A new kinetic model for the acid-catalysed reactions of N-(2-aminophenyl)phthalamic acid in aqueous media

Abstract

The acid-catalysed breakdown of N-(2-aminophenyl)phthalamic acid has been studied in dilute aqueous acids in the pH range 0–6. The dominant reaction is the formation of N-(2-aminophenyl)phthalimide (between ∼80 and ∼100% yields in the pH range studied) and its subsequent rearrangement to 2-(2-carboxyphenyl)benzimidazole, occurring as consecutive pseudo-first-order processes. Anomalously, only a minor hydrolysis reaction is observed.A kinetic model for these processes has been constructed and rate constants and activation parameters evaluated. Mechanisms involving pre-equilibria to form the kinetically significant species have been proposed for the consecutive processes. The approach has been adapted to account for the observed kinetics of acid catalysed formation of benzimidazoles from o-aminoanilides.