Revising the Role of a Dioxirane as an Intermediate in the Uncatalyzed Hydroperoxidation of Cyclohexanone in Water

The mechanism of the oxidation of cyclohexanone with an aqueous solution of hydrogen peroxide has been investigated. Experiments revealed the preliminary formation of an intermediate, identified as cyclohexylidene dioxirane, in equilibrium with the ketone, followed by formation of 1-hydroperoxycyclohexanol (Criegee adduct). Computational analysis with explicit inclusion of up to two water molecules rationalized the formation of the dioxirane intermediate via addition of the hydroperoxide anion to the ketone and revealed that this species is not involved in the formation of the Criegee adduct. The direct addition of hydrogen peroxide to the ketone is predicted to be favored over hydrolysis of the dioxirane, the latter in competition with ring opening to carbonyl oxide followed by hydration. However, dioxirane may account for the formation of the bis-hydroperoxide derivative.