Nucleophilic displacement on 4-nitrophenyl dimethyl phosphinate by ethoxide ion: alkali metal ion catalysis and mechanism
作者:Erwin Buncel、Kendall G. Albright、Ikenna Onyido
DOI:10.1039/b314886f
日期:——
interpreted in terms of a stepwise mechanism involving rate-limiting formation of a pentacoordinate intermediate. Comparison of the present results with those of Williams on the aqueous alkaline hydrolysis of Me(2)P(O)-OPhX and Ph(2)P(O)-OPhX esters, establishes the rationale for a change in mechanism in the more basic EtO(-)/EtOH nucleophile/solvent system by a stepwise mechanism instead of a concerted
我们报告了在25℃下Li(+)和K(+)阳离子对乙醇中4-硝基苯基二甲基次膦酸酯()乙醇化的影响的分光光度动力学研究。在不存在和存在18-冠-6醚(18-C-6)的情况下,LiOEt和KOEt的亲核取代反应提供了观察到的一级速率常数,该速率常数按EtO(-) Li(+)的小ΔG(ip)和K(+)的小ΔG(ts)[小] G(ip)。这些结果表明,Li(+)具有中等催化作用,与以前研究的其他底物相比,对催化作用的敏感性更低。芳基二甲基次膦酸酯与游离EtO(-)反应的二级速率常数从log k(obs)vs的图获得。[KOEt],在过量18-C-6存在下测得。具有σ和σ°取代基常数的哈米特图比σ(-)具有明显更好的速率相关性,并产生适度的大[小rho](小rho [°])值。这是通过逐步限制五配位中间体形成速率的机理来解释的。本结果与Williams对Me(2)P(O)-OPhX和Ph(2)P(O