Continuous Flow Oxidation of Alcohols to Carboxylic Acids Using a Ternary Pd/C‐Pt/C‐Ru/C Catalyst and Molecular Oxygen. Application to the Synthesis of 2,5‐Frandicarboxylic Acid

A ternary metal catalyst system based on Pd/C‐Pt/C‐Ru/C and molecular oxygen is found to be very effective and robust in oxidizing alcohols to carboxylic acids. Using the ternary catalyst and a flow‐setup, the conversion of 5‐hydroxymethylfurfural (HMF, 1 ) to 2,5‐furandicarboxylic acid (FDCA, 2 ), a bioplastics precursor, proceeded quite rapidly with a residence time of 1 min at 120 °C under 0.28 MPa of molecular oxygen. Catalyst activity remains stable for at least 2 weeks, giving 66.8 g (60% yield) of the analytically pure FDCA ( 2 ). The ternary catalyst system combined with a flow setup is successfully applied to the rapid conversion of ordinary alcohols 3 to aromatic and aliphatic carboxylic acids 4 in good yields.