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Kinetics and reaction mechanism of aminolyses of benzyl 2-pyridyl carbonate and t-butyl 2-pyridyl carbonate: Effect of nonleaving group on reactivity and reaction mechanism

Title
Kinetics and reaction mechanism of aminolyses of benzyl 2-pyridyl carbonate and t-butyl 2-pyridyl carbonate: Effect of nonleaving group on reactivity and reaction mechanism
Authors
Kang J.-S.Lee J.-I.Um I.-H.
Ewha Authors
엄익환
SCOPUS Author ID
엄익환scopusscopus
Issue Date
2012
Journal Title
Bulletin of the Korean Chemical Society
ISSN
0253-2964JCR Link
Citation
vol. 33, no. 5, pp. 1551 - 1555
Indexed
SCI; SCIE; SCOPUS; KCI WOS scopus
Abstract
Second-order rate constants (kN) have been measured spectrophotometrically for the reactions of benzyl 2- pyridyl carbonate 7 and t-butyl 2-pyridyl carbonate 8 with a series of alicyclic secondary amines in l 2O at 25.0 ° C. Substrate 8 is less reactive than 7. Steric hindrance exerted by the bulky t-Bu group of 8 has been suggested to be responsible for the decreased reactivity. The Brønsted-type plots for the reactions of 7 and 8 are linear with ß nuc = 0.49 and 0.44, respectively, which is typical for reactions reported previously to proceed through a concerted mechanism. Aminolyses of 7 and 8 were expected to proceed through a zwitterionic tetrahedral intermediate T± , which would be stabilized through an intramolecular H-bonding interaction. However, the kinetic results suggest that the reactions proceed through a concerted mechanism. The H-bonding interaction in T± has been suggested to accelerate the rate of leaving-group expulsion from T± . Another factor that might accelerate expulsion of the leaving group is the "push" provided by the RO group in T± through resonance interactions. Thus, it has been concluded that the enhanced nucleofugality through the H-bonding interaction and the "push" provided by the RO group forces the reactions to proceed through a concerted mechanism. Copyright © 2005 KCSNET.
DOI
10.5012/bkcs.2012.33.5.1551
Appears in Collections:
자연과학대학 > 화학·나노과학전공 > Journal papers
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