Experimental and computer studies of the thermolysis of some methylsilanes.

The thermolysis of tetramethylsilane was investigated over a wide temperature range, 840K to 1055K, to elucidate the mechanism of the reaction and determine the silicon-methyl bond dissociation energy. At low temperatures, below 955K, the thermolysis was found to proceed by a chain mechanism, however as the temperature was increased the chain length became shorter, until at 955K the reaction became non-chain. The production of methane was then rate determined by reaction (1), and the activation energy could be identified with D (Me3Si-Me). A mechanism was advanced to explain the low temperature chain reaction. Due to its complexity and to the occurance of several termination reactions of similar rate this mechanism could not be treated be conventional steady state methods. To overcome this problem a computer program using a multi-step, implicit, predictor-corrector formula was used to numerically integrate the differential equations corresponding to the mechanism. Using this method a satisfactory mechanism was arrived at which accounted for all the experimental results. This in turn enabled a mechanism to be proposed for the thermolysis of a similar compound, trimethylsilane. Although more complicated, due to the prescence of two types of hydrogen atom in the molecule, this mechanism satisfactorily rationalised a previous study of this thermolysis.