The H/(CH<sub>3</sub>)<sub>3</sub>SiH/C<sub>2</sub>H<sub>4</sub> reaction system and the addition of (CH<sub>3</sub>)<sub>3</sub>Si to ethene. An end-product study
Me3Si and C2H5 radicals have been generated by the reaction of H atoms with mixtures of Me3SiH and C2H4 and the subsequent reactions studied by end-product analysis. The primary radicals undergo self- and cross-combination and disproportionation reactions. The Me3Si radical also adds to the C2H4, generating another radical, Me3SiCH2CH2. This radical in turn undergoes a variety of self- and cross-combination as well as disproportionation reactions with all the radicals present, A number of relative rate constants were extracted from the data. In particular the ratio k(H + Me3SiH)/k(H + C2H4) was found to be in good agreement with recent absolute determinations of these two rate constants. For the addition reaction we obtained the relative rate constant k(Me3Si + C2H4)/k1/2(2Me3Si) = (8.7 ± 0.2) × 10-10 cm3/2 s-1/2 at room temperature. From studies in the temperature range 300-470 K the following values of the Arrhenius parameters for the addition reaction were obtained: 11.6 ≤ Ea/kJ mol-1 ≤ 14.1 and 7.1 × 10-13 ≤ A/cm3 s-1 ≤ 1.9 × 10-12. In addition, it was found that alkyl and silyl radicals closely obey the geometric mean rule and that disproportionation reactions between alkyl and silyl radicals are of only minor importance. The reactivity of the silyl radical is much higher than that of the alkyl radical in adding to C2H4, and this can be explained in terms of polar effects
