Aminolysis of S-4-Nitrophenyl X-Substituted Thiobenzoates: Effect of Nonleaving-Group Substituents on Reactivity and Mechanism

• Published in: Bulletin of the Korean Chemical Society Vol. 32; no. 4; pp. 1153 - 1157
• Main Authors: Im, Li-Ra, Jeon, Sang-Eun, Um, Ik-Hwan
• Format: Journal Article
• Language: English
• Published: 대한화학회 20.04.2011
• Subjects: 화학
• ISSN: 0253-2964; 1229-5949
• DOI: 10.5012/bkcs.2011.32.4.1153

A kinetic study is reported for aminolysis of S-4-nitrophenyl X-substituted thiobenzoates 3a-g in 80 mol %H_2O/20 mol % DMSO at 25.0 ± 0.1 ^oC. Thiol esters 3a-g are 7.8-47.6 fold more reactive than the corresponding oxygen esters (i.e., 4-nitrophenyl X-substituted benzoates 1a-g). Such reactivity order appears to be in accordance with the expectation that 4-nitrothiophenoxide in 3a-g is a better nucleofuge than 4-nitrophenoxide in 1a-g since the former is 2.64 pK_a units less basic than the latter. Hammett plot for the reactions of 3a-g exhibit poor correlation coefficients (R2 = 0.977-0.986) with negative deviation by substrates possessing an electrondonating group (EDG), while the Yukawa-Tsuno plots result in excellent linear correlation (R^2 = 0.995-0.997)with ρ = 0.93-1.23 and r = 0.57-0.67, indicating that the negative deviation shown by substrates possessing an EDG is caused by ground-state stabilization through resonance interactions but not due to a change in ratedetermining step upon changing the nonleaving-group substituent X. The ρ value increases as the incoming amine becomes more basic and more reactive, indicating that the RSP is not operative in the current reactions. KCI Citation Count: 0