Density functional theory study on the initial reactions of d-Xylose and d-Xylulose dehydration to furfural

The mechanism of the initial reactions in the acid-catalytic conversion of d-xylose/d-xylulose to furfural was studied with density functional theory. The reactions included mutual transformations among d-xylose, d-xylulose and the intermediate of 1,2-enediol. The catalytic performances of several acids including H₂SO₄, HNO₃, HCl, HBr and HI, and the solvent effects of water and THF (tetrahydrofuran) were studied. A simplified kinetic model of the d-xylose/d-xylulose-to-furfural conversion in water solvent was built, with the assumption that the conversion from 1,2-enediol to furfural was the rate-limiting step and could be treated as one-step reaction. The simulation can well fit the experimental regulation, which verifies the rationality of the model simplification. The dominant reaction pathways from d-xylose/d-xylulose to furfural were deduced based on the calculated energy barriers and corresponding reaction rate constants, with different acid catalysis and reaction mediums.