复合离子液体的制备、性质及在硝基苯电还原中的应用研究

【作者】 张冰；

【导师】 陈松；

【作者基本信息】 江西理工大学 ， 化学工艺， 2012， 硕士

【摘要】 硝基化合物还原制备胺类、偶氮类、氨基酚类等芳香化合物是重要的有机合成反应,具有较高的经济和社会效益。离子液体代替传统溶剂和电解质应用于电化学还原硝基化合物的反应,相对于传统合成方法具有组成简单、分离方便、介质循环使用的绿色化特点。而功能化离子液体的研究和应用对于提高硝基化合物电还原性能具有重要作用。课题根据亲水性离子液体1-丁基-3-甲基咪唑四氟硼酸盐(BMimBF4)和疏水性离子液体1-丁基-3-甲基咪唑六氟磷酸盐(BMimPF6)的不同特性,设计把两者按不同体积比进行二元复合,实现功能的互补和提高,以简单经济的方式进行离子液体的功能化,并将其应用于硝基苯的电还原研究。课题制备了BMimBF4和BMimPF6复合离子液体(体积比4：1、3：1、2：1、1：1、1：2、1：3、1：4),研究了复合离子液体以及与水组成的三元混合体系的相互作用,并测定体系的电化学窗口、运动粘度、电导率等性质。研究了上述体系与硝基苯的相互作用,测定了体系的运动粘度、电导率的变化规律。采用不同的电化学测试方法(循环伏安法CV、交流阻抗EIS、稳态极化曲线I/E、计时电量Q-t、计时电流I-t),探索硝基苯在复合离子液体及其与水组成的混合介质中的电化学行为和动力学特性,并采用不同的电解技术(恒电位电解和恒电流电解)对硝基苯进行选择性电还原。结果表明,与单一离子液体相比,不同BMimBF4和BMimPF6二元复合离子液体中硝基苯、苯胺及偶氮苯的紫外光谱与单一离子液体中的吸收峰类似；复合离子液体中硝基苯、苯胺及偶氮苯的吸收峰强度随浓度呈现规律性变化。不同复合离子液体的电化学窗口成不规则变化,复合离子液体可改善BMimBF4电化学窗口较窄的缺点；不同复合离子液体体系的运动粘度和电导率基本呈现规律性变化,且加入水和硝基苯后,变化规律基本不变。上述复合离子液体性质上的变化规律使其动力学性质具有可控性。复合离子液体中硝基苯在微铂圆盘电极和铜盘电极上电还原,3：1、4：1复合离子液体中,均出现在不同温度下性能较单一离子液体中明显改善的现象；同样复合离子液体-水体系中也有类似的现象。BMimBF4:BMimPF6=4:1的复合离子液体中硝基苯的电化学行为研究受扫描速度、温度、浓度、加水量、电极材料的影响较大。随着扫描速度加快,两还原峰电流的值增大,峰2处电位负移,峰1处电位基本不变,溶液中的反应主要是受扩散控制；随着温度的升高,两峰电流增大,峰1电位略微负移,峰2电位基本不变；随着硝基苯浓度增加,两峰电流增大,峰电位有所负移；随着扫描周期数的增加,会不断出现还原峰,峰电流不断减小,并且慢慢趋缓；随着加入体系中水的量的增加,峰电位正移,峰电流变大；不同电极材料,以微铂圆盘电极和铜盘电极的对硝基苯的电还原选择性较好；随着温度的升高,硝基苯在不同离子液体/电极体系的传递系数和扩散系数增大；采用不同电解条件所得产物主要是苯胺和偶氮苯。更多还原

【Abstract】 The production of amine azo and aminophenol aromatic compounds by reducing nitrocompounds is important organic synthesis reaction, which has high economic and social value. Ionic liquids taking the place of traditional solvent and electrolyte in electrochemical reduction of nitrocompounds has green characteristics of simple composition, easy separation and media recycle. It is important for researches and applications of functionalized ionic liquids to improve the electroreduction property of nitrocompounds. Binary composite ionic liquids by different volume ratio of hydrophilic ionic liquids1-Butyl-3-methylimidazolium tetrafluoroborate (BMimBF4) and hydrophobic ionic liquids1-Butyl-3-methylimidazolium hexafluorophosphate (BMimPF6) in accordance with their different properties are synthesized in the study. It can be complemented and improved each other in the nature of the properties of functionalized ionic liquids in a simple and inexpensive way, which can be used to the study of electroreduction of nitrobenzene.Composite ionic liquids of BMimBF4and BMimPF6(volume ratio of4:1,3:1,2:1,1:1,1:2,1:3,1:4) are prepared. The interactions between binary composite ionic liquids, among ternary mixture system with water or nitrobenzene, electrochemical window, kinematic viscosity and electroconductibility, and the change regularity of different system are determined. Explore electrochemical and kinetic behavior of nitrobenzene in composite ionic liquid and composite ionic liquid-H2O by different electrochemical measuring technology (cyclic voltammetry CV, electrochemical impedance spectroscopy EIS, steady-state polarization curves I/E, chronocoulometry Q-t, chronoampermetry I-t). The nitrobenzene is reducted selectively by different electrolytic technologies (potentiostatic electrolysis and constant current electrolysis).The results indicated that the absorption peaks of ultraviolet spectrophotometry (UV) of nitrobenzene, aniline and azobenzene in different composite ionic liquids are similar to pure ionic liquid. The absorption intensity changes with the concentration of nitrobenzene, aniline and azobenzene in composite ionic liquid. The electrochemical window of different composite ionic liquids has an irregular change, which improves the shortcoming of electrochemical window of BMimBF4. Kinematic viscosity and electroconductibility of different composite ionic liquids has a regular change, and this change remains when adding in water and nitrobenzene. The kinetic property of composite ionic liquids can be controlled easily due to that change.The electroreduction characteristics of nitrobenzene on Pt and Cu in composite ionic liquids (3:1and4:1) are improved remarkably in comparison with pure ionic liquid, which is similar to composite ionic liquids-H2O. The main influence factors of the electrochemical reduction of nitrobenzene in4:1composite ionic liquids are scan rate, scan cycle, temperature, concentration of nitrobenzene, concentration of water and electrode material. With increasing the scan rate, cyclic voltammetry has a regular change, the first peak potential has no change and the second peak potential is shifted to the negative direction and the responding peak current is increasing. The reaction velocity of nitrobenzene in composite ionic liquid on Pt is controlled by diffusion. With increasing temperature, the peak current is increased, and the first peak potential is shifted to the negative direction slightly and the second peak potential has no change. With increasing the concentration of nitrobenzene, the peak current is increased and the peak potential is shifted to the negative direction slightly, correspondingly. Reduction peak is coming up and responding current is decreased when scan cycle rising, and the decrease is slow gradually. With increasing water to composite ionic liquid, the first and second peak potential is shifted to the positive direction and the responding peak current is increasing. Pt and Cu have more superior selectivity in electroreduction of nitrobenzene in different electrode material. With increasing temperature, transfer coefficient and diffusion coefficient of nitrobenzene in different ionic liquid/electrode system is increasing. The main product is aniline and azobenzene under different conditions of electrolysis.更多还原