【作者】 钮东方；

【导师】 陆嘉星；

【作者基本信息】 华东师范大学 ， 物理化学， 2010， 博士

【摘要】 随着人类进入21世纪,社会的可持续发展及其所涉及的生态环境、资源、经济等方面的问题越来越成为国际社会的焦点。保护环境的法规不断出台,使得化学工业界把注意力集中到如何从源头上杜绝或减少废物的产生。这对化学提出了新的要求和挑战。环境经济性正成为技术创新的主要推动力之一。因此合成化学重要的不是合成什么,而在于怎么合成的问题,合成化学正朝着绿色合成的方向发展。电化学提供了一种简单方便的合成技术,它直接以电子作为反应试剂,反应物可以在电极上通过得失电子达到还原或氧化的目的,无需额外的添加还原剂或氧化剂。与传统的有机合成反应前加入一定量的氧化还原剂不同,电合成可以根据反应中底物的实际消耗情况来控制通电量。因此,电子被认为是一种清洁、可控制的无污染的氧化还原剂。有机电合成完全符合绿色化学“原子经济性”的要求,与传统的有机合成方法相比,是一种绿色的合成技术。CO2是造成全球日渐变暖的主要温室气体,将其固定利用不仅可以控制温室气体排放,减少环境污染,而且可以利用廉价而且丰富的Cl资源合成有用的化工产品。但由于CO2热力学性质稳定,传统的活化方式都需要高温高压,而电化学方法在温和条件下就可以活化CO2,因此其已经成为固定利用CO2的一条有效途径。离子液体是一种无挥发的新型的绿色溶剂,其本身可以通过离子导电,以及具有良好的溶解有机物的能力。在电化学领域,离子液体由于不需用添加支持盐就可以直接应用于电化学研究,而且最大程度的方便了产物分离的过程,因此,离子液体在电化学研究中具有良好的应用前景。氨基甲酸酯和碳酸二甲酯都是用途广泛的化学品。碳酸二甲酯(DMC)不仅可以作为一种有机合成中间体进行羰基化剂和甲基化剂等反应,而且还可以作为高能电池电解液和环保型车用汽油添加剂,是近年来颇受国内外重视的新型“绿色”化工产品。氨基甲酸酯和碳酸二甲酯传统的合成方法通常需要使用易燃、易爆、有毒的试剂、昂贵复杂的催化剂、高温高压的反应条件等,而且产率都不高。因此,急需找到一条新的,更为绿色化的合成路线。另外,有机卤化物广泛应用于杀虫剂中,是一类毒性强、易致癌、难生物降解的环境污染物。因此,从环境保护的角度出发,将有机卤化物转化为有用的化工产品具有很重要的意义。将电化学合成技术应用于CO2的固定,使之转化为有用的化工产品,方法简单,条件温和。特别是将绿色溶剂离子液体应用于CO2的固定方面的研究具有很重要的现实意义。本论文的主要内容如下：(1)电化学还原二氧化碳合成苯氨基甲酸乙酯室温、一个大气压的CO2气氛下,在含0.1 mol L-1四乙基溴化铵(Et4NBr)的N,N-二甲基甲酰胺(DMF)的溶液中,以苯胺为原料,通过电化学活化CO2有效地合成了苯氨基甲酸乙酯。为了优化反应条件,分别考察了工作电极材料、电量、温度、支持电解质以及电流密度对产率的影响。在优化后的条件下,即20℃下,以不锈钢(Stainless steel)为阴极,Ru为阳极,在CO2的还原电位(-2.2 V)下进行恒电位电解,当通过3 F mol-1于苯胺的电量后,苯氨基甲酸乙酯的产率达到66%。(2)电催化活化二氧化碳合成氨基甲酸酯类化合物在常温常压下,通过循环伏安法探讨了Ni(bpy)3Cl2催化剂对CO2间接电化学活化的机理及CO2与苯胺、碘乙烷合成苯氨基甲酸乙酯的反应机理。结果表明,Ni(bpy)3Cl2催化剂对CO2的活化具有很高的催化效率,DMF溶液中加入Ni(bpy)3Cl2催化剂可使CO2的电化学还原电位由-2.3 V正移到-1.6 V,从而可大大改善合成苯氨基甲酸乙酯反应的条件。在恒电位电解下,分别考察了催化剂用量、电解电位、电极材料、温度、支持电解质和通电量对苯氨基甲酸乙酯产率的影响。另外,在优化后的条件下,还考察了其他胺类化合物与CO2的电羧化反应,结果都得到了一定产率的氨基甲酸酯类化合物(15.8%-82.2%),且胺类化合物的亲核性对产率有很大的影响。(3)温和条件下CO2为原料电合成碳酸二甲酯常温常压下,研究了以CO2和甲醇为原料电合成碳酸二甲酯的反应。在四乙基溴化铵(Et4NBr)为支持电解质的乙腈(CH3CN)溶液中,通过恒电流电解得到了唯一的产物碳酸二甲酯。在恒电流电解下,分别考察了工作电极、电流密度、支持电解质、通电量以及电解前后加入甲醇顺序的不同等因素对该反应的影响。以铜为工作电极,石墨为对电极,在17 mAcm-2的电流密度下电解,当通过2 Fmol-1的电量后,碳酸二甲酯的产率可达74%,大大高于文献报道值。(4)脂肪族卤化物在银电极上的电催化羧化单室型的电解池中,以饱和了CO2的乙腈为溶剂,银为工作电极,镁棒为牺牲阳极的反应体系,为脂肪族卤化物进行电羧化反应提供了一种既简单又有效的方法。在恒电位电解下,以3-氯-2-甲基丙烯为模板原料,分别考察了电极材料、支持电解质以及温度对该反应的影响。在优化后的反应条件下,还考察了其他脂肪族卤化物与CO2的电羧化反应,分别得到了不同产率的羧酸产物(22%-89%)。通过循环伏安法分别在Ag、Cu、Ni以及Ti电极上研究了3-氯-2-甲基丙烯的电化学行为,得到的循环伏安图表明了银电极对脂肪族卤素的还原羧化具有良好的电催化效果。(5)苄基氯在离子液体中的电催化羧化在饱和了CO2的室温离子液体BMIMBF4中,以银为工作电极第一次探讨了苄基氯电羧化反应的可行性。通过循环伏安法分别在Ag, Cu以及Ni电极上研究了苄基氯的电化学行为,得到的循环伏安图表明了银电极对苄基氯的还原羧化具有良好的电催化效果。在恒电流电解下,分别考察了电极材料、温度以及电流密度对产率的影响。在优化后的反应条件下,得到的苯乙酸产率为45%。此外,该离子液体可以重复使用至少4次而不明显影响产率。(6)离子液体中溴苄和溴苯在银电极上的电催化二聚温和条件下,以银为催化电极探讨了溴苄和溴苯在离子液体BMIMBF4中进行电化学二聚的可行性。通过循环伏安法分别在Ag、Cu、Ni以及Ti电极上研究了溴苄的电化学行为,得到的循环伏安图表明了银电极对溴苄的还原具有良好的电催化效果。以溴苄为模板原料,重点考察了电极材料和温度对该反应的影响。在优化后的反应条件下,考察了其他芳香族溴化物的电化学二聚反应,得到的二聚物的产率为12%-68%。此外,该离子液体可以重复使用至少4次而不明显影响产率。更多还原

【Abstract】 As entering into the 21 century, the international community has focused on the sustainable development referring to the ecological environment, natural resources, economy and so on. With the establishment of many policies concerning environmental protection, the chemistry industry has concentrated on how to eliminate or reduce the waste from the source, which poses new demands and challenges for the chemisty. The environmental economy has becoming one of primary drive for technology innovation. Consequently, the most importance for the synthesis chemistry is not what to prepare, but how to prepare. At present, synthesis chemistry is developing towards the green chemistry.Electrochemisty provides a simple, convenient synthetic technique. Electron is used as reagent in electroorganic synthesis, avoiding the use of other reducing agent and oxidant. The reactant could be reduced or oxidized on the electrode by getting or losing electrons. In electrochemistry processes, the electrons are consumed stoichiometrically