Abstract:

The tautomeric distribution of monosaccharides could influence reaction pathways and product selectivity during their conversion and utilization. Using DMSO-d₆ as cosolvent, we investigated the tautomeric distribution of monosaccharides in imidazolyl ionic liquids at 25 ℃ using quantitative ¹H NMR. In acidic ionic liquids, the results indicate that the proportion of β-pyranose after equilibrium decrease in the following order: D-glucose > D-glucosamine hydrochloride > N-acetyl-D-glucosamine > D-mannose. D-fructose is almost completely converted to 5-hydroxymethylfurfural (formed by the furanose) in [HSO₃-BMIM]HSO₄. In other ionic liquids, the proportion of furanose even exceeds that of pyranose after equilibrium. The introduction of amphoteric metal chloride and fluorine may lead to the production of a higher proportion of furanose. The addition of [BMIM]BF₄ and other reagents may inhibit the tautomeric conversion of monosaccharides. The fundamental data of tautomeric distribution of monosaccharide provides guidance for the selection and design of ionic liquids for biomass conversion.

Key words: monosaccharides, imidazolyl ionic liquids, NMR, tautomeric distribution