Effect of Amine Nature on Rates and Mechanism: Pyridinolyses of 4-Nitrophenyl Benzoate

doi:10.5012/bkcs.2003.24.9.1245

Cited by 8 publications

(4 citation statements)

References 37 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The pyridinolysis of 4-nitrophenyl benzoate in water shows a linear Brønsted-type plot with slope 1.1, consistent with a stepwise mechanism where breakdown of the intermediate T ± is rate-determining . This result is in agreement with the curved Brønsted plot, with p = 9.7, obtained for the pyridinolysis of thiolbenzoate 1 in aqueous ethanol (this work), on the following grounds.…”

Section: Resultssupporting

confidence: 89%

“…Even the amidium cations derived from very basic pyridines are rapidly hydrolyzed. 1-Benzoyl-4-(dimethylamino)pyridinium could not be detected in the reaction of this pyridine with 4-nitrophenyl benzoate in water . Nevertheless, the acetylpyridinium derivatives are more stable toward hydrolysis, as indicated by the fact that 1-acetyl-4-(dimethylamino)pyridinium has been observed spectrophotometrically in the reaction of this pyridine with acetic anhydride and 2,4-dinitrophenyl thiolacetate in aqueous solution .…”

Section: Methodsmentioning

confidence: 82%

See 1 more Smart Citation

Kinetics and Mechanism of the Pyridinolysis of S-4-Nitrophenyl 4-Substituted Thiobenzoates in Aqueous Ethanol

et al. 2004

View full text Add to dashboard Cite

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.

show abstract

Section: Resultssupporting

confidence: 89%

Section: Methodsmentioning

confidence: 82%

Kinetics and Mechanism of the Pyridinolysis of S-4-Nitrophenyl 4-Substituted Thiobenzoates in Aqueous Ethanol

et al. 2004

View full text Add to dashboard Cite

show abstract

“… a The p K a data in 80 mol % H 2 O/20 mol % DMSO were taken from ref . b Determined in this study by using the method shown in ref . …”

Section: Resultsmentioning

confidence: 99%

Effect of Changing Electrophilic Center from CO to CS on Rates and Mechanism: Pyridinolyses of O-2,4-Dinitrophenyl Thionobenzoate and Its Oxygen Analogue

Han

Baek

et al. 2004

J. Org. Chem.

View full text Add to dashboard Cite

Second-order rate constants have been measured spectrophotometrically for the reactions of O-2,4-dinitrophenyl thionobenzoate (1) and 2,4-dinitrophenyl benzoate (2) with a series of substituted pyridines in 80 mol % H(2)O/20 mol % DMSO at 25.0 +/- 0.1 degrees C. The Brønsted-type plots obtained are nonlinear with beta(1) = 0.26, beta(2) = 1.07, and pK(a) degrees = 7.5 for the reactions of 1 and beta(1) = 0.40, beta(2) = 0.90, and pK(a) degrees = 9.5 for the reactions of 2, suggesting that the pyridinolyses of 1 and 2 proceed through a zwiterionic tetrahedral intermediate T(+/-) with a change in the rate-determining step at pK(a) degrees = 7.5 and 9.5, respectively. The thiono ester 1 is more reactive than its oxygen analogue 2 except for the reaction with the strongest basic pyridine studied (pK(a) = 11.30). The k(1) value is larger for the reactions of 1 than for those of 2 in the low pK(a) region, but the difference in the k(1) value becomes negligible with increasing the basicity of pyridines. On the other hand, 1 exhibits slightly larger k(2)/k(-1) ratio than 2 in the low pK(a) region but the difference in the k(2)/k(-1) ratio becomes more significant with increasing the basicity of pyridines. Pyridines are more reactive than alicyclic secondary amines of similar basicity toward 2 in the pK(a) above ca. 7.2 but less reactive in the pK(a) below ca. 7.2. The k(1) value is slightly larger, but the k(2)/k(-1) ratio is much smaller for the reactions of 2 with pyridines than with isobasic secondary amines in the low pK(a) region, which is responsible for the fact that the weakly basic pyridines are less reactive than isobasic secondary amines.

show abstract

“…Ester hydrolysis is an important type of reaction that has received a great deal of attention in both organic chemistry and biochemistry, and it has been subjected to many investigations. − …”

Section: Introductionmentioning

confidence: 99%

Kinetic and Theoretical Studies on the Mechanism of Intramolecular Catalysis in Phenyl Ester Hydrolysis

2006

View full text Add to dashboard Cite

The kinetic study of the hydrolysis reaction of Z-substituted phenyl hydrogen maleates (Z = H, m-CH3, p-CH3, m-Cl, p-Cl and m-CN) was carried out in aqueous solution, and the results were complemented with theoretical studies. Under some experimental conditions, two kinetic processes were observed. One of them was ascribed to maleic anhydride formation and the other to the anhydride hydrolysis. The Brönsted-type plot for the leaving-group dependence was linear with slope beta(lg) = -1. The experimental results are consistent with a mechanism that involves significant bond breaking in the rate-limiting transition state (alpha(lg) = 0.64). Theoretical results for the reaction in the gas phase showed an excellent Brönsted-type dependence with a beta(lg) of -1.03. A tetrahedral intermediate (TI) could not be found through DFT gas-phase studies (B3LYP/6-311+G*). Calculations carried out within a continuous solvation model or with discrete water molecules failed to find a stable TI. With both models, a flat region on the potential-energy surface is found and a tight optimization of the structures led back to starting materials. The theoretical results do not discard the possible existence of an unstable intermediate on the free-energy surface, but the analysis of the whole body of results compared with other acyl transfer reactions lead us to suggest that an enforced concerted mechanism is the most appropriate to describe these reactions.

show abstract

Effect of Amine Nature on Rates and Mechanism: Pyridinolyses of 4-Nitrophenyl Benzoate

Cited by 8 publications

References 37 publications

Kinetics and Mechanism of the Pyridinolysis of S-4-Nitrophenyl 4-Substituted Thiobenzoates in Aqueous Ethanol

Kinetics and Mechanism of the Pyridinolysis of S-4-Nitrophenyl 4-Substituted Thiobenzoates in Aqueous Ethanol

Effect of Changing Electrophilic Center from CO to CS on Rates and Mechanism: Pyridinolyses of O-2,4-Dinitrophenyl Thionobenzoate and Its Oxygen Analogue

Kinetic and Theoretical Studies on the Mechanism of Intramolecular Catalysis in Phenyl Ester Hydrolysis

Contact Info

Product

Resources

About