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.