- Kinetic study on nucleophilic substitution reactions of 4-Nitrophenyl X-Substituted-Benzoates with potassium ethoxide: Reaction mechanism and role of K+ Ion
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A kinetic study on nucleophilic substitution reactions of 4-nitrophenyl X-substituted-benzoates (7a-i) with EtOK in anhydrous ethanol at 25.0 ± 0.1 °C is reported. The plots of pseudo-first-order rate constants (kobsd) vs. [EtOK] curve upward. Dissection of kobsd into the second-order rate constants for the reactions with the dissociated EtOV and ion-paired EtOK (i.e., kEtO-and kEtOK, respectively) has revealed that the ion-paired EtOK is more reactive than the dissociated EtOV. Hammett plots for the reactions of 7a-i with the dissociated EtOV and ion-paired EtOK exhibit excellent linear correlations with aX = 3.00 and 2.47, respectively. The reactions have been suggested to proceed through a stepwise mechanism in which departure of the leaving-group occurs after the RDS. The correlation of the kEtOK/kEtO{ ratio with the aX constants exhibits excellent linearity with a slope of V0.53. It is concluded that the ion-paired EtOK catalyzes the reaction by increasing the electrophilicity of the reaction center rather than by enhancing the nucleofugality of the leaving group.
- Kim, Song-I,Kim, Min-Young,Um, Ik-Hwan
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p. 225 - 230
(2014/02/14)
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- Structure-reactivity correlations in nucleophilic substitution reactions of Y-substituted phenyl X-substituted benzoates with anionic and neutral nucleophiles
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A kinetic study is reported for the reactions of 4-nitrophenyl X-substituted benzoates (1a-l) and Y-substituted phenyl benzoates (2a-l) with two anionic nucleophiles (OH- and CN-) and three amines (piperidine, hydrazine, and glycylglycine) in 80 mol% H2O-20 mol% dimethyl sulfoxide (DMSO) at 25.0 ± 0.1 °C. Each Hammett plot exhibits two intersecting straight lines for the reactions of 1a-l with the anionic nucleophiles and piperidine, while the Yukawa-Tsuno plots for the same reactions are linear. The Hammett plots for the reactions of 2a-l with hydrazine and glycylglycine demonstrate much better linear correlations with σ- constants than with σ° or σ constants, indicating that the leaving group departure occurs at the rate determining step (RDS). On the contrary, σ- constants result in poorer Hammett correlation than σ° constants for the corresponding reactions with OH- and CN-, indicating that the leaving group departure occurs after the RDS for the reactions with the anionic nucleophiles. The large ρX value (1.7 ± 0.1) obtained for the reactions of 1a-l with the anionic nucleophiles supports the proposal that the reactions proceed through an addition intermediate with its formation being the RDS. The Royal Society of Chemistry 2006.
- Um, Ik-Hwan,Lee, Ji-Youn,Fujio, Mizue,Tsuno, Yuho
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p. 2979 - 2985
(2008/02/11)
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- Pd-catalyzed decarbonylative olefination of aryl esters: Towards a waste-free Heck reaction
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Easy and clean: A palladium (0)-catalyzed decarbonylative Heck olefination of activated esters of aryl, heteroaryl, and vinyl carboxylic acids opens up an opportunity for a novel waste-free Heck olefination process (see scheme).
- Goossen, Lukas J.,Paetzold
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p. 1237 - 1241
(2007/10/03)
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