碱性溶液中H_2O_2-S_4O_6^(2-)反应动力学及机理研究

Kinetics and Mechanism of H_2O_2-S_4O_6^(2-) Reaction in Basic Solutions

S_4O_6^(2-)是S_2O_3^(2-)氧化过程重要的中间产物。在p H值9.5~11.0范围内,用毛细管电泳方法对S_4O_6^(2-)的H_2O_2氧化反应进行了动力学研究。在反应溶液中检测到的产物包括S_2O_3^(2-)、S_2O_6^(2-)和S_3O_6^(2-)。在动力学研究中发现,氧化剂H_2O_2的浓度对S_4O_6^(2-)的降解速率影响不大,这可能是由于H_2O_2-S_4O_6^(2-)氧化体系中,优先发生的反应不是S_4O_6^(2-)的氧化,而是它的碱性分解反应,H_2O_2只对S_4O_6^(2-)的降解产物进行氧化。在考察p H值范围内,S_4O_6^(2-)的氧化降解速率受pH值影响较大,但速率常数与S_4O_6^(2-)碱性分解反应速率十分接近。提出了13步反应机理,通过数值拟合计算得到的动力学曲线与实验曲线较好地吻合。

Tetrathionate( S_4O_6^(2-)) is one of the intermediates in the oxidation of thiosulfate( S_2O_3^(2-)). The kinetics of the H2 O2-S_4O_6^(2-)reaction in the p H range 9. 5 ~ 11. 0 was studied with capillary electrophoresis. S_2O_3^(2-),S_2O_6^(2-) and S_3O_6^(2-)were detected in the reaction solutions. No other SnO_6^(2-) was detected due to the presence of oxidant and the basic condition. The degradation of S_4O_6^(2-)was not affected by the concentration of H_2O_2,which implying that the hydrolysis of S_4O_6^(2-)occurred previous to its oxidation under strong basic conditions,while H_2O_2 only oxidized the degradation products of S_4O_6^(2-). Similar with hydrolysis of S_4O_6^(2-),the oxidative degradation of S_4O_6^(2-)strongly depended on the p H,sharing similar reaction constant. The proposed 13-step mechanism simulated well compared to the kinetic curves.