The Basic Research On Paired Electrosynthesis Process Of The L-cysteine Hydrochloride And The Nicotinic Acid

Both L-cysteine and nicotinic acid, which are important fine chemicals, are used as intermediates of synthesizing medicine, raw materials of chemical industries, and additives of food, drink and feed. With their applied technology development, market demand for both increase year by year. The methods of synthesizing them are various, including chemical synthesis, electrochemical synthesis and biological synthesis etc. Electrochemical synthesis as a green and pollution-free production technology, is a ideal method of synthesizing L-cysteine and nicotinic acid in the future, but there are some problems such as cost and technology at present, to limit the industrial development of electrochemical synthesis of L-cysteine and nicotinic acid. Therefore, the paired electrosynthesis is promised to be a prospective way to synthesize L-cysteine and nicotinic acid, and has important application value.Paired electrosynthesis, which is developed in recent years of new electrochemical synthesis method, is used the reaction of the cathode and the anode at the same time, to get one or two useful products. This method has some advantages, can greatly improve the current efficiency, time and space efficiency, and reduce costs and energy. In recent years, it is broadly attracted by electrochemical workers at home and abroad, but only a few products of paired electrosynthesis achieve a synthesis of industrialization, therefore it need to be more in-depth research and development.We integrate the reduction of L-cystine at the cathodic and the oxidation of 3-methyl-pyridine at the anode into an electrochemical system. In an electrolytic cell with proton exchange membrane, electrolyzing L-cystine and 3-methyl-pyridine with constant current, the experiment conditions were as follows:PbO2-F electrode as the anode. Pb electrode as the cathode, temperature 25℃, in the anode electrolyte containing lmol/L sulfuric acid,1.2 mol/L 3-methyl-pyridine, and in the cathode electrolyte containing 2 mol/L hydrochloric acid,0.7 mol/L L-cystine. Affecting factors for the paired electrosynthesis, such as the concentration of 3-methyl-pyridine, current density, reaction temperature and the ratio of anode and cathodic on the current efficiency and the selectivity were explored. In the process of paired electrosynthesis. it was found that the current efficiency and the selectivity of cathodic reaction would decrease, Because of 3-methyl-pyridine through the proton exchange membrane to the cathode, and chloride ion through the membrane could also affect the anode reactions.By electrolyzing L-cystine and 3-methyl-pyridine with constant current, effect of the concentration of 3-methyl-pyridine, current density, the concentration of sulfuric acid, and reaction temperature on the current efficiency and the selectivity were explored, and the optimum experiment conditions were determined. The optimum experiment conditions were as follows:3-methyl-pyridine 1.2 mol/L. current density 80 mA/cm2, sulfuric acid 1.5 mol/L, temperature 30℃. Under optimum conditions, the selectivity of the cathode and the anode reach 98% and 86%, the current efficiency of the cathode and the anode reach 93% and 52%, and the total current efficiency reach 145%.