Kinetics of dopamine oxidation by sodium N-bromo-p-toluenesulphonamide in acid medium. A mechanistic approach

The oxidation kinetics of dopamine (DPM) by sodium N-bromo-p-toluenesulphonamide (bromamine-T or BAT) was investigated at 40°C in HClO4 medium. The rate is first order in BAT0, fractional order in DPM0 and inverse fractional in H+. Addition of reaction product, p-toluenesulphonamide, or halide ions and variation of ionic strength of the medium have no significant effect on the rate. The dielectric effect is positive. The solvent isotope effect has been studied in D2O medium. The reaction fails to induce the polymerisation of acrylonitrile. The Michaelis-Menten type of kinetics is observed. Activation parameters for the overall reaction and also for the rate-limiting step were computed. Dopa-o-quinone or 2-(3â²4â²-benzoquinone) ethylamine was identified as the oxidation product of DPM. A mechanism consistent with the observed kinetics is proposed and discussed