2‐Hydroxyadipic Acid Production by Oxidation of 2‐Hydroxycyclohexanone with Molecular Oxygen

Abstract Oxidation of 2‐hydroxycyclohexanone (2‐HCO) which can be synthesized from both petroleum and biomass was investigated with heteropolyacids and oxygen as catalysts and oxidant, respectively. 2‐Hydroxyadipic acid (2‐HAA) was obtained in moderate yields, and H 4 PVW 11 O 40 gave the highest yield (39 %). 2‐HAA is a dicarboxylic acid expected to be a monomer, and this work is the first report for production of 2‐HAA by catalytic oxidation reactions. The oxidation of 1,2‐cyclohexanedione (CHDO), which is a potential intermediate of 2‐HCO oxidation, produced similar yield of 2‐HAA even without catalyst. The effects of catalyst amount (first order), oxygen pressure (almost zero order) and the addition of radical scavenger (no effect) on the 2‐HCO oxidation with H 4 PVW 11 O 40 catalyst were similar to those in a related case of 2‐methoxycyclohexanone oxidation to adipic acid with heteropolyacid catalyst. 2‐HCO is proposed to be oxidized to CHDO as a precursor of 2‐HAA in a similar mechanism to 2‐methoxycyclohexanone oxidation.