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Kinetic study on quinuclidinolysis of O-4-nitrophenyl X-substituted thionobenzoates and O-3,4-dinitrophenyl thionobenzoate: Effect of amine nature on reactivity and reaction mechanism

Title
Kinetic study on quinuclidinolysis of O-4-nitrophenyl X-substituted thionobenzoates and O-3,4-dinitrophenyl thionobenzoate: Effect of amine nature on reactivity and reaction mechanism
Authors
Yang E.-J.Kim M.-Y.Um I.-H.
Ewha Authors
엄익환
SCOPUS Author ID
엄익환scopusscopus
Issue Date
2015
Journal Title
Bulletin of the Korean Chemical Society
ISSN
0253-2964JCR Link
Citation
vol. 36, no. 6, pp. 1551 - 1556
Keywords
Concerted mechanismO-aryl thionobenzoatesQuinuclidinolysisResonance stabilizationSteric hindrance
Publisher
Korean Chemical Society
Indexed
SCI; SCIE; SCOPUS; KCI WOS scopus
Abstract
Second-order rate constants (k<inf>quin</inf>) have been measured spectrophotometrically for the reactions of O-3,4-dinitrophenyl thionobenzoate (1a) with a series of quinuclidine derivatives and of O-4-nitrophenyl X-substituted thionobenzoates (2a-2f) with quinuclidine in 80 mol% H<inf>2</inf>O/20 mol% DMSO at 25.0 ± 0.1 °C. Quinuclidine is less reactive toward the thione esters than less basic benzylamine. Steric hindrance exerted by the tertiary amine is responsible for the decreased reactivity. The Hammett plot for the reactions of 2a-2f with quinuclidine consists of two intersecting straight lines, while the Yukawa-Tsuno plot for the same reactions exhibits an excellent linear correlation with ρ<inf>X</inf> = 1.10 and r = 0.71. This indicates that the nonlinear Hammett plot is not due to a change in the rate-determining step but is caused by ground-state stabilization of substrates possessing an electron-donating group in the thionobenzoyl moiety through resonance interactions. Brønstedtype plot for the reactions of 1a with quinuclidines is linear with β<inf>nuc</inf> = 0.89, which is typical for reactions reported to proceed through a stepwise mechanism. However, the reactions have been concluded to proceed through a forced concerted mechanism. Instability of a plausible intermediate T± forces the reactions to proceed through such a mechanism. © 2015 Korean Chemical Society, Seoul & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.
DOI
10.1002/bkcs.10293
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자연과학대학 > 화학·나노과학전공 > Journal papers
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