Oxidation with metal oxides—VIII: Oxidation of bisphenylhydrazones of 1,2-diketones with nickel peroxide

The nickel peroxide oxidation of bisphenylhydrazones of 1,2-diketones gives rise to a variety of products such as bisphenylazoolefins, phenylazopyrazoles and triazoles, depending on the reaction conditions. Thus, glyoxal bisphenylhydrazone in benzene at room temperature gave bisphenylazoethylene5a, whereas methylglyoxal bisphenylhydrazone gave a mixture of bisphenylazoolefin10a and phenylazopyrazole14a. The oxidation of phenylglyoxal bisphenylhydrazone, on the other hand, gave a mixture of the triazole33 and a tetraazapentalene derivative40. Reasonable mechanisms for the formation of the various oxidation products have been suggested.