Assessment of the electrochemical synthesis route to silicones starting from slica as feedstock

Abstract

We successfully achieved methylation of various SiO2 sources to cyclic methylsiloxanes via electroreduction reaction. Contrary to previous assumptions, the reaction does not start from methanol as methyl radical source, that results in methoxylation of the electrolyte solvent. Methylammonium cations were found to enable the direct conversion, strongly dependent on the radical intermediate stabilization by the electrolyte. THF/Bu4NCF3SO3 is the sole applicable system with yields below 14 % referred to the methylammonium cations for the highest amount of product obtained so far. Mechanistic insights show that methylation does not occur via the supposed hydrolysis of dimethoxydimethylsilane intermediate, but via a direct conversion reaction, as comparative studies of a Fenton-type procedure clearly indicate. Further, cyclic methylsiloxane products are prone to subsequent electrochemical equilibration, strongly directed by the electrolyte solvent.