Effects Of PH And Buffer Capacity On Electrochemical Behavior Of Nitrobenzene And P-Aminophenol

Nitrobenzene（NB）and p-aminophenol（PAP）are both important chemical raw materials and intermediates in industrial production,and a variety of products with application value can be produced by redox.When electrochemical method is used to study the redox mechanism,changing p H and buffer medium can adjust the reaction path of NB on the electrode surface and affect the redox products of PAP.Cyclic voltammetry is an effective method to study proton coupled electron transfer（PCET）reaction.When the concentration of buffer solution is low and it can’t completely play a buffering role,the release and absorption of protons in PCET reaction will cause changes in peak shape and potential.In this paper,the effects of p H and buffer capacity on the electrochemical reduction of NB in aqueous solution were studied by cyclic voltammetry.The results show that the reaction path of NB can be adjusted by controling the buffer capacity.In the process of electrochemical reduction of NB,the reduction of NB in high concentration buffer solution follows the PCET reaction mechanism,and phenylhydroxylamine is generated by 4H⁺and4e^-transfer.When the concentration of buffer solution is low,NB produces a new reduction peak at a more negative potential,and a pair of new reversible redox peaks appear in the subsequent reverse scanning.We have proved through experiments that the appearance of new redox peak pairs is related to the reduction of NB at negative potential,and has nothing to do with solution p H and buffer solution concentration.We infer that NB generates stable free radical anions when the buffer is insufficient,and the free radicals are oxidized on the electrode surface,or some coupling reaction takes place to form a new redox peak.This reaction process involves only the gain and loss of electrons.In this paper,the electrochemical oxidation behavior of p-aminophenol was studied in acidic medium（acetic acid-sodium acetate）,neutral medium（sodium monohydrogen phosphate-sodium dihydrogen phosphate）and alkaline medium（Tris-HCl,sodium carbonate-sodium bicarbonate）.During the oxidation of PAP,protons will be released,which will be accepted by proton receptors in buffer solution.It is found that the cyclic voltammetric behavior of PAP in dilute buffer solution is complicated,and multiple redox peaks appear.In alkaline medium,we think that the new peak at the lower negative potential is caused by the amino group of PAP itself acting as proton acceptor,while in acidic and neutral medium,-NH₂is protonated and cannot accept protons,so this peak does not appear.In neutral and alkaline media,the corrected potential also has an oxidation peak with water molecules as receptors.The peak potentials of the two new peaks are not affected by the type and p H of the buffer solution,and the peak intensity is only related to the concentration of the buffer solution.Only when the amount of the buffer solution is added can it release/absorb the protons needed or generated by the electrochemical reaction can it play a sufficient buffering role.