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

Aerobic oxidative C−C bond cleavage reaction of lignin-derived 2-hydroxycyclohexanone to 2-hydroxyadipic acid, a potential monomer, was discovered. This new reaction was catalyzed by various substances, and phosphovanadotungstic acid was the best catalyst.

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 H₄PVW₁₁O₄₀ 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 H₄PVW₁₁O₄₀ 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.

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