Catalytic conversion of glucose in dimethylsulfoxide/water binary mix with chromium trichloride: Role of water on the product distribution

The production of 5-Hydroxymethylfurfural (HMF) from hexoses is a stoichiometric dehydration process. Water content in a solvent is expected to play an important role in HMF formation by affecting the equilibrium and the reaction kinetics. In this work, the impact of water content on the catalytic conversion of glucose was investigated in detail in different dimethylsulfoxide (DMSO)/H 2 O mixtures ( χ w   =   0–1) with chromium trichloride hexahydrate (CrCl 3 ·6H 2 O) as the catalyst at 110–130   °C. Water content in the binary mix was found to dominantly affect the product distribution. Anhydrous DMSO system is favored for HMF formation from glucose but caused a number of side reactions, especially the undesired dehydration of glucose into cellobiose. Adding an appropriate amount of water in DMSO ( χ w   =   0.17–0.50) was found to significantly suppress the undesired dehydration side reactions while preserving high HMF yield over the CrCl 3 ·6H 2 O catalyst, therefore remarkably improving the total selectivity of HMF and fructose from glucose conversion. While CrCl 3 ·6H 2 O was essential in isomerizing glucose into fructose, hydrochloric acid (HCl) from CrCl 3 ·6H 2 O hydrolysis in DMSO/H 2 O mixed system catalyzed the dehydration of in situ formed fructose to HMF. Although effective water removal was pronounced toward improving HMF yield from hexose dehydration in previous work, the results of this work indicate that a controlled amount of water in the non-aqueous system is favorable to drive the thermodynamic equilibrium for high HMF yield and desired product selectivity, providing reference information on designing a one-pot process for HMF synthesis from cellulosic materials.