高碘酸盐氧化硫脲的非线性动力学行为和机理

Nonlinear Kinetic Behavior and Mechanism of the Oxidation of Thiourea by Periodate

在酸性介质中 ,高碘酸盐氧化硫脲的非线性反应呈现多种不同的化学计量方程式 .当 [KIO4] 0 /[SC(NH2 ) 2 ] 0 >4时 ,计量方程为 4IO-4+SC(NH2 ) 2 + 3H2 O =4IO-3 +SO2 -4+CO2 -3 + 2H+ + 2NH+ 4 ;当 [KIO4] 0 /[SC(NH2 ) 2 ] 0 =8∶7时 ,计量方程为8IO-4+ 7SC(NH2 ) 2 + 17H2 O =4I2 + 7SO2 -4+ 7CO2 -3 + 6H+ + 14NH+ 4 ;而当 [KIO4] 0 /[SC(NH2 ) 2 ] 0 <1时 ,反应的主要计量方程为IO-4+ 4SC(NH2 ) 2 + 8H2 O =I-+ 4S + 4CO2 -3 + 8NH+ 4 .同时反应体系在氧化剂过量的条件下碘钟产生的诱导期与 1/[H+ ] 2 成正比 ;而当还原剂过量时 ,体系I2 逐渐累积至极值的诱导期与体系初始pH呈线性关系 .运用包含质子平衡反应、碘化合物自身反应、碘化合物 -硫化合物反应以及硫 -硫反应的 15步反应机理较好地模拟出封闭体系中pH ,[I-]以及 [I2 ]的准振荡行为 .

The reaction between periodate and thiourea in acidic medium has been investigated in a batch. The stoichiometries of the reaction are: 4IO(4)(-) + SC(NH2)(2) + 3H(2)O = 4IO(3)(-) + SO42- + CO32- + 2H(+) + 2NH(4)(+) ([IO4-]/[SC(NH2)(2)] > 4) (1) 8IO(4)(-) + 7SC(NH2)(2) + 17H(2)O = 4I(2) + 7SO(4)(2-) + 7CO(3)(2-) + 6H(+) + 14NH(4)(+) ([IO4-]/[SC(NH2)(2)] approximate to 8:7) (2) and mixed reaction of (1) and (2) (7/8 < [IO4-]/[SC(NH2)(2)] < 4), respectively. In closed systems the reaction is autocatalytic in H+ and I-, and can be characterized by two different induction periods. In excessive periodate, the induction period defined as the time between the beginning of reaction and the appearance of a red-brown colour, indicating the product of, iodine, has a linear relation with 1/[H+](2). In excessive thiourea, the induction period from the start of reaction to maximal [I-2] is directly proportional to the initial pH. A fifteen-step mechanism, including iodine-iodine reactions, iodine-sulfur reactions and sulfur-sulfur reactions, simulated the observed kinetics.