THE SOLVENT AS H-ATOM DONOR IN ORGANIC ELECTROCHEMICAL REACTIONS - REDUCTION OF AROMATIC HALIDES
THE SOLVENT AS H-ATOM DONOR IN ORGANIC ELECTROCHEMICAL REACTIONS - REDUCTION OF AROMATIC HALIDES
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DOI：
10.1021/ja00532a023
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发表时间：
1980-01-01
影响因子：
15
通讯作者：
SAVEANT, JM
中科院分区：
文献类型：
--
作者：
MHALLA, F;PINSON, J;SAVEANT, JM
在芳族卤化物的电化学还原中阴离子自由基最初形成之后的第一步是CX键的断裂，产生中性的Ar·自由基。后一种物质经历三个同时发生的反应：从溶剂中提取氢原子以及在电极和/或从初始阴离子自由基中转移电子。这种三重竞争的定量分析允许人们预测内在（速率常数）和操作（浓度、搅拌速率、细胞几何形状）参数的影响。它是氘化水或溶剂掺入氘的结果可用作研究反应机理和确定特征速率常数的工具的基础。通过对 MeaSO 和乙腈中三种芳香族残基（9-蒽基、1-萘基和 4-氰基苯基）的氯、溴和碘衍生物的研究来说明这一点。结果表明，在每种情况下确实遵循了所提出的减少机制，并且可以评估三个并发步骤之间的竞争程度。使用独立获得的氯化合物阴离子自由基裂解值（通过循环伏安法或氧化还原催化），确定溴代和碘代衍生物的相应速率以及氢原子转移到三个芳香族自由基的速率和相应的氘同位素效应的大小。
The first step following the initial formation of the anion radical in the electrochemical reduction of aromatic halides is the cleavage of the CX bond leading to the neutral Ar· radical. The latter species undergoesthree concurrent reactions: H-atom abstraction from the solvent and electron transfer at the electrode and/or from the initial anion radical. The quantitative analysis of this threefold competitionallows one to predict the effect of the intrinsic (rate constants) and operational (concen-tration, stirring rate, cell geometry) parameters. It is the basis on which the results of deuterium incorporation by deuterated water or solvent can be used as a tool to investigate the reaction mechanism and to determine the characteristic rate constants. This is illustrated by the study of the chloro, bromo, and iodo derivatives of three aromatic residues (9-anthryl, 1-naphthyl, and 4-cyanophenyl) in MeaSO and acetonitrile. It is shown that the proposed reduction mechanism is indeed followed in each case and the degree of competition between the three concurrent steps can be evaluated. Using the values obtained independently (by cyclic voltammetry or redox catalysis) for the cleavagerate of the anion radicals of the chloro compounds, the corresponding rates for the bromo and iodo derivatives are determined as well as the rates of H-atom transfer to the three aromatic radi-cals and themagnitude of the corresponding deuterium isotope effects.