Reactivity of Silicates. 1. Kinetic Studies of the Hydrolysis of Linear and Cyclic Siloxanes as Models for Defect Structure in Silicates

摘要

The kinetics of hydrolysis of hexamethylcyclotrisiloxane and di-t-butyldmesitylcyclodisiloxane in tetrahydrofuran solution have been determined and compared to hydrolysis rates of silica defects. In the presence of sufficient excess water, the first-order rate constant of the cyclotrisiloxane, K = 3.8 x 10 sup -3 min sup -1 , of the disappearance of the D2 raman silica defect band it has been proposed to model. Limited hydrolysis rate data for the cyclodisiloxane suggest that it hydrolyzes at least four times faster than the cyclotrisiloxane. These data are consistent with rate data available for silica crack growth and supports the assignment of highly strained siloxane bonds at the crack tip to cyclodisiloxanes. Infrared spectra determined for the cyclodisiloxanes lend further support to this model. 41 refs., 3 figs., 1 tab. (ERA citation 11:034441)