(608c) Understanding Solvent Effects In the Selective Conversion of Fructose to HMF: A Molecular Dynamics Investigation

Selective conversion of fructose to 5-hydroxymethyl-furfural (HMF) involves the participation of high-boiling solvents like dimethyl sulfoxide (DMSO). In order to replace DMSO with low-boiling solvents, it is imperative that we understand the effect of DMSO solvation in protecting HMF from further rehydration reactions and fructose from side reactions other than the dehydration to HMF. In the present work, molecular dynamics simulations of HMF and fructose in water and DMSO mixtures are carried out using the OPLS-AA force field. Radial pair distribution functions, coordination numbers and hydrogen-bond network between the HMF/fructose molecule and the solvent molecules are analyzed. We show preferential coordination of DMSO around certain carbon atoms of the HMF molecule and explain how this has a shielding effect, thus protecting HMF from further rehydration to levulinic acid and formic acid. We also show that, in the case of fructose, the presence of DMSO protects the molecule from side reactions that would lead to condensation or reversion products. However, the local 3-dimensional arrangement of water and DMSO molecules around the fructose molecule also reveals that the presence of DMSO molecules does not hamper the water molecules coming into the contact of the hydroxyl groups of fructose, which is required for the proton transfer step to initiate the dehydration reaction to HMF.