| The bromination of aromatic hydrocarbons is an important organic reaction in organic synthesis. Its product which is called aryl aromatic compounds can be widely used in many areas. It not only can be converted to organ metallic compounds to react with other compounds, but also can produce a series of coupling reaction with olefin, terminal alkynes, amines, aromatic halides and metal organic compounds. The traditional aromatic halogenation reaction belongs to electrophilic substitution. However this method has its apparent disadvantages: with the generation of each bromine production, the reaction will produce a corrosive by-product hydrogen bromide. In addition, this by-product is not only corrosive, but also yield less than 50% efficiency in the utilization of bromine atoms in bromine material, which does not meet with the requirements of green chemistry. Besides that, many other disadvantages such as harsh reaction conditions, complicated operation and so on also make the development of a green, mild and economical method of bromine become the hotspot of research.The oxidation of bromine seems to be able to solve the problem of low utilization of bromine atom as adding oxidant to the reaction system, the by-product of hydrogen bromide was oxidized to bromine with reactive activity. In this way, either from the perspective of the raw material cost or environmental protection, oxygen is the most ideal oxidant. Therefore, this study uses oxygen as oxidant.After analyzing a large number of data, anisole is chosen as substrate model, nitrogen dioxide as catalyst, Liquid bromine(Br2) as brome source to have a research on catalytic oxidative bromination of aromatic compounds. Meanwhile, we also make a systematic investigation on the amount of nitrogen dioxide, the amount of bromine source, reaction time, reaction atmosphere and solvent type. Finally, we make a conclusion that the best condition of methoxy benzene as 0.5mmol substrate, 8.2%mol nitrogen dioxide as catalyst, residual air in glass reaction tubes as oxidant, 0.25 mmol Br2 for bromine as bromine source and the reaction at room temperature for two hours. At the same time, based on the optimization of benzoic oxygen, examine the aromatic ethers, aromatic hydrocarbons, aromatic amines and aromatic heterocyclic and about 20 kinds of substrate. The method is found to be applicable to the synthesis of bromide on the naphthalene ring and with electron donating group on the benzene ring activation bromide, However, it’s not suitable for aromatic heterocyclic.On the basis of the study of single bromine reaction, I can obtain dibrominated products by changing the amount of bromine(Br2) and prolonging the reaction time. Through the investigation of reaction conditions, I finally discover that when the amount of bromine(Br2) increases to 1.3 equivalents, the reaction time is extended to 24 h, and most of them are connected with the benzene ring and naphthalene ring, in such a condition I can do the bromide efficiently.Through the preliminary investigation of reaction mechanism, the conclusion is that: after the reaction of molecular bromine and aromatic ring, we will get the corresponding bromide and hydrogen bromide. The generated hydrogen bromide was oxidized to bromine with reactive activity by oxygen under the catalysis of nitrogen oxides and then the generated bromine can participate in the bromide reaction.In conclusion, this project successfully developed a catalytic oxidation of bromide system model Br2/CH3CN/NO2/Air, the mild reaction conditions, high atom economy, using air as oxidant. In addition, it’s a nonmetallic compounds, easy to remove from the products, rarely stains final products and has a high potential in industrial application. |
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