Design of Acyl Donor for Environmentally Benign Acylation of Cellulose Using an Ionic Liquid

Esterification is the most important derivatization to utilise cellulose as a sustainable resource for the materials industry. Homogeneous esterification is generally the most convenient means to achieve this aim. We found that N-methyl-N-(2-methoxyethyl)pyrrolidinium acetate [P1ME][OAc] easily dissolved cellulose. To achieve the environmental benign acylation of cellulose, we attempted to design acyl donor molecules under strong base catalyst-free conditions. It was found that a [P1ME][OAc] solution of cellulose when mixed with 2,2,2-trifluoroethyl benzoates at 80°C afforded the corresponding cellulose benzoate with a perfect (3.0) degree of substitution (DS) value in almost quantitative yield. We also succeeded in preparing 4-[(4-hydroxyphenyl)diazenyl]benzoate or 4-[(4-methoxyphenyl)diazenyl]benzoate of the cellulose with a DS value of 2.38 or 2.67 by the same protocol, respectively; the DMSO solution prepared by the resulting compounds exhibited a photochromic property, although only a slight colour change from light yellow to colourless was obtained by UV irradiation.