Molten Salt Alcohols: A New Class of Organic Solvents for Carbohydrate Dissolution and Isomerization

Abstract

Abstract Carbohydrate conversion in alcoholic solvents offers unique selectivity; however, poor carbohydrate solubility limits its practical applications. Herein, we demonstrate that salt–alcohol–carbohydrate interactions in molten salt alcohol (MSA) solvents enhance both carbohydrate solubility and isomerization efficiency. Two MSAs were investigated: CaCl2-methanol (MSA-1) and LiBr-methanol (MSA-2). At 60 °C, glucose solubility reached 58.5 and 24 g/100 mL in MSA-1 and MSA-2, respectively. Without added catalyst, glucose isomerized to fructose with yields of 56.4 and 61.4% in MSA-1 and MSA-2, respectively, and selectivity exceeding 85% in both systems. CaCl2, fructose, and glucose were recovered from MSA-1 at 99, 95.5, and 91.5%, respectively, via antisolvent precipitation and differential dissolution. NMR titration revealed that conversion of α-D-glucopyranose to β-D-glucopyranose in MSA is critical for isomerization efficiency. Furthermore, molybdate-catalyzed epimerization of glucose to mannose and of arabinose to ribose in MSA-1 achieved yields of 66.6 and 53.3%, respectively.