with respect to the substrate, Unlike classical organic synthesis, a certain amount of oxidant or reducing reagent is added before reaction, so it is the electrons that are used as clean, controlled, and nonpolluting redox reagents. This feature is often considerd as being environmentally favorable. So compared with classical organic synthesis, electrochemistry synthesis is greener.Carbon dioxide is the largest contributor to the green house effect, which may increase the earth average temperature to such a value that may cause catastrophic events. Therefore, great efforts have been placed toward the utilization of CO2, which can control the emission of CO2, reduce the environmental pollution and convert CO2 into the commodities. However, since CO2 shows a very low reaction activity, its activation could be realized only under severe reaction conditions via the conventional chemical methods. In contrast to thermo-chemical reactions, CO2 can be readily activated through an electrochemical reaction at mild conditions. An electrochemical method has become one of efficient routes for the utilization of CO2. Ionic liquids are non-volatile novel green solvents which combining ionic conductivity and good solvating properties for organic compounds. In fact, such a non-volatile systems, used instead of conventional organic solvent/supporting electrolyte system and maximally facilitating products isolation procedure, seem to be an ideal media for electrochemistry.Organic carbamates and dimethyl carbonate(DMC) are an important class of compounds whose versatility allows their application in several fields of the chemical and pharmaceutical industry. Dimethyl carbonate can be used not only as a carboxylation and methylation agent in organic synthesis, but also as a high energy battery electrolyte and environment-friendly gasoline additives for mobile. Therefore, dimethyl carbonate has been highly regarded as a novel green chemical product in the world. The conventional synthetic methods for the carbamates and DMC have several drawbacks:the use of hazardous reagents, expensive and complicated catalysts, high pressure and high temperature, and low yields. Consequently, alternative methods of the synthesis are highly desirable. On the other hand, organic halides are widely used in insecticide. They represent a class of toxic, carcinogenic and nonbiodegradable organic pollutants. Considering the environmental protection, it is very important to convert the organic halides into the useful chemical products.Under mild condition, electrochemical activation of CO2 to the useful chemical products is a simple procedure. Specially, application of ionic liquid in fixation of CO2 is of great practical significance. The details are given as follows:(1) Electrochemical activation of CO2 for the synthesis of ethyl phenylcarbamate under mild conditionsA novel electrochemical procedure for the synthesis of ethyl phenylcarbamate from aniline and carbon dioxide was developed via the selective cathodic reduction of carbon dioxide in CO2-saturated DMF solution containing 0.1 mol L-1 Et4NBr at room temperature, followed by the addition of EtI as an alkylating agent. The synthesis was carried out under mild[p(CO2)=0.1 MPa, t=20℃] and safe conditions. Influences of the nature of the electrodes, the current densities, the passed charges during electrolysis, temperature, and supporting electrolytes on the yield of ethyl phenylcarbamate were studied to optimize the electrolytic conditions.