The reaction of silicon with methanol using copper(I) chloride as a catalyst gives HSi(OCH3)3 and Si(OCH3)4, the selectivity for HSi (OCH3)3 being dependent on the conditions of the treatment of the silicon-catalyst mixture as well as the reaction conditions. The selectivity for HSi(OCH3)3 was 64% when a silicon-copper(I) chloride mixture was preheated at 723 K and the reaction was carried out at 513 K. The addition of a small amount of thiophene to the feed increased the selectivity to almost 100%. A separate experiment showed that metallic copper catalyzes the reaction of HSi(OCH3)3 and methanol to give Si(OCH3)4, this reaction being completely inhibited by thiophene. It is concluded that HSi(OCH3)3 is a sole primary product and that Si(OCH3)4 is formed by the secondary reaction of HSi(OCH3)3 with methanol on metallic copper, which is formed on the silicon surface during the silicon-methanol reaction. Alkyl chlorides such as methyl and propyl chloride also were found to be effective additives for improving the selectivity. Copper(I) chloride serves as the catalyst for forming intermetallic Cu-Si species. The presence of copper(I) chloride in the reaction system also serves to enhance the selectivity for HSi(OCH3)3. It is suggested that the chloride ions are transferred to the surface of metallic copper formed in the course of the reaction to poison the catalytic activity for the HSi(OCH3)3-methanol reaction. The reaction mechanism involving surface silylene species is proposed for the exclusive formation of HSi(OCH3)3.
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