The use of polar aprotic solvents in acid-catalyzed biomass conversion reactions can lead to improved reaction rates and selectivities. We show that further increases in catalyst performance in polar aprotic solvents can be achieved through the addition of inorganic salts, specifically chlorides. Reaction kinetics studies of the Brønsted acid-catalyzed dehydration of fructose to hydroxymethylfurfural (HMF) show that the use of catalytic concentrations of chloride salts leads to a 10-fold increase in reactivity. Furthermore, increased HMF yields can be achieved using polar aprotic solvents mixed with chlorides. Ab initio molecular dynamics simulations (AIMD) show that highly localized negative charge on Cl− allows the chloride anion to more readily approach and stabilize the oxocarbenium ion that forms and the deprotonation transition state. High concentrations of polar aprotic solvents form local hydrophilic environments near the reactive hydroxyl group which stabilize both the proton and chloride anions and promote the dehydration of fructose.
Bibliographical noteFunding Information:
This material is based upon work supported in part by the Great Lakes Bioenergy Research Center, U.S. Department of Energy, Office of Science, and Office of Biological and Environmental Research under Award Numbers DE-SC0018409 and DE-FC02–07ER64494. W.A.E. and R.M.R. acknowledge funding from the Department of Energy, Office of Basic Energy Sciences, Chemical Sciences, Geosciences, and Biosciences Division, and Catalysis Sciences Program under grant number DE-SC0016192. Further support was provided in part by the National Science Foundation Engineering Research Center for Biorenewable Chemicals (CBiRC; https://www.cbirc.iastate.edu) under Award No. EEC-0813570. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation. J.A.D. was supported by the U.S. Department of Energy, Office of Basic Energy Sciences (DE-SC0014058). The authors acknowledge the Environmental Molecular Sciences Laboratory (EMSL) and the Minnesota Supercomputing Institute (MSI) at the University of Minnesota for the computational resources to carry out the simulations.
© 2019, The Author(s).