A Kinetic Study of Alkaline Hydrolysis of β-Arylaminoacrolein

• Published in: Chemical & pharmaceutical bulletin Vol. 37; no. 11; pp. 2902 - 2908
• Main Authors: ONO, Machiko, TODORIKI, Reiko, MITAKE, Akihisa, YUKAWA, Miho, GOTO, Yoshinobu, TAMURA, Shinzo
• Format: Journal Article
• Language: English
• Published: Tokyo The Pharmaceutical Society of Japan 1989; Maruzen
• Subjects: activation parameter; alkaline hydrolysis; Chemistry; Exact sciences and technology; isotope effect; kinetic study; Kinetics and mechanisms; MO calculation; Organic chemistry; reaction mechanism; Reactivity and mechanisms; β-arylaminoacrolein; Hydrolysis; MNDO method; Basic solution; Aliphatic compound; Theoretical study; Activation parameter; Enaminoaldehyde; Rate constant; Thermodynamic properties; Conformation
• DOI: 10.1248/cpb.37.2902
• ISSN: 0009-2363

Alkaline hydrolysis of β-arylaminoacrolein (1), a vinylog of amides, was studied kinetically. The kinetics involved terms both first and second order in hydroxide ion. The first step of the reaction (rate constant k1) is an attack of hydroxide ion on the β-position of 1, and the tetrahedral intermediate formed was partitioned in two ways : one without the aid of hydroxide ion (k2(k1/k-1)), and the other with the aid of hydroxide ion (k3(k1/k-1)). The rate constants, k1, k2(k1/k-1) and k3(k1/k-1) were obtained for 12 substrates, and the activation parameters, ΔH≠ and ΔS≠, of each step were evaluated for 5 substrates. The k2/k-1 values decreased with increasing electron-withdrawing effect of aryl substituents. The differences of ΔHf between the intermediates and the starting materials were evaluated by molecular orbital (MO) calculatins. The results showed that k2 decreases with increasing electron-withdrawing effect of the substitutents. The second step of the second-order reaction, k2(k1/k-1), is partitioning of anionic intermediates catalyzed by water as a general acid. While the second step of the third-order reaction, k3(k1/k-1), for "typical" substrates is departure of the arylamino group from the anionic intermediates catalyzed by both hydroxide ion and water, that for β-(p-nitrophenylamino)acrolein (1j) is direct expulsion of p-nitroanilide ion from the dinegatively charged intermediate.