Kinetic and ESR studies of the CuII-halides mediated oxidation of promazine by dioxygen in acidic aqueous solutions

The Cu^sup II^-mediated oxidation of promazine by dioxygen to form promazine 5-oxide was studied in the presence of a large excess of dioxygen, Cu^sup II^-halides (Cl^sup -^, Br^sup -^) and H^sup +^ ions using u.v.-vis and ESR spectroscopies. The first step is a fast reaction between promazine and C...

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Published in:Transition metal chemistry (Weinheim) 2007-10, Vol.32 (7), p.857-863
Main Authors: Wiśniewska, Joanna, Kita, Przemysław, Wrzeszcz, Grzegorz
Format: Article
Language:English
Subjects:
Aqueous solutions
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Summary:The Cu^sup II^-mediated oxidation of promazine by dioxygen to form promazine 5-oxide was studied in the presence of a large excess of dioxygen, Cu^sup II^-halides (Cl^sup -^, Br^sup -^) and H^sup +^ ions using u.v.-vis and ESR spectroscopies. The first step is a fast reaction between promazine and Cu^sup II^-halides leading to the production of a stable promazine radical with much higher yield in bromide than chloride media. ESR results provide clear evidence for the formation of this radical. In the second step the cation radical is oxidized by dioxygen to a dication hydrolyzing to promazine 5-oxide. The promazine-superoxide complex, concentration of which is determined by steady-state approximation, is postulated as a significant intermediate resulting from the reduction of dioxygen by the cation radical. The final product, promazine 5-oxide, is formed via a spontaneous and a Cu^sup II^-assisted reaction path way. Cu^sup II^ controls the reaction rate through: (i) oxidation of promazine to the promazine radical, (ii) acting as a scavenger of superoxide, and (iii) slow oxidation of the promazine radical in the parallel reaction. The rate is independent of [H^sup +^], linearly dependent on [O^sub 2^] and only slightly dependent on [Cu^sup II^] within the excess concentration range of the Cu^sup II^ complexes used. Mechanistic consequences of all these results are discussed.[PUBLICATION ABSTRACT]
ISSN:0340-4285
1572-901X
DOI:10.1007/s11243-007-0219-1