对硝基甲苯电化学还原的研究

STUDIES OF ELECTROCHEMICAL REDUCTION OF p-NlTROTOLUENE

研究了以醇水混合液为底液,分别以盐(NaCl,Na_2SO_4),碱(NaOH,KOH)和酸(H_2SO_4,HClO_4)为支持电解质时,对硝基甲苯在Cu,Ag,Pt,Pb电极上电化学还原的循环伏安行为,从而选择出以Cu电极,H_2SO_4为支持电解质作为较理想的体系.对于该体系,用循环伏安法研究了浓度、扫描速度、搅拌强度与峰电流、峰电势的关系.结果表明,对硝基甲苯电化学还原的峰电势大约在(-0.5V,vs.SCE)处,且其还原与扩散有关;采用恒电压稳态极化法,测出稳态极化曲线,得到电势与ln((Id-I)/I)(I:电流,I_d:极限电流)成线性关系.从而确认该体系中对硝基甲苯电化学还原的电极过程为动力学和扩散混合控制过程;初步确认Ti^(4+)/Ti^(3+)电对对于对硝基甲苯在该体系中电化学还原具有一定的催化活性.探讨了在硝基苯的苯环上的不同位置接入不同的自由基后,对于硝基的电化学还原的影响,表明在苯环上接入吸电子基后,有利于它的电化学还原,而接入供电性基因后则不利于它的电化学还原,特别是在硝基的邻位和对位上接入时,这种效应特别明显.讨论了p^H值对于对硝基甲苯电化学还原的影响,表明在一定范围内,当p^H值较低时,有利于它的电化学还原.

The electrochemical reduction of p-nitrotoluene on Cu, Ag, Pt, Pb electrodes was studied by Cycle Voltammetry. The basic solution was alcohol-water. The salt (NaCl, Na2SO4), alkali (NaOH, KOH) as well as acid (H2SO4, HClO4) were used as supporting electrolyte respectively.The researched system consited of a Cu electrode as working electrode and H2SO4 as supporting electrolyte was investigated. The relations among the concentration, the sweep rate as well as the stirring condition with peak current, peak potential were measured by Cycle Voltammetry. The results show that reductive dynamic process may be considered to be related to diffusion. Moreover, from the stead-state polarization measurement the linearly relationship between V and ln(Id-I/I)was obtained. So the electrode process for the electrochemical reduction of p-nitrotol-uene is controlled by both process of dynamic process and diffusion process. The preliminary experiment showed that Ti4+//Ti3+ is catalytic active for the electrochemical reduction of p-nitrotoluene. When different substitutes are connected with the different position of nitrobenzene ring, the effect of these substitutes on the reduction of NO2- is studied. The results showed that electr-ophobic substitutes contributed to its reduction and electrophilic substitutes weaken its reductive ability, especially when the substitutes are at the ortho-or para- position of the NO2-. The effect of pH values on the electrochemical reduction of p-nitrotoluene was also studied.