Dehydration mechanism of fructose to 5-hydroxymethylfurfural catalyzed by functionalized ionic liquids: a density functional theory study

Ionic liquids (ILs) have shown great catalytic effects in the conversion of fructose to 5-hydroxymethylfurfural (HMF) but the dehydration mechanism remains ambiguous. In this work, density functional theory (DFT) calculations have been carried out for the mechanism of the dehydration of fructose to HMF, catalyzed by functionalized ILs. ILs with different kinds of functionalized imidazolium-based cations and SO3 group-based anions have been used to investigate the catalytic effects of different anions and cations on the dehydration of fructose. The whole reaction process of fructose to HMF includes three dehydration steps. The overall rate-determining step is the second dehydration, and the functionalized cations showed good proton transfer ability to catalyze the reaction in the dehydration steps. The proton shuttling ability of cations is better than that of anions. The anions can form strong H-bonds with the fructose and cations and provide a polar environment to stabilize intermediates and transition states. The high catalytic activity is attributed to the synergetic catalysis of cations and anions to complete the dehydration of fructose. The dehydration reaction mechanism from fructose to HMF catalyzed by [BmimHSO(3)][HSO4]-functionalized ILs has been proposed by DFT calculations. This study emphasizes the catalytic performance of functionalized ILs replaced by different substituent groups and the dehydration mechanism of fructose to HMF.

Automated summary

This study investigates the dehydration mechanism of fructose to HMF catalyzed by different functionalized ILs using density functional theory calculations. The overall reaction process includes three dehydration steps, with the second step being the rate-determining step. Functionalized cations show good proton transfer ability and catalyze the dehydration reaction. Anions can form strong H-bonds with fructose and cations, providing a polar environment for stabilizing intermediates and transition states. The high catalytic activity is attributed to the synergetic catalysis of cations and anions in completing the dehydration of fructose.