Four Fe-containing ionic liquids (ILs) were synthesized by coupling of conventional imidazole ionic liquids [Cxmim]Cl (x = 4, 8, 12, 16) with FeCl3 and were characterized by FT-IR, Raman, ESI–MS and TG. All of the Fe-containing ILs were applied to the conversion of fructose into 5-hydroxymethylfurfural (HMF) in 1-butyl-3-methylimidazolium chloride ([Bmim]Cl) subsequently and the result showed that [C16mim]FeCl4 exhibited excellent catalytic performance. Then the different reaction parameters with [C16mim]FeCl4 as catalyst were studied in detail. A 92.8% yield of HMF was obtained with 0.03 g [C16mim]FeCl4 and 0.1 g fructose in 1.0050 g [Bmim]Cl at 80 °C for 40 min in fructose/[Bmim]Cl solution.

In this work, D001-cc cation-exchange resin was modified by CrCl3 using an ion exchange method to obtain a Cr3+-D001-cc catalyst. FT-IR, UV-vis, SEM, EDX, ICP-OES and Py-IR were used to characterize the catalyst. Subsequently, the effects of the modified metal ion and different cation-exchange resin on the direct conversion of glucose to 5-hydroxymethylfurfural in [Bmim]Cl were examined. The results showed that Cr3+-D001-cc resin exhibited excellent catalytic performance. Moreover, with Cr3+-D001-cc resin as a catalyst, the influence of the reaction conditions on the dehydration of glucose was investigated in detail. 61.3% yield of 5-hydroxymethylfurfural was achieved in the [Bmim]Cl ionic liquid at 110 °C for 30 min with 0.1 g catalyst. Finally, a recycling experiment was performed. The result indicated that the HMF yield in the Cr3+-D001-cc resin and [Bmim]Cl system significantly decreased after six recycles.

•(NH4)2S2O3 and [Bmim]Cl could be an excellent combination for the conversion of fructose to HMF.•The catalytic system had a good tolerance for high concentration fructose and water.•The catalytic system exhibited constant stability and activity.Some sulfur oxyacid salts with weak acidity or alkalinity, including Na2SO4, (NH4)2SO4, (NH4)2S2O3 and Na2S2O3, were applied to the conversion of fructose to 5-hydroxymethylfurfural. The results indicated that (NH4)2S2O3 had excellent catalytic performance for the conversion of fructose. A desired HMF yield of 81.6% was obtained with only 5 mg (NH4)2S2O3 as the catalyst in [Bmim]Cl at 120 °C for 50 min. Furthermore, the HMF yield remained at 76.6% with 60 wt% water in the IL–water mixture solvent. In addition, the system of (NH4)2S2O3 and [Bmim]Cl exhibited a constant stability and activity, and a good HMF yield was maintained after nine recycles.A agreeable HMF yield of 81.6% was reached with only 5 mg (NH4)2S2O3 as the catalyst in [Bmim]Cl at 120 °C for 50 min, although S2O32− had the similar structure as SO42−.