Spectrophotometric and high-performance liquid chromatographic determination of the kinetics and mechanisms of hydrolysis, isomerisation and cyclisation of both E and Z isomers of 2-{[(2-amino-5-chlorophenyl)phenylmethylene]amino}acetamide

Abstract

The behaviour of 2-{[(2-amino-5-chlorophenyl)phenylmethylene]amino}acetamide in aqueous solution was investigated in the pH range 1.0–8.0, with respect to the E or Z configuration around the imine bond. The E isomer yields kinetic data that obey the kinetic law for successive first-order reactions. The first step consists of the isometric transformation of the E to the Z isomer. The second step implies a parallel reaction mechanism, i.e., either a hydrolysis yielding 2-amino-5-chlorobenzophenone or an intramolecular ring closure reaction yielding desmethyldiazepam. This parallel route constitutes a major reaction at pH values below the pK_a of the immonium-imine equilibrium, as demonstrated by UV spectrophotometry and high performance liquid chromatography.