Description
Kinetic and product studies of the pyrolyses of dimethylsilane in a stirred flow system (890-1000°K) are reported. The major products were methane, ethylene and acetylene. Methane is formed mainly by molecular elimination from dimethylsilane, while ethylene and acetylene are proposed to arise from subsequent decompositions of the primary dissociation reaction product, dimethylsilene. The reaction is non-chain under stirred flow conditions (k=10¹³˙⁹e⁻⁽⁶⁶,⁹⁹⁰±³²⁵⁰⁾ ᶜᵃˡ/ᴿᵀsec⁻¹, in agreement with the static results of Neudorfl and Strausz) but involves both silylene and free-radical chains under shock tube decomposition conditions. The decomposition of ethynylsilane (ES) was studied by both stirred flow (606-784°K) and single pulse shock tube (1082-1284°K) techniques. The reaction is surface catalyzed (low temperature, stirred flow), and also subject to chain reactions (high temperature, stirred flow and shock tube). The chains are inhibited by butadiene in the shock tube reaction and the overall reaction involves four contributing primary dissociation reactions, shown below. Silacyclopropene, formed intramolecularly from ES, is the precursor of rxns 1-3, while rxn4 is the usual 1, 1-H₂ elimination reaction common to all monoalyysilane decompositions. Rate constant assignments for rxns 1-4, by thermochemical kinetic estimation techniques and by kinetic analogies, are shown by RRKM calculation techniques to be in agreement with product and rate constant data. The decomposition kinetics of disilane were investigated via a stirred flow system (601-756°K). The results, (k = 10¹⁴.²³e⁻⁽⁴⁸,³⁷²±³³⁰⁸⁾ᶜᵃˡ/ᴿᵀsec⁻¹), are in excellent agreement with the statically induced results of Bowery and Purnell. The relative rate of silylene insertion into methanol, acetylene and ethylene versus 1,3-butadiene was investigated by a combination of stirred flow (628-756°K) and single pulse shock tube (936-1032°K) techniques. The relative rate data obtained for methanol versus 1,3-butadiene were in excellent agreement with absolute measurements obtained by Gaspar on an analogous system (MePhSi: insertion into 2,3-dimethylbutadiene versus ethanol) at 25° C. Using deduced Arrhenius parameters for the MeOH + :SiH₂ reaction (A= 10⁷.²⁰sec⁻¹, E = -808 cal at 25° C), the following absolute Arrhenius parameters for the substrates investigated here were deduced:
