Aromatic reactivity. Part XXXV. Alkali cleavage of aryltrimethylstannanes: an unusual electrophilic aromatic substitution
Aromatic reactivity. Part XXXV. Alkali cleavage of aryltrimethylstannanes: an unusual electrophilic aromatic substitution
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芳香反应性。
DOI：
10.1039/j29670001036
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发表时间：
1967
期刊：
影响因子：
--
通讯作者：
D. Walton
中科院分区：
文献类型：
--
作者：
C. Eaborn;H. Hornfeld;D. Walton
用分光光度法测定了一系列X·C6H4·SnMe3化合物中芳基锡键在甲醇碱作用下的裂解速率。该反应的速率决定步骤可能是碳离子X·C6H4 -的分离，中间取代基的影响符合Hammett σ常数（σ= 2·18），而对取代基的影响则表现出异常模式。例如，不仅吸电子基团如p-CF3和p-Cl会加速，通常释放电子的基团如p-OMe和p-NMe2也会加速。对对取代基的影响与它们的σ1常数基本一致。讨论了与碱催化芳香族交换氢的类比，并比较了两种反应的取代基效应。根据解理的结果，对先前提出的氢交换异常的解释进行了检验。
We have measured spectrophotometrically the rates of cleavage by aqueous methanolic alkali of the aryl–tin bonds in a series of X·C6H4·SnMe3 compounds. In this reaction, the rate-determining step of which probably involves separation of the carbanion X·C6H4–, the effects of meta substituents are in accord with the Hammett σ constants (σ= 2·18), but the effects of para substituents show an abnormal pattern. For example, there is rate-acceleration not only by electron-withdrawing groups such as p-CF3 and p-Cl, but also by normally electron-releasing groups such as p-OMe and p-NMe2. For the para substituents, the effects are roughly in line with their σ1 constants.The analogy with base-catalysed aromatic hydrogen-exchange is discussed, and substituent effects in the two reactions are compared. An explanation previously advanced for the abnormalities in the hydrogen exchange is examined in the light of the results for the cleavage.