exclusively; the half-life of the rearrangement reaction is ca. 50 min. Pyrolysis of the rearranged silane at 225 °C gives 1,1-dichloroethylene and a mixture of chlorofluorosilanes. Photochemical reaction of 1,2-dichloro-1,2-difluoroethylene with trichlorosilane gives a mixture of 1,2-dichloro-1,2-difluoroethyltrichlorosilane and 2-chloro-1,2-difluoroethyltrichlorosilane. 1,2-Dichloro-1,2-difluoroethyltrichlorosilane decomposes readily at 225 °C into a mixture of chlorofluorosilanes, 1,1-dichloro-2-fluoroethylene, and trichloroethylene. Photochemical reaction of chlorine with 1,2,2-trifluoroethyltrichlorosilane gives mainly 1-chloro-1,2,2-trifluoroethyltrichlorosilane, which on pyrolysis at 225 °C affords a mixture of chlorofluorosilanes, 1-chloro-2,2-difluoroethylene, and 1,1-dichloro-2-fluoroethylene; at 160 °C 1,1-dichloro-2,2-difluoroethyldichlorofluorosilane is formed exclusively.