Efficient Conversion Of Glucose And Sucrose To5-Hydroxymethylfurfural Catalyzed By Metal Chlorides

At a time when the focus is on global warming, air pollution, and secure energysupply, the use of renewable energy resources is essential. Abundant biomassresources, including carbohydrates, are carbon-neutral renewable energy resources forthe production of biofuels and valuable chemicals.5-Hydroxymethylfurfural （5-HMF）,a versatile platform chemical derived from biomass feedstocks, has been identified as“key substances bridging carbohydrate chemistry and petroleum-based industrialchemistry” because of a variety of value-added chemicals that it can produce. Inrecent years, the efficient catalytic transformation of sugars into5-HMF has attracteda great deal of attention worldwide.In this work, a highly efficient and selective production of5-HMF has beenachieved from glucose and sucrose in the presence of metal chlorides and ammoniumbromide under mild conditions. The main contents in this work are as follows:（1） We tried to catalyze the dehydration of glucose to5-HMF at100°C byadditon of a catalytic amount of a number of metal chlorides. Only two catalysts,CrCl₃and SnCl₄, gave5-HMF in yields above30%. Different solvents, includingprotic and aprotic ones, were studied in reaction system. The results indicated thatpolar aprotic solvents are more suitable for the formation of5-HMF from glucose, inwhich N, N-dimethylacetamide （DMAc） is the most effective. A variety of additiveswere used in combination with catalysts, and we found that bromides are moreefficient additives than chlorides and iodides. When ammonium bromide or alkalimetal bromides were employed as the additive in CrCl₃-catalyzed dehydration, theyield of5-HMF was elevated to73%-74%at100oC for1.0h. Then, we usedCrCl₃-NH₄Br as the catalyst system, studying the influence of various factorsincluding catalyst loading, additive concentration, reaction temperature and time onthe yield of5-HMF.（2） Various catalytic systems including metal chlorides and additives were alsoemployed in the dehydration of sucrose. As a result,87%yield of HMF was obtainedfrom sucrose in the presence of CrCl₃and ammonium bromide at100oC for1.0h in DMAc. Ammonium halides are more effective as additives than alkali metal halides inthis process. As with glucose, we observed a marked halide effect in the coversion ofsucrose, bromides showed the unique ability to mediate the formation of5-HMF fromsucrose. The effects of catalyst loading, additive concentration, solvent, reactiontemperature and time were investigated in detail, and a possible mechanism has beenproposed to explain the good results for ammonium bromide.（3） We examined the recycle of catalyst and solvent, and tried to separate5-HMFfrom reaction mixutures in two different ways.