Polyfluoroalkyl derivatives of silicon. Part XIII. Preparation and pyrolysis of trifluoro(halogenovinyl)silanes and (1-fluoro-2-halogenoethyl)trihalogenosilanes

Abstract

Treatment of 1-chloro-2-fluoroethyl- or 1,2-dichloroethyl-trichlorosilane with quinoline gives trichloro(1-chlorovinyl)silane; trichloro(1,2-dibromoethyl)silane dehydrohalogenates similarly. In contrast 2-chloro-1-fluoro-ethyl- and 1,2-difluoroethyl-trichlorosilane give vinyl fluoride under comparable conditions. Both 1-chlorovinyl-and 1-bromovinyl-trifluorosilane, prepared from the trichlorosilyl analogues, decompose slowly at 280 °C to afford acetylene and tetrahalogenosilanes via the suspected intermediacy of the alkylidenecarbene CH₂:C:. Pyrolysis of (2-chloro-1-fluoroethyl)trifluorosilane gives vinyl chloride via a carbene intermediate, but the trichlorosilyl analogue yields the rearrangement compound dichloro(1,2-dichloroethyl)fluorosilane. 1,2-Difluoroethyl-trifluorosilane and -trichlorosilane both decompose via a non-carbene mechanism involving β elimination.