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

Abstract

The electrochemical behavior of 1,4-dinitrobenzene (PNB) in the aprotic solvent containing CO2 was investigated by using CO2 instead of proton donor to eliminate the interference of hydrogenation reaction. In the absence of CO2, the electrochemical behavior of PNB was a chemical reversible two-steps one-electron transfer process, but with the introduction of CO2, 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 CO2 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 CO2 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 13C NMR, 1H 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.