Vinyl ether hydrolysis. 30. Effect of ?-carboxy and ?-carbomethoxy substitution
作者:A. J. Kresge、D. Ubysz
DOI:10.1002/poc.610070608
日期:1994.6
retardations, ranging from 2000- to 25 000-fold, for both Z- and E-isomers in both the acrylic and methacrylic acid series. The rate profile for (Z)-β-methoxymethacrylic acid indicates that ionization of this substrate to the carboxylate ion form rises the rate of hydrolysis by a factor of 240. It is argued that this difference in reactivity of ionized and non-ionized forms of the substrate is due to conjugative
在高氯酸水溶液中测量(Z)-和(E)-β-甲氧基丙烯酸和(Z)-和(E)-β-甲氧基甲基丙烯酸的乙烯基醚官能团及其甲酯的水解速率。还对低至pH 7的缓冲溶液中的一种底物(Z)-β-甲氧基甲基丙烯酸进行了其他速率测量,并构建了速率分布图。结果表明,对于丙烯酸和甲基丙烯酸系列中的Z-和E-异构体,β-羧基和β-羰基甲氧基取代基均产生强的速率延迟,范围为2000至25000倍。(Z的速率曲线)-β-甲氧基甲基丙烯酸表明该底物离子化为羧酸根离子形式,使水解速率提高了240倍。有人认为,该离子化形式和非离子化形式的底物的反应性差异是由于共轭引起的。取代基的诱导作用,而不是如先前在不同系统中观察到相同现象所建议的那样形成β-内酯。