【作者】 葛小芳；

【导师】 马淳安； 褚有群；

【作者基本信息】 浙江工业大学 ， 应用化学， 2005， 硕士

【摘要】 芳族氨基酚是一类重要的有机化工原料及中间体,广泛应用于医药、农药及染料工业。采用电化学方法合成芳族氨基酚类化合物是目前国内外学者研究的热点课题之一。本文以电还原硝基苯制备对氨基苯酚的反应为模型,采用循环伏安法、稳态极化曲线法、计时电量法等电化学测试手段,深入研究了取代基的位置及性质对硝基电还原行为的影响;同时还考察了硫酸浓度对取代硝基化合物电还原性能的影响。 研究结果表明:取代基的电子效应和空间位阻效应对不同性质取代的硝基苯的电还原性能均有十分显著的影响。硝基苯的邻位、间位或对位被氯、甲基或羟基取代时,取代基的推电性越强,硝基的还原峰电位越负,反应所需的表观活化能越大。邻位取代硝基苯的还原电流受取代基的电子效应和空间位阻效应共同影响,而间位、对位取代硝基苯的还原电流受电子效应影响,推电性越强,还原电流越大。由于电解液中乙醇的影响,使得取代硝基苯甲酸中羧基对硝基的电还原性能的影响不同于其他取代硝基化合物。 当硝基苯环上的不同位置含有相同取代基时:间位取代硝基苯的还原峰电位最正,发生电还原所需的表观活化能最小;邻位取代硝基苯的还原峰电位最负,发生电还原所需的表观活化能最大。对位取代硝基苯电还原所产生的峰电流最大,而邻位取代硝基苯所产生的峰电流最小。 扩散系数的大小与取代基并无直接联系。除了溶剂化作用外,含吸电性取代基的硝基苯容易得到3个电子而被还原成氧化偶氮苯类化合物,而含推电性取代基的硝基苯容易得到4个电子或6个电子而被还原成酚类化合物或胺类化合物。 电解液中硫酸浓度由5%增高到20%时,由于邻位取代基性质的差异,使得邻氯硝基苯和邻硝基甲苯在还原电位和还原电流上的变化趋势并不相同,但扩散系数、溶液电阻及反应电阻等的变化趋势基本一致。更多还原

【Abstract】 Aryl aminophenol compounds are very important organic chemical materials and intermediates, which are widely applied in pharmacy, pestcide and dye industries. At the present time, preparation of p-aminophenol by electroreduction nitrobenzene is one of the most interesting research fields. In this dissertation, the reduction of nitrobenzenes to the corresponding p-aminophenols was selected out as a model, the effects of the nature and the position of substituted groups on the characteristics of the electroreduction of substituted nitrobenzenes were studied in detail by electrochemical methods such as cyclic voltammery, potentiostatic polarization, chronocoulometry and etc. In addition, the effects of concentration of H2SO4 on the electroreduction behaviors were also investigated .The experimental results showed that the different substituted group on the same location of the benzene cycle, the properties of substituted nitrobenzene were greatly affected by the electronic domino effect and space resistance of the substituted group. An increase in the electron-donor properties of the substituent at different position made the reduction potential more negative and the apparent activity energy more bigger. The current of o-substituted nitrobenzene was affected by both the electronic domino effects and space resistance, while that of m, p-substituted was depend on the electronic domino effects, an increase in the electron-donor properties of substituent made the current more bigger. Due to the effect of the solution, COOH-substituted group had an effect on the electroreduction of nitrobenzene which was different from that of other group.If the same substituted group on the different location of the benzene cycle, the reduction potential of m-substituted nitrobenzene was the most positive and the apparent activity energy was the smallest; While the reduction potential of o-substituted nitrobenzene was the most negative and apparent activity energy was the biggest. The peak current of the p-substituted nitrobenzene was the biggest, and that of o-substituted nitrobenzene was the smallest.The diffusion coefficient was not affected by the nature of the substituted group.更多还原