Effect of Electron-Donating Groups on the Electrochemical Degradation of Aromatic Nitro Compounds in Aprotic Media Containing CO2

Abstract

The electrochemical degradation of p-nitrochlorobenzene in aprotic media containing CO2 is reported. Little is known about the effects of electron-donating groups on electrochemical degradation of aromatic nitro compounds. Accordingly, electrochemical behavior of nitrobenzene (NB), para-nitrotoluene (PNT), and para-nitroanisole (PNA), in an aprotic solvent containing CO2, was investigated by cyclic voltammetry (CV), in situ Fourier transform infrared (FT-IR) spectroscopy, and potenstiostatic electrolysis. It was established that their electrochemical reduction was an irreversible four-electron transfer process. Based on cyclic voltabsorptometry (CVA), derivative cyclic voltabsorptometry (DCVA), and chronoamperometry (CA), a mechanism of electroreduction of aromatic nitro compounds in the presence of CO2 was proposed. The products of potenstiostatic electrolysis, in the presence of CO2, were characterized by X-ray single-crystal diffraction, 13C NMR, and 1H NMR. NB and PNT gave only the corresponding azo compound with a 99% conversion rate. However, the conversion rate of PNA was lower (78%) due to the effect of the strong electron-donating methoxy group. The intermediate reduction product 4,4′-dimethoxyazoxybenzene was formed along 4,4′-dimethoxyazobenzene. In the process, CO2 was converted to CO32–. This constitutes a new way of carbon sequestration.