CC BY 4.0 UnportedDrabo, PeterFischer, MatthiasEmondts, MeikeHamm, JegorEngelke, MatsSimonis, MarcQi, LongScott, Susannah L.Palkovits, ReginaDelidovich, Irina2023-02-102023-02-102022https://oa.tib.eu/renate/handle/123456789/11370http://dx.doi.org/10.34657/10404Rational catalyst design and optimal solvent selection are key to advancing biorefining. Here, we explored the organocatalytic isomerization of D-fructose to a valuable rare monosaccharide, D-allulose, as a function of solvent. The isomerization of D-fructose to D-allulose competes with its isomerization to D-glucose and sugar degradation. In both water and DMF, the catalytic activity of amines towards D-fructose is correlated with their basicity. Solvents impact the selectivity significantly by altering the tautomeric distribution of D-fructose. Our results suggest that the furanose tautomer of D-fructose is isomerized to D-allulose, and the fractional abundance of this tautomer increases as follows: water < MeOH < DMF ≈ DMSO. Reaction rates are also higher in aprotic than in protic solvents. The best D-allulose yield, 14 %, was obtained in DMF with 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) as the catalyst. The reaction kinetics and mechanism were explored using operando NMR spectroscopy.enghttps://creativecommons.org/licenses/by/4.0540AmineD-alluloseD-fructoseD-glucoseIsomerizationNMRSolvent effectArticle