Brian Michael Naasz

Chemistry of the direct synthesis of methylchlorosilanes. UHV study of the chemisorbed fragments methyl and chlorine on copper silicide and their desorption pathways

Abstract The Direct Synthesis of methylchlorosilanes from methyl chloride and silicon, catalyzed by copper and minor promoter elements was reviewed with respect to use of ultra-high vacuum (UHV) surface reaction techniques to uncover the mechanism of the reaction. In particular, recent results were presented for sequentially adsorbing methyl radicals and chlorine on polycrystalline Cu3Si alloy under ultra-high vacuum conditions. Methyl monolayers in the absence of chlorine produced primarily trimethylsilane, and chlorine monolayers in the absence of methyl produced SiCl4. However, mixed monolayers of methyl groups with chlorine atoms abandoned these separate pathways and instead reacted at similar temperatures on the surface to produce methylchlorosilanes with selectivities to 85% Me2SiCl2 with Zn, Sn, and Al as promoters.

A new approach to understanding the Rochow process: synthesis of methylchlorosilanes from CH3+Cl monolayers on Cu3Si in vacuum

Publisher Summary The Rochow Process refers to the synthesis of liquid methylchlorosilanes from metallurgical silicon powder and gaseous methyl chloride. This chapter discloses a new approach for applying vacuum surface analysis techniques to understand the Rochow Process. Prior attempts to study the molecular details of this reaction in vacuum on polycrystalline Cu 3 Si have been hampered by the desorption of physisorbed CH 3 Cl before the temperature can be raised high enough to effect dissociative chemisorption. In the present study, the sluggish C–Cl bond scission step is circumvented by adsorbing methyl radicals and chlorine separately onto cold Cu 3 Si surfaces. It is found that these methyl + chlorine monolayers are active in forming methylchlorosilanes. In addition, the studies of samples with and without promoters show changes in activity and selectivity that parallel those found over real catalysts, and the results are beginning to show the ways in which these additives influence the catalytic process.