Investigation of the Halogenate-Hydrogen Peroxide Reactions Using the Electron Paramagnetic Resonance Spin Trapping...

The differences in the mechanism of the halogenate reactions with the same oxidizing/reducing agent, such as H₂O₂ contribute to the better understanding of versatile halogen chemistry. The reaction between iodate, bromate, and chlorate with hydrogen peroxide in acidic medium at 60 °C is investigated by using the electron paramagnetic resonance (EPR) spin trapping technique. Essential differences in the chemistry of iodate, bromate, and chlorate in their reactions with hydrogen peroxide have been evidenced by finding different radicals as governing intermediates. The reaction between KIO₃ and H₂O₂ is supposed to be the source of IO₂^• radicals. The KBrO₃ and H₂O₂ reaction did not produce any EPR signal, whereas the KClO₃-H₂O₂ system was found to be a source of HO^• radical. Moreover, KClO₃ dissolved in sulfuric acid without hydrogen peroxide produced HO^• radical as well. The minimal-core models explaining the origin of obtained EPR signals are proposed. Current findings suggested the inclusion of IO₂^• and HOO^• radicals, and ClO₂^• and HO^• radicals in the particular kinetic models of iodate-hydrogen peroxide and chlorate-hydrogen peroxide systems, as well as possible exclusion of BrO₂^• radical from the kinetic scheme of the bromate-hydrogen peroxide system. Obtained results may pave the way for understanding more complex, nonlinear reactions of these halogen-containing species.