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- ItemSolvent effects on catalytic activity and selectivity in amine-catalyzed D-fructose isomerization(Amsterdam [u.a.] : Elsevier, 2022) Drabo, Peter; Fischer, Matthias; Emondts, Meike; Hamm, Jegor; Engelke, Mats; Simonis, Marc; Qi, Long; Scott, Susannah L.; Palkovits, Regina; Delidovich, IrinaRational 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.