scholarly journals Metal Ion Catalysis and Inhibition in Nucleophilic Substitution Reactions of 4-Nitrophenyl Nicotinate and Isonicotinate with Alkali Metal Ethoxides in Anhydrous Ethanol

2011 ◽  
Vol 32 (6) ◽  
pp. 1951-1956 ◽  
Author(s):  
Seo-Young Choi ◽  
Yeon-Ju Hong ◽  
Ik-Hwan Um
Keyword(s):  
Alkali Metal ◽  
Nucleophilic Substitution ◽  
Metal Ion ◽  
Anhydrous Ethanol ◽  
Substitution Reactions ◽  
Nucleophilic Substitution Reactions ◽  
Metal Ion Catalysis

Alkali metal ion catalysis and inhibition in alkaline ethanolysis of O-Y-substituted-phenyl O-phenyl thionocarbonates: contrasting M+ ion effects upon changing electrophilic centre from C=O to C=S

2017 ◽  
Vol 95 (1) ◽  
pp. 45-50 ◽  
Author(s):  
Ik-Hwan Um ◽  
Ji-Sun Kang ◽  
Julian M. Dust
Keyword(s):  
Alkali Metal ◽  
Metal Ion ◽  
Order Rate Constant ◽  
Substitution Reactions ◽  
First Order ◽  
Order Rate ◽  
Metal Ion Catalysis ◽  
Upward Curvature ◽  
Pseudo First Order ◽  
Ion Effects

Pseudo-first-order rate constants (kobsd) were measured for nucleophilic substitution reactions of O-Y-substituted-phenyl O-phenyl thionocarbonates (4a–4h) with alkali metal ethoxides (EtOM, M = Li, Na, or K) in anhydrous ethanol at 25.0 ± 0.1 °C. Plots of kobsd vs. [EtOM] exhibited upward curvature for the reaction of O-4-nitrophenyl O-phenyl thionocarbonate (4a) with EtOK in the presence of 18-crown-6-ether (18C6), but showed downward curvature for the reaction with EtOLi, indicating that the reaction is catalyzed by the 18C6-crowned K+ ion, but is inhibited by Li+ ion. The kobsd values were dissected into kEtO− and kEtOM, the second-order rate constant for the reaction with dissociated EtO− and ion-paired EtOM, respectively. The reactivity of EtOM toward 4a increases in the order EtOLi < EtONa < EtO− < EtOK < EtOK/18C6, which is in contrast to that reported previously for the corresponding reaction of 4-nitrophenyl phenyl carbonate (a C=O analogue of 4a), e.g., EtO− ≈ EtOK/18C6 < EtOLi < EtONa < EtOK. The reaction mechanism, including the transition-state model and the origin of the contrasting reactivity patterns found for the reactions of the C=O and C=S compounds, are discussed.

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