Investigation on the electroreduction azo coupling mechanism of 1,4-dinitrobenzene in aprotic media containing CO2

The electrochemical behavior of 1,4-dinitrobenzene (PNB) in the aprotic solvent containing CO 2 was investigated by using CO 2 instead of proton donor to eliminate the interference of hydrogenation reaction. In the absence of CO 2 , the electrochemical behavior of PNB was a chemical reversible two-steps one-electron transfer process, but with the introduction of CO 2 , it was transformed into an irreversible 7-electrons transfer process. In the potential range between −0.3 V and −1.7 V, three reduction peaks were observed, and minutely studied by cyclic voltammetry, chronoamperometry, and in situ FT-IR spectroelectrochemistry methods, respectively. The results show that CO 2 is involved in five steps reaction during the electroreduction process of PNB, which plays a key role in PNB electroreduction azo coupling. The electroreduction azo coupling mechanism of PNB in the presence of CO 2 is exposed, which will provide a theoretical basis for precise control of the electroreduction degradation of dinitrobenzene. The product obtained by potentiostatic electrolysis is confirmed as 4,4′-dinitrosoazobenzene by 13 C NMR, 1 H NMR, MS and FTIR because of the instability of the final product, which is consistent with the mechanism inference. It has been well-proved that in situ FT-IR spectroelectrochemistry is an applicable method to study the wide range of complex electrochemical process.