停止-流动分光光度法研究铕(Ⅱ)与二甲酚橙快速电子转移反应动力学

STUDIES ON KINETICS OF THE ELECTRON TRANSFER REACTION BETWEEN Eu(Ⅱ)AND XYLENOL ORANGE BY STOP-FLOW METHOD

用停止-流动分光光度法研究了Eu^(2+)与二甲酚橙(XO)间快速电子转移反应的动力学规律。求得了速控步骤的动力学参数。如反应级数(n=2)、几个不同温度下的速率常数(k_(278K)=5.7×10~8L·mol^-·s^(-1),k_(s38K)=1.01×10~9L·mol^(-1)·s^(-1))、活化能(E=7.6×10~3J·mol^(-1)),以及指前因子(A=1.5×10^(10)L·mol^(-1)·s^(-1)),并判断出其为溶液中扩散控制型反应。根据实验现象与测试结果,提出了Eu^(2+)与XO的反应分别在Eu^(2+)相对过量和在XO过量时的反应机理,并判断了各反应步骤速率常数之间的相对关系。

The kinetics and mechanism of the reaction between Eu^(2+) and Xylenol orange(XO) in aqueous solution has been studied by means of stop-flow spectrophotometricmethod. The kinetic parameters of the rate-controlling step, i,e, reaction order (n=2), rate constant at various temperatures (k_(278K)=5. 7×10~8L·mol^(-1)·s^(-1),k_(338K)=1. 01×10~9L·mol^(-1)·s^(-1)…), activation energy (E=7. 6×10~3J·mol^(-1)) and preexponentialfactor (A=1. 5×10^(10)L·mol^(-1)·s^(-1)) have been determined. It has been established thatthe electron transfer reaction between Eu^(2+) and XO is a diffusion controlled reaction. The possible mechanisms of the reaction between Eu^(2+) and XO both in the pre-sence of excess XO and Eu^(2+) also have been suggested. The relation between the rateconstants of each step were estimated.