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

The performance of DMSO for the dehydration of fructose to 5-hydroxymethylfurfural (HMF) in the presence and absence of Brensted acid has been theoretically investigated at G4 level in DMSO solution. The most stable form of fructose is (beta-D-fructofuranoses in DMSO solution. When Bronsted acid is present in the reaction system, H+ prefers to interact with DMSO other than fructose, forming [DMSOFI](+) 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, [DMSOFI](+) 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.