Concerted Mechanisms of the Reactions of Methyl Aryl Carbonates with Substituted Phenoxide Ions
作者:Enrique A. Castro、Paulina Pavez、José G. Santos
DOI:10.1021/jo010022j
日期:2001.5.1
respectively) with substituted phenoxide ions are subjected to a kinetic study in water at 25.0 degrees C, ionic strength 0.2 M (KCl). Production of the leaving groups (the nitro derivatives) is followed spectrophotometrically. Under excess of the phenoxide ions pseudo-first-order rate coefficients (k(obsd)) are found throughout. Plots of k(obsd) vs substituted phenoxide concentration at constant pH
对4-硝基苯基,2,4-二硝基苯基和2,4,6-三硝基苯基碳酸甲基酯(分别为NPC,DNPC和TNPC)与取代的酚盐离子的反应在水中于25.0℃下进行动力学研究,离子强度0.2 M(KCl)。分光光度法测定离去基团(硝基衍生物)的产生。在过量的酚盐离子下,始终会发现伪一阶速率系数(k(obsd))。在恒定pH下,k(obsd)与取代的苯酚的浓度关系图呈线性关系,斜率(k(N))与pH无关。对于NPC,DNPC和TNPC的酚醛化作用,布朗斯台德型图(苯酚的log k(N)与pK(a))呈线性,斜率分别为β= 0.67、0.48和0.52。这些布朗斯台德斜率的大小与协调机制一致。在NPC发生酚醛化的特殊情况下,对于逐步机理而言,Brönsted图的预期假想曲率中心应为pK(a)(0)= 7.1(4-硝基苯酚的pK(a))。该曲率未出现在所研究的取代酚的pK(a)范围内(5.3--10.3),表