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

✍ Scribed by Anna Katafias; Joanna Fenska

Publisher
John Wiley and Sons
Year
2011
Tongue
English
Weight
475 KB
Volume
43
Category
Article
ISSN
0538-8066

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✦ Synopsis

Abstract

Azure B (AB) and thionine (TH) cationic phenothiazyne dyes undergo an oxidative degradation by cerium(IV) in sulfuric acid media. TLC analysis of the reaction mixture containing an excess of the oxidant has shown the presence of thionine and/or methylene violet (Bernthsen) and other unidentified species. The kinetics of (i) two AB oxidation steps, namely the formation of a colored radical and its further decomposition, and (ii) the TH disappearance was studied using visible absorption spectroscopy combined with a stopped‐flow method. Generation of the AB radical was confirmed by continuous flow electron paramagnetic resonance (EPR) spectroscopy. The reactions are first order in the total dye concentration, [S]. The kinetics of the studied systems is described by a common general rate law:

equation image

The reactivity of the reductants in their protonated and unprotonated forms is expressed by products of preequilibrium constants and electron transfer (within encounter complex) rate constants. The mechanism of the overall process is discussed. © 2011 Wiley Periodicals, Inc. Int J Chem Kinet 43: 523–536, 2011

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