Phenolysis and aminolysis of 4-nitrophenyl and 2,4-dinitrophenyl S-methyl thiocarbonates in aqueous ethanol

Enrique A. Castro, Margarita E. Aliaga, Marjorie Cepeda, José G. Santos

Resultado de la investigación: Article

8 Citas (Scopus)

Resumen

The reactions of S-methyl O-(4-nitrophenyl) thiocarbonate (1) and S-methyl O-(2,4-dinitrophenyl) thiocarbonate (2) with a series of secondary alicyclic (SA) amines and phenols are subjected to a kinetic investigation. Under nucleophile excess, pseudo-first-order rate coefficients (kobs) are obtained. Plots of kobs against the free nucleophile concentration at constant pH are linear with slopes kN. The BrØnsted plots (log kN vs. nucleophile pKa) for the reactions are linear with slope (β) values in the 0.5-0.7 range, in accordance with concerted mechanisms. Comparison of the SA aminolysis of 1 with the same one carried out in water shows that the change of solvent from water to aqueous ethanol destabilizes the zwitterionic tetrahedral intermediate, changing the mechanism from stepwise to concerted. This destabilization is greater than that due to the change from SA amines to quinuclidines. For the phenolysis reactions, the kN values in aqueous ethanol are smaller than those for the same reactions in water. Considering that the nucleophile is an anion, this result is unexpected because the anion should be more stabilized in the more polar solvent. This result is explained by the facts that the phenoxide reactant has a negative charge that is delocalized in the aromatic ring and the transition state is highly polar.

Idioma originalEnglish
Páginas (desde-hasta)353-358
Número de páginas6
PublicaciónInternational Journal of Chemical Kinetics
Volumen43
N.º7
DOI
EstadoPublished - jul 2011

Huella dactilar

Nucleophiles
nucleophiles
ethyl alcohol
Ethanol
Amines
Anions
Water
Quinuclidines
amines
plots
Phenols
water
slopes
anions
destabilization
phenols
Kinetics
4-nitrophenyl
rings
kinetics

ASJC Scopus subject areas

  • Biochemistry
  • Physical and Theoretical Chemistry
  • Organic Chemistry
  • Inorganic Chemistry

Citar esto

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abstract = "The reactions of S-methyl O-(4-nitrophenyl) thiocarbonate (1) and S-methyl O-(2,4-dinitrophenyl) thiocarbonate (2) with a series of secondary alicyclic (SA) amines and phenols are subjected to a kinetic investigation. Under nucleophile excess, pseudo-first-order rate coefficients (kobs) are obtained. Plots of kobs against the free nucleophile concentration at constant pH are linear with slopes kN. The Br{\O}nsted plots (log kN vs. nucleophile pKa) for the reactions are linear with slope (β) values in the 0.5-0.7 range, in accordance with concerted mechanisms. Comparison of the SA aminolysis of 1 with the same one carried out in water shows that the change of solvent from water to aqueous ethanol destabilizes the zwitterionic tetrahedral intermediate, changing the mechanism from stepwise to concerted. This destabilization is greater than that due to the change from SA amines to quinuclidines. For the phenolysis reactions, the kN values in aqueous ethanol are smaller than those for the same reactions in water. Considering that the nucleophile is an anion, this result is unexpected because the anion should be more stabilized in the more polar solvent. This result is explained by the facts that the phenoxide reactant has a negative charge that is delocalized in the aromatic ring and the transition state is highly polar.",
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Phenolysis and aminolysis of 4-nitrophenyl and 2,4-dinitrophenyl S-methyl thiocarbonates in aqueous ethanol. / Castro, Enrique A.; Aliaga, Margarita E.; Cepeda, Marjorie; Santos, José G.

En: International Journal of Chemical Kinetics, Vol. 43, N.º 7, 07.2011, p. 353-358.

Resultado de la investigación: Article

TY - JOUR

T1 - Phenolysis and aminolysis of 4-nitrophenyl and 2,4-dinitrophenyl S-methyl thiocarbonates in aqueous ethanol

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AU - Santos, José G.

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AB - The reactions of S-methyl O-(4-nitrophenyl) thiocarbonate (1) and S-methyl O-(2,4-dinitrophenyl) thiocarbonate (2) with a series of secondary alicyclic (SA) amines and phenols are subjected to a kinetic investigation. Under nucleophile excess, pseudo-first-order rate coefficients (kobs) are obtained. Plots of kobs against the free nucleophile concentration at constant pH are linear with slopes kN. The BrØnsted plots (log kN vs. nucleophile pKa) for the reactions are linear with slope (β) values in the 0.5-0.7 range, in accordance with concerted mechanisms. Comparison of the SA aminolysis of 1 with the same one carried out in water shows that the change of solvent from water to aqueous ethanol destabilizes the zwitterionic tetrahedral intermediate, changing the mechanism from stepwise to concerted. This destabilization is greater than that due to the change from SA amines to quinuclidines. For the phenolysis reactions, the kN values in aqueous ethanol are smaller than those for the same reactions in water. Considering that the nucleophile is an anion, this result is unexpected because the anion should be more stabilized in the more polar solvent. This result is explained by the facts that the phenoxide reactant has a negative charge that is delocalized in the aromatic ring and the transition state is highly polar.

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