N-Methyl-3,4-dihydroisoquinolinium-catalysed oxidation of calmagite by peracetic acid: kinetics and mechanism of catalyst inactivation

Abstract

The azo dye, calmagite, is oxidized by peracetic acid and a catalytic amount of N-methyl-3,4-dihydroisoquinolinium p-toluenesulfonate by in situ formation of the corresponding oxaziridinium salt. The kinetics of the reaction have been examined under steady-state conditions in aqueous solution at pH 10. Under pseudo-first-order conditions employing an excess of calmagite relative to peracetic acid, no catalyst degradation is observed. Under near equimolar concentration of reactants, however, catalyst inactivation is found to be significant. Two major decomposition products have been isolated. Kinetic and product analyses indicate that catalyst inactivation occurs through the oxaziridinium salt intermediate by two major pathways; alkaline hydrolysis, which accounts for 60% of catalyst decomposition, and nucleophilic attack by peracid on the oxaziridinium salt.