The kinetics of the reactions of silicon compounds. Part IX. The gas-phase thermal decomposition of trimethyl-1,1,2,2-tetrafluoroethylsilane

Abstract

The gas-phase thermal decomposition of trimethyl-1,1,2,2-tetrafluoroethylsilane into trifluoroethylene and fluorotrimethylsilane, at temperatures from 300 to 370 °C and with initial pressures from 9 to 197 Torr, is kinetically first order; the rate constant is independent of pressure and surface: volume ratio, and is given by equation (i). log₁₀(k/s^–1)=(13·93 ± 0·22)–(197·7 ± 2·5) kJ mol^–1/2·303RT(i) In the presence of cis-but-2-ene the reaction remains first order and the rate of decomposition is unchanged, but two cyclopropanes are now found in the products, having the structures expected for the products of stereospecific addition of the carbene CHF₂·CF: to cis-but-2-ene. It is concluded that the reaction, like the decomposition of trifluoro-1,1,2,2-tetrafluoroethylsilane, involves unimolecular α-fluorine elimination to give fluorotrimethylsilane and difluoromethylfluorocarbene which isomerises to trifluorethylene or undergoes other characteristic carbene reactions.