Effect of organic solvent and Brønsted acid on 5-hydroxymethylfurfural preparation from glucose over CrCl3

Abstract

In the present work, the influence of organic solvent on the mechanism of 5-hydroxymethylfurfural (HMF) preparation from glucose over CrCl₃ and the role of Brønsted acid (N-methyl-2-pyrrolidone hydrogen sulfate ([NMP]HSO₄), N-methyl-2-pyrrolidone bromide ([NMP]Br), N-methyl-2-pyrrolidone chlorine ([NMP]Cl), H₂SO₄, HBr and HCl) during the reaction were researched by a complementary computational and experimental study. It was found that dimethyl sulfoxide (DMSO) gave the lowest conversion of glucose by surrounding CrCl₃, forming a six-coordinated structure (CrCl₃–3DMSO). Glucose conversion in N,N-dimethylformamide (DMF) was not selective. N,N-Dimethylacetamide (DMA) and n-butyl alcohol exhibited superior selectivity towards HMF from glucose. Then the role of different Brønsted acids in DMA was expounded. On increasing the dosage of [NMP]HSO₄, glucose conversion decreased. A computational study found that HSO₄⁻ could also combine with CrCl₃, forming six-coordinate complexes. Addition of [NMP]Br and [NMP]Cl accelerated the generation of HMF significantly but didn’t increase the yield. An experimental method preliminarily confirmed that they were mainly responsible for fructose dehydration to HMF. A subsequent computational study further verified that the two kinds of ILs had no effect on glucose isomerization.