Phenolysis of diaryl thiolcarbonates and thionocarbonates

Enrique A. Castro, Marjorie Cepeda, Paulina Paveza, José G. Santos

Resultado de la investigación: Article

7 Citas (Scopus)

Resumen

The phenolysis of phenyl S-4-nitrophenyl thiolcarbonate (1), 4-chlorophenyl S-4-nitrophenyl thiolcarbonate (2), phenyl 4-nitrophenyl thionocarbonate (3), 3-chlorophenyl 4-nitrophenyl thionocarbonate (4) and 3-methoxyphenyl 4-nitrophenyl thionocarbonate (5) are studied kinetically in 44 wt% ethanol-water, at 25.0 °C, ionic strength 0.2 M. The Brøpnsted plots (log kN vs. PKa of phenols) for the reactions of 1 and 2 are linear and those of 3, 4 and 5 are curved. The Brønsted slopes for 1 and 2 are 0.64 and 0.60, respectively, which suggest a concerted mechanism for these reactions. The curved Brønsted plots for the reactions of 3, 4 and 5 show slope values of 1.0, 1.1 and 1.1, respectively, at low pKa and 0.39, 0.28 and 0.34, respectively, at high pK a. The shape and slope values of these Brønsted plots are in accordance with a stepwise mechanism. The reactivity towards phenoxides of the thiocarbonates increases with the increase in the Hammett σ value for the substituents in the non-leaving group. The fact that the phenolysis of 3 is stepwise, whereas that of phenyl 4-nitrophenyl carbonate is concerted can be attributed to the destabilization of the intermediate T-. A similar argument explains the stepwise phenolysis of 3, in contrast to the concerted phenolysis of 1, where there is an additional destabilization of T- caused by the change of the leaving group, from 4-nitrophenoxide in 3 to 4-nitrobenzenethiolate in 1. Thiolcarbonates 1 and 2 in 44 wt% ethanol-water are less reactive towards phenoxide anions (ca. 100-fold) than their corresponding oxycarbonates in water.

Idioma originalEnglish
Páginas (desde-hasta)455-459
Número de páginas5
PublicaciónJournal of Physical Organic Chemistry
Volumen22
N.º5
DOI
EstadoPublished - may 2009

Huella dactilar

plots
destabilization
slopes
ethyl alcohol
water
Water
Ethanol
phenols
carbonates
reactivity
Phenols
anions
Ionic strength
Anions
4-nitrophenyl

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Organic Chemistry

Citar esto

Castro, Enrique A. ; Cepeda, Marjorie ; Paveza, Paulina ; Santos, José G. / Phenolysis of diaryl thiolcarbonates and thionocarbonates. En: Journal of Physical Organic Chemistry. 2009 ; Vol. 22, N.º 5. pp. 455-459.
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title = "Phenolysis of diaryl thiolcarbonates and thionocarbonates",
abstract = "The phenolysis of phenyl S-4-nitrophenyl thiolcarbonate (1), 4-chlorophenyl S-4-nitrophenyl thiolcarbonate (2), phenyl 4-nitrophenyl thionocarbonate (3), 3-chlorophenyl 4-nitrophenyl thionocarbonate (4) and 3-methoxyphenyl 4-nitrophenyl thionocarbonate (5) are studied kinetically in 44 wt{\%} ethanol-water, at 25.0 °C, ionic strength 0.2 M. The Br{\o}pnsted plots (log kN vs. PKa of phenols) for the reactions of 1 and 2 are linear and those of 3, 4 and 5 are curved. The Br{\o}nsted slopes for 1 and 2 are 0.64 and 0.60, respectively, which suggest a concerted mechanism for these reactions. The curved Br{\o}nsted plots for the reactions of 3, 4 and 5 show slope values of 1.0, 1.1 and 1.1, respectively, at low pKa and 0.39, 0.28 and 0.34, respectively, at high pK a. The shape and slope values of these Br{\o}nsted plots are in accordance with a stepwise mechanism. The reactivity towards phenoxides of the thiocarbonates increases with the increase in the Hammett σ value for the substituents in the non-leaving group. The fact that the phenolysis of 3 is stepwise, whereas that of phenyl 4-nitrophenyl carbonate is concerted can be attributed to the destabilization of the intermediate T-. A similar argument explains the stepwise phenolysis of 3, in contrast to the concerted phenolysis of 1, where there is an additional destabilization of T- caused by the change of the leaving group, from 4-nitrophenoxide in 3 to 4-nitrobenzenethiolate in 1. Thiolcarbonates 1 and 2 in 44 wt{\%} ethanol-water are less reactive towards phenoxide anions (ca. 100-fold) than their corresponding oxycarbonates in water.",
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Phenolysis of diaryl thiolcarbonates and thionocarbonates. / Castro, Enrique A.; Cepeda, Marjorie; Paveza, Paulina; Santos, José G.

