Hydrolysis of alkoxysilanes

Abstract

Alkoxysilanes are hydrolyzed with water in the presence of various hydrolysis catalysts. The hydrolysis catalysts include the solid oxides of the Group IIa metals and solid acid catalysts. The solid acid catalysts are used in conjunction with neutralizing agents and optionally with condensation catalysts. Generally, the process for hydrolyzing alkoxysilanes comprises: mixing an alkoxysilane, a stoichiometric excess of water and an effective catalytic amount of hydrolysis catalyst selected from the group consisting of a solid oxide of a Group IIa metal, a solid acid catalyst and mixtures thereof; neutralizing the hydrolysis mixture with a sufficient amount of neutralizing agent, for example, magnesium oxide; and separating the hydrolysis product from the mixture. When a Group IIa metal oxide hydrolysis catalyst is used, the liquid portion of the hydrolysate is neutral, and no additional neutralizing agent is required in the mixture. By the process of the present invention, the average chain length of silanol-stopped polysiloxanes can be controlled. A stabilized, crystalline tetramethyldisiloxane diol and a crystalline dimethyldisilanol have also been prepared by modified catalytic hydrolysis processes using solid acid catalysts to catalyze the hydrolysis of dimethyldimethoxysilane with water.