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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
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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
  • Effect of Alkali Metal Ions on Nucleophilic Substitution Reactions of 4-Nitrophenyl X-Substituted Benzoates with Alkali Metal Ethoxides in Anhydrous Ethanol
저자명
Seo. Jin-A,Kim. Song-I,Hong. Yeon-Ju,Um. Ik-Hwan
간행물명
Bulletin of the Korean Chemical Society
권/호정보
2010년|31권 2호|pp.303-308 (6 pages)
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대한화학회
파일정보
정기간행물|ENG|
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이 논문은 한국과학기술정보연구원과 논문 연계를 통해 무료로 제공되는 원문입니다.
서지반출

기타언어초록

Pseudo-first-order rate constants ($k_{obsd}$) 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 $25.0{pm}0.1^{circ}C$. The plots of $k_{obsd}$ 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., $k_{EtO^-}$ and $k_{EtO^-M^+}$, respectively) have been calculated from ion-pair treatment for the reactions of 5a and 5b. However, such ion-pair treatment has failed to determine $k_{EtO^-}$ and $k_{EtO^-M^+}$ 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.