title: 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.
abstract: 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 degrees 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.
authors.affiliation: Department of Chemistry and Nano Science, Ewha Womans University, Seoul 120-750, Korea. ihum@ewha.ac.kr
authors.forename: Ik-Hwan
authors.initials: IH
authors.lastname: Um
authors.forename: So-Jeong
authors.initials: SJ
authors.lastname: Hwang
authors.forename: Sora
authors.initials: S
authors.lastname: Yoon
authors.forename: Sang-Eun
authors.initials: SE
authors.lastname: Jeon
authors.forename: Sun-Kun
authors.initials: SK
authors.lastname: Bae