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Effect of alkali metal ions on nucleophilic substitution reactions of 4-Nitrophenyl X-substituted benzoates with alkali metal ethoxides in anhydrous ethanol

Title
Effect of alkali metal ions on nucleophilic substitution reactions of 4-Nitrophenyl X-substituted benzoates with alkali metal ethoxides in anhydrous ethanol
Authors
Seo J.-A.Kim S.-I.Hong Y.-J.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. 2, pp. 303 - 308
Indexed
SCI; SCIE; SCOPUS; KCI WOS scopus
Abstract
Pseudo-first-order rate constants (kobsd) have been measured spectrophotometrically for nucleophilic substitution reactions of 4-nitrophenyl benzoate (5a), 4-nitrophenyl 4-methoxybenzoate (5b), and 4-nitrophenyl 4-hydroxybenzoate (5c) with alkali metal ethoxides, EtO-M+ (M+= Li+, Na+ and K+) in anhydrous ethanol (EtOH) at 25.0 ± 0.1 ° C. The plots of kobsd vs. [EtO -M+] exhibit upward curvatures in all cases, indicating that M+ ions catalyze the reactions and ionpaired EtO -M+ species are more reactive than dissociated EtO -. Second-order rate constants for reactions with dissociated EtO- and ion-paired EtO-M+ (i.e., kEtO - and kEtO-M+, respectively) have been calculated from ion-pair treatment for the reactions of 5a and 5b. However, such ion-pair treatment has failed to determine kEtO- and kEtO -M+ values for the reactions of 5c. It has been concluded that reactions of 5a and 5b are catalyzed by one metal ion, which increases electrophilicity of the reaction center through coordination on the carbonyl oxygen. In contrast, reactions of 5c have been suggested to involve two metal ions, i.e., the one coordinated on the carbonyl oxygen increases the electrophilicity of the reaction center while the other one associated on the phenoxy oxygen decreases the charge repulsion between the anionic reagents (i.e., EtO- and deprotonated 5c). It has been found that the rate equation derived from the mechanism involving two metal ions fits nicely to the kinetic results obtained for the reactions of 5c.
DOI
10.5012/bkcs.2010.31.02.303
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자연과학대학 > 화학·나노과학전공 > Journal papers
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