A Study Of Dechlorination Of Polychloropyridines

Dechlorination of polychloropyridines is a new attempt for halogenated pyridines synthesized.Based on the research and development of synthesis of halogenated pyridines the paper chose the electrochemical reduction as a research direction,and to 3,4,5,6-tetrachloropicolinic acid,pentachloropyridine,3,4,5,6-tetrachloro-2-trichloro methylpyridine for raw materials,the reduction behavior on silver and carbon -containing silver electrode was mainly studied.ChapterⅠdiscussed the character,use and synthesis of 3,6-dichloropicolinic acid, 2,3,5,6-tetrachloropyridine,3,4,5,6-tetrachloro-2-dichloromethylpyridine which were production of dechlorination of the three raw materials,the electrode materials applications were also disscussed.Provide background for the research.ChapterⅡfocuses on the experiment contents and methods.In chapterⅢ,electrochemical reduction behavior of 3,4,5,6-tetrachloro-2-trichloromethylpyridine on silver electrode was disscussed.The cathodic reduction behavior,the reaction kinetics and course of 3,4,5,6-tetrachloro-2-trichloromethylpyridine were carried out a detailed study by cyclic voltammetry,chronocoulometry and potential-controlled electrolysis.The results showed that:silver electrode had a high electro-catalytic activity to 3,4,5,6-tetrachloro-2-trichloromethylpyridine;the reduction of 3,4,5,6-tetrachloro-2-trichloromethylpyridine on silver electrode was a diffusion-controlled irreversible process;the process was an EC （electrochemistry-chemistry）process;3,4,5,6-tetrachloro-2-trichloromethylpyridine in pure acetonitrile,acetonitrile / water mixture solution,N,N-dimethylformamide, ethanol can be reduct;Potential-controlled electrolysis experiments showed that the main product were dechlorination and hydrogenation products,less byproducts had been produced at low potential;The byproducts can be reduced in the solvent containing water.The diffusion coefficient of 3,4,5,6-tetrachloro-2-trichloro methylpyridine in the mixed solvent which were acetonitrile:water = 5:1 was find out by chronocoulometry.D = 2.7×10^-5cm² / s.The major studies of Chapter IV were preparation methods of carbon containing silver,and its catalytic properties.It was analyzed that the effection on the preparation of carbon contained silver of different function ions of pre-adsorption,and silver ion concentration;and it was made of powder microelectrode testing electro-catalytic properties of 3,4,5,6-tetrachloropicolinic acid,pentachloropyridine, 3,4,5,6-tetrachloro-2-trichloromethylpyridine by cyclic voltammetry.The results show that:use of functional ions pre-adsorption method can be effectively dispersed the silver,the order of decentralized capacity of functional ions: Cl^-＜Br^-<I^-;When the concentration were 50～500mg/L,catalytic effect increase with silver ion concentration increased but reduced at 1000mg/L.Carbon containing silver electrode electrochemical test results demonstrate that in the dechlorination of 3,4,5,6-tetrachloropicolinic acid,pentachloropyridine,3,4,5,6-tetrachloro-2-trichloro methