Reactions of trimethylsilylated silicate anions in acidic medium. Part 1. Effect of Amberlyst 15 cation-exchange resin on the products of trimethylsilylation of hexameric ring silicates

Abstract

Chemical and structural transformations induced by proton–donor catalysts (Amberlyst 15 cation-exchange resin and trichloroacetic acid) have been studied using the silicate derivatives Si₆O₁₅(SiMe₃)₆ and Si₆O₁₈(SiMe₃)₁₂ as model compounds. The experiments were performed in hexamethyldisiloxane solutions using a standard quality Amberlyst 15. Gas chromatography with a glass capillary column was used for detection of the composition changes in the reaction mixtures. Present and former results have permitted a probable structural presentation of the reaction pathways to be made. The transformations tend to produce structures containing only tetrameric siloxane rings when starting from cyclic and polycyclic silicate derivatives containing trimeric, (pentameric), or hexameric siloxane rings. Three different reaction types are suggested for the interpretation of the transformations. Amberlyst 15 was found to contribute significantly to side reactions during the Amberlyst treatment following the trimethylsilylation of silicates under the usual conditions employed.