Preparation of functionalized diallylimidazole ionic liquid and its application in conversion of D-fructose into HMF

Abstract

A kind of functionalized diallylimidazole ionic liquids (CnDAIMF) was synthesized and applied in the dehydration of D-fructose to produce 5-HMF under the microwave radiation. The results showed that X-ray, 1H NMR and FT-IR confirmed the production. The target ILs existed in a highly centrally symmetric, and crystalline state at room temperature, with a good thermal stability up to 300 °C (HTD ≥ 340 °C). In the experiments of conversion D-fructose to 5-HMF, 5-HMF could be obtained via the catalysis of diallylimidazole IL whether in water or DMSO. The catalytic performance of these ILs was not much different from that of solid acid (like camphor sulfonic acid or solid carbon sulfonic acid), and which was higher than that of the monoimidazole hexafluorophosphate or imidazole class bromine salt, but there were no obvious changes can be found with the variation of carbon chain length between imidazole rings in diallylimidazole IL. The effects of temperature and solvent on the reaction were more significant. The optimized yield of 5-HMF was 52.59% at 185 °C in a water-C2DAIMF solvent (t = 10 min), while 73.71% at 195 °C in DMSO-C2DAIMF solvent. Furthermore, six CnDAIMF have a considerable effect on the conversion in water and 5-HMF yield of about 50% could be obtained, which is satisfactory compared with other similar processes, especially in the microwave system of aqueous solution. Therefore, this process may be benefit for many researches and applications related to functionalized ionic liquid research and biomass conversion applications.