Reactivity of Superoxide Ion with Ethyl Pyruvate, α-Diketones, and Benzil in Dimethylformamide

Article abstract of DOI:10.1021/jo00169a024

The dominant net reaction of O2(1-) radical with α-dicarbonyls such as ethyl pyruvate, 2,3-butanedione, and 2,3-pentanedione is proton abstraction from their enol tautomer.The rate-limiting step is first order for each reactant, the net products are enolate plus O2 and H2O2, and the second-order rate constants (k) are the same, within experimental error, for the three substrates (k = (4+/-1) x 10³ M^-1 s^-1).For the reaction of benzil (an α-dicarbonyl that cannot enolize) with O2(1-) radical the rate-limiting step is first order for each reactant, and the second- order rate constant (k) is (2+/-1) x 10³ M^-1 s^-1.The process appears to involve an initial nucleophilic addition by O2(1-) radical to carbonyl carbon, followed by a dioxetane closure on the other carbonyl carbon and reductive cleavage by a second O2(1-) radical to give two benzoate ions and O2.