Catalytic oxidation of 5-hydroxymethylfurfural into 2,5-diformylfuran using V-containing heteropoly acid catalysts

2,5-Diformylfuran (DFF) is an attractive and challenging compound that can be synthesized with good selectivity by the oxidation of bio-based 5-hydroxymethylfurfural (5-HMF) using specific catalysts. Vanadium-containing heteropoly acids (PMoV HPAs) are highly active oxidation catalysts whose activity can be tuned by changing vanadium(V) (V-V) content. This study reports the preparation of a number of PMoV HPAs with different V-V amount and type of outer-sphere cation and investigating their catalytic performance in 5-HMF-to-DFF conversion. The characterization of synthesized HPAs by simple instrumental methods (pH-measurement, potentiometry, and titration analysis) and NMR revealed retaining Keggin structure and increasing oxidation potential with rising V-V amount. The complete optimization of reaction conditions allowed one to reach a DFF yield of 92% using Co2H6P3Mo18V7O84 at 110 degrees C in water/MIBK for 90 min under atmospheric pressure. The described method of 5-HMF oxidation is based on using effective soft oxidants that can be easily recycled and reused at least five times without significant loss of catalytic activity.