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Kinetic and mechanistic studies on quinuclidinolysis of Y-substituted-phenyl picolinates: Effect of amine nature on reactivity and transition- state structure

Title
Kinetic and mechanistic studies on quinuclidinolysis of Y-substituted-phenyl picolinates: Effect of amine nature on reactivity and transition- state structure
Authors
Um I.-H.Kim M.-Y.Kang Y.
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. 5, pp. 1405 - 1410
Keywords
Brønsted-type plotQuinuclidinolysisRate-determining stepY-substituted-phenyl picolinatesYukawa-Tsuno plot
Publisher
Korean Chemical Society
Indexed
SCI; SCIE; SCOPUS; KCI WOS scopus
Abstract
Second-order rate constants (k<inf>N</inf>) have been measured spectrophotometrically for reactions of Y-substitutedphenyl picolinates (7a-7i) with a series of quinuclidines in 80 mol% H<inf>2</inf>O/20 mol% DMSO at 25.0 ± 0.1 °C. The Brønsted-type plot for the reactions of 7a-7i with quinuclidine is linear with β<inf>lg</inf> = -0.80. The Yukawa- Tsuno plot exhibits an excellent linear correlation with ρ<inf>Y</inf> = 2.37 and r = 0.52, indicating that a negative charge develops partially on the O atom of the leaving group in the rate-determining transition state (TS). The Brønsted-type plot for the reactions of 2-chloro-4-nitrophenyl picolinate (7a) with a series of quinuclidines is also linear with β<inf>nuc</inf> = 0.83. Thus, it was concluded that the reactions proceed through a stepwise mechanism, in which expulsion of the leaving group occurs in the rate-determining step. Comparison of the current kinetic data with those reported previously for the corresponding reactions with piperidine revealed that quinuclidine is ca. 102 -fold less reactive than piperidine. This is in contrast to the reports that quinuclidines are more reactive than isobasic secondary amines toward diaryl carbonates and related esters. Effects of amine nature on reactivity and TS structures are discussed. © 2015 Korean Chemical Society, Seoul & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.
DOI
10.1002/bkcs.10272
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자연과학대학 > 화학·나노과학전공 > Journal papers
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