Acid-Catalyzed Conversion of Xylose in 20 Solvents: Insight into Interactions of the Solvents with Xylose, Furfural, and the Acid Catalyst

Abstract

In this study, the acid-catalyzed conversion of xylose to furfural was investigated in 20 solvents ranging from water, alcohol, ketones, furans, ethers, esters, hydrocarbons, and aromatics with the aim to understand their involvement in each step from xylose to furfural. Compared with water, alcohols can stabilize the reactive intermediates, promote the formation of furfural, and slow its degradation with prolonged reaction times. Iso-propanol and 2-butanol can direct the conversion of xylose to levulinic esters via transfer hydrogenation catalyzed by a Bronsted acid catalyst. The other solvents with the carbonyl groups (i.e., ketones) or conjugated π bonds (e.g., furan) react with both xylose and furfural. Either xylose cannot make its way to furfural or furfural cannot survive for long in these solvents. In ethers, hydrocarbons, and aromatics, the formation of furfural is quick but so is the degradation of furfural due to the aprotic properties of these solvents. In an ester like methyl formate, xylose ...