Origin of the Regioselectivity in the Aldol Condensation between Hydroxymethylfurfural and Levulinic Acid: A DFT Investigation.

Our previous work demonstrated that hydroxide ion (OH) was able to catalyze aldol condensation reaction at room temperature between 5-hydroxymethylfurfural (HMF) and levulinic acid (LA). This work identified three primary reaction steps in this condensation reaction using density functional theory (DFT): (1) deprotonation of LA to generate LA ions, (2) LA ions addition at hydroxymethyl site of HMF, and (3) internal dehydration to form the condensation product. The reaction pathway through the C5 of LA forms a linear product that is favored with respect to both energy and configuration in all three elementary reaction steps.