(2) Activation of carbon dioxide by electrocatalysis for synthesis of carbamatesCO2 was electrochemically activated by the Ni(bpy)3Cl2 catalyst and reacted with amines and iodoethane to give carbamates (15.8%-82.2%) under mild conditions [p(CO2)= 0.1 MPa,20℃]. The CO2 activation mechanism and the synthesis reaction mechanism were proposed. The electroreductive potential of CO2 was moved from-2.1 V to-1.6 V owing to the Ni(bpy)3Cl2 catalyst in DMF solution, indicating that the reaction condition was effectively improved. The catalyst showed a good effect on the CO2 activation. The effects of the catalyst, the electrolytic potentials, the nature of the working electrodes, the temperature, the supporting electrolytes, and the passed charge amount per mole of aniline supplied to the electrode on the yield of ethyl phenylcarbamate were studied.(3) Electrosynthesis of dimethyl carbonate from CO2 in mild conditionElectrosynthesis of dimethyl carbonate from methanol was studied at room temperature in the presence of atmospheric pressure of CO2. The only product obtained was dimethyl carbonate in a CH3CN-Et4NBr (tetraethylammonium bromide) solution previously electrolyzed under galvanostatic control. Influences of the nature of working electrodes, current densities, the passed charges on electrolysis, supporting electrolytes and different procedures of adding methanol were studied to optimize the electrolytic conditions, The maximal yield is 74% on Cu/C electrodes under a constant current of 17 mA cm-2 until 2 F mol-1 of charge has passed through the cell. With respect to the methods so far reported, the yield of dimethyl carbonate in this paper is highest.(4) Electrocatalytic carboxylation of aliphatic halides at silver cathode in acetonitrileA simple and efficient electrocarboxylation reaction of aliphatic halides has been developed using silver as cathode, magnesium as anode, and CH3CN saturated CO2 as solvent in an undivided cell. The influence of some key factors (such as the nature of electrode materials, supporting electrolytes, and temperature) on this reaction was investigated. Under the optimized condition, the corresponding carboxylic acids were obtained in moderate to good yields(22%-89%). The electrochemical behaviour was studied at different electrodes (Ag, Cu, Ni and Ti) by cyclic voltammetry, which showed significant electrocatalytic effect of the silver electrode towards the reductive carboxylation of aliphatic halides. (5) Electrocatalytic carboxylation of benzyl chloride at silver cathode in ionic liquid BMIMBF4The feasibility of electrocarboxylation of benzyl chloride has been investigated at silver cathode in CO2-saturated room-temperature ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate (BMIMBF4) solution for the first time. The electrochemical behavior was studied at different electrodes by cyclic voltammetry, which showed significant electrocatalytic effect of the silver electrode on the reduction of benzyl chloride. The highest yield of 45% of phenylacetic acid was obtained under optimal conditions. The recovered ionic liquid was reused for four times with gradual decrease in the yield of phenylacetic acid.(6) Electrocatalytic dimerisation of benzyl bromides and phenyl bromide at silver cathode in ionic liquid BMIMBF4A simple and eco-friendly electrochemical route was developed by using silver as the cathode, magnesium as the anode and ionic liquid BMIMBF4 as solvent for the electrochemical dimerisation of aromatic bromides. The electrochemical behaviour was studied at different electrodes (Ag, Cu, Ni and Ti) by cyclic voltammetry, which shows significant electrocatalytic effect of the silver electrode towards the reductive dimerisation of aromatic bromides. Biaryls were obtained in moderate to good yield (12%-68%). A recycling study confirmed that the solvent can be reused multiple times without activity loss.更多还原