36228-61-2Relevant articles and documents
Electronic nature of substituent X governs reaction mechanism in aminolysis of 4-pyridyl X-substituted-benzoates in acetonitrile
Um, Ik-Hwan,Bae, Ae Ri
body text, p. 5781 - 5787 (2012/08/29)
A kinetic study is reported for aminolysis of 4-pyridyl X-substituted-benzoates 5a-i. Plots of pseudo-first-order rate constants (k obsd) vs [amine] curve upward for the reactions of substrates possessing a strong electron-withdrawing group in the benzoyl moiety (5a-d) but are linear for the reactions of those bearing an electron-donating group (5e-i), indicating that the electronic nature of substituent X governs the reaction mechanism. The k1k2/k-1 and k1k 3/k-1 values were calculated from the intercept and slope of the linear plots of kobsd/[amine] vs [amine], respectively. The Hammett plot for k1k2/k-1 consists of two intersecting straight lines, while the Yukawa-Tsuno plot exhibits an excellent linear correlation with ρX = 0.41 and r = 1.58, implying that the nonlinear Hammett plot is not due to a change in rate-determining step but is caused by stabilization of substrates possessing an electron-donating group through resonance interactions. The small ρX suggests that the k2/k-1 ratio is little influenced by the nature of substituent X. The Bronsted-type plots for aminolysis of 4-pyridyl 3,5-dinitrobenzoate 5a are linear with βnuc = 0.98 and 0.79 for k1k2/k-1 and k1k3/k -1, respectively. The effect of amine basicity on the microscopic rate constants is also discussed.
Effect of alkali metal ions on alkaline ethanolysis of 2-pyridyl and 4-pyridyl benzoates in anhydrous ethanol
Lee, Jae-In,Kang, Ji-Sun,Kim, Song-I,Um, Ik-Hwan
experimental part, p. 2929 - 2933 (2012/05/05)
Pseudo-first-order rate constants (kobsd) have been measured for nucleophilic substitution reactions of 2-pyridyl benzoate 5 with alkali metal ethoxides (EtOM, M = Li, Na, K) in anhydrous ethanol. The plots of k obsd vs. [EtOM]o are curved upwardly but linear in the excess presence of 18-crown-6-ether (18C6) with significant decreased k obsd values in the reaction with EtOK. The kobsd value for the reaction of 5 with a given EtONa concentration decreases steeply upon addition of 15-crown-5-ether (15C5) to the reaction medium up to ca. [15C5]/[EtONa]o = 1, and remains nearly constant thereafter, indicating that M+ ions catalyze the reaction in the absence of the complexing agents. Dissection kobsd into kEtO- and k EtOM, i.e., the second-order rate constants for the reaction with the dissociated EtO. and the ion-paired EtOM, respectively has revealed that ion-paired EtOM is 3.2-4.6 times more reactive than dissociated EtO. It has been concluded that M+ ions increase the electrophilicity of the reaction center through a 6-membered cyclic transition state. This idea has been examined from the corresponding reactions of 4-pyridyl benzoate 6, which cannot form such a 6-membered cyclic transition state.
