Kinetics and Mechanism of the Reduction of Dodecatungstocobaltate(III) by Iminodiacetate, Nitrilotriacetate, and Ethylenediaminetetraacetate. A Comparative Study of the Reactivity of Different Amine-<i>N</i>-carboxylates
作者:Swapan K. Saha、Prabir Bhattacharya、Mahammad Ali、Pradyot Banerjee
DOI:10.1246/bcsj.62.3320
日期:1989.10
The kinetics of reduction of dodecatungstocobaltate(III) by iminodiacetate (IDA), nitrilotriacetate (NTA), and ethylenediaminetetraacetate (EDTA) have been studied in aqueous solution at 50 °C, 30 °C, and 15 °C respectively. In general, the reactivity of the amine-N-carboxylates is in the order EDTA>NTA>IDA. All the anionic species have been found to undergo oxidation via both a spontaneous and an alkali metal ion-catalyzed pathway, while molecular form of the acids are oxidized only via spontaneous pathway. The rate of oxidation is given by a general expression kox=k°+k[M+]n where kox=kobs/2[L]T([L]T=total concentration of a particular amine-N-carboxylate) and n may have values 1 or 2 depending on the nature of M+. The terms k° and k account for the rate constants of the spontaneous and catalyzed paths respectively. A general trend K+>Na+>Li+ for the catalyzed path has been observed for the oxidation of these amine-N-carboxylates. Reactivities of different species present in the experimental pH range have been evaluated by carrying out experiment at different pH and using these data in appropriate rate expressions. The reactivities (50 °C) of Hida− are k°=4.70×10−5 dm3 mol−1 s−1 and k1=3.44×10−4 dm6 mol−2 s−1 for the spontaneous and Na+ catalyzed paths respectively. For NTA oxidation (30 °C), rates are k10°(H3nta)=1.11×10−3 dm3 mol−1 s−1, k11°(H2nta−, spontaneous)=7.00×10−3 dm3 mol−1 s−1, k11(H2nta−, Na+ catalyzed)=3.50×10−2 dm6 mol−2 s−1, k12°(Hnta2−, spontaneous)=7.20×10−3 dm3 mol−1 s−1, k12(Hnta2−, Na+ catalyzed)=4.01×10−2 dm6 mol−2 s−1. The corresponding reactivities (15 °C) for EDTA oxidation are k20°(H4edta, spontaneous)=6.80×10−3 dm3 mol−1 s−1, k21°(H3edta−, spontaneous)=4.80×10−2 dm3 mol−1 s−1, k21(H3edta−, Na+ catalyzed)=0.48 dm9 mol−3 s−1, k22°(H2edta2−, spontaneous)=0.21 dm3 mol−1 s−1, k22(H2edta2−, Na+ catalyzed)=1.70 dm6 mol−2 s−1, k23°(Hedta3−, spontaneous)=1.71 dm3 mol−1 s−1, k23(Hedta3−, Na+ catalyzed)=30.00 dm6 mol−2 s−1. A plausible mechanism considering an outersphere association between the complex and reductant has been suggested where the alkali metal ions are assumed to act as a bridge between the reactants.
研究了亚氨基二乙酸酯(IDA)、次氨基三乙酸酯(NTA)和乙二胺四乙酸盐(EDTA)分别在 50 ℃、30 ℃ 和 15 ℃ 的水溶液中还原十二钨酸钴(III)的动力学。一般来说,胺-N-羧酸盐的反应性顺序为 EDTA>NTA>IDA。研究发现,所有阴离子种类都会通过自发途径和碱金属离子催化途径发生氧化,而分子形式的酸只通过自发途径发生氧化。氧化速率由一般表达式 kox=k°+k[M+]n 得出,其中 kox=kobs/2[L]T([L]T=特定胺-N-羧酸盐的总浓度),n 的值可以是 1 或 2,取决于 M+ 的性质。k° 和 k 分别表示自发和催化途径的速率常数。在这些胺-N-羧酸盐的氧化过程中,可以观察到催化路径的总体趋势是 K+>Na+>Li+ 。通过在不同 pH 值下进行实验,并将这些数据用于适当的速率表达式,评估了实验 pH 值范围内不同物种的反应活性。Hida- 的反应活性(50 °C)为 k°=4.70×10-5 dm3 mol-1 s-1 和 k1=3.44×10-4 dm6 mol-2 s-1,分别为自发途径和 Na+ 催化途径。对于 NTA 氧化(30 °C),速率为 k10°(H3nta)=1.11×10-3 dm3 mol-1 s-1,k11°(H2nta-,自发)=7.00×10-3 dm3 mol-1 s-1,k11(H2nta-,Na+ 催化)=3.50×10-2 dm6 mol-2 s-1,k12°(Hnta2-,自发)=7.20×10-3 dm3 mol-1 s-1,k12(Hnta2-,Na+催化)=4.01×10-2 dm6 mol-2 s-1。EDTA 氧化的相应反应活性(15 °C)为 k20°(H4edta, 自发)=6.80×10-3 dm3 mol-1 s-1,k21°(H3edta-, 自发)=4.80×10-2 dm3 mol-1 s-1,k21(H3edta-, Na+ 催化)=0.48 dm9 mol-3 s-1, k22°(H2edta2-, spontaneous)=0.21 dm3 mol-1 s-1, k22(H2edta2-, Na+ catalyzed)=1.70 dm6 mol-2 s-1, k23°(Hedta3-, spontaneous)=1.71 dm3 mol-1 s-1, k23(Hedta3-, Na+ catalyzed)=30.00 dm6 mol-2 s-1.有人提出了一种合理的机理,认为络合物和还原剂之间存在着球外结合,碱金属离子被假定为反应物之间的桥梁。