REACTION BETWEEN TETRAETHYOXYSILANE AND CHLORAL HYDRATE IN ETHANOL. A 29Si NMR INVESTIGATION

Abstract

ABSTRACT The hydrolysis of tetraethylsilane can be carried out and using chloral hydrate as the source of water. The first step of the hydrolysis, formation of triethoxysilanol is the rate determining step. The hydrolysis thus resembles that of aectals, ketals and orthoesters. In unbuffered media the reaction is sufficiently slow to follow the decrease of Si(OEt)4, and changes in concentrations of Si(OEt)3(OH) and Si(OH)4 by 29Si NMR The most rapidly formed dimeric species has two OH groups on a given Si atom. Formation of oligomers involves one or more hydrolyzed momoners. In solutions acidified by HCI and containing small amount of water, both hydrolysis and formation of oligomers by condensation occurs faster. The intermediate Si(OEt)2(OH)2 is also detected, indicating that the rate of the first step of hydrolysis increase with increasing acidity more than that of the second step.