Performance of Dimethyl Sulfoxide and Brønsted Acid Catalysts in Fructose Conversion to 5-Hydroxymethylfurfural

Abstract

The performance of DMSO for the dehydration of fructose to 5-hydroxymethylfurfural (HMF) in the presence and absence of Brønsted acid has been theoretically investigated at G4 level in DMSO solution. The most stable form of fructose is β-D-fructofuranoses in DMSO solution. When Brønsted acid is present in the reaction system, H+ prefers to interact with DMSO other than fructose, forming [DMSOH]+ as the catalytically active species. For the dehydration of fructose to HMF, the catalytic performance of DMSO stems from the valence unsaturation of both S and O atoms and the unsaturated double bond of S═O, and the catalytic role of [DMSOH]+ originates from the valence unsaturation of both S and O atoms, as well as the H-mediated effect of −SOH group. For the initial and third water molecule release steps from fructose, both DMSO and [DMSOH]+ exhibit catalytic activity. Nevertheless, for the second water molecule release step from fructose, [DMSOH]+ displays catalytic activity, but DMSO does not. The active species [DMSOH]+ exhibits better catalytic performance than DMSO. The turnover frequency analysis shows that an intermolecular hydride transfer between DMSO or [DMSOH]+ moiety and fructose moiety is the rate-controlling step, which is associated with the C–H bond cleavage of the −CH2OH group of fructose moiety. The present study brings some insight into the role of DMSO for the acid-catalyzed dehydration of carbohydrates to HMF in DMSO solution.