The oxidative degradation and C–C coupling reaction of dibenzoazepine derivatives by peroxydisulfate ion and sulfate radical in aqueous media

Abstract

The kinetics of the oxidation of imipramine and opipramol using peroxydisulfate salts in the presence of a large excess of dibenzoazepine derivative (TCA) in acidic sulfate media was studied using UV–vis spectroscopy. The reaction between imipramine and S2O8 2− proceeds via the formation of two intermediates: a free organic radical and a dimeric dication. Further reaction of the intermediate dimeric dication leads to a positively charged radical dimer as one final product. Simultaneously, two other substituent cleavage degradation processes occur, leading to two dimeric derivatives. The first product, the positively charged radical dimer, and the next main product, a radical dimer without one alkyl substituent, were identified by EPR measurements. The measured kinetic trace is not first order and revealed a sigmoid shape with a characteristic induction time. The rate constants were determined by numerical analysis based on ordinary differential equations (ODEs). The reaction between opipramol and S2O8 2− proceeds by a two consecutive reaction scheme. The kinetics of the first degradation step were studied independently of the slower degradation reactions. Linear dependences, with zero intercept, of the pseudo-first-order rate constants (k obs) on [TCA] were determined for the first degradation process of opipramol.