Regioselectivity in Acetylation of Cellulose in Ionic Liquids

Distribution of substituents on the anhydroglucose unit of cellulose (at C2, C3 and C6 positions) is one of the important topics in the derivatization chemistry, but the regioselectivity control is generally difficult. In this report, we exemplified that cellulose acetates having a similar total degree of substitution (similar to 2.3) were obtained in the relevant derivatization but regioselectivity (C6 > C3 > C2, C2 > C6 > C3, C6 > C2 > C3, or C6 > C3 = C2) by a simple one-pot reaction (25 degrees C; 3 h) with acetyl chloride or acetic anhydride in various ionic liquids (ILs). The order of the regional degree of substitution associated with the C2 and C3 positions was successfully correlated with the variation of anion species incident to the acetylating reagent-IL combination. In the use of acetyl chloride, the observed difference in the substituent distribution was attributable to whether a pre-reaction between the in-fed reagent and the anion moiety of the solvent IL was possible or not.