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Metal Ion Catalysis in Nucleophilic Displacement Reactions of 2-Pyridyl X-Substituted Benzoates with Potassium Ethoxide in Anhydrous Ethanol
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  • Metal Ion Catalysis in Nucleophilic Displacement Reactions of 2-Pyridyl X-Substituted Benzoates with Potassium Ethoxide in Anhydrous Ethanol
  • Metal Ion Catalysis in Nucleophilic Displacement Reactions of 2-Pyridyl X-Substituted Benzoates with Potassium Ethoxide in Anhydrous Ethanol
저자명
Lee. Jae-In,Kang. Ji-Sun,Im. Li-Ra,Um. Ik-Hwan
간행물명
Bulletin of the Korean Chemical Society
권/호정보
2010년|31권 12호|pp.3543-3548 (6 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

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 ($k_{obsd}$) vs. $[EtOK]_o$ exhibit upward curvature. The $k_{obsd}$ value at a fixed $[EtOK]_o$ decreases steeply upon addition of 18-crown-6-ether (18C6) to the reaction mixture up to [18C6]/$[EtOK]_o$ = 1 and then remains nearly constant thereafter. In contrast, $k_{obsd}$ increases sharply upon addition of LiSCN or KSCN. Dissection of $k_{obsd}$ into $k_{EtO^-}$ 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 $ ho$ values of 3.01 and 2.67, respectively. The $k_{EtOK}/k_{EtO^-}$ 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.