Efficient conversion of fructose into 5-ethoxymethylfurfural with hydrogen sulfate ionic liquids as co-solvent and catalyst

Hydrogen sulfate ionic liquid as co-solvent and as homogeneous catalyst in ethanol solvent allows efficient conversion of fructose into 5-ethoxymethylfurfural (5-EMF) directly at mild conditions. Ionic liquids [A][B] ([A]+ = 1-methylimidazolium, [C1im]+; 1-ethyl-3-methylimidazolium, [C2mim]+; or 1-butyl-3-methylimidazolium, [C4mim]+, [B]− = hydrogen sulfate, [HSO4]−; acetate, [AC]−; diethylphosphate, [DEP]−); dimethylphosphate, [DMP]−) or chloride, [Cl]− were studied. In the [C4mim][HSO4]-ethanol system, 83% 5-EMF yields were obtained from fructose at 130 °C in 20 min reaction time that can be attributed to the anion acidity and to a stabilizing hydrogen bond that forms between the ionic liquid and 5-HMF. The ionic liquid was demonstrated to be reusable for five times with minimal loss in catalytic activity (ca. 3% loss in 5-EMF yield). Hydrogen sulfate ionic liquids as co-solvent and catalyst in ethanol allow efficient conversion of biomass-related mixtures that contain fructose or a 5-HMF intermediate into biofuels.