取代基结构-活性关系对电化学降解取代苯胺的影响

以Na2SO4为支持电解质, 使用Ti/PbO2电极, 研究了带有推电子基(—CH3)和吸电子基(—NO2, —Cl)的邻或对位取代基苯胺类化合物的电催化氧化降解过程. 研究结果表明, 带有取代基苯胺类化合物的氧化降解是在羟基自由基进攻下生成氨基酚类化合物, 然后在电极表面失去电子生成苯醌继续氧化的过程. 带有推电子基团苯胺的电催化降解速度比带有吸电子基团的苯胺降解速度快, 这是因为推电子基团使苯环电子云密度提高, 有利于羟基自由基的进攻; 吸电子基团使苯环电子云密度降低, 不利于羟基自由基的进攻. 由于阴极还原反应的作用, 化学反应活性和电化学反应活性并不完全一致. 氯代苯胺在羟基自由基进攻下—Cl离去, 以Cl-离子形式进入溶液中, 被氧化生成有效氯, 加快降解反应速度. 硝基虽然是强吸电子基, 但是可以转化为对苯二胺, 进一步活化苯环, 其降解速度较快.

Effect of Structure-Activity Relationship on Electrochemical Degradation of Substituted Aniline

The electrochemical oxidation degradation process of substituted aniline with electron-donating group(—CH3) and electron-withdrawing groups(NO2, Cl-) was studied on PbO2/Ti electrode by using sulfate as the support electrolyte. The results show that the oxidation degradation routes of substituted aniline were all started from hydroxyl radical attacking to form anilinophenol compound, then the anilinophenol compound changed into quinone intermediate on the electrode surface by the losing electron. The electrocatalysis degradation rate of substituted aniline with electron-doning groups was higher than the one with electron-withdrawing groups, because of the higher electron cloud density of benzene ring, it is convenient for hydroxyl attacking. On the contrary, it was difficult for hydroxyl attacking because electron-withdrawing groups could make the electron cloud density of benzene ring lower. The chemistry reaction activity is not consistent with electrochemistry reaction activity for the reason of cathode deoxidization reaction. When the hydroxyl radical attacks the chloroaniline, —Cl leaves and Cl- enters the electrolyte, at the same time, it is oxidized into available chlorine and the degradation rate increased. Although the nitro group is a strong electron-withdrawing group, it can be changed into p-phenylenediamine, then the benzene ring activity was stimulated, finally its degradation rate is much higher.