Free-radical chain dechlorination of chloroethanes in liquid triethylsilane

The kinetics and mechanism of the free-radical chain dechlorination of C₂Cl₆, C₂Cl₅H, and sym-C₂Cl₄H₂ in Et₃SiH wereinvestigated over a wide temperature range. The propagation step of the dechlorination of chloroethanes (C₂Cl_x H_6?x) proceeds by the following reactions: Analysis of the temperature dependence of product formation gave the Arrhenius expressions for k₄/k₃ which in turn were utilized for the estimation of the absolute Arrhenius parameters for hydrogen abstraction from Et₃SiH. Our results show that the values of E_abs are lower in Et₃SiH than in c-C₆H₁₂ by about 2–3 kcal/mol, while the A factors are almost equal. In competitive studies k₂ was determined versus Br abstraction from n-C₅H₁₁Br. The relative Arrhenius parameters determined by this method show that variations in both A factors and activationenergies are responsible for the reactivity trends observed in the Cl transfer reactions of Et₃Si radicals.