Aminolysis of O-Aryl Thionobenzoates: Amine Basicity Combines with Modulation of the Nature of Substituents in the Leaving Group and Thionobenzoate Moiety to Control the Reaction Mechanism

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• 作者：Ik-Hwan Um ; So-Jeong Hwang ; Sora Yoon ; Sang-Eun Jeon ; Sun-Kun Bae
• 刊名：Journal of Organic Chemistry
• 出版年：2008
• 出版时间：October 3, 2008
• 年：2008
• 卷：73
• 期：19
• 页码：7671-7677
• 全文大小：226K
• 年卷期：v.73,no.19(October 3, 2008)
• ISSN：1520-6904

文摘

A kinetic study is reported for aminolysis of O-Y-substituted phenyl thionobenzoates (1a−f) and O-4-nitrophenyl X-substituted thionobenzoates (2a−f) in 80 mol % H₂O/20 mol % DMSO at 25.0 ± 0.1 °C. The reaction proceeds through one or two intermediates (i.e., a zwitterionic tetrahedral intermediate T^± and its deprotonated form T⁻) depending on the basicity difference between the nucleophile and nucleofuge, that is, the reaction proceeds through T^± when the leaving aryloxide is less basic than the attacking amine, but through T^± and T⁻ when the leaving group is more basic than the amine. However, the reaction mechanism is not influenced by the electronic nature of the substituent X in the nonleaving group. The Hammett plot for the reactions of 2a−f with benzylamine is consisted of two intersecting straight lines, which might be interpreted as a change in the rate-determining step (RDS). However, the Yukawa-Tsuno plot for the same reactions exhibits an excellent linear correlation, indicating that the nonlinear Hammett plot is not due to a change in the RDS but caused by stabilization of the ground-state of the substrate through resonance interaction between the electron-donating substituent X and the thionocarbonyl moiety.