Organophosphorus chemistry. Part XVI. Kinetics and mechanism of the gas-phase thermal addition of tetramethyldiphosphine to tetrafluoroethylene

Abstract

Addition of tetramethyldiphosphine to tetrafluoroethylene in the gas phase at 240–280 °C gives 1,2-bis(dimethylphosphino)tetrafluoroethane [reaction (i)] with a rate expression (ii) where log₁₀[K/(dm³ mol^–1)^0·6 s^–1]=(10·87 ± 0·37)–(129·₂± 4) kJ mol^–1/2·303RT. A free radical mechanism is proposed, in which dimethyl- P₂Me₄+ C₂F₄→ Me₂P·CF₂·CF₂·PMe₂(i), d[Me₂P·CF₂·CF₂·PMe₂]/dt=k[P₂Me₄]^0·5[C₂F₄]^1·1(ii) phosphino radicals are formed by reversible dissociation of the diphosphine. An approximate bond energy D(Me₂P–PMe₂)ca. 160 kJ mol^–1 is deduced.