Theoretical study on the mechanism of the side reaction of 1-butyl-3-methylimidazolium cation with d-glucose

To understand the non-inert nature of ionic liquids in cellulose chemistry, density functional theory calculations were carried out to investigate the reaction of 1-butyl-3-methylimidazolium cation ([bmim]+) with model compounds α- and β-glucoses (the basic units of cellulose and its degradation products) in the absence and presence of base, triethylamine (TEA).The calculated energy barriers for the reactions of [bmim]+ with α- and β-glucoses without TEA were 67.97 and 66.19 kcal mol−1, respectively. With the assistance of TEA, the barriers were reduced to 48.17 and 46.96 kcal mol−1, due to the enhanced electrophilic abilities of H6 and nucleophilic abilities of C2 induced through deprotonation of the C2 atom, respectively. The present results rationalize the experimental finding well and provide a clear explanation on why imidazolium-based ionic liquids are considered as non-inert solvents in cellulose chemistry.