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Alkali-Metal Ion Catalysis in Nucleophilic Substitution Reactions of 5-Nitro-8-quinolyl Picolinate with Alkali Metal Ethoxides: Effect of Modification of Nonleaving Group from Benzoyl to Picolinyl on Reactivity and Transition State Structure
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  • Alkali-Metal Ion Catalysis in Nucleophilic Substitution Reactions of 5-Nitro-8-quinolyl Picolinate with Alkali Metal Ethoxides: Effect of Modification of Nonleaving Group from Benzoyl to Picolinyl on Reactivity and Transition State Structure
  • Alkali-Metal Ion Catalysis in Nucleophilic Substitution Reactions of 5-Nitro-8-quinolyl Picolinate with Alkali Metal Ethoxides: Effect of Modification of Nonleaving Group from Benzoyl to Picolinyl on Reactivity and Transition State Structure
저자명
Jeon. Seong Hoon,Yoon. Jung Hwan,Kim. Min-Young,Um. Ik-Hwan
간행물명
Bulletin of the Korean Chemical Society
권/호정보
2014년|35권 5호|pp.1506-1510 (5 pages)
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대한화학회
파일정보
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 substitution reaction of 5-nitro-8-quinolyl picolinate (6) with alkali-metal ethoxides (EtOM; M = K, Na, and Li) in anhydrous ethanol is reported. The plot of $k_{obsd}$ vs. [EtOM] curves upward in the absence of crown ethers but is linear with significantly decreased reactivity in the presence of crown ethers. Dissection of $k_{obsd}$ into $k_{EtO}$- and $k_{EtOM}$ (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 significantly more reactive than the dissociated $EtO^-$ (e.g., $k_{EtOM}/k_{EtO^-}$ = 33.4-141). This indicates that the reaction of 6 is catalyzed by $M^+$ ions in the order $Na^+$ > $Li^+$ > $K^+$ and the catalytic effect disappears in the presence of a proper crown ether. Picolinate ester 6 is much more reactive and is more strongly catalyzed by $M^+$ ions than 5-nitro-8-quinolyl benzoate (5). It has been concluded that $M^+$ ions catalyze the reaction of 6 by increasing electrophilicity of the reaction center through a cyclic transition state, which is structurally not possible for the reaction of 5.