The kinetics and mechanism of electrophilic substitution of heteroaromatic compounds. Part XVI. Acid-catalysed hydrogen exchange of some pyridazine derivatives

Abstract

4-Aminopyridazine exchanges in acid solution as the conjugate acid at the 5-position. In the low acidity region, the conjugate acid exchanges by the ylid mechanism at the 3- and 6-positions. Pyridazin-4-one exchanges by the acid-catalysed mechanism as the neutral species at the 5-position; ylid-mechanism exchange on the conjugate acid occurs at the 3- and 6-positions. Pyridazin-3-one exchanges in acid solution at the 5-position; the mechanism probably involves a hydrated species. Rate constants are measured and discussed.