Very efficient conversion of glucose to 5-hydroxymethylfurfural in DBU-based ionic liquids with benzenesulfonate anion

Efficient conversion of glucose to 5-hydroxymethylfurfural (HMF), an important platform molecular for fuels and chemicals, is a promising topic in green chemistry. In this work, several new DBU-based (DBU = 1,8-diazabicyclo[5.4.0]undec-7-ene) ionic liquids (ILs) with benzene sulfonate (BS) anion were synthesized and used as the solvents for the dehydration of glucose to HMF. It was found that all the ILs were excellent solvents for the dehydration of glucose to form HMF using CrCl3 as the catalyst. The effects of various factors, such as kind of catalysts, catalyst amount, reaction time and reaction temperature, on the yields of HMF were studied systematically in the Et-DBUBS/CrCl3 catalytic system. The yield of HMF from glucose could reach 83.4% under the optimized reaction conditions, and the reasons for the high yield were investigated on the basis of control experiments. The Et-DBUBS/CrCl3 system could be reused at least five times without considerable reduction in the efficiency. Further study indicated that the catalytic system was also very efficient for transformation of fructose, inulin, and cellobiose to HMF.