of SA amines with PNPTC and ClPNPTC are linear with slopes 0.59 and 0.54, respectively. The values of these slopes are in accordance with a concerted mechanism. The Brønsted-type plots for the pyridinolysis reactions are biphasic, suggesting a stepwise mechanism with a change in the rate-determining step, from breakdown to formation of a tetrahedral intermediate, as the basicity of the pyridines increases
进行O-
苯基S-(4-
硝基苯基)
硫代
碳酸酯(
PNPTC)和O-(4-
氯苯基)S-(4-
硝基苯基)
硫代
碳酸酯(Cl
PNPTC)与一系列仲脂环族(
SA)胺和
吡啶的反应在25.0°C和0.2 M的离子强度下,在44 wt%的
乙醇-
水中进行动力学研究。分光光度法在420 nm(
4-硝基苯硫醇根阴离子外观)上跟踪反应。在胺过量的情况下,发现伪一阶速率系数(k obs)。对于所有这些反应,在恒定pH下k obs与游离胺浓度的关系图是线性的,斜率(k N)与pH无关。一系列
SA胺与
PNPTC和Cl
PNPTC的反应的Brønsted型图(胺的共轭酸的log k N vs p K a)分别为线性,斜率分别为0.59和0.54。这些斜率的值符合协调机制。
吡啶分解反应的布朗斯台德图是两相的,表明随着
吡啶碱度的提高,速率决定步骤从分解到四面体
中间体形成的逐步机理。版权所有©2008 John Wiley&Sons,Ltd