Design and synthesis of Brønsted-Lewis acidic tetraimidazolyl ionic liquids for efficient catalytic conversion of glucose to 5-hydroxymethylfurfural in water/1-octanol

Abstract 5-Hydroxymethylfurfural (5-HMF) is a key platform compound in the catalytic conversion of biomass. Ionic liquids (ILs) have attracted much attention due to their unique tunable structures and wide applications. A series of Brønsted-Lewis acidic tetraimidazolyl ionic liquids ([TeimILs]) were designed and synthesized by introducing Brønsted acid (-SO3H) in the cation and Lewis acid (AlCl3) in the anion. Among them, [Teim-PS][AlCl4]4 exhibited good catalytic performance in the conversion of glucose to 5-HMF in the biphasic system of H2O: 1-octanol= 1:2, and the conversion of glucose and the yield of 5-HMF can reach 94 % and 71.3 %, respectively. [Teim-PS][AlCl4]4 as the catalyst can be reused at least six times, the yield of 5-HMF does not decrease significantly. The biphasic system was beneficial for the recycling of [Teim-PS][AlCl4]4 and the separation of 5-HMF. In addition, the kinetic analysis was performed on the catalytic system, and its activation energy was only 49.98 KJ/mol. This work provides a new solution for the efficient and green conversion of glucose to HMF.