Transfer of a positively charged acyl group between substituted phenolate ion nucleophiles: the brønsted β for the calibrating equilibrium for N-methylisonicotinyl (4-carbonyl-N-methylpyridinium) transfer
作者:Matthew J. Colthurst、Matilde Nanni、Andrew Williams
DOI:10.1039/p29960002285
日期:——
measured for the reaction of substituted phenolate ions with aryl acetate esters and with aryl N-methylisonicotinate esters in aqueous solution. A new method is demonstrated for determining βeq for group transfer from 4-nitrophenyl esters; it employs the rate constant for the reaction of 2,6-difluorophenolate ion with substituted phenyl ester as a surrogate for the reactivity of the 4-nitrophenolate ion
已经测量了在水溶液中取代酚盐离子与乙酸芳基酯和与芳基N-甲基异烟酸酯的反应的速率常数。一种新方法被证明用于确定β当量从4-硝基苯基酯基转移; 它采用的速率常数的反应2,6- difluorophenolate离子取代的苯基酯作为4-硝基苯酚盐离子和产量的反应性的替代β当量= 1.55为Ñ -methylisonicotinyl转移反应。苯甲酸根离子对4-硝基苯基N-甲基异烟酸根酸酯的进攻速率常数的布朗斯台德图在p K a范围内是线性的值从5.5到10,并为该反应的协调位移机制提供了很好的证据。所述的反应性Ñ -methylisonicotinate酯酚离子是比相应的乙酸酯的大约300次,但较大的β NUC值(0.90与0.74比较)提出了一种“后面”过渡结构。所述的校准β与对应的值β当量给出莱弗勒α NUC为= 0.58和0.42 Ñ -methylisonicotinate和乙酸分别,与