Autocatalytic dehydration of xylose to furfural was studied in pure aqueous and monophasic organic/water mixtures to determine the effect reaction media and conditions have on conversion and yield. This study identified that the severity (R o ) of the reaction and polarity, as determined by the Hansen Solubility Parameter, δ P , strongly correlate with xylose conversion and furfural yield. Increasing the R o and δ P increased both conversion and yield in pure aqueous and organic/water mixtures of sulfolane, γ-butyrolactone, γ-valerolactone, γ-hexalactone, and tetrahydrofuran. Additionally, it was found that at a specified R o and δ P , similar conversions and yields were achieved using different combinations of time, temperature, and solvent mixture. Using principal component analysis and projection to latent structures, a semi-empirical model was developed that provided estimates of xylose conversion and furfural yield over a range of experimental R o and δ P values.Furfural has been recognized as an important building block for fuels, solvents, and other value-added chemicals, [1] and numerous recent publications have focused on optimizing furfural production from model sugars and lignocellulosic biomass. The use of organic solvents for xylose dehydration reactions has recently gained interest due to faster reaction rates [2] and the higher furfural yields obtained, which have been reported as high as 80 % in biphasic systems. [3] Solvent selection has been identified as an important reaction variable with mentions of solvent polarity [4] and the number of oxygen containing groups [5] being potential explanations as to why solvents improve furan yields, but currently no systematic method for solvent selection exists. Researchers have previously used Kamlet-Taft theory [6] or Hansen Solubility Parameters (HSPs) [7] to explain differences in selectivities, conversions, and yields; however, the HSP parameters (dispersion (δ D ), polarity (δ P ), and hydrogen bonding (δ H )) are functions of both solvent mixture and temperature, [8] which often times are not considered.This work aims to bridge the gap between xylose conversion, furfural yield, and solvent properties to guide solvent selection in monophasic, autocatalytic systems. Previous research has explored acid-catalyzed reactions in organic solvent mixtures for both monophasic and biphasic systems. [3,9] In biphasic systems using aluminium sulfate as the catalyst, Yang et al. hypothesized that as the polarity of a solvent increases, furfural yields increase in γ-valerolactone (GVL), methyl isobutyl ketone, tetrahydrofuran (THF), and 2-methyltetrahydrofuran; [10] however, no direct measure of solvent polarity was provided.Although acid catalysts increase the rate of reaction, furans can be produced through an autocatalytic process (Scheme 1), with the mechanism initiated by the formation of hydronium ions in high temperature water. [11] Additionally, formic acid, a degradation product, has been shown to contribute to the reaction activity. [12] Previous pu...
