Aminolysis of 2,4-Dinitrophenyl X-Substituted Benzoates and Y-Substituted Phenyl Benzoates in MeCN: Effect of the Reaction Medium on Rate and Mechanism
作者:Ik-Hwan Um、Sang-Eun Jeon、Jin-Ah Seok
DOI:10.1002/chem.200500647
日期:2006.1.23
indicating that the electronic nature of the substituent X in the nonleaving group does not affect the rate-determining step (RDS) or reaction mechanism. The Hammett correlation with sigma- constants also exhibits good linearity with a large slope (rho(Y) = 3.54) for the reactions of 2 a-h with piperidine, implying that the leaving-group departure occurs at the rate-determining step. Aminolysis of 2,4-dinitrophenyl
分光光度法测定了2,4-二硝基苯基X-取代的苯甲酸酯(1af)和Y-取代的苯基苯甲酸酯(2ah)与一系列脂环族仲胺的反应的二级速率常数(k(N))在25.0 +/- 0.1摄氏度下的MeCN。MeCN中的k(N)值仅比H2O中的稍大,尽管所研究的胺在非质子溶剂中的碱性比H2O中的碱性高约8 pK(a)单位。1 af的氨解的Yukawa-Tsuno图是线性的,表明非离去基团中取代基X的电子性质不影响速率确定步骤(RDS)或反应机理。对于2 ah与哌啶的反应,具有sigma常数的Hammett相关性也表现出良好的线性,且具有较大的斜率(rho(Y)= 3.54),暗示离开组离开发生在速率确定步骤。2,4-二硝基苯甲酸苯甲酸酯(1 c)的酶解作用产生线性布朗斯台德图,β(nuc)值为0.40,这表明攻击胺与1 c的羰基碳原子之间的键形成几乎不进行。过渡状态(TS)。提出了一种协同机制,用于MeCN中1