Reactive silica: VIII. Methoxylation of silica using trimethoxymethane

Abstract

Trimethoxymethane (TMM) sorption by severely and partially dehydroxylated, as well as fully deuterated silicas, was followed by infrared spectroscopic techniques. TMM is physically adsorbed at 25 °, interacting with surface silanols to yield a hydroxyl shift of 350 cm −1. The weakly adsorbed TMM can be removed at 25 °. Near 300 ° the reaction SiOH + HC(OCH 3) 3 → SiOCH 3 + CH 3OOCH + CH 3OH becomes dominant, and all accessible surface hydroxyls are readily removed in the 300–500 ° range. Above 500 ° the thermal decomposition of TMM is dominant. These decomposition products, as well as hydrolysis products, play a minor role in modifying silica surfaces in the 25–275 ° range, most effects being caused by methanol contaminant.