ALKYLCHLOROSILANE REACTIONS AT THE SILICA SURFACE

This paper reviews recent work on the reaction of alkyltrichlorosilanes with a pure silica surface. In the absence of moisture these reactions do not occur at temperatures below 300 degrees C. Specifically, it is shown that octadecyltrichlorosilane (OTS) in carbon tetrachloride solution does not react with the surface at room temperature. Reaction does occur with molecular water which is either adsorbed on the surface or dissolved in the CCl4. The polymeric species which is formed can then physically adsorb onto the silica surface causing perturbation and H-bonding of the surface hydroxyls, but not reaction. A room temperature reaction can be induced by the use of a two-step mechanism. In the first step a strong lone pair base such as triethylamine is H-bonded to the surface hydroxyl groups. This induces a strongly nucleophilic oxygen at the hydroxyl site, which is then able to interact with the incoming chlorosilane to form a genuine surface compound. The base is released as the chloride salt.