Kinetics of the reactions of silicon compounds. Part 10. Kinetics and mechanism of the gas-phase thermal reactions of trichloro-(1,1-difluoroethyl)silane. An intramolecular halogen exchange reaction

Abstract

The gas-phase thermal isomerisation of trichloro-(1,1-difluoroethyl)silane (I) to chloro-(1,1-dichloroethyl)-difluorosilane (II) is a first-order homogeneous process at 375–416 K and 11–67 mmHg initial pressure. The reaction is unaffected by the presence of the radical inhibitors 2,3-dimethylbut-2-ene and nitric oxide, and it is concluded that the rate-determining step is a unimolecular isomerisation of (I) to dichloro-(1-chloro-1-fluoroethyl)fluorosilane (III), which then undergoes a secondary fast isomerisation to the observed product (II). [graphic omitted], log₁₀k₁/s^–1=(13.38 ± 0.05)–(127.2 ± 0.4) kJ mol^–1/RT ln 10 The data suggest a transition state in which the fluorine atom transfer is more advanced than the chlorine atom transfer. The minor products vinyl chloride and dichlorodifluorosilane are shown to arise from thermal and chemically activated decomposition of the initially formed (II) and/or (III).