Kinetics and mechanism of the hypochlorous acid-trithionate reaction
György Csekő1, Evelin Rauscher, Attila K Horváth
1Department of Inorganic Chemistry, University of Pécs , Ifjúság útja 6, H-7624 Pécs, Hungary , and János Szentágothai Research Center , Ifjúság útja 20, H-7624 Pécs, Hungary.
Abstract:
The trithionate-hypochlorous acid reaction has been studied by the stopped-flow technique and conventional spectrophotometry between pH = 6.59-12.2 monitoring absorbance-time profiles at 285 and 225 nm. We showed that the formal kinetic order of Cl(I) is nearly 2; however, those of hydrogen ion and trithionate are significantly lower than unity, suggesting complex kinetics. It was also demonstrated that both forms of Cl(I) are kinetically active within the concentration range studied. Simultaneous evaluation of the kinetic curves revealed that the reaction was initiated by a formal Cl(+) transfer to the partially negatively charged β-sulfur of trithionate. S3O6Cl(-) formed in the first step was also found to be equilibrating with S3O6OH(-) via a simple chlorine-OH exchange reaction followed by their subsequent oxidation of hypochlorite and hypochlorous acid, respectively. A six-step kinetic model is proposed and discussed with having four fitted and four fixed parameters.
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