Kinetic Study of the Aminolysis and Pyridinolysis of <i>O-</i>Phenyl and <i>O</i>-Ethyl <i>O</i>-(2,4-Dinitrophenyl) Thiocarbonates. A Remarkable Leaving Group Effect
作者:Enrique A. Castro、María Cubillos、Margarita Aliaga、Sandra Evangelisti、José G. Santos
DOI:10.1021/jo035451r
日期:2004.4.1
The smaller pKa0 value for the reactions of SA amines with 2 than with O-ethyl S-(2,4-dinitrophenyl) dithiocarbonate (pKa0 = 9.2) is explained by the greater nucleofugality from T⧧ of 2,4-dinitrophenoxide (DNPO-) relative to the thio derivative. The stepwise reactions of SA amines with 1 and 2, in contrast to the concerted mechanisms for the reactions of the same amines with the corresponding carbonates
一系列仲脂环族(SA)胺与O-苯基和O-乙基O-(2,4-二硝基苯基)硫代碳酸酯(分别为1和2)以及一系列吡啶与前一种底物的反应在25.0°C的水中进行离子动力学研究,离子强度为0.2 M(KCl)。在胺超过底物过量的情况下,所有反应都遵循假一级反应动力学,并且在胺中是一级反应。该布朗斯台德型绘图是双相的,斜率(在高μ ķ一个的β)1 = 0.20为SA胺与反应1和2和β 1 = 0.10的pyridinolysis1,用斜率(在低p- ķ一个)的β 2 = 0.80,SA胺与反应1和2和β 2 = 1.0的pyridinolysis 1。曲率中心处的p K a值(p K a 0)分别为7.7、7.0和7.0。这些结果与两性离子四面体中间体(T⧧)的存在以及速率确定步骤随胺碱性的变化而变化是一致的。较大的p ķ一个0为的pyridinolysis值1相比,对于2(p K a 0 = 6.8)和SA胺与1相对于2的反应中较大的p