A highly effective approach to enhance the performance of biomass-derived acid for fructose conversion to 5-hydroxymethylfurfural

Synthesis of 5-hydroxymethylfurfural (HMF) from carbohydrate is one of vital step for bio-refinery development. In this work, a novel strategy was developed for catalytic conversion of fructose to HMF in 2-butanol. The inexpensive ionic liquids were used to adjust the acidity of biobased acid catalyst for enhancing the dehydration of fructose to HMF. The combination of 1-butyl-3-methylimidazolium chloride ([Bmim]Cl) with oxalic acid afforded an excellent HMF yield of 97.1% at 98.7% fructose conversion under mild conditions of 100 °C and 60 min, owing to the enhanced dissociation ability of oxalic acid by [Bmim]Cl. A possible dissociation mechanism of oxalic acid induced by [Bmim]Cl was proposed based on control experiments and detailed analyses with NMR and FT-IR techniques. It involved that the [Bmim]Cl interacted with oxalic acid through hydrogen bond , which decreased the electron density of oxygen atom on hydroxyl group and weakened the O-H bond, thus making the hydrogen in the O-H group to easily dissociate in the form of H + . Moreover, the reusability of oxalic acid and [Bmim]Cl was demonstrated, and both could be reused up to six times without significant loss in activity