Kinetics and Mechanism of the Aminolysis of <i>O</i>-Aryl <i>S</i>-Methyl Thiocarbonates
作者:Enrique A. Castro、Margarita Aliaga、José G. Santos
DOI:10.1021/jo047742l
日期:2005.4.1
the reactions of SA amines with 3. The magnitude of the slopes indicates that both aminolyses of 1 are governed by stepwise mechanisms, through a zwitterionic tetrahedral intermediate (T±), where expulsion of the nucleofuge from T± is the rate-determining step. The values of the Brønsted slopes found for the aminolyses of thiocarbonates 2 and 3 suggest that these reactions are concerted. By comparison
仲脂环族(SA)胺和喹核苷(QUI)与4-硝基苯基和2,4-二硝基苯基S-甲基硫代碳酸酯(分别为1和2)以及SA胺与2,3,4,5,6的反应在水溶液中,25.0°C和0.2 M(KCl)的离子强度下对-五氟苯基S-硫代碳酸甲酯(3)进行动力学研究。硫代碳酸盐的反应中1,2,和3在400,360和220nm处,用分光光度计分别跟随。在胺过量的情况下,发现伪一阶速率系数(k obsd)。的曲线图ķ实测在恒定pH值下,胺与胺的浓度成线性关系,斜率(k N)与pH值无关。所述布朗斯台德型图(日志ķ Ñ VS p ķ一个铵离子)是线性的对所有的反应中,用斜率β= 0.9为那些的1与SA胺和QUI,β= 0.36和0.57的反应2与SA胺和QUI,分别和β= 0.39 SA的反应与胺3。斜率的大小表明1的两个氨基酸水解都是通过两性离子四面体中间体(T ±)通过逐步机制控制的,其中从T ±驱逐出是速率确