Reaction of Halogenonitrobenzenes with Electro-generated Superoxide Ion

The reaction of halogenonitrobenzenes (XNBs) with electrogenerated superoxide ion in N,N-dimethylformamide was studied electrochemically using cyclic voltammetry (CV) and controlled potential macro-electrolysis. It was shown in the CV that electro-generated superoxide ion reacts with all of the o- and p-isomers of iodo-, bromo-, and chloronitrobenzene in the dissolved oxygen medium. However the superoxide ion did not react with the other XNBs during CV. Controlled potential macro-electrolysis of oxygen in the presence of o- and p-bromonitrobenzene yielded the corresponding nitrophenols as the main products. The reaction mechanism via nucleophilic attack of the superoxide ion on the XNB, in the preference to an electron-transfer mechanism, is proposed.