Infra-red spectroscopic investigation of the interaction of BCl3 with aerosil silicas

Abstract

The reaction of BCl₃ with the surface hydroxyl groups of Aerosil silicas has been examined using infra-red spectroscopic techniques. The results indicate that BCl₃ may not react with all the hydroxyl groups situated on external surfaces. With microporous solids a significant fraction of the surface groups available for exchange with molecular D₂O are unavailable for reaction with BCl₃. Reaction of the silica with BCl₃ followed by hydrolysis of the resulting reaction product produces a surface that contains two chemically distinct types of hydroxyl groups. It is proposed that the closely adjacent hydroxyl groups are replaced by a bridged structure:— [graphic omitted] The fundamental stretching frequency of the single surface boron hydroxyl was 3695 cm^–1. The isolated surface silanol groups are regenerated on hydrolysis of the BCl₃ reaction products, with the concomitant formation of boric acid.