光透薄层光谱电化学法研究紫脲酸铵电还原过程

采用金网橱光透薄层电解池, 配合紫外可见光谱技术现场监测了有机染料紫脲酸铵的电还原过程。用光透薄层光谱电化学方法测定了紫脲酸铵在pH5.0醋酸盐缓冲溶液中的式电极电位和电子转移数。薄层循环伏安法和薄层光谱电化学法研究表明, 紫脲酸铵在金网栅电极上的还原为双电子转移不可逆过程, pH<8时, 还原产物双巴比士亚胺进一步分解为尿咪和巴比士酸。用双电位跃-计时吸收谱法研究了双巴比士亚胺在不同pH缓冲溶液中的分解动力学过程, 测定了拟-级反应动力学常数。

STUDIES ON THE REDUCTION OF MUREXIDE BY OPTICALLY TRANSPARENT THIN-LAYER SPECTROELECTROCHEMISTRY

The reduction process of murexide (or ammoniumm purpurate) has been inves- tigated at gold minigrid electrode in optically transparent thin-layer cell, using UV-VIS spectroscopy technique. From the experimental results of thin-layer cyclic voltammograms of murexide (or purpurate ion) in different pH system and UV-VIS spectra from the reduction of purpurate ion obtained in situ by spectro- electrochemistry, it was found that the reduction of purpurate ion is a two electron transfer irreversible process, accompanied with a subsequent chemical reaction at pH<8 in which the reduction product, dibarbituylamine decomposed into uramil and barbituric acid. In addition, the formal potential, E~0′ and electron transfer number, n were calculated from spectra at different potentials. Double potentialstep chronoabsorptometry was employed for measuring the decomposition rate constant of dibarbituylamine. The pseudo-firstorder rate constants at pH4.0, 5.0, 5.5 and 6.4 were 6.6, 5.0, 3.4 and 2.6×10~(-4) s~(-1), respectively.