Electrocatalytic Carboxylation Of Arylic Bromides In The Presence Of Carbon Dioxide

As paying the more attention to the awareness of protecting the environment, the conception of Green Chemistry is appearing. Green Chemistry includes many aspects such as the process that eliminate hazardous substances, the manufactures of environmentally friendly product and green chemical procedure. Green chemistry is intended for re-examining and reforming the entire chemical and chemical engineering from the view point of the resource conservation and pollution prevention. One of principles for Green Chemistry is to maximize atom economy, which is to design synthesis process so that the final product contains the maximum proportion of the starting materials. In electro organic synthesis, the electron has been used as reagent. So it is called a green synthetic technique.At the same time, with the development of the global economy and the increased need of the energy resource, the amount of CO2 in atmosphere is increasing greatly and it is the primary component of greenhouse gases. So the study on the transformation of it into chemical product can help us reduce the environmental pollution by controlling the emission of greenhouse gases and utilize the cheap and abundant C1 resource. Therefore it is one of the most valuable things in the whole world.The benzoic acids are of great interest in the pharmaceutical industry and organic synthesis. In the traditional syntheses of benzoic acids, there were several drawbacks such as the use of expensive and complicated catalysts, the requirement of high pressure and high temperature, and low yields. Since the electro organic synthesis requires only mild reaction condition, it has been used to do the fixation of greenhouse gas-CO2 to produce benzoic acids. Now the electro organic synthesis is becoming an important green synthetic method.The paper concerns with the study on the electrocarboxylation of arylic bromides into benzoic acid or its derivatives. It is divided into four parts. The influences of some key factors on the electrocarboxylation of arylic bromides were investigated and the reaction mechanisms were brought forward. The details are given as follows:Firstly, at the atmospheric pressure and room temperature, electrocarboxylation of bromobenzene were carried out in an undivided cell in the N,N-dimethylformamide(DMF) using tetraethylammoniumiodide(TEAI) as the supporting electrolyte with galvanostatic electrolysis. The influences of some key factors(such as the nature of electrode materials, current density, the reduction charge supplied to the electrodes(Q), temperature) on this reaction were investigated. Under the optimal condition, the maximal yield of 78.2% for benzoic acid has been reached. The optimal conditions were then applied to the electro carboxylation of p-bromotoluene, p-bromoanisoles,4-bromochlorobenzene and benzyl bromide in order to convert them to their corresponding benzoic acid derivatives. The corresponding yield is between 20.6% and 35.3%. The electrochemical reduction behaviour of bromobenzene was studied by cyclic voltammetry. Also, the influence of carbon dioxide on above electrochemical reduction was investigated. In the end, on the basis of the electrolysis results and the concerned cyclic voltammograms, the mechanism of electrocarboxylation of bromobenzene was put forward.Secondary, the electrochemical behaviour of p-bromoanisoles was studied at different electrodes by cyclic voltammetry. Under normal temperature and pressure, electrocarboxylation of p-bromoanisole was carried out in an undivided cell in the N,N-dimethylformamide(DMF) using tetrabutyl ammonium iodine (TBAI) as the supporting electrolyte using galvanostatic electrolysis. The influences of supporting electrolytes, working electrodes, current densities, the charge supplied to the electrode(Q) and temperature were investigated to optimize the electrolytic conditions. At 0℃, the maximal yield of 4-methoxybenzoic acid reached 68.7% at Ag-Mg electrodes under 5 mA·cm-2 of current density until 2 F·mol-1 of charges was passed through the cell.Thirdly, at the atmospheric pressure and room temperature, the electrocarboxylation of methyl 4-bromobenzoate were carried out in an undivided cell in the N,N-dimethylformamide(DMF) using tetrabuthylammoniumiodide(TBAI) as the supporting electrolyte under galvanostatic electrolysis. The influences of some key factors(such as the nature of electrode materials, current density, charge supplied to the electrodes(Q) and temperature) on this reaction were investigated. Under the optimal conditions, the yield of concerned product reached 60.4%. And the involved electrochemical behaviors were also studied by cyclic voltammetry under normal temperature and pressure.Finally, under the atmospheric pressure and room temperature, the electrocarboxylation of benzyl bromide were carried out in an undivided cell in the N,N-dimethylformamide(DMF) using tetraethylammoniumiodide(TEAI) as the supporting electrolyte with galvanostatic electrolysis. The influences of working electrodes, current densities and charge supplied to the electrode (Q) on the electrocarboxylation of benzyl bromide were investigated. The electrochemical behavior was studied at different electrodes by cyclic voltammetry. At the temperature of 0℃and the current density of 5 mA·cm-2, the yield of phenyl acetic acid reached 74%, using silver as work electrode, magnesium as counter electrode.