LAUSR

The "degradative condensation" of hexose, originated from the C-C cleavage of hexose and condensation of degraded-hexose-fragment, is one of the possible reaction pathways for the formation of humins in hexose dehydration to 5-hydroxylmethylfurfural (HMF). In this work, we report the impacts of several polar aprotic solvents on the degradative condensation of fructose to small-molecular carboxylic acids and oligomers (possible precursors of humins). In particular, we demonstrate a close relationship between the tautomeric distribution of fructose in solvents and the mechanism of degradative condensation. Typically, α-fructofuranose in 1,4-dioxane and acyclic open-chain fructose in THF favor the conversion of fructose to formic acid and oligomers, α-fructopyranose in GVL or NMP favors levulinic acid and oligomers, whereas β-fructopyranose in MIBK favors acetic acid and corresponding oligomers. This close correlation highlights a general understanding on the solvent-controlled formation of oligomers, which represents an important step toward the rational design of effective solvent systems for HMF production.