Kinetics and Mechanism of the Aminolysis of Phenyl and Methyl 4-Nitrophenyl Thionocarbonates
作者:Enrique A. Castro、Claudia Saavedra、José G. Santos、María I. Umaña
DOI:10.1021/jo990084y
日期:1999.7.1
alicyclic amines with the title substrates are subjected to a kinetic study in aqueous solution, 25.0 degrees C, ionic strength 0.2 (KCl), by following spectrophotometrically the release of 4-nitrophenoxide ion. Under amine excess, pseudo-first-order rate coefficients (k(obsd)) are found. For the reactions of phenyl 4-nitrophenyl thionocarbonate (1), linear plots of k(obsd) vs [NH] (NH is the free amine)
脂环族仲胺与标题底物的反应在25.0摄氏度,离子强度0.2(KCl)的水溶液中进行动力学研究,方法是分光光度法测定4-硝基苯氧根离子的释放。在胺过量下,发现伪一阶速率系数(k(obsd))。对于苯基4-硝基苯基硫代碳酸酯(1)的反应,除了与哌嗪鎓离子的反应外,还获得了k(obsd)对[NH](NH为游离胺)的线性图,该图显示了非线性的向上图。4-硝基苯基硫代碳酸甲酯(2)的氨解显示k(obsd)对[NH]的非线性图,但哌啶是线性的。1的布朗斯台德型图是线性的,斜率β= 0.25,表明四面体加成中间体(T(+/-))的形成(k(1)步骤)是速率决定的。对于2的氨解(哌啶除外),k(-)(1)大约为k(3)[NH]> k(2),其中k(-)(1),k(3)和k(2)分别是胺驱出,胺去质子化和离开基团从T(+/-)驱出的速率系数。对于2与哌啶的反应,k(-)(1)