The Transformation And Utilization Of Carbon Dioxide Oriented By Fine Chemicals

The researches in this thesis involve in two parts, including the electrochemical utilization of CO₂ and electro-synthesis of oxygen- and nitrogen-heterocycles. The paper mainly focused on developing an efficient electrochemical method for the conversion of CO₂ as well as for the synthesis of oxygen- and nitrogen-heterocycles.In the paper, a simple and efficient electrochemical method was developed by using Ni cathode and Al anode for the synthesis of unsaturated 1,6-dioic acids from 1,3-dienes and CO₂. The electrosynthesis was smoothly carried out in an undivided cell containing n-Bu4NBr-DMF electrolyte with a constant current under 3 MPa pressure of CO₂ at room temperature in the absence of additional catalysts, and the corresponding 1,6-dioic acids were afforded in moderate to high yields (80-90%) and high selectivity (98%). With 1,3-butadiene as the model compound, the influence of some key factors (such as electrode materials, current density and CO₂ pressure) on the results of the electrosynthesis was investigated. Based on the results of electrosynthesis and cyclic voltammetry (CV), the electrochemical reaction mechanism was also briefly discussed. In succession, the electroreduction of 3-hexene-1,6-dioic acid into adipic acid was further investigated. The influenced factors (temperature and current density) on the results of the electroreduction were examined and the plausible electroreduction mechanism was discussed briefly. The process of adipic acid originated from 1,3-butadiene and CO₂ is very important for the utilization of CO₂ and the ever-growing demand for adipic acid.The electrochemical method was further applied for the electrocarboxylation of CO₂ with 1,4-diphenylbuta-1,3-diyne and its derivatives. The experimental results indicate that the method is feasible for the electro-dicarboxylation of 1,4-diphenylbuta-1,3-diyne and its derivatives with CO₂. Electrocarboxylation of 1,4-diphenylbuta-1,3-diyne and its derivatives with CO₂ was carried out in an undivided cell fitted with Ni cathode and Al anode, containing n-Bu4NBr-DMF electrolyte with a constant current under CO₂ pressure of 4 MPa, affording the novel cyclic dicarboxylation products in moderate to good yields with metal salt catalysts (such as CuI) or the mono-carboxylic acid without any catalysts. The plausible electrochemical mechanism and the role of the metal salts were also discussed. On the basis of this work, with some common metal salts (CuI, FeCl₃) as catalysts, the electrocarylation of alkynes with CO₂ were further investigated. The saturated tricarboxylic acids besides the dicarboxylic acids were obtained in good yields.An efficient method has been developed for the synthesis of oxygen- and nitrogen-heterocycles from electron-deficient alkynes and alcohol or amines via electrochemically induced two-step process. The first step involves that the electrogenerated base (EGB) catalyzes hydroalcoholization or hydroamination process. In the second step, Fe3+ ions and strong bases electrogenerated can synergically catalyze the cyclization process to give symmetrical heterocycles. Some key factors were investigated and the reaction mechanism was discussed.