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

The kinetics of the oxidation of promazine (PMZ) by hydrogen peroxide was studied in the presence of a large excess of H 2 O 2 in 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-firstorder rate constants (k 1 and k 2 ) on [H 2 O 2 ] 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 O 2 , indicating the role of the OH • radicals on the redox process, which are transformed into the Cl −• 2 radicals. The mechanism of the overall reaction is discussed on the basis of all these kinetic measurements. C 2009 Wiley Periodicals, Inc. Int J Chem Kinet 42:

Sulfuric acid controlled oxidative degradation of azure B and thionine dyes by cerium(IV)

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