Dual catalytic function of 1,3-dialkylimidzolium halide ionic liquid on the dehydration of fructose to 5-hydroxymethylfurfural

In the fructose dehydration to 5-hydroxymethylfurfural (HMF) in dimethyl sulfoxide, the catalytic function of 1,3-dialkylimidazolium-based ionic liquids with different counter-anions was investigated. It was found that the effects of alkyl chain length and additional alkyl group in Cl-containing ionic liquids were negligible whereas the activity of 1-butyl-3-methylimidazolium-based ionic liquids was considerably changed by varying the anion (particularly, halide ions). The latter finding was confirmed by the control experiment result that the addition of KBr or Ca(CH3COO)2 dramatically tuned the catalytic activity of 1-butyl-3-methylimidazolium chloride. From these results and the proposed reaction pathway, it was consequently believed that 1,3-dialkylimidazolium halide contained the dual catalytic function to act as both Brönsted acid and nucleophile for the fructose dehydration to HMF.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► The anion of imidazolium-based ionic liquids affects the fructose dehydration. ► 1,3-Dialkylimidazolium halide substantially converts fructose to HMF. ► 1,3-Dialkylimidazolium halide contains the dual catalytic function on the reaction. ► 1.3-Dialkylimidazolium halide acts as both Brönsted acid and nucleophile.