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

• Published in: Journal of organic chemistry Vol. 73; no. 19; pp. 7671 - 7677
• Main Authors: Um, Ik-Hwan, Hwang, So-Jeong, Yoon, Sora, Jeon, Sang-Eun, Bae, Sun-Kun
• Format: Journal Article
• Language: English
• Published: WASHINGTON American Chemical Society 03.10.2008; Amer Chemical Soc
• Subjects: Amines - chemistry; Benzoates - chemistry; Chemistry; Chemistry, Organic; Exact sciences and technology; Kinetics; Kinetics and mechanisms; Organic chemistry; Physical Sciences; Reactivity and mechanisms; Science & Technology; 4-SUBSTITUTED THIOBENZOATES; NONLEAVING GROUP; KINETICS; BENZOATES; ELECTROPHILIC CENTER; O-4-NITROPHENYL THIONOBENZOATE; ESTER AMINOLYSIS; 4-NITROPHENYL PHENYL CARBONATE; PYRIDINOLYSIS; PHENACYL BROMIDES; Water; Reaction intermediate; Nitro compound; Correlation; Stabilization; Ground state; Zwitterion; Yukawa Tsuno equation; Reaction rate; Leaving group effect; Hammett function; Methyl sulfoxide; Amine; Thione; Aminolysis; Thioacid; Reaction mechanism; Benzenic compound; Alkalinity; Kinetics; Arylamine; Electron donor; Deprotonation; Nucleophile
• ISSN: 0022-3263; 1520-6904
• DOI: 10.1021/jo801539w

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.