(426d) Effects of Chloride Ions in Acid-Catalyzed Biomass Dehydration Reactions in Polar Aprotic Solvents

The addition of polar aprotic co-solvents in acid-catalyzed biomass conversion processes can lead to enhanced reaction rates and selectivities compared to reactions in aqueous media. Further increases on reaction rates in co-solvent mixtures can be achieved through the use of inorganic salts, specifically chlorides. We will present fundamental reaction kinetics studies for the Brønsted acid-catalyzed dehydration of fructose to hydroxymethylfurfural (HMF) in the presence of catalytic concentrations (e.g., 5 mM) of chloride salts using three polar aprotic co-solvents: gamma-valerolactone; 1,4-dioxane; and tetrahydrofuran. We will present the effects of metal halides on this extensively characterized reaction, which serves as a model system to study the mechanisms behind observed solvent effects, for a variety of strong homogenous and heterogeneous acid catalysts, and salts in polar aprotic solvent mixtures with water. We show that significant increases in reactivity (e.g., 10-fold) and product selectivities (> 80% yields) were observed for the fructose conversion to HMF with the addition of chloride salts (e.g., KCl) in various mixtures of co-solvents with water. With the help of Ab initio molecular dynamics simulations, we also demonstrate that the effects of metal halides on reaction kinetics can be elucidated by the stabilization of the oxocarbenium ion and the protonated transition state via highly delocalized negative charge on Cl^-. We utilize these effects of polar aprotic solvents and chloride salts to accomplish high yields in versatile chemical production from biomass.