Intramolecular general base catalysis exerted by the carboxilate group in the spontaneous dehydration of the carbinolamine formed from benzoylformic anion and hydroxylamine at early values of pH

Abstract

Data obtained from the reaction of oxime formation from benzoylformic anion lead to the suggestion that the spontaneous dehydration observed after pH ∼ 5.0, proceeds through a transition state in which an intramolecular general base catalysis is exerted by the carboxylate group. Copyright © 2007 John Wiley & Sons, Ltd.

Kinetics and Mechanism for Oxime Formation from 4-Pyridinecarboxaldehyde N-Oxide

“…At pH 7.50, the progress of the reaction was followed by the initial rate method since the rate was very slow as described in our previous paper. 8 Equilibrium constant for addition The equilibrium constant for carbinolamine formation, K add, from hydroxylamine to 4-pyridinecarboxaldehyde N-oxide was determined at 30 o C, μ = 0.5 (KCl), in aqueous solution, at pH 7.26 (sodium hydrogen phosphate 0.16 M), under accumulation conditions, in the zone where the rate constants increase less rapidly than the hydroxylamine concentration (see Fig. 1).…”

Kinetics and mechanism for oxime formation from benzoylformic acid: Electrostatic interactions in the dehydration of carbinolamines

“…Glass‐distilled water was used throughout. Benzoylformic acid oxime was prepared and characterized in a previous paper 8.…”

“…UV spectra of benzoylformic acid oxime obtained at pH from about 0.25 to 5.5 indicate quantitative kinetic yields. All rate measurements were determined as previously described 8. Rate constants were measured in water at 30°C and ionic strength 0.5 (KCl) under pseudo‐first‐order conditions.…”

“…Second‐order rate constants, k obs /[NH 2 OH] fb , were obtained from slopes of plots of the first‐order rate constants against the concentration of hydroxylamine free base and were corrected for accumulation of carbinolamine intermediate using k = k (1 + K add [NH 2 OH] fb ). In the pH range of ∼4 to ∼5.5, the progress of the reaction was followed by the initial rate method because the rate of the process was very slow as described in our previous paper 8.…”

“…In previous works, we studied the formation of oxime from methyl benzoylformate and benzoylformic anion, to (1) model the behavior of the benzoylformic acid 7 and (2) evaluate the equilibrium constant of addition and the specific acid‐catalyzed dehydration of the anionic carbinolamine 8.…”