Electrochemical Fixation Of CO₂ With Aromatic Halides

Due to the improvement of the current economic level,people have become overly dependent on fossil fuels.This will not only lead to energy crisis,but will also cause the continuous increase of carbon dioxide?CO₂?content in the atmosphere,which will increase global warming.There are two ways to solve this problem:one is to seek and develop new energy sources to replace traditional fuels,and the other is to convert CO₂into useful organic chemicals.Solar energy is a renewable energy.Dye-sensitized solar cells can effectively convert solar energy into electrical energy,and it has received widespread attention due to its advantages of high conversion efficiency and low manufacturing cost.CO₂ is a broad,non-toxic carbon source.However,due to its stable thermodynamic properties,it will be difficult to complete the study of its activation and utilization.Compared with the traditional high-temperature and high-pressure technology,electrochemical synthesis technology can realize the activation and utilization of CO₂ at normal temperature and pressure into important carboxylic acids or carboxylic acid derivatives.The main contents of this thesis are as follows:1.Electrocarboxylation of dichlorobenzenesTaking 1,4-dichlorobenzene as the model compound,under normal temperature and pressure,galvanostatic electrolysis of 1,4-dichlorobenzene was carried in an undivied cell with an air inlet and an air outlet,and obtained methyl benzoate,methyl p-chlorobenzoate and dimethyl terephthalate.In the experimental process,we investigated the influence of current density,supporting electrolyte,electric charge and temperature on the total yield of electrocarboxylation.The experimental results show that under the optimal reaction conditions,an overall yield of 46.3%can be obtained.In addition,under the optimal condition,1,2-dichlorobenzene and 1,3-dichlorobenzene were electrolyzed respectively,and the carboxylation yields of 49.5%and 49.2%were obtained in turn.In this experiment,the electrochemical behavior of dichlorobenzene on GC and Ag electrodes was studied by cyclic voltammetry.The charge numbers of carbon and carbon anions and their respective energies were calculated by Gaussian calculations.Combined with the electrochemical behavior of dichlorobenzene and its calculation results of Gaussian and experimental electrolysis results,our group speculates the reaction mechanism of the reaction.2.Dye-sensitized solar cells be applied to electrocarboxylation of 1,4-dibromobenzeneThe electrochemical behavior of 1,4-dibromobenzene on Ag electrode was studied by cyclic voltammetry.Based on the reduction peak potential of 1,4-dibromobenzene on Ag electrode,potentiostatic electrolysis of 1,4-dichlorobenzene was carried in an undivied cell with TBABr-DMF solution was used as the reaction system and Ag-Mg as the electrode system,and obtioned methyl benzoate,methyl p-bromobenzoate,dimethyl terephthalate product.The experimental results show that the highest yield reached 70.3%under a controlled potential-1.7 V until 4.0 F/mol of charge passed through the cell at 0.0?.The dye-sensitized solar cell produced by our group was fabricated using TiO₂ as a photoanode,Pt as a counter electrode,N-719 dye,and I^3-/I^-electrolyte,with a single cell voltage of 0.7 V.We examined the influence of phtovoltage and illumination time provided by dye-sensitized solar cells on the yield of carboxylation were also investigated.The results show that when the phtovoltage is 2.1 V and illumination time is 8.0 h,the total carboxylation yield can reach up to 66.8%.3.Dye-sensitizedsolarcellsbeappliedtoelectrocarboxylationof2-amino-5-bromopyridineUnder normal temperature and pressure,galvanostatic electrolysis of2-amino-5-bromopyridine was carried in an undivied cell,and the effect of the supporting electrolyte on the reaction product was investigated.The results show that the highest yield of 41.2%6-aminonicotinic acid available from electrolysis of 2-amino-5-bromopyridine at a current density of 8.0 mA/cm² in TBABr-DMF solution.The peak potential reduction of2-amino-5-bromopyridine on Ag electrode was based on potentiostatic electrolysis of2-amino-5-bromopyridine and found that the yield was up to 46.0%when the electrolysis potential was-2.7 V.Subsequently,the effect of phtovoltage and illumination time provided by dye-sensitized solar cells on the yield of carboxylation were also investigated.The data shows that when the phtovoltage is 2.1 V and the illumination time is 13.2 h,the yield is up to 35.3%.