A Kinetic Study of Alkaline Hydrolysis of 1-Arylamino-3-arylimino-1-butene

Alkaline hydrolysis of 1-arylamino-3-arylimino-1-butene (1) was studied kinetically. The reaction proceeded in two ways; by hydrolysis at the 1-position of 1 to give β-arylaminocrotonaldehyde (2) and arylamine (pathway A), and by hydrolysis at the 3-position of 1 to give 4-arylamino-3-buten-2-one (3) and arylamine (pathway B), of which the former predominated. In the first step of pathway A, 1-position of 1 is attacked by hydroxide ion to give a tetrahedral intermediate which is then transformed into 2 and arylamine in the second step. Plots of the rate constants of pathway A, kA, vs. [OH-] were concave downward because the rates of the two steps are of similar order of magnitude. We were able to calculate the hydroxide ion-catalyzed rate constant (kOH1) of the first step of pathway A for 4 substrates, 1a-d. The kOH, 1s decreased with increasing electron-withdrawing effect of the aryl substituents. The reaction mechanism is discussed.