Synergetic Effect of Brønsted/Lewis Acid Sites and Water on the Catalytic Dehydration of Glucose to 5-Hydroxymethylfurfural by Heteropolyacid-Based Ionic Hybrids.

The effective dehydration of glucose to 5-hydroxymethylfurfural (HMF) has attracted increasing attention. Herein, a series of sulfonic-acid-functionalized ionic liquid (IL)-heteropolyacid (HPA) hybrid catalysts are proposed for the conversion of glucose to HMF. A maximum total yield of HMF and levoglucosan (LGA; ≈71 %) was achieved in the presence of pyrazine IL-HPA hybrid catalyst [PzS]H2 PW in THF/H2 O-NaCl (v/v 5:1). The mechanism of glucose dehydration was studied by tailoring the Brønsted/Lewis acid sites of the hybrid catalysts and altering the solvent composition. It was found that water and heteropolyanions have a significant effect on the reaction kinetics. Heteropolyanions are able to stabilize the intermediates and promote the direct dehydration of glucose and intermediate LGA to HMF. A small amount of water could facilitate the conversion of glucose to LGA and suppress the dehydration of LGA to levoglucosenone. In addition, the synergetic effect of Brønsted/Lewis acid sites and a little water was conducive to accelerated proton transfer, which improved the yield of HMF from glucose dehydration.