Selective hydrogenation of 5-hydroxymethylfurfural and its acetal with 1,3-propanediol to 2,5-bis(hydroxymethyl)furan using supported rhenium-promoted nickel catalysts in water†
The high reactivity of the formyl group of 5-hydroxymethylfurfural (5-HMF) is problematic, because it leads to undesired oligomerization reactions. This is usually countered by working in dilute non-aqueous solutions. Here, we present a novel approach to convert concentrated aqueous solutions of 5-HMF to 2,5-bishydroxymethylfuran (BHMF), which is a prospective monomer for polyesters and self-healing polymers. Our approach is based on the protection of the formyl group of 5-HMF using acetalization with 1,3-propanediol. Hydrogenation is carried out using an optimized bimetallic Ni–Re catalyst supported on TiO2 at a carefully controlled pH, resulting in balanced rates of deprotection and hydrogenation and high BHMF yield. Under optimized conditions at a benign temperature of 40 °C, hydrogenation of concentrated solutions (10–20 wt%) of protected 5-HMF in water gave 81–89% yields of BHMF without having to resort to platinum-group metals such as palladium or platinum.