Conversion of selected carbohydrates into furan aldehydes in aqueous media. Effect of cation structure of imidazolium ionic liquids on the selectivity phenomena

Abstract

This paper reports a study on the catalytic conversion of selected carbohydrates (glucose, xylose, fructose) to furan aldehydes: furfural and 5-hydroxymethylfurfural in water as solvent. The catalytic system consists of relatively weaker acidic hydrogen sulfate imidazolium ILs and strong protic Brønsted acid (H2SO4). All experiments were carried out at elevated temperatures (140–160 °C) in stainless pressure reactor under autogenic pressure. Studies have shown that the conversion of glucose, xylose and fructose was significantly depended on structural parameters of the ionic liquid used as a catalyst as well as the presence or absence of Brønsted acid used as a co-catalyst. This effect can be considered as a manifestation of specific synergism of acidic IL and Brønsted acid. The selectivity to furan aldehydes was high and usually exceed 90% regardless of carbohydrate and IL used in reaction. This may confirm the postulated thesis about the significant and beneficial impact of imidazolium ionic liquids on the selectivity to furfural and 5-hydroxymethylfurfural arising as a result of dehydration of carbohydrates.