Kinetics And Mechanism Of The Thiosulfatolysis Reaction Of Pentathionate

The kinetic dynamics of thiosulfatolysis reaction of pentathionate system were studied by the means of reversed phase ion-pair high performance liquid chromatographic(HPLC).The kinetics and mechanism of the thiosulfatolysis reaction of pentathionate were studied in the p H range of 4.5 to 8.0 at T = 25.0±0.1?C. By adjusting the concentration of ion-pair reagent in the mobile phase, the percentage of acetonitrile, p H value and flow rate, an optimized separation condition to detect the species in the reaction, such as S2O32- and Sx O62-(x = 4, 5 and 6).The preliminary kinetics study by liquid chromatographic method shows that S2O32- is a conceivable catalyst within the experimental conditions. And the catalytic ability of thiosulfate have a certain limit. The initial reaction rate of S5O62- and initial concentration of S2O32- had good linear relationship in the initial concentration of S2O32- range of 1.0 to 8.0 m M,while had no linear relationship when the initial concentration of S2O32- above 8.0 m M. In S2O32-- S5O62- reaction system, the reaction rate is proportional with ion strengths and affected by the type of buffer salt. The change of the initial concentration of the reactants has no effect on reaction of the intermediate species, but is proportional with the reaction rate. The p H-dependence of the reaction emerges from the different buffer solutions, and the rate of the reaction is independent on the p H value of the solution as in the same buffer solution.The reaction orders in the thiosulfatolysis reaction of pentathionate system were determined to be first for S2O32- and S5O62-, zero for H+ by initial rate method. The k in the buffer solution of CH3COOH-CH3COO- is(1.242 ± 0.01649) ×10-2 M-1·s-1 and in the buffer solution of H2PO42-- HPO42- is(1.641 ± 0.01853) ×10-2 M-1·s-1. Combined with experimental results and related references, a 10 steps kinetic model of reaction mechanism is proposed and the concentration distribution of sulfocompound at the end of the reaction of S2O32-- S5O62- system is studied, [S4O62-] : [S5O62-] : [S6O62-] is similar to 10 : 4.7 : 1.