Analytical Sciences

Evaluation of the Kinetic Parameters of First-Order Reactions Following Charge Transfer by Applying a Long-Path-Length Spectroelectrochemical Technique

Jingdong ZHANG, Shouzhuo YAO, Lihua NIE, and Wanzhi WEI *

College of Chemistry and Chemical Engineering, Hunan University, Changsha 410082, P. R. China

A long-path-length spectroelectrochemical technique was developed for investigating the EC mechanism and evaluating the kinetic parameters under a semi-infinite condition. The chronoabsorbances were obtained by a digital simulation method. Simulated results showed that the shapes of A-t curves are markedly dependent upon the relative values of the molar absorptivities of spieces A, B and C. When e_A=0, e_B/ e_C < = 5 or e_C=0, 0 = < e_A/ e_B < 0.5, the system absorbance passes through a maximum (A_t^max) interestedly. While e_B=0, 0.2 = < e_A/ e_C = < 1, there appears a minimum (A_t^min). Either A_t^max or A_t^min is closely related to the chemical reactions following charge transfer. When there is A_t^max at moment t_max in the A-t curve, increasing the value of the first-order rate constant (k₁) causes A_t^max and t_max to decrease; while increasing the diffusion coefficient (D_B) for species B causes A_t^max to increase, but t_max to decrease. This opposite effect enables us evaluate k₁ and D_B both simultaneously and precisely. The elctrooxidation of p-aminophenol in an acid aqua solution was experimentally investigated by a long-path-length spectroelectrochemical technique. The pseudo first-order rate constant and the diffusion coefficient for the electrooxidized intermediate quinone imine were successfully evaluated by this method.

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