(237g) Unifying Mechanistic Analysis of the Primary Factors Controlling Selectivity in Fructose Dehydration By Acid Catalysts

US interest in biomass as an alternative energy source continues to increase in demand with growing political, economic and environment concerns associated with the consumption of fossil fuels. One potential route for converting cellulosic biomass to fuels is through the dehydration of fructose to produce 5-hydroxymethylfurfural (HMF), followed by the catalytic conversion of HMF to renewable fuels, such as dimethylfuran (DMF). Economically viable production of HMF from fructose requires high selectivities and yields. However, mechanistic aspects of fructose conversion to HMF are still unclear, making the design of catalysts that enable high yield HMF production difficult. Various reports have proposed different factors that control selectivity including the acid type, fructose tautomer distribution, and solvent type. In order to develop detailed insights into the factors that control HMF yields, we executed extensive kinetic analysis using a variety of solvent systems, reaction conditions, acid types and acid concentrations in a high-throughput reactor to determine the mechanism and selectivity controlling factors in fructose dehydration to HMF by homogeneous acid catalysts. Detailed NMR analysis of the relative distribution of fructose tautomers as a function of solvent type and temperature were also executed. Through these studies we strongly support the hypothesis that selectivity in fructose conversion to HMF is controlled by the equilibrium between the tautomeric forms of fructose in solution, by directly correlating HMF selectivity with the distribution of furanose and open-chain forms of fructose. We will describe the implication of these mechanistic insights in the context of the design of heterogeneous systems that allow for operation of this reaction with high selectivity in low boiling point solvents.