Sulfuric Acid → (S)-2-Methoxycyclohexanone

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A 500-ml four-mouth flask equipped with a thermometer, dropping funnel, condenser, and stirrer was charged with 13.0 g (0.1 mol) of (S)-2-methoxycyclohexanol having an optical purity of 99.8% ee, 7 g of dichloromethane, and 30 g of 10% aqueous solution of sulfuric acid (30 mmol). The reactants were stirred at 20-25° C. The flask was further charged with 60 g of aqueous solution of sodium hypochlorite containing 12.1% effective chlorine over about 1 hour. Stirring was continued for 30 minutes. The reaction solution was analyzed by gas chromatography to confirm that the peak due to (S)-2-methoxycyclohexanol had disappeared. The reaction solution was given 2 g of sodium hydrogensulfite with stirring. It was confirmed that the reaction solution did not change potassium iodide starch paper into purple any longer. The reaction solution was extracted twice with 200 g of dichloromethane. The dichloromethane layers were combined together and washed with 30 g of 30% aqueous solution of sodium carbonate. After stirring at 20-25° C. for 1 hour, it was confirmed that the water layer had a pH higher than 7.5. The water layer was discharged, and the dichloromethane layer was washed with saturated aqueous solution of sodium chloride. Upon concentration and distillation, there was obtained 11.5 g (90 mmol) of (S)-2-methoxycyclohexanone. The chemical purity of this compound was 99.6%. One gram of this compound was placed in a glass ample and sealed, with the atmosphere therein replaced with argon. The ample was heated at a prescribed temperature for 60 hours. After cooling to room temperature, the ample was opened and the content was tested for optical purity. The results are shown in Table 2.

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