ROLE OF METALLIC PROMOTERS IN THE DIRECT SYNTHESIS OF METHYLCHLOROSILANES

Overall reaction rates and selectivities for dimethyldichlorosilane were determined for the direct reaction of silicon with methyl chloride to produce methylchlorosilanes. Copper was used as the catalyst, and zinc, tin, and aluminum were investigated as promoters. To unambiguously determine effects of the promoters, high-purity reagents were used for contact mass sample preparation. Others have reported that tin significantly increases both reaction rate and selectivity for samples prepared using technical grade silicon. However, promotion of high purity samples with tin alone (i.e., SiCuSn) significantly decreased both the reaction rate and selectivity. These conflicting results are explained in terms of the aluminum impurities present in technical grade silicon. Tin is suggested to promote this reaction synergistically with zinc and aluminum by lowering the melting points and surface tensions of the catalyst/promoter alloys which form on the surface. © 1991.