Metal Chlorides In Ionic Liquids To Convert Saccharide Dehydration To 5-hydroxymethyl-furaldehyde

With the rapid consumption of non-renewable fossil materials, the utilization of renewable resources to replace the non-renewable ones is attracting more and more attention all over the world. 5-hydroxymethyl-furaldehyde (5-HMF), which can be obtained from biomass and can be directly converted into fuel through further reaction or useful chemicals, is believed to be a very important intermediate for the use of biomass.Early studies showed that 5-HMF can be obtained in high yields from fructose using acids as catalysts. There are many shortages in this pathway, such as high cost of raw materials, serious corrosion of equipment, by-products formation, waste water emissions, which can not keep with the requirements of green chemical.In this work, the process of glucose dehydration to 5-HMF by using [BMIm]Cl as solvent and metal chlorides as catalysts was studied.1-buthyl-3-methylimidazolium chloride ([BMIm]Cl) was first synthesized from N-methylimidazole and 1-buthyl chloride. The purity of [BMIm]Cl was measured by titrating with silver nitrate, and its qualitative analysis was conducted by UV-Vis and IR. The results showed that the yield of [BMIm]Cl was up to 84% and [BMIm]Cl had a purity of 98.8% at reaction temperature 90℃, reaction time 48h and molar ratio of N-methylimidazole : 1-buthyl chloride 1:1.05.The reaction conditions of glucose dehydration to 5-HMF by using metal chlorides as catalysts and [BMIm]Cl as solvent were studied. The effects of metal chlorides, catalyst content, reaction time, reaction temperature and glucose content on the conversion of glucose and the yield of 5-HMF were investigated. The optimal conditions of glucose dehydration to 5-HMF were found as follows: reaction temperature 120℃, reaction time 3h, 10 wt.% glucose (based on [BMIm]Cl) and 10 mol.% ClCl3 (based on [BMIm]Cl). Under these conditions, the glucose conversion was 98.2%, and the 5-HMF yield was 77.4%.The 5-HMF recovery from the ionic liquid and competitive reactions with glycerol or glyceraldehydes as well as the experiments with the addition of 2,2′-bipyridineas a strongly coordinating ligand were conducted to shed light on the reaction mechanism. It is believed that hemiacetal in the glucose combines with [BMIm]CrCl4 firstly, then enolization occurs; and 5-HMF is produced in one of the two ways: either the key intermediate is converted into 5-HMF by dehydration directly, or the intermediate isomerizes into fructose firstly, then fructose dehydrates to 5-HMF.