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Alumina catalyzes the Baeyer–Villiger oxidation of cyclohexanone, using 70 wt.% aqueous or anhydrous hydrogen peroxide as oxidant. The best methodology was to carry out the reaction in ethyl acetate under azeotropic water removal at 90 °C, and a molar ratio cyclohexanone:oxidant of 1:4. Under these conditions, the conversion was 53% with a selectivity of 98% for ɛ-caprolactone. The weak and strong acid sites of alumina were correlated with the substrate conversion and hydrogen peroxide consumption for the Baeyer–Villiger oxidation. It is shown that the weak acid sites, which activate hydrogen peroxide for the catalytic epoxidation of nucleophilic olefins, are also responsible for the Baeyer–Villiger oxidation. Stronger acid sites, however, also participate in the Baeyer–Villiger oxidation, by activation of the carbonyl group. The interaction of the carbonyl group with strong acid sites also reduces the hydrogen peroxide decomposition. |
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