Oxidation of cyclohexanediol derivatives with 12-tungstophosphoric acid-hydrogen peroxide system.

Oxidation of cyclohexanediol derivatives with 12-tungstophospholic acid-hydrogen peroxide system was investigated focusing on a reaction mechanism in the preparation of dicarboxylic acids from olefin because oxidative cleavage of vicinal diols would be a rate-determining step in oxidative cleavage of carbon-carbon double bonds. trans-1,2-Cyclohexanediol (DHC) was converted to adipic acid almost quantatively, while 1-hydroxy-2-methoxycyclohexane (HMC) gave a mixture of adipic acid, glutaric acid and monomethyl adipate. In the case of 1,4-cyclohexanediol, 4-hydroxy-cyclohexanone and many hyperoxidated products were obtained. Based on results for HMC, it is concluded that following route would be also reasonable in oxidative cleavage of vicinal diol with 12-tungstophospholic acid-hydrogen peroxide system: (1) first oxidation of vicinal diol to alpha-hydroxyketone, (2) nucleophilic attack of hydrogen peroxide attacks to carbonyl carbon, (3) Baiyer-Villiger rearrangement of dihydroxy-hydroperoxide to a cyclic ester, (4) hydrolysis and final oxidation to dicarboxylic acid.