Study On Electron Transfer And Proton Transfer Of Aromatic Nitro Compounds By In FT-IR Spectroelectrochemistry

In this report, reduction methods and development of aromatic nitro compounds were reviewed firstly. And then a detailed description on the the electrochemical reduction of aromatic nitro compounds was given also.Cyclic voltammetry (CV), IR spectroelectrochemistry cyclic voltabsorptometry (CVA),derivative cyclic voltabso-rptometry (DCVA) technique and reconstructed i-E curves were used to investigate the electrochemical reduction process of nitrobenzene(NB) and 1,4-dinitrobenzene (PNB) in aprotic media. In addition, the electron transfer and proton transfer mechanism of 1,4-dinitrobenzene were studied through the methods mentioned in the presence of proton donors mixed media. The paper mainly included the following research works.1. The electrochemical reduction behavior of nitrobenzene and 1,4-dinitrobenzene was studied in aprotic media. The results showed that electrochemical reduction of nitrobenzene was provided with the characteristics of single-electron reaction. However, The CV of 1,4-dinitrobenzene showed two coupled redox waves, suggested that 1,4-dinitrobenzene was reversibly reduced in two - step one -electron transfer. A series of IR absorption bands at 1348;1525; 1232 and 1055 cm-1 tracing to NB and NB- were observed. In addition, a series of IR absorption bands at 1549; 1056; 1210; 1356 and 1464 cm-1, tracing to PNB; PNB- and PNB2- were observed clearly in the 3D spectra. What is more, the electrochemical reduction mechanism was given intuitively though analyzing cyclic voltabsorptometry, derivative cyclic voltabsorptom -etry and reconstructed i-E curves. The mechanism can be expressed as:NB(?)NB·-; PNB(?)PNB·-(?)PNB2-.2. Addition of D2O or C2H5OH to CH3CN have a marked effect on the electrochemical behavior of PNB. It is found that (no more than 5%D2O or 20% C2H5OH) the bands at 1356 and 1464 cm-1, which are traced the absorption of PNB2-, shift to higher frequency in the light concentration of proton donors. The fact that the IR band at 1210 cm-1, traced the absorption of PNB·-, not only take place red shift, but also get wider. The results suggest that hydrogen-bonding is formed between the electrochemical products, PNB·-, PNB2- and proton donors in the concentration. It is well-proved that the dianion (PNB2-) as a good hydrogen-bonding acceptor is much stronger than the anion radica (PNB·-), and much easier to form hydrogen-bonding with proton donors than the anion radica (PNB·-). It is estimated that one PNB·-combines with about 2.3 D2O molecular and 1.98 C2H5OH to form hydrogen-bonding by using electrochemical parameters, respectively. The electrochemical behavior of 1,4-dinitrobenzene is changed obviously when the concentration of heavy water and ethanol reach to 7% and 30%, respectively. The result of forming aromatic nitroso is supported by the fact that two new IR absorption bands at 1149 and 1587 cm-1 appear. In other words,1,4-dinitrobenzene has been reduced into aromatic nitroso compound in proton donors mixed media with high concentration of heavy water or ethanol.3 The electrochemical reduction behavior of 1,4-dinitrobenzene is a more complex process in the CH3CN-DCl mixed solvent. In the light concentration of DCl, there is no significant effect on the electrochemical. However, the electrochemical reduction is significantly different with increasing concentration of DCl. FT-IR 3D spectra is analyzed through CVA and DCVA techniques.1,4-dinitrobenzene is reduced to p-nitrophenylhydroxylamine in a single four-electron reduction step.