Insights into the Play of Novel Bronsted Acid-Based Deep Eutectic Solvents for the Conversion of Glucose into 5-Hydroxymethylfurfural without Additional Catalysts

5-Hydroxymethylfurfural (5-HMF) is a versatile bio-platform chemical that connects biomass to a variety of different fuels, chemicals, and materials. In this work, novel Brunsted acid-based deep eutectic solvents (DESs) with both solvent and catalytic functionalities for glucose dehydration into 5-HMF were developed without the need of additional metal salt catalysts or heterogeneous catalysts. The types of hydrogen bond donor (HBD) and hydrogen bond acceptor (HBA), the ratio of HBD to HBA of the DES, heating time, reaction temperature, initial glucose concentration, and moisture content of the DES were systematically investigated to reveal the interplay of the DES in the conversion of glucose to 5-HMF. The most effective DES was found to be triethyl benzyl ammonium chloride (TEBAC)/formic acid (FA) (molar ratio: 2:1) with a 5-HMF yield of 30.5 +/- 1.0% in glucose dehydration and approximately 100% glucose conversion (initial glucose concentration: 2.5 wt %) in 60 min at 150 degrees C. Most importantly, after five cycles, the TEBAC/FA (1:2) DES retained high stability and catalytic activity, with the yield of 5-HMF remaining 30.1 +/- 0.5%. Interestingly, as the water content of the DES increased to 70%, the 5-HMF yield increased to 36.5 +/- 1.0% along with an 8.01 +/- 1.4% yield of levulinic acid. The finding of this study provided insights into the TEBAC/FA (1:2) DES with dual capabilities that might support more efficient bio-based commodity chemical production methods.

Automated summary

This study developed novel Brunsted acid-based deep eutectic solvents (DESs) with both solvent and catalytic functionalities for glucose dehydration into 5-HMF. The most effective DES was found to be TEBAC/FA with high stability and catalytic activity. The water content of the DES was also found to affect the yield of 5-HMF.