Interaction mechanism between cellobiose and imidazolium halide-based ionic liquids

Abstract

Ionic liquids (ILs) are excellent solvents for cellulose, but the dissolution mechanism is not deeply understood. In the present study, cellobiose was used as a model of cellulose, and the imidazolium halide-based ILs with the same cation of 1-butyl-3-methylimidazolium (Bmim+) including BmimCl, BmimBr, and BmimI were used as solvents. The interaction mechanism between the ILs and cellobiose was analyzed by carbon-13 nuclear magnetic resonance (13C NMR). The results showed that the strength of hydrogen bonds formed between the hydroxyl groups of cellobiose and the ILs was greatly affected by the position of hydroxyl groups and the electro-negativity and size of the anions. Compared with the secondary alcoholic hydroxyl groups, the primary alcoholic hydroxyl groups (C6–OH and C12–OH) on the glucopyranose rings of cellobiose more easily formed hydrogen bonds with the ILs. The strength of hydrogen bonds formed between the protons on the imidazolium cation and cellobiose varied with the positions of the protons. The formation of hydrogen bonds between the halogen anions and cellobiose was the main reason for the dissolution of cellobiose in the ILs. The ability of the three ILs to form hydrogen bonds with cellobiose followed the order: BmimCl > BmimBr > BmimI.