Catalytic Dehydration of Fructose into 5-Hydroxymethylfurfural by a DMSO-like Polymeric Solid Organocatalyst

Novel polymeric solid catalysts, Au@(polythiophene-polythiophene oxides) (Au@ PTh-PThOx, x= 1-2), are prepared by chemical over-oxidative polymerization of thiophene in the presence of Au nanoparticles. These organocatalysts show significantly higher activity than their liquid analogs (i.e., DMSO, a frequently-used solvent and catalyst) for the catalytic dehydration of fructose into 5-hydroxymethylfurfural (HMF) and exhibit a complete inhibiting effect on HMF rehydration to undesired levulinic acid in low-boiling solvents. We demonstrate that the sulfoxide (-SO) group in Au@ PTh-PThOx is more active than the sulfone (-SO2) group, although the formation of the former could be maximized by lowering the concentration of surfactant or improving the concentration of oxidant used in catalyst preparation. The highest HMF yields of 72.6% and 39.7% are achieved over Au@ PTh-PThO catalyst in 1,4-dioxane and water, respectively. This catalyst could be completely recycled for use in water without activity loss.