A kinetic study of alkaline hydrolysis of .BETA.-arylaminoacrolein.
作者:Machiko ONO、Reiko TODORIKI、Akihisa MITAKE、Miho YUKAWA、Yoshinobu GOTO、Shinzo TAMURA
DOI:10.1248/cpb.37.2902
日期:——
Alkaline hydrolysis of β-arylaminoacrolein (1), a vinylog of amides, was studied kinetically. The kinetics involved terms both first and second order in hydroxide ion. The first step of the reaction (rate constant k1) is an attack of hydroxide ion on the β-position of 1, and the tetrahedral intermediate formed was partitioned in two ways : one without the aid of hydroxide ion (k2(k1/k-1)), and the other with the aid of hydroxide ion (k3(k1/k-1)). The rate constants, k1, k2(k1/k-1) and k3(k1/k-1) were obtained for 12 substrates, and the activation parameters, ΔH≠ and ΔS≠, of each step were evaluated for 5 substrates. The k2/k-1 values decreased with increasing electron-withdrawing effect of aryl substituents. The differences of ΔHf between the intermediates and the starting materials were evaluated by molecular orbital (MO) calculatins. The results showed that k2 decreases with increasing electron-withdrawing effect of the substitutents. The second step of the second-order reaction, k2(k1/k-1), is partitioning of anionic intermediates catalyzed by water as a general acid. While the second step of the third-order reaction, k3(k1/k-1), for "typical" substrates is departure of the arylamino group from the anionic intermediates catalyzed by both hydroxide ion and water, that for β-(p-nitrophenylamino)acrolein (1j) is direct expulsion of p-nitroanilide ion from the dinegatively charged intermediate.
这项研究探讨了β-芳胺基丙烯醛(1)(一种酰胺的乙烯基类似物)的碱性水解动力学。研究发现动力学涉及羟离子的一级和二级项。
反应的第一步(速率常数k1)是羟离子对1的β位置的进攻,形成的四面体中间体有两种分解途径:
1. 不需要羟离子辅助的途径(k2(k1/k-1))
2. 需要羟离子辅助的途径(k3(k1/k-1))
研究对12种底物测定了速率常数k1、k2(k1/k-1)和k3(k1/k-1),并对其中5种底物评估了每个步骤的活化参数ΔH≠和ΔS≠。随着芳基取代基吸电子效应的增强,k2/k-1值降低。
通过分子轨道(MO)计算评估了中间体与起始物质之间的ΔHf差异。结果表明,随着取代基吸电子效应的增强,k2降低。
二级反应的第二步k2(k1/k-1)是水作为普通酸催化阴离子中间体的分解。对于"典型"底物,三级反应的第二步k3(k1/k-1)是在羟离子和水的共同催化下芳胺基团从阴离子中间体上离去,而对于β-(对硝基苯胺基)丙烯醛(1j),则是对硝基苯胺负离子直接从双负电荷中间体上消除。