Silylcellulose from silylation/desilylation of cellullose in ammonia

Silylation of cellulose with hexamethyldisilazane (HMDS) in liquid ammonia is described emphasizing mechanistic features. Conditions for complete as w ell as for stoichiometric partial silylation have been established which pr oved that the ratio of silylating agent and hydrogen bonding capability of the solvent are crucial for complete silylation. The heterogeneous reaction follows first order kinetics in the presence of saccharine as catalyst ind icating that the accessability of hydroxy groups is not the rate determinin g factor. Stoichiometric desilylation of trimethylsilyl cellulose is also p ossible in tetrahydrofurane containing ammonia as hydrogen bond donor. Trim ethylsilyl celluloses have a solubility window in THF with a DS from 1.6 to 2.6 which is narrower for higher molecular weight of the cellulose. Trimet hylsilyl celluloses with DS above 2.7 show thermotropic behaviour.