Electrode Reaction Kinetics, Structural Optimization And Application Of Triarylimidazole Derivatives As Electrochemical Organic Redox Mediator

Organic electrochemical synthesis achieves organic compounds by electron transferation, the using of oxidant and reductant is avoided, which is a green method.Direct C-H activation-functionalization has become a hot topic at present, and achieving direct C-H activation-functionalization by indirect electrochemical oxidation is one of the effective paths.In the previous work, our group designed and synthesized a series of triarylimidazole(TAI) derivatives which has properties of indirect redox mediator.They are confirmed to oxidate benzyl alcohol and benzyl ether successfully. However,the cation radical of triarylimidazole is not stable enough, may decompose at the presence of base, TAI mediator also has narrow application range.To solve these problems, this research mainly includes two aspects:(1) Electrode reaction kinetics investigation of triarylimidazole(TAI) redox mediator. The influence of electrolyte and concentration to the stability of redox mediator cation radical was investigated by cyclic voltammetry. Research shows that TAI mediator has better reversibility in low concentration of LiClO4/CH3 CN electrolyte. The electrode reaction kinetic performance of TAI redox mediator was investigated by cyclic voltammetry and AC impedance, calculated the diffusion coefficient, heterogeneous rate constant, and homogeneous rate constant for the oxidation of 4-methoxybenzyl, then compared with triarylamine mediator. The results show that TAI mediator has similar electrochemical performance and parameters to that of TBPA, has larger heterogeneous rate constant when using GC electrode as working electrode, has larger homogeneous rate constant for the oxidation of4-methoxybenzyl alcohol compared with TBPA. Further investigation shows that smaller oxidation potential difference between the mediator and 4-methoxybenzyl alcohol leads to higher reaction velocity of the oxidation for 4-methoxybenzyl alcohol to 4-methoxybenzaldehyde.(2) Structural optimization and application of triarylimidazole(TAI) redox mediator. The structure of the decomposition product of TAI mediator was identified by spectrum methods, the decomposition factors was analyzed, synthesized a new redox mediator based on [9,10-d]phenantroimidazole framework, the stability of redox mediator was improved. Based on this result, more types of reaction was attempted by using the improved redox mediator, the electrolysis condition was optimized. However, didn’t obtain ideal results.