HETEROGENEOUS AND HOMOGENEOUS ELECTRON TRANSFERS TO AROMATIC HALIDES - ELECTROCHEMICAL REDOX CATALYSIS STUDY IN THE HALOBENZENE AND HALOPYRIDINE SERIES
HETEROGENEOUS AND HOMOGENEOUS ELECTRON TRANSFERS TO AROMATIC HALIDES - ELECTROCHEMICAL REDOX CATALYSIS STUDY IN THE HALOBENZENE AND HALOPYRIDINE SERIES
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DOI：
10.1021/ja00507a002
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发表时间：
1979-01-01
影响因子：
15
通讯作者：
SAVEANT, JM
中科院分区：
文献类型：
--
作者：
ANDRIEUX, CP;BLOCMAN, C;SAVEANT, JM
卤代苯类和卤代吡啶类化合物发生两电子不可逆还原裂解。它涉及到假定的阴离子自由基中间体Arx-·(k|Sl或<；JCRŧ104 S-1)的快速分解。和中性自由基Ar的瞬时形成。比起始分子更容易还原。除Phi外。电化学反应受初始电子转移步骤的动力学控制。电化学技术的标准应用提供了转移系数和正向电子转移速率常数，但没有提供关于标准电位和标准速率常数的信息。通过对电化学还原均相氧化还原催化剂的动力学分析，可以确定后者的量。讨论了以下问题：均相电子转移的活化与扩散控制；阴离子自由基作为实际反应中间体的存在与碳-卤键的同时电子转移和断裂；均相电子转移与非均相电子转移之间的关联；标准电势和标准速率常数的测定；结构与电子转移热力学和动力学之间的关系。与分子大小相似的芳香族和杂芳族化合物相比，电子转移的显著缓慢意味着，除了溶剂重组外，由于从起始分子向阴离子自由基传递时碳-卤键的伸展，还意味着显著的内部重组。
Halobenzenes and halopyridincs undergo a two-electron irreversible reductive cleavage. It involves fast decomposition of the assumed anion radical intermediate, ARX-·(k| Sl or< jcr ŧ 104 s-1). and transient formation of a neutral radical, Ar. easier to reduce than the starting molecule. With the exception of Phi. the electrochemical reaction is under the kinetic control of the initial electron transfer step. Standard application of the electrochemical techniques provides the transfer coefficients and the forward electron transfer rate constants but no information about the standard potentials and the standard rate con-stants. The latter quantities can be determined through the kinetic analysis of homogeneous redox catalysts of the electrochemical reduction. The following points are discussed: activation vs. diffusion control of the homogeneous electrontransfer; existence of the anion radical as an actual reaction intermediate vs. simultaneous electron transfer and breaking of the carbon-halogen bond; correlation between homogeneous and heterogeneous electron transfers; determinationof the standard potentials and the standard rate constants; relationships between structure and electron transfer thermodynamics and kinetics. The remarkable slowness of the electron transfer as compared to aromatic and heteroaromatic compounds of similar molecular size implies, besides solventreorganization, a significant internal reorganization due to stretching of the carbon-halogen bond when passing from the starting molecule to the anion radical.