Partial silylation of cellulose with predictible degree of silylation - stoichiometric silylation with hexamethyldisilazane in ammonia

Abstract

The silylation of cellulose with hexamethyldisilazane (HMDS) in liquid ammonia at elevated temperature has been extended to the synthesis of partly silylated trimethylsilylcellulose. Predictable degrees of silylation (DS) were obtained either with excess ammonia or in a nearly 1: 1 ratio of NH 3 /AGU (anhydroglucose unit) or with toluene as co-solvent. Complete reaction of the silylating agent allows to adjust the DS directly by simple variation of the ratio of OH groups to trimethylsilyl groups of the silylating agent. With chlorotrimethylsilane more than the stoichiometric amount of silylating agent is required to obtain a desired DS and the work up is more tedious. A simple method to determine the DS of trimethylsilylcellulose based on infrared spectroscopy is proposed. It is applicable to cellulose with a DS greater than 1.3.