Reactions of cellulose in ammonia - Silylation and desilylation

Activation of cellulose with ammonia has been known for long time. A drawba ck of LAT cellulose is the competition of residual ammonia with mast of the reagents used for derivatisation reactions. Silylation of polysaccharides is one of the reactions where ammonia does no t compete with the hydroxy groups. Mono- and disaccharides, cellulose and starch can be silylated with hexamet hyldisilazane in an autoclave in liquid or supercritical ammonia at elevate d temperature. Ammonia, the only byproduct formed in this reaction, is remo ved together with the ammonia used as reaction medium. The influence of amm onia on the silylation as well as on the desilylation reaction has been inv estigated The degree of silylation can be adjusted by the ratio of HMDS/OH groups. The reaction proceeds under mild and non acidic conditions and is s trictly polymeranalogous. Properties of silylated cellulose in relation to the parameters of the synt hesis will also be discussed.