High-pressure raman study of the hydrolysis reaction in tetramethylorthosilicate (TMOS)

Abstract

The hydrolysis reaction of etramethylorthosilicate is investigated at pH 4.9, 6.0, 7.5 at room temperature and at pressures from 1 to 2000 bar. The rate of reaction is determined using Raman spectroscopy. It is shown that the rate of the hydrolysis reaction is independent of the viscosity of the sol-gel system. The increased mobility and concentration of hydronium and hydroxyl ions at higher pressures and their role in the reaction are also discussed. The pressure-induced changes in the kinetics of the hydrolysis reaction are attributed primarily to the decreasing volume of activation. The volume of activation is found from the pressure dependence of the rate constant and the results are analyzed in terms of the intrinsic and solvent components. It is argued that these results indicate the formation of a pentacoordinate intermediate.