Solvent-promoted selective hydroxymethylation of biomass-derived furan compounds

Valorization of biomass-derived industrially-accessible C5 furan compounds like furfural (FF) and furfuryl alcohol (FA) to bifunctionalized furan-based derivatives is of great importance to biorefinery processes, yet remains challenging. We report herein the catalytic hydroxymethylation of FA rather than the conventional hydrogenation of costly 5-hydroxymethylfurfural (HMF), giving high yield to 2,5-dihydroxymethylfuran (DHMF), a versatile intermediate. Using formalin/1,4-dioxane mixture as the solvent system, DHMF yield reaches 76.4% over Hβ zeolite at 60°C within 60 min, which considerably exceeding the yields in single formalin and the state-of-art reports on FF hydroxymethylation to HMF. The co-solvent 1,4-dioxane serves as a catcher of formaldehyde hydrate to access substrate FA and as a shield to restrain undesirable condensation reactions. Impressively, the developed protocol reveals excellent universality in boosting the hydroxymethylation of electrondrawing group-free furan molecules (e.g., furan, 2-methylfuran). The understanding of these solvation effects can be employed to manipulate the hydroxymethylation of biomass-related furan compounds.