二羟基二过碘酸合镍(IV)氧化氨基丙酸的动力学

在碱性介质中研究了二羟基二过碘酸合镍（Ⅳ）配离子（DDN）氧化α－氨基丙酸的动力学，结果表明，反应对DDN为一级，对α－氨基丙酸为正分数级，准一级速率常数，k_(obs)，随［OH~－］增加而增加，随［IO~-_4］增加而减小，无盐效应也未检出自由基1/k_(obs)对［IO~-_4］有直线关系，表明二羟基一过碘酸合镍（Ⅳ）（DMN）是氧化剂的活性物种，据此很出了一个包括DDN与DMN存在前期平衡和内层一步双电子转移的反应机理．导出的速率方程园满地解释了全部实验现象，并且计算出速控步聚的速率常数，前期平衡常数和活化参数．

Kinetics and Mechanism of Oxidation of α-alanine by Dihydroxydiperiodatonickelate (IV) Complex Ion

The kinetics of oxidation of α-alanine by dihydroxydiperiodatonickelate (Ⅳ) ion was studied by spectrophotometry in aqueous alkaline medium. The reaction rate showed first order dependence in okidant, and positive fractional order dependence in α-alanine. It was found that the pseudo first-order (Ala]_o>>Ni(Ⅳ)]_o) rate constant, k_(obs), increases with the increase of OH~-] and decreases with the increase of IO~-_4], which implies that before the rate-determining step there is a preequulibrium in which one of the periodate ligands of the oxidant is deprotonated and the other is dissociated. Under the protection of nitrogen the reaction system does not induce polymerization of acrylamide indicating that an innersphere one-step two-electron tranfer is involved in the oxidation. Based on the experimental results a mechanism involving a preequilibrium of an adduct formation between Ni(IV) and α-alanine has been proposed. The rate equations derived from the mechanism explained all the experimental results satisfactorily and the preequilibrium constants, rate constant of the rate-determining step together with the activation parameters were evaluated.