氮氧自由基研究——XVIII.水溶液中哌啶氮氧自由基单电子氧化电极反应动力学参数的测定

Studies on Nitroxides——XVIII. Determination of One-Electron Oxidation Electrode Reaction Kinetic Parameters of Piperidine Nitroxides in Aqueous Solution

氮氧自由基可作为电子给体或受体,与氧化剂或还原剂发生单电子转移反应,也能在电极上被氧化或还原。深入研究氮氧自由基的电化学行为,对于阐明氮氧自由基的电子转移反应机理有着重要的意义,以往,仅Suemmermann报道过哌啶氮氧自由基在乙腈溶液中单电子氧化电极反应的动力学参数。

The diffusion coefficients of 2, 2, 6, 6-tetramethyl-4-hydroxypiperidine-1-oxyl (1) and 2, 2, 6, 6-tetramethylpiperidine-1-oxyl (2) have been determined by current step and chronocoulometric methods. Using cyclovoltammetric and potential step methods, the transfer coefficients and the standard rate constants for the one-electron oxidation electrode reaction of 1 and 2 have also been measured. In strong alkaline medium (pH 12), the cyclovoltammetric results showed that the relationship between oxidation current of 2 and scan rate is consistent with the theoretical curve of catalytic electrode reaction. Thus it is confirmed that nitroxides undergo catalytic electrode reaction in aqueous alkaline solution. The catalytic electrode reaction rate constant of 2 was determined to be 6.3×10^(-1)dm^3·mol^(-1)·s^(-1) by potential step method.