2,3,5,6-四溴-对苯醌与米氏碱氢负离子转移反应的反应动力学及机理(英文)

Kinetics and Mechanism of Hydride Transfer Reaction between Michler's Hydride and 2,3,5,6-tetrabromo-p-benzoquinone

应用分光光度法研究了有机溶剂中米氏碱的2,3,5,6 四溴 对苯醌氧化反应的动力学与反应机理,以及反应的溶剂效应与压力效应.结果表明:该反应是对每种反应物均为一级的二级反应,为包含电荷转移复合物中间体的电子 质子 电子转移的多步反应.该反应的活化体积为-34cm3·mol-1,显示从反应物到过渡态体系的极性增加较大.不同溶剂中的反应速率大小依次为二氯甲烷,乙氢,丙酮.以N,N 甲基 对甲苯胺为模型物,从机理上探讨了产生溶剂效应与压力效应相异的原因.

The kinetics of oxidation of Michler's Hydride with 2,3,5,6-tetrabromo-p-benzoquinone was investigated spectrphotometrically. The reaction followed a second-order rate law with first order with respect to each reactant. It was found that the reaction proceeded faster in dichloromethane than in acetonitrile and acetone. The formation of charge-transfer complex was observed at low temperatures. The results support a general mechanism with stepwise electron-proton-electron transfer through a charge-transfer complex. Intermediate N,N-dimethyl-p-toluidine was chosen as a model compound for insight into the reaction mechanism. From the pressure dependence of the rate, the activation volume was estimated to be -34 cm^(3)·mol^(-1). This large-negative activation volume indicates that a step with a large polarity increase is involved from the initial to the transition state. The discrepancy between the results of pressure effect and solvent effect was discussed.