Study On Reduction Mechanism Of Monochloronitrobenzene Based On GC And Ag Electrode

Chloronitrobenzene compound is an important raw material in the chemical industry,primarily used in the production of dyes,pesticides,rubber chemicals,pharmaceuticals,preservatives and other products.These compounds are with durability,stability and do extremely serious harm to the environment and human health.They are highly toxic and can cause methemoglobinemia,also with weak carcinogenic,mutagenic effect.They have been listed as the priority control pollutant in many countries in the world.Therefore,how to effectively remove chlorinated nitrobenzene comounds has become an important issue.In this study,the electrochemical reduction of three kinds of monochlorobenzenes was investigated by cyclic voltammetry in N,N-dimethylformamide solution by using different electrode materials(GC and Ag electrodes).The electrochemical reduction mechanism of chloronitrobenzene was discussed.In this study,the electrolysis experiment of p-chloronitrobenzene was carried out in the aprotic solvent and in the presence of proton donor by using Ag electrode as the working electrode.It was found that p-chloronitrobenzene could be completely converted under different solvent conditions to produce p-chloroaniline,azobenzenes and other products.The electrolytic product depends on the solvent properties:the aprotic solvent is not conducive to the formation of the main product,and the presence of the proton donor contributes to the formation of the product of hydrogenation reduction,p-chloroaniline and azobenzene.The electrochemical reduction mechanism of p-chloronitrobenzene was proposed by analyzing the intermediates.The main contents of the study include:The electrochemical reduction characteristics of o-nitrobenzene,m-nitrobenzene and p-chloroaniline on GC and Ag electrodes were investigated in N,N-dimethylformamide solution.Through the cyclic voltammetry curve analysis,it was found that the presence of chlorine substituents had some influence on the catalytic performance of nitrobenzene at the electrode,and that the position of the chlorine substituents was different and the degree of influence was different.M-chloronitrobenzene,p-chloronitrobenzene and nitrobenzene have two reversible reduction peaks on both Ag and GC electrodes,presumably two groups of redox couple.And the reduction potential of the same pollutant on the two electrodes of Ag and GC is almost coincident with each other,so that the Ag electrode does not exhibit the catalytic reduction property compared to the GC electrode.O-chloronitrobenzene on the GC electrode also appeared two reversible reduction peaks,but in the Ag electrode shows three reduction peaks,presumably three reduction process.While the p-chloroaniline did not show any reduction peak on both electrodes,suggesting that the dechlorination reaction exceeded the potential window range,which was consistent with the results of the reduction of the chloronitrobenzene.The position of the oxidation peak relative to the first reduction peak can be determined by controlling the potential after the first reduction peak and before the start of the second reduction peak.Through the cyclic voltammetry curve of the multi-cycles sweep of each pollutant,it was found that a new reduction peak appeared before the original first reduction peak appeared,except that the peak shape of the first circle was repeated in the second lap scan.In this study,we investigated the constant potential electrolysis process of p-chloronitrobenzene on the presence of(DMF),weak proton donor(DMF + H2O),strong proton donor(DMF + acetic acid),three different systems under Ag electrode catalysis.It was found that the presence of proton donor(acetic acid and water)could further activate the catalytic reduction activity of p-chloronitrobenzene on Ag electrode,and promote the positive shift of reduction potential(110 mV,225 mV),and had a significant effect on the reaction mechanism.From the aprotic solvent(DMF)to the weak proton donor(DMF + H2O),the reaction was carried out in the production of p-chloroaniline and azobenzene compounds in two directions at the same time.The conversion rates were 40%and 55%respectively.And then to the presence of strong proton(DMF + acetic acid),clearly showing the formation of azobenzene compounds,the conversion rate was up to 85%.The electrochemical reduction mechanism of p-chloronitrobenzene on Ag electrode was studied by analyzing the electrolytic product.In this study,we first discussed the reduction mechanism of chloronitrobenzene on the inert and catalytic electrode surface,and it is expected to provide guidance for the electrochemical reduction and removal of chloronitrobenzene,and also of great significance for the electrochemical synthesis of p-chloroaniline and azobenzene compounds.