Base-catalysed solvolysis of N-(trialkylsilyl)anilines

Abstract

Rates of solvolysis have been measured for the compounds PhNHSiMe 3, PhNHSiEt 3, m-ClC 6H 4NHSiEt 3, PhNMeSiEt 3, and PhNEtSiEt 3 in a mixture of methanol (5 vol) and aqueous potassium hydroxide (2 vol), and for most of these compounds in mixtures of dimethyl sulphoxide (6 vol) and aqueous alkali (1 vol). All the compounds react rapidly with neutral aqueous methanol. For the secondary compounds PhNHSiMe 3 and PhNHSiEt 3, the rates fall when a little alkali is added and the oxonium ion catalysed reaction is suppressed, but then rise as the alkali concentration is increased further, and a base-catalysed reaction takes over. Base catalysis is, however, very much less effective than acid catalysis. There is also a significant “spontaneous” reaction involving catalysis by neutral molecules. For the tertiary compounds PhNMeSiEt 3 and PhNEtSiEt 3, base catalysis is not significant in MeOH/H 2O but does contribute in DMSO/H 2O. There is a very large difference in reactivity between PhNHSiMe 3 and PhNHSiEt 3 in the base-catalysed reaction in MeOH/H 2O, the former being ca. 2.5 x 10 4 times more reactive; this is attributed to unusually severe steric hindrance. Mechanisms are suggested for the neutral, base-catalysed, and spontaneous reactions.