THE INHIBITING EFFECTS OF TETRAALKYLAMMONIUM CATIONS ON SIMPLE HETEROGENEOUS ELECTRON-TRANSFER REACTIONS IN POLAR APROTIC-SOLVENTS
THE INHIBITING EFFECTS OF TETRAALKYLAMMONIUM CATIONS ON SIMPLE HETEROGENEOUS ELECTRON-TRANSFER REACTIONS IN POLAR APROTIC-SOLVENTS
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DOI：
10.1021/j100203a069
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发表时间：
1992-11-26
影响因子：
--
通讯作者：
OPALLO, M
中科院分区：
文献类型：
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作者：
FAWCETT, WR;FEDURCO, M;OPALLO, M
测定了在不同链长的四烷基铵盐存在下，亚硝基均三甲苯在碳酸亚丙酯中汞的电还原动力学数据，它们是电极电位和温度的函数。尽管标准速率常数随阳离子尺寸的增大而减小，但由于阳离子在四乙基铵和四辛基铵之间的变化，实验测定的活化热与阳离子无关。这些结果表明，四烷基铵离子吸附在电极上，形成了一层封闭层，其厚度随烷基链长度的增加而增加。电子向氧化还原中心的转移是通过隧穿该膜来实现的。对活化能的理论估计支持这一结论，并表明氧化还原反应发生在溶剂重组决定其大小的最大部分的区域。
Kinetic data for the electroreduction of nitromesitylene at mercury in propylene carbonate have been determined in the presence of tetraalkylammonium salts of varying chain length, both as a function of electrode potential and temperature. Although the standard rate constant decreases with increase in cation size, the experimental activation enthalpy is independent of the cation for variation in this ion from tetraethylammonium to tetraoctylammonium. These results indicate that the tetraalkylammonium ions am adsorbed on the electrode forming a blocking layer whose thickness increases with alkyl chain length. Electron transfer to the redox center takes place by tunneling through this film. Theoretical estimates of the activation enthalpy support this conclusion and suggest that the redox reaction occurs in a region where solvent reorganization determines the largest portion of its magnitude.