INTRA- AND INTER-MOLECULAR CATALYSIS AND HYDROGEN ISOTOPE EFFECTS IN THE IODINATION OF o-AND p-CARBOXYACETOPHENONE.
INTRA- AND INTER-MOLECULAR CATALYSIS AND HYDROGEN ISOTOPE EFFECTS IN THE IODINATION OF o-AND p-CARBOXYACETOPHENONE.
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邻-和对-羧基苯乙酮碘化中的分子内和分子间催化以及氢同位素效应。
DOI：
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发表时间：
1972
期刊：
影响因子：
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通讯作者：
J. Henshall
中科院分区：
文献类型：
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作者：
R. Bell;B. Cox;J. Henshall
测定了邻、对羧基苯乙酮及其氘化类似物的碘化速率。这些反应对碘来说是零级的，测量的速率代表乙酰基的电离速率。在邻位化合物的自缓冲溶液中，速率可完全归因于分子内质子从乙酰基向羧酸基的转移。在醋酸和吡啶缓冲液中，也有分子间质子转移到醋酸离子或吡啶的作用，这是对化合物检测到的唯一一种过程。分子内过程（kH/kD= 5·4）的氢同位素动力学效应明显大于任何分子间过程（kH/kD= 4·0）。研究了羧基苯乙酮的阴离子对硝酰胺分解和葡萄糖的催化作用。这导致对邻羧基苯乙酮中羧基的“真实”酸碱性质的估计，从而对分子内催化和分子间催化进行定量比较；在水溶液中，81%的未解离酸以环状互变异构体的形式存在。
Measurements have been made of the rate of iodination of o- and p-carboxyacetophenone and their deuteriated analogues. These reactions are of zero order with respect to iodine, the measured rate representing the rate of ionization of the acetyl group. In self-buffered solutions of the ortho-compound the rate can be attributed solely to intramolecular proton transfer from the acetyl to the carboxylate group. In acetate and pyridine buffers there is also a contribution from intermolecular proton transfer to acetate ion or pyridine, and this is the only type of process detectable for the para-compound. The kinetic hydrogen isotope effect for the intramolecular process (kH/kD= 5·4) is considerably greater than that for any of the intermolecular processes (kH/kD= 4·0). A study was also made of the catalytic effect of the anions of the carboxyacetophenones in the decomposition of nitramide and the mutarotation of glucose. This leads to an estimate of the ‘true’ acid–base properties of the carboxy-group in o-carboxyacetophenone, and hence to a quantitative comparison between intra- and inter-molecular catalysis; it also shows that in aqueous solution 81% of the undissociated acid exists as the cyclic tautomer.