The pyridinolysis of S-4-nitrophenyl 4-X-substituted thiobenzoates (X = H, Cl, and NO2; 1, 2, and 3, respectively) is studied kinetically in 44 wt % ethanol-water, at 25.0 degrees C and an ionic strength of 0.2 M (KCl). The reactions are measured spectrophotometrically (420-425 nm) by following the appearance of 4-nitrobenzenethiolate anion. Pseudo-first-order rate coefficients (kobsd) are obtained throughout, under excess of amine over the substrate. Plots of kobsd vs [free amine] at constant pH are linear with the slope (kN) independent of pH. The Brnsted-type plot (log kN vs pKa0 of the conjugate acids of the pyridines) for the reactions of thiolbenzoate 1 is curved with a slope at high pKa, beta1 = 0.20, and slope at low pKa0, beta2 = 0.94. The pKa value for the center of the Brnsted curvature is pKa0 = 9.7. The pyridinolysis of thiolbenzoates 2 and 3 show linear Brnsted-type plots of slopes 0.94 and 1.0, respectively. These results and other evidence indicate that these reactions occur with the formation of a zwitterionic tetrahedral intermediate (T+/-). For the pyridinolysis of thiolbenzoate 1, breakdown of T+/- to products (k2 step) is rate-limiting for weakly basic pyridines and T+/- formation (k1 step) is rate-determining for very basic pyridines. The k2 step is rate-limiting for the reactions of thiolbenzoates 2 and 3. The smallest pKa0 value for the reaction of 1 is due to the weakest electron withdrawal of H (relative to Cl and NO2) in the acyl group, which results in the smallest k-1/k2 ratio. The pKa0 values for the title reactions are smaller than those for the reactions of secondary alicyclic amines with thiolbenzoates 1-3. This is attributed to a lower leaving ability from the T+/- of pyridines than isobasic alicyclic amines. The lower p value found for the pyridinolysis of 2,4-dinitrophenyl benzoate (pKa0 = 9.5), compared with that for the pyridinolysis of 1, is explained by the greater nucleofugality from T+/- of 2,4-dinitrophenoxide than 4-nitrobenzenethiolate, which renders the k-1/k2 ratio smaller for the reactions of the benzoate relative to thiolbenzoate 1. The title reactions are also compared with the aminolysis of similar thiolbenzoates in other solvents to assess the solvent effect.
En este artículo examinamos la aplicación de la lógica desde dos concepciones filosóficas opuestas y evaluamos comparativamente sus méritos. La primera es una concepción monista platonista, que caracteriza la relación de consecuencia lógica como una relación abstracta entre proposiciones. Esta propuesta, que insiste en el tema de la neutralidad, armoniza muy bien con la objetividad que naturalmente le atribuimos a la lógica. Desde esta perspectiva, la neutralidad de la lógica garantizaría que no haya restricciones derivadas de temas particulares, siendo así, un sistema universal y, por tanto, aplicable a contextos variables. En contraste, presentamos una concepción pluralista no-platonista, que caracteriza la variedad de relaciones de consecuencia lógica como algo concreto, dependiente del contexto, involucrado en casos particulares y dependiente de temas. Esta concepción no requiere de la suposición de entidades que pueden parecer altamente misteriosas, por lo que encuentra un camino adecuado para explicar las aplicaciones lógicas. Concluimos que, dado que cada postura tiene sus propias virtudes explicativas, el debate ontológico deberá dirimirse apelando a un análisis que considere también otras instancias además de la cuestión de las aplicaciones de la lógica.
José Ferreirós y Abel Lasalle Casanave (coordinadores), El árbol de los números: cognición, lógica y práctica matemática, Editorial Universidad de Sevilla, Sevilla, 2015, 256 pp.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.