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Metal-ion catalysis in alkaline ethanolysis of 2-pyridyl thionobenzoate: Effects of modification of electrophilic center from C=O to C=S

Title
Metal-ion catalysis in alkaline ethanolysis of 2-pyridyl thionobenzoate: Effects of modification of electrophilic center from C=O to C=S
Authors
Um I.-H.Song Y.-J.Kim M.-Y.Lee J.-I.
Ewha Authors
엄익환
SCOPUS Author ID
엄익환scopusscopus
Issue Date
2013
Journal Title
Bulletin of the Korean Chemical Society
ISSN
0253-2964JCR Link
Citation
vol. 34, no. 5, pp. 1525 - 1529
Indexed
SCI; SCIE; SCOPUS; KCI WOS scopus
Abstract
Pseudo-first-order rate constants (kobsd) have been measured spectrophotometrically for the nucleophilic substitution reactions of 2-pyridyl thionobenzoate (5b) with alkali-metal ethoxides (EtOM, M+ = Li +, Na+, K+, and 18-crown-6-ether complexed K+) in anhydrous ethanol at 25.0 ± 0.1 oC. The plots of kobsd vs. [EtOM]o curve upward regardless of the nature of the M+ ions, while those of kobsd/[EtO -]eq vs. [EtO-]eq are linear with a positive intercept. Dissection of kobsd into kEtO- and kEtOM (i.e., the second-order rate constants for the reactions with the dissociated EtO- and ion-paired EtOM, respectively) has revealed that the ion-paired EtOM is more reactive than the dissociated EtO-, and M+ ions catalyze the reactions in the order K+ Na + Li+ 18C6-complexed K+. The plot of log k EtOM vs. 1/rStokes results in an excellent linear correlation, indicating that the reactions are catalyzed by the solvated M + ions but not by the bare M+ ions. The reactions of 5b with EtOM have been concluded to proceed through a six-membered cyclic TS, in which the solvated M+ ions increase the electrophilicity of the reaction center and the nucleofugality of the leaving group.
DOI
10.5012/bkcs.2013.34.5.1525
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자연과학대학 > 화학·나노과학전공 > Journal papers
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