Selective oxidation of 5-hydroxymethyl-2-furaldehyde to furan-2,5-dicarboxaldehyde by catalytic systems based on vanadyl phosphate

The selective oxidation of 5-hydroxymethyl-2-furaldehyde (HMF) to furan-2,5-dicarboxaldehyde (FDA) has been studied under different conditions, in terms of reaction temperature, oxidant agent (air, oxygen and their pressure), type of solvent (water, organic), in the presence of heterogeneous catalysts based on VOPO4·2H2O (VOP). The attempt of obtaining in a one-pot reaction FDA from fructose passing through HMF as an intermediate product failed both in water and in a mixed water/methyl isobutyl ketone (MIBK) medium. The best performances in the direct oxidation of HMF to FDA have been obtained when VOP and N,N-dimethylformamide (DMF) were used as a heterogeneous catalyst and a reaction medium, respectively, under mild conditions (100 °C and room pressure of O2). Productivity up to 8.13 mmol of FDA/(g catalyst h) was achieved with 95% selectivity at low HMF conversion. The modification of the heterogeneous catalysts, obtained by partial substitution of VO3+ with different metal cations (Fe3+, Cr3+, Ga3+, Mg2+, Cu2+ and Pd2+), did not cause any improvement on the performances in this reaction.