Thermodynamic substantiation for non-radical mechanism of thiosulfate (hyposulfite) oxidation by hydrogen peroxide in aqueous solution

Autor: Anton A. Chumakov, Tamara S. Minakova, Yurij G. Slizhov
Rok vydání: 1970
Předmět:
Zdroj: IZVESTIYA VYSSHIKH UCHEBNYKH ZAVEDENII KHIMIYA KHIMICHESKAYA TEKHNOLOGIYA.
ISSN: 2500-3070
0579-2991
DOI: 10.6060/ivkkt201962fp.5733
Popis: Thiosulfate (hyposulfite) anion S2O32− is oxidized by hydrogen peroxide in aqueous solution directly (non-catalytically) and exothermically with significant thermal effect. The reaction mechanism is not verified until now. Literature data evidence the Wackenroder's solution of polythionates as oxidation product. The kinetics of polythionates generation in system and the mechanism of hydrogen peroxide oxidative activation are indeed an interesting task of fundamental chemistry. Its solution can contribute to growth of reaction applied value. We composed 25 reaction equations, among which 1–21 are proposed intermediate steps of whole process, 22–24 are summarized equations, and the equation 25 is final overall one. Thermodynamic analysis of reactions was carried out using reference values of standard thermodynamic functions of reagents and products of reactions and applying known laws and equations of thermochemistry. Results show that only one proposed intermediate step among all is endothermic and endergonic reaction. This is the reaction of thiosulfate hydrolysis into hydrosulfide HS− and bisulfate HSO4−. Other reactions are exothermic and exergonic. There are steps with releasing of significant heat amount. Therefore, an endothermic/endergonic step is possible by coupling with exothermic/exergonic reactions. The idea of coupled thiosulfate hydrolysis with generation of large amount of hydrosulfide ions substantiates a mechanism of polythionate ions formation through oxidative generation of polysulfide ions. The argued mechanism of conversions in reaction system S2O32−/H2O2/H2O is illustrated in three figures. The conception used for hydrogen peroxide oxidative activation excludes free radicals generation. We proposed an intramolecular proton transfer with oxywater H2O+−O− formation. Further, it heterolytically dissociates into water and oxygen atom (oxene) in 1D-singlet quantum state. This is non-radical particle (2p[↑↓][↑↓][__]), which oxidizes substrates targeting their electron pairs by its vacant atomic orbital.
Databáze: OpenAIRE
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