En: Journal of Physical Organic Chemistry, Vol. 22, N.º 5, 05.2009, p. 455-459.

Resultado de la investigación: Article

TY - JOUR

T1 - Phenolysis of diaryl thiolcarbonates and thionocarbonates

AU - Castro, Enrique A.

AU - Cepeda, Marjorie

AU - Paveza, Paulina

AU - Santos, José G.

PY - 2009/5

Y1 - 2009/5

N2 - The phenolysis of phenyl S-4-nitrophenyl thiolcarbonate (1), 4-chlorophenyl S-4-nitrophenyl thiolcarbonate (2), phenyl 4-nitrophenyl thionocarbonate (3), 3-chlorophenyl 4-nitrophenyl thionocarbonate (4) and 3-methoxyphenyl 4-nitrophenyl thionocarbonate (5) are studied kinetically in 44 wt% ethanol-water, at 25.0 °C, ionic strength 0.2 M. The Brøpnsted plots (log kN vs. PKa of phenols) for the reactions of 1 and 2 are linear and those of 3, 4 and 5 are curved. The Brønsted slopes for 1 and 2 are 0.64 and 0.60, respectively, which suggest a concerted mechanism for these reactions. The curved Brønsted plots for the reactions of 3, 4 and 5 show slope values of 1.0, 1.1 and 1.1, respectively, at low pKa and 0.39, 0.28 and 0.34, respectively, at high pK a. The shape and slope values of these Brønsted plots are in accordance with a stepwise mechanism. The reactivity towards phenoxides of the thiocarbonates increases with the increase in the Hammett σ value for the substituents in the non-leaving group. The fact that the phenolysis of 3 is stepwise, whereas that of phenyl 4-nitrophenyl carbonate is concerted can be attributed to the destabilization of the intermediate T-. A similar argument explains the stepwise phenolysis of 3, in contrast to the concerted phenolysis of 1, where there is an additional destabilization of T- caused by the change of the leaving group, from 4-nitrophenoxide in 3 to 4-nitrobenzenethiolate in 1. Thiolcarbonates 1 and 2 in 44 wt% ethanol-water are less reactive towards phenoxide anions (ca. 100-fold) than their corresponding oxycarbonates in water.

AB - The phenolysis of phenyl S-4-nitrophenyl thiolcarbonate (1), 4-chlorophenyl S-4-nitrophenyl thiolcarbonate (2), phenyl 4-nitrophenyl thionocarbonate (3), 3-chlorophenyl 4-nitrophenyl thionocarbonate (4) and 3-methoxyphenyl 4-nitrophenyl thionocarbonate (5) are studied kinetically in 44 wt% ethanol-water, at 25.0 °C, ionic strength 0.2 M. The Brøpnsted plots (log kN vs. PKa of phenols) for the reactions of 1 and 2 are linear and those of 3, 4 and 5 are curved. The Brønsted slopes for 1 and 2 are 0.64 and 0.60, respectively, which suggest a concerted mechanism for these reactions. The curved Brønsted plots for the reactions of 3, 4 and 5 show slope values of 1.0, 1.1 and 1.1, respectively, at low pKa and 0.39, 0.28 and 0.34, respectively, at high pK a. The shape and slope values of these Brønsted plots are in accordance with a stepwise mechanism. The reactivity towards phenoxides of the thiocarbonates increases with the increase in the Hammett σ value for the substituents in the non-leaving group. The fact that the phenolysis of 3 is stepwise, whereas that of phenyl 4-nitrophenyl carbonate is concerted can be attributed to the destabilization of the intermediate T-. A similar argument explains the stepwise phenolysis of 3, in contrast to the concerted phenolysis of 1, where there is an additional destabilization of T- caused by the change of the leaving group, from 4-nitrophenoxide in 3 to 4-nitrobenzenethiolate in 1. Thiolcarbonates 1 and 2 in 44 wt% ethanol-water are less reactive towards phenoxide anions (ca. 100-fold) than their corresponding oxycarbonates in water.

KW - Bronsted plots

KW - Kinetics

KW - Mechanism

KW - Phenolysis

KW - Thiocarbonates

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