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Metal ion catalysis in nucleophilic displacement reactions of 2-pyridyl X-substituted benzoates with potassium ethoxide in anhydrous ethanol

Title
Metal ion catalysis in nucleophilic displacement reactions of 2-pyridyl X-substituted benzoates with potassium ethoxide in anhydrous ethanol
Authors
Lee J.-I.Kang J.-S.Im L.-R.Um I.-H.
Ewha Authors
엄익환
SCOPUS Author ID
엄익환scopusscopus
Issue Date
2010
Journal Title
Bulletin of the Korean Chemical Society
ISSN
0253-2964JCR Link
Citation
vol. 31, no. 12, pp. 3543 - 3548
Indexed
SCI; SCIE; SCOPUS; KCI WOS scopus
Abstract
A kinetic study on nucleophilic displacement reactions of 2-pyridyl X-substituted benzoates 1a-e with potassium ethoxide (EtOK) in anhydrous ethanol is reported. Plots of pseudo-first-order rate constants (kobsd) vs. [EtOK]° exhibit upward curvature. The kobsd value at a fixed [EtOK]° decreases steeply upon addition of 18-crown-6-ether (18C6) to the reaction mixture up to [18C6]/[EtOK]° = 1 and then remains nearly constant thereafter. In contrast, kobsd increases sharply upon addition of LiSCN or KSCN. Dissection of kobsd into kEtO- and k EtOM has revealed that ion-paired EtOK is more reactive than dissociated EtO , indicating that K+ ion acts as a Lewis acid catalyst. Hammett plots for the reactions of 1a-e with dissociated EtO and ion-paired EtOK result in excellent linear correlation with p values of 3.01 and 2.67, respectively. The kEtOK/kEtO ratio increases as the substituent X in the benzoyl moiety becomes a stronger electron-donating group. K+ ion has been concluded to catalyze the current reaction by stabilizing the transition state through formation of a 6-membered cyclic complex.
DOI
10.5012/bkcs.2010.31.12.3543
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자연과학대학 > 화학·나노과학전공 > Journal papers
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