Kinetic Analysis Of Sulfitolysis And Thiosulfatolysis For Polythionates

The Kinetics and mechanism of the oxidation of thiosulfate, the sulfitolysis and thiosulfatolysis of polythionates were studied by the means of high-performance liquid chromatography spectrometry(HPLC), capillary electrophoresis(CE) and ultraviolet spectrophotometer(UV-Vis), which could reveal the detailed mechanism and provide experimental evidences for the nonlinear phenomena of sulfur containing species.The Br O3-- S2O32- system had been studied by reversed phase ion-pair high performance liquid chromatographic method. An optimized separation condition of bromate, thiosulfate and SxO62-(x = 4- 5), only needs 8 minutes, was obtained through adjusting the species of ion-pair reagents, the concentration of different ion-pair reagents. The mixture of TEAOH and TPAOH in the mobile phase was used in the separation of the reaction. The Br O3-- S2O32- was studied at T = 25.0 ± 0.1oC and during the range of p H 4.25- 5.50. Several intermediates, including HSO3-, SO42-, S4O62- and S5O62- were detected simultaneously in the oxidation of thiosulfate by bromate, where S4O62- as the primary intermediate. In preliminary study by liquid chromatographic method, it can be found that concentration-time curves of S2O32- and S4O62- display a sigmoidal shape in a slightly acidic, well-buffered medium, meaning that some sort of autocatalysis is involved. When adding a trace amount of HSO3-into the reacting solutionsat the beginning of the reaction, the reaction rate also significantly improved. Which clearly prove that HSO3- is the autocatalyst under the experimental conditions. The oxidation rate was decreased and the induction time was increased as the increasing of p H and the decrease of initial concentration of oxidant Br O3-. The reaction orders of Br O3-, S2O32- and H+in Br O3-- S2O32- system were determined as 1st for by initial rate method. A kinetis model with 8 step was proposed based on the online simultaneously monitoring the concentrations of S2O32- and S4O62-during the reaction process.The kinetics of the reaction of tetrathionate with S(IV) species and with thiosulfate in slightly acidic media was studied concurrently in presence of acetic acid/acetate buffer at T = 25.0 ± 0.1℃ by high-performance liquid chromatography monitoring the concentration of polythionates(including trithionate, tetrathionate and pentathionate), thiosulfate and sulfite, simultaneously. The tetrathionate–sulfite as well as the tetrathionate–thiosulfate reactions are first order with respect to both reactants. A simple three-step kinetic model was proposed involving two reversible reactions and the value of the forward and reverse rate coefficients could be determined from our experiments. p H-dependence of the tetrathionate–sulfite reaction emerges from the reactivity difference of sulfite and hydrogen-sulfite towards the β-sulfur of tetrathionate. The tetrathionate–thiosulfate reaction, however, was found to be p H-independent reaction suggesting that S(IV) species is a short-lived intermediate during the course of this reaction.The preparations and alkaline decompositions of pentathionate ions were studied in the thesis by the means of High Performance Liquid Chromatography(HPLC) and Capillary Electrophoresis(CE) monitoring sulfur-containing species during the decomposition reaction. The sulfur-containing species and other species could be determined simultaneously reagents, products and intermediates the dependence of concentrations of the mainly species such as on the reaction time was plot.Alkaline decomposition of pentathionate was studied by high-performance liquid chromatography, which allows us to track different sulfur-containing species simultaneously in the presence of a carbonate/hydrogen carbonate buffer and at a constant ionic strength. The reaction of pentathionate decomposition is first order for pentathionate and hydroxide, and the reaction rate of the decomposition of pentathionate, which is equal to 0.805 M-1s-1, was obtained through the initial rate method. On the basis of these observations, a 10-step kinetic model with five fitted and five fixed rate coefficients is suggested and discussed to take all of the most important characteristics of the decomposition into account.The kinetics of the reaction of pentathionate with sulfite in slightly acidic media was studied concurrently in presence of acetic acid/acetate buffer at T = 25.0 ± 0.1℃ by High Performance Liquid Chromatography monitoring the concentration of tetrathionate, pentathionate, thiosulfate and sulfite, simultaneously. The pentathionate-sulfite reactions were found to be first order with respect to both reactants. A simple four-step kinetic model is proposed p H-dependence of the pentathionate–sulfite reaction emerges from the reactivity difference of sulfite and bisulfite.