Kinetics and Mechanism for Pyridine N-Oxide Carboxaldehyde Phenylhydrazone Formation

Article abstract of DOI:10.1021/ja00532a029

Phenylhydrazone formation from the three isomeric pyridine N-oxide carboxaldehydes occurs with two breaks in the pH-rate profiles.Under alkaline conditions, nonlinearity between first-order rate constants and amine concentration established that carbinolamine dehydration is rate determining.Under more acidic conditions, structure-reactivity correlations and susceptibility to general acid catalyis, as well as the break in the pH-rate profile, strongly suggest that stepwise formation of carbinolamine becomes the rate-determining step.Finally, the second break in the pH profile is interpreted as reflecting a transition to rate-determining concerted formation of the carbinolamine.