NMR Insights on the Properties of ZnCl2 Molten Salt Hydrate Medium through Its Interaction with SnCl4 and Fructose

The solvent properties of ZnCl2 molten salt medium and its synergic effect with the Lewis acid catalyst, Sn4+, for biomass conversion, were investigated by nuclear magnetic resonance. The tautomeric distribution of fructose in the ZnCl2 molten salt medium was examined, and its effect for humins formation during the biomass conversion was evaluated. The ion complex composed by Sn4+ and Zn2+ indicated that there is a synergic catalytic effect between these two Lewis acid ions. C-13 NMR spectra of fructose in different ZnCl2 molten salt hydrate concentrations revealed that the concentration of beta-furanose and alpha-furanose tautomers, which lead to 5-HMF, were significantly decreased with increased salt concentration. Meanwhile the beta-pyranose tautomer, which is correlated with humins formation, was increased significantly.