THE DIRECT SYNTHESIS OF METHYLCHLOROSILANES .1. STEADY-STATE AND TRANSIENT REACTION-KINETICS

Reaction kinetics under steady-state and transient conditions were used to study the effects of the catalyst (copper) and promoters (zinc and tin) on the direct reaction of methyl chloride with silicon to produce methylchlorosilanes. Use of infrared spectroscopy allowed rapid analysis of the gas-phase product composition. This allowed the accurate measurement of the apparent activation energy and the apparent reaction order for each product. An improved method for calculating direct reaction rates is also introduced. Addition of Zn as a promoter to Cu did not change the overall reaction rate but increased the selectivity for more methylated silanes. Tin promotion increased the selectivity for more chlorinated silanes, while having little affect on the overall reaction rate. Copromotion with zinc and tin increased the overall reaction rate; however, the selectivity for dimethyldichlorosilane (DMDC) was dependent on the concentration of tin. A trace amount of tin (ca. 0.005-0.01 wt%) produced the highest selectivity for DMDC; however, increasing the amount of tin to 0.2 wt% decreased the selectivity. We propose that the primary role of zinc is to direct the dissociative adsorption of McCl such that the methyl group is attached to the Si and the Cl group is attached to the Zn. © 1992.