Some aspects of acylation of cellulose under homogeneous solution conditions

Commercially available cellulose (Avicell PH101) was successfully acylated under homogeneous solution conditions by the following procedure: 2.0 g of cellulose were stirred with 75 mL of N,N-dimethylacetamide for 1 h at 150°C, 3.5 g of LiCl were added, the temperature was raised to 170°C, ca. 18.5 mL of the solvent were distilled and the suspension was cooled to room temperature and stirred overnight. The temperature of the clear cellulose solution was raised to 110°C, kept at that temperature for 1 h, an acid anhydride was added and the solution stirred at 110°C for additional 4 h. Acetates, propionates, butyrates, and acetate/propionate mixed ester were prepared with excellent control of the degree of substitution, DS, 1 to 3 for acetates, 2 and 3 for propionates and butyrates, and 3 for acetate/propionate. The degree of polymerization of cellulose is negligibly affected under these reaction conditions. The distribution of the acetyl moiety among the three OH groups of the anhydroglucose unit shows a preference for the C6 position.