溴甲酚紫的极谱研究

溴甲酚紫是一应用广泛的有机式剂^1-4]。关于羟基三苯甲烷类染料的极谱研究报导不多^5]。Ghoneim^6]曾报导溴甲酚紫在pH<7时产生一个2电子还原波,当pH大于10时,可产生两个1电子还原波。Goel^7]只研究了第一波的还原机理。本文用普通极谱、脉冲极谱、循环伏安等方法较详细地研究了溴甲酚紫的电还原。提出一电还原机理,解释了半波电位随pH变化的特殊规律。

ELECTROREDUCTION OF BROMOCRESOL PURPLE

The electroreduction of bromocresol purple was studied by d.c.polarography, differential pulse polarography and cyclic voltammetry. Three or four polarographic reduction waves (peaks) appeared at different pH. First three waves were observed over pH range of 2—9. When pH<9 waves Ⅱ and Ⅲ were overlapped with an appearance of a new wave Ⅳ. Wave Ⅰ was a diffusioncontrolled, irreversible, two electron one, the E_1/2(E_p) of which shifted towards more negative potentials with increasing pH. Wave Ⅱ was so small, it could be seen only in differential pulse polarograph.Wave Ⅲ being adsorptive in nature was an irreversible, two-electron one, the E_1/2 (E_p) of which was independent of pH.Wave Ⅳ was a diffusion controlled, two-electron one. Considering acidbase equilibrium of both oxidized form and reduced form,a formula expressing the relationship between pH and E_1/2 has been derived, and the plot of pH-E_1/2 for wave Ⅰ has been explained. The mechanism for the reduction of bromocresol purple is discussed.