ENHANCED SILYLATION REACTIVITY OF A MODEL FOR SILICA SURFACES

The relative silylation reactivities of structurally similar silanols (1-4a) containing one, two, and three potentially hydrogen-bonded siloxy groups have been explored for the first time. In the absence of amine bases, silylation with TMSC1 is sluggish and there is very little kinetic selectivity for silylation of either isolated silanols or intramolecularly hydrogen-bonded silanols. In the presence of Et3N or pyridine, the rates for silylation of all types of silanols are greatly increased and there appears to be a slight kinetic preference for the silylation of vicinally hydrogen-bonded silanols over isolated, non-hydrogen-bonded silanols. Most significantly, there is remarkable selectivity for the monosilylation of 1 in the presence Et3N. The experimental results suggest that the most reactive sites for silylation of hydroxylated silica surfaces may be those possessing at least three mutually hydrogen-bonded hydroxy groups. © 1990, American Chemical Society. All rights reserved.