Kinetics and mechanism of the pyridinolysis of aryl dithiobenzoates in acetonitrile
作者:Hyuck Keun Oh、Jae Myon Lee、Hai Whang Lee、Ikchoon Lee
DOI:10.1002/kin.20000
日期:2004.8
the zwitterionic tetrahedral intermediate, T±, at pKa = 5.2 as the pyridine basicity is increased. Rates are compared with those corresponding values for aryl dithioacetates (R = Me). The faster rates for R = Me than for R = Ph, for the rate-limiting formation of T±, can be attributed to the hyperconjugative charge transfer effect of the Me group, pseudo-πMe π*C=S. Clear-cut change in the cross-interaction
研究了二硫代苯甲酸芳基酯 (RC(S)SC6H4Z; R = Ph) 与吡啶 (XC5H4N) 在乙腈中在 60.0°C 下氨解的动力学和机理。在 pKa° = 5.2 时,斜率从大值 (βX ≅ 0.7–0.8) 变为小值 (βX ≅ 0.2) 得到双相布朗斯特图,这被解释为表明速率决定步骤的变化随着吡啶碱度的增加,在 pKa = 5.2 时从分解到形成两性离子四面体中间体 T±。将速率与芳基二硫代乙酸酯 (R = Me) 的相应值进行比较。对于 T± 的限速形成,R = Me 比 R = Ph 更快的速率可归因于 Me 基团的超共轭电荷转移效应,伪 πMe π*C=S。交叉相互作用常数 ρXZ 从 +1.47 到 -0 的明显变化。20 支持提议的机制更改。目前工作中 R = Ph 的 pKa° = 5.2 处的断点与 R = Me 和 2-呋喃基的吡啶解的断点一致,并证明了酰基 R