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Effect of Alkali Metal Ions on Alkaline Ethanolysis of 2-Pyridyl and 4-Pyridyl Benzoates in Anhydrous Ethanol
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  • Effect of Alkali Metal Ions on Alkaline Ethanolysis of 2-Pyridyl and 4-Pyridyl Benzoates in Anhydrous Ethanol
  • Effect of Alkali Metal Ions on Alkaline Ethanolysis of 2-Pyridyl and 4-Pyridyl Benzoates in Anhydrous Ethanol
저자명
Lee. Jae-In,Kang. Ji-Sun,Kim. Song-I,Um. Ik-Hwan
간행물명
Bulletin of the Korean Chemical Society
권/호정보
2010년|31권 10호|pp.2929-2933 (5 pages)
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대한화학회
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정기간행물|ENG|
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이 논문은 한국과학기술정보연구원과 논문 연계를 통해 무료로 제공되는 원문입니다.
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기타언어초록

Pseudo-first-order rate constants ($k_{obsd}$) have been measured for nucleophilic substitution reactions of 2-pyridyl benzoate 5 with alkali metal ethoxides (EtOM, M = Li, Na, K) in anhydrous ethanol. The plots of $k_{obsd}$ vs. $[EtOM]_o$ are curved upwardly but linear in the excess presence of 18-crown-6-ether (18C6) with significant decreased $k_{obsd}$ values in the reaction with EtOK. The $k_{obsd}$ value for the reaction of 5 with a given EtONa concentration decreases steeply upon addition of 15-crown-5-ether (15C5) to the reaction medium up to ca. [15C5]/$[EtONa]_o$ = 1, and remains nearly constant thereafter, indicating that $M^+$ ions catalyze the reaction in the absence of the complexing agents. Dissection $k_{obsd}$ into $k_{EtO^-}$- and $k_{EtOM}$, i.e., the second-order rate constants for the reaction with the dissociated $EtO^-$ and the ion-paired EtOM, respectively has revealed that ion-paired EtOM is 3.2 - 4.6 times more reactive than dissociated $EtO^-$. It has been concluded that $M^+$ ions increase the electrophilicity of the reaction center through a 6-membered cyclic transition state. This idea has been examined from the corresponding reactions of 4-pyridyl benzoate 6, which cannot form such a 6-membered cyclic transition state.