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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 35, Number 2
BKCSDE 35(2)
February 20, 2014 

 
Title
Kinetic Study on Aminolysis of Y-Substituted-Phenyl X-Substituted-Benzoates: Effects of Substituents X and Y on Reactivity and Reaction Mechanism
Author
Seong Hoon Jeon, Hyun Soo Kim, Young Joon Han, Min-Young Kim, Ik-Hwan Um*
Keywords
Brønsted-type plot, Hammett plot, Yukawa-Tsuno plot, Nucleofugality, Steric hindrance
Abstract
A kinetic study on aminolysis of 2-chloro-4-nitrophenyl X-substituted-benzoates (2a-k) in 80 mol % H2O/20 mol % DMSO at 25.0 oC is reported. The Brønsted-type plot for the reactions of 2-chloro-4-nitrophenyl benzoate (2g) with a series of cyclic secondary amines curves downward (e.g., 1 = 0.25, 2 = 0.85 and pKa o = 10.3), which is typical of reactions reported to proceed through a stepwise mechanism with a change in ratedetermining step (RDS). The Hammett plot for the reactions of 2a-k with piperidine consists of two intersecting straight lines, while the corresponding Yukawa-Tsuno plot exhibits an excellent linear correlation with X = 1.15 and r = 0.59. Thus, it has been concluded that the nonlinear Hammett plot is not due to a change in RDS but is caused by stabilization of substrates through resonance interactions between the electron-donating substituent and the C=O bond. Substrates possessing a substituent at the 2-position of the leaving aryloxide deviate negatively from the curved Brønsted-type plot for the reactions of Y-substituted-phenyl benzoates (3ai), implying that the steric hindrance exerted by the substituent at the 2-position is an important factor which governs the reactivity of Y-substituted-phenyl benzoates.
Page
471 - 476
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