Highly Effective Production of 5-Hydroxymethylfurfural from Fructose with a Slow-Release Effect of Proton of a Heterogeneous Catalyst

Highly effective production of 5-hydroxymethylfurfural (HMF) from biobased sugar is one of the vital steps for the synthesis of a fuel precursor. In this work, a slow-release effect of proton from a heterogeneous catalyst induced by 1-butyl-3methylimidazole chloride ([Bmim]Cl) ionic liquids was found and employed to effectively convert biobased fructose to HMF. Under mild conditions of 100 degrees C and 60 min, a promising HMF yield of 94.6% with a fructose conversion of 99.1% could be achieved in a tetrahydrofuran solvent over the synergy of Amberlyst-15 with [Bmim]Cl, owing to the slow-release effect. Based on extensive control experiments and characterizations, a mechanism of slow release of proton induced by [Bmim]Cl was proposed to better understand the catalytic performance, mainly involving that proton in the -SO3H group of Amberlyst-15 was gradually replaced by the [Bmim]+ of the [Bmim]Cl additive. Additionally, the effect of various parameters (e.g., different ionic liquids and solvents, the loading of the ionic liquid and catalyst, and reaction temperature and time) was systematically investigated. Meanwhile, the stability of Amberlyst-15 and [Bmim]Cl was tested; both could be reused four times. This work provides a novel and highly effective strategy for conversion of biomass-based feedstock toward fuel precursors