Efficient glucose-to-HMF conversion in deep eutectic solvents over sulfonated dendrimer modified activated carbon

In this study, a solid acid catalyst was designed by growing thiol-based dendrimer up to third generation on the surface of activated carbon (AC) by the thiol-ene click reaction and subsequent transformation to sulfonic acid groups. Characterization results displayed the successful grafting of sulfonic acid groups with high density on dendrimer functionalized AC through the oxidation of thiol groups. The efficiency of the obtained catalyst was explored in the acid-catalyzed transformation of glucose to 5-Hydroxymethylfurfural (HMF) using deep eutectic solvents (DESs). The most effective DES was choline chloride:urea (ChCl:urea), which provided an HMF yield of 96% after 1 h of reaction time at 100 °C from glucose. Some control experiments demonstrated that the alkalinity of nitrogen in the dendrimer structure combined with of urea has an important synergistic effect in enhancing the glucose isomerization to fructose, thus improving the reaction efficiency. Additionally, the presence of dendritic structure contributed to the catalytic activity by making the sulfonic acid group highly reactive. Both the catalyst and DES were used for five cycles without significant descent in catalytic activity.