Study On The Factors Influencing The Proton Coupled Electron Transfer Electrochemical Behavior Of Phenol

Proton coupled electron transfer（PCET）reactions are widely present in the fields of chemistry and biochemistry,and the study of the mechanism of PCET is very important because it involves the order of proton transfer and electron transfer,and affects the mechanism and path of the reaction.Related researchers have found that in non buffered solutions,phenol（p K_a=9.99）exhibits a new voltammetric peak in the cyclic voltammogram when the p H of the solution approaches itself.They believe that the generation of a new peak represents a change in the oxidation pathway of phenol,that is,a transition from a proton electron co transfer（CPET）pathway to a proton transfer followed by electron transfer（PTET）pathway.However,we believe that it cannot be simply determined that the generation of new anode peaks is due to the opening of the PTET pathway,and the true reason for their formation should also be considered.Our experimental group has explained through cyclic voltammetry experiments of quinone（Q）and hydroquinone（QH₂）the reason for the formation of two anode peaks in the electrooxidation of hydroquinone in low buffer capacity solutions.The high potential anode peak is generated by the electrooxidation of hydroquinone at low p H,while the low potential new voltammetry peak is generated by the sudden change in p H near the electrode surface caused by the release of protons in the electrooxidation of hydroquinone,Rather than the generation of new substances.Similarly,when exploring the proton coupled electron transfer reaction（PCET）of phenol,experiments can also be attempted in low buffer capacity solutions.Due to the fact that some macromolecular phenolic compounds are not easily soluble in water,but are easily soluble in organic solvents.Therefore,we can investigate the effect of a mixed solvent of monohydrate and acetonitrile on the electrochemical behavior of phenol.Because water contains a large amount of hydroxyl groups that can form hydrogen bonds with hydroxyl groups in phenol and promote proton transport,we can also explore the effect of hydrogen bonds on the proton coupled electron transfer reaction of phenol.In this thesis,we used cyclic voltammetry to study the effect of proton receptors on the proton coupled electron transfer reaction of phenol.Through the cyclic voltammetry behavior of phenol in low concentration phosphate or carbonate buffer solutions,we found that the new anodic peak generated during the electrooxidation process of phenol is due to the depletion of the buffer material in the solution,and the water continues to accept protons,resulting in a sharp decrease in p H on the electrode surface,rather than the opening of the PTET pathway.Due to the fact that the peak position and current intensity of the new anode peak are only dependent on the p H of the solution,the concentration of the buffer solution,and its p K_a,and are not related to the phenolic anion,we once again prove that the new cyclic voltammetry peak cannot be used as a basis for inferring the new mechanism of PCET reaction.In addition,we found in acetonitrile solvent that after electrochemical oxidation of phenol to phenoxy radicals,it further reacts with water to generate p-benzoquinone and o-benzoquinone.When water and ethanol are added gradually to acetonitrile solvent containing phenol,phenol will be affected by hydrogen bonding effect during the electrooxidation process,leading to a shift in the anode peak potential towards low potential.