Formation of a promazine radical and promazine 5‐oxide in the reaction of promazine with hydrogen peroxide: Mechanistic insight from kinetic and EPR measurements

Abstract

AbstractThe kinetics of the oxidation of promazine (PMZ) by hydrogen peroxide was studied in the presence of a large excess of H2O2in acidic chloride media using UV–vis spectroscopy. The reaction proceeds via two consecutive steps. In the first step, oxidation leads to formation of a promazine radical. In the second step, the promazine radical is oxidized to promazine 5‐oxide. Electron paramagnetic resonance spectroscopy (EPR) results provide clear evidence for the formation of an intermediate promazine radical. Linear dependences of the pseudo‐first‐order rate constants (k1andk2) on [H2O2] with a nonzero intercept were established for the first and the second process, respectively. The rate of the first stage of the reaction increased slightly with increasing concentration of O2, indicating the role of the OH•radicals on the redox process, which are transformed into the Clradicals. The mechanism of the overall reaction is discussed on the basis of all these kinetic measurements. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 42: 1–9, 2010