Studies On Kinetics And Mechanism Of Oxidation Of Some Amino Compounds By Ni(iv) Complex Ion

Kinetics and mechanism of oxidation of L-lysine, L-ornithine, N,N-Dimethylethanolamine, N,N-diethylethanolamine, N-methyldiethanolamine, 2-aminoethanol and sodium sulfanilate by Ni(IV) in alkaline medium were studied by spectrophotometry in this paper. The change of kobs with different [reductant], [OH-], [IO4-] and ionic strength were studied, the determining-step rate constants at different temperatures and the activation parameters at 298.2 K were evaluated.Through the experimentation, we find that the main existed form of DPN is the deprotonated complex [Ni(OH)2(H2IO6)2]4- in alkaline medium, and we proposed that the mechanism should be that the deprotonated complex [Ni(OH)2(HIO6)]2- was the activation center, forming the intermediate adduct with the reductant and obtain the product through electron transfer.The results show that the reactions were first order with respect to DPN, fractional order to L-lysine, L-ornithine, N,N-Dimethylethanolamine, N,N-diethylethanolamine, N-methyldiethanolamine, 2-aminoethanol and sodium sulfanilate. We also find that: The reaction rate constant of the determining-step of amino acid is larger than the other amino compounds, because in the reaction system, amino acid formed the more stable hexa-cyclic intermediate compounds with Ni(IV). When the amino compounds oxidation by DPN, the reaction rate changed with the length of carbon chain, when the reaction of the similar compounds oxidation by Ni(IV). At the same temperature, the reaction rate constant of the determining-step has such a sequence: L-ornithine > L-lysine, N,N-dimethylethanolamine > N,N-diethylethanolamine.The supposed mechanism could favorably explain the reaction results. The hypothesis that the complex was existed as the deprotonated form was supported by our experimental results. Form the macrosopical experimentation phenomena, we can explain the microstructure of the complex, and conjecture the stability and stucture of the transition state, it is very significative for the development of theory of coordination chemistry.