Rapid, High-Yield Fructose Dehydration to 5-Hydroxymethylfurfural in Mixtures of Water and the Noncoordinating Ionic Liquid [bmim][OTf]

The noncoordinating ionic liquid [bmim][OTf] (bmim=1-butyl-3-methylimidazolium) is an effective and versatile solvent for the high-yield dehydration of fructose to the platform chemical 5-hydroxymethylfurfural (HMF) over short reaction times. In contrast to prior studies in which low yields were obtained for this transformation in ionic liquids (ILs) with noncoordinating anions, this contribution reveals that the water content is an essential parameter for an efficient reaction in ILs. Achieving the optimum amount of water can increase the yield dramatically by regulating the acidity of the catalyst and partially suppressing the side reaction caused by self-condensation of HMF. Using acid catalysis in [bmim][OTf] with 3.5 % water content, yields above 80 % can be achieved at 100 °C in only 10 min, even at high (14 %) fructose loading. These results also suggest that [bmim][OTf] represents a superior medium for solvent extraction of HMF compared to halide-based ILs, allowing the option of isolation or further valorization of the HMF formed.