Chemo-enzymatic Conversion of Glucose in 5-Hydroxymethylfurfural: The Joint Effect of Ionic Liquids and Ultrasound

For the valorization of lignocellulosic biomass, a key step is unlocking the conversion of glucose to suitable chemical platforms. To this aim, we herein describe the sequential chemo-enzymatic conversion of glucose into 5-hydroxymethylfurfural (5-HMF), in two steps: glucose isomerization to fructose, catalyzed by glucose isomerase (GI) and fructose dehydration to 5-HMF promoted by Amberlyst 15. The novelty of our approach lies in the use of crude cell extracts of Streptomyces coelicolor showing GI activity, as isomerization catalysts, along with a commercial immobilized GI. Under optimized reaction conditions, we obtained a conversion to 5-HMF (C5-HMF) from glucose of 50% in the H2O/[bmim][Cl]0.5[BF4]0.5 1:3 w-w ternary mixture. We also carried out both reactions under sonochemical activation, obtaining a conversion to fructose (Cfructose) of 50% and C5-HMF 74% for the isomerization and dehydration respectively, with a drastic reduction in reaction time and temperature. In this case, the amount of substrate processed was 50 times higher than in silent conditions.