碱性介质中二羟基二过碘酸合镍(Ⅳ)配离子氧化乙二胺的动力学及机理  

Kinetics and Mechanism of Oxidation of Ethylenediamine by Dihydroxydiperidatonickelate(Ⅳ) Complex Ion in Alkaline Medium

作　　者：李志庭[1] 常青[1] 李宝文 杨利庭[1] 王安周[1] 

机构地区：[1]河北大学化学系,保定071002

出　　处：《高等学校化学学报》2000年第5期747-751,共5页Chemical Journal of Chinese Universities

摘　　要：在恒定离子强度（μ＝０． ４０ ｍｏｌ／Ｌ）的碱性介质中，于 ２０～３５℃ 用分光光度法研究了二羟基二过碘酸合镍（ Ⅳ）配离子（ＤＤＮ）氧化乙二胺的动力学．结果表明，反应对 ＤＤＮ为一级，对乙二胺为正分数级．准一级速率常数 ｋｏｂｓ随〔ＯＨ－］增加而增加， １／ｋｏｂｓ对［ＩＯ４－］有线性关系，表明二羟基一过碘酸合镍（Ⅳ）配离子（ＤＭＮ）是氧化剂的活性物种．无盐效应未检出自由基存在，据此提出了包括ＤＤＮ和ＤＭＮ存在前期平衡和内层一步双电子转移的氧化反应机理．The kinetics of oxidation of ethylenediamine(en)by dihydroxydiperiodatonickelate(Ⅳ) complex 0. 40) at 20-35℃. The reaction rate showed first-order dependence in oxidant and positive fractional order dependence in ethylenediamine. The pseudo first-order ([en]>> [DDN]) rate constant kobs increases with the increase of [OH-] and decreases with the increase of [IO4-], which implies that before the ratedetermining step there is a preequilibrium in which one of the periodate ligands of the oxidant is deprotonated and the other is dissociated, and dihydroxymonoperiodate (Ⅳ) complex (DMN ) is the reactive species. In addition, no salt effect and no free radical was observed, which indicates that an innersphere one-step two-electron transfer mechanism without free radical intermediate may be in operation. Based on the experimental results a mechanism involving a preequilibrium of an adduct formation between the [Ni(OH)2(HIO6)]2- and ethylenediamine has been proposed. The rate equation derived from the mechanism can be used to explain all the experimental results satisfactorily and the preequilibrium constants, rate constant of the rate-determining step together with the activation parameters were evaluated.

关 键 词：二羟基二过碘酸合镍 乙二胺 氧化还原 动力学 

分 类 号：O614.813[理学—无机化学] O623.73[理学—化学]