1H NMR study of the hydrolysis of vinyltrialkoxysilanes

1H NMR spectroscopy was used to investigate the hydrolysis of vinyltrimethoxysilane (VTMS) and vinyltriethoxysilane (VTES) in water–acetonitrile media in neutral, acidic and basic conditions. Apparent rate constants of the hydrolysis of VTMS and VTES in such conditions were determined. It was shown that in neutral conditions the hydrolysis of vinyltrialkoxysilanes in acetonitrile is an extremely slow process with k=1.3×10−6 M−1 s−1. However, in the presence of even very small amounts either of acid or base the rate constants increased dramatically up to four orders of magnitude. It was found that in the conditions of acidic hydrolysis the steric effect of an alkoxy group did not have serious influence. However, in basic conditions the hindrance of an ethoxy group made the hydrolysis of VTES about 50 times slower with respect to that of VTMS. Also, both acid and base dramatically increased the rates of intermolecular condensation. It was qualitatively confirmed by an extensive NMR line broadening of the vinyl proton signals.