Kinetics of the reactions of silicon compounds. Part VI. Photolytic addition of trimethylsilane to tetrafluoroethylene

Abstract

Irradiation of trimethylsilane–tetrafluoroethylene mixtures at λ 250 nm leads to no reaction in the absence of mercury-photosensitisation. Kinetic studies reveal that the photochemical addition reaction which is normally observed: Me₃SiH + C₂F₄ [graphic omitted] Me₃Si·CF₂·CHF₂ is sensitised by the traces of mercury vapour which are almost inevitably present in the systems used for preparative work. The reaction is initiated by Hg 6(³P₁) sensitised dissociation of trimethylsilane to give trimethylsilyl radicals and hydrogen atoms; the latter abstract hydrogen atoms from trimethylsilane to produce molecular hydrogen. The trimethylsilyl radicals enter a free-radical chain propagating sequence leading to the production of the 1 : 1 and 2 : 1 adducts Me₃Si(CF₂·CF₂)_nH, where n= 1 or 2, and the kinetics of the formation of these compounds are consistent with the proposed chain mechanism, which involves termination predominantly by tetrafluoro-2-trimethylsilylethyl radical recombination.

Preliminary results are presented for the trimethylsilane–1,1-difluoroethylene system, which fails to yield useful quantities of adduct.