ALKALINE SOLVOLYSIS OF TRIPHENYLSILANE .2. INFLUENCE OF THE WATER-CONTENT ON THE KINETICS IN ACETONITRILE

The influence of the composition of acetonitrile-water mixtures on the kinetics of the alkaline hydrolysis of triphenylsilane is investigate d, by hydrogen volumetry, at 25-degrees-C. Within the range of increas ing molarities 1.09 less-than-or-equal-to [H2O] (mol l-1) less-than-or -equal-to 11.98, a slight decrease of the second order rate constant ( k(II) = rate/[SiH][OH-]) is observed. A tentative interpretation, taki ng into account the variation of the transfer activity coefficient of OH-, leads to a 4th order with respect to water, which would normally imply that four water molecules are involved in the transition state, but this conclusion could be questionable, since the structure of the mixture is deeply modified when the water content is varied. The value s of the Gibbs function of transfer for the activated state in the rat e determining step are close to those for OH-, indicating a structure with original bonds almost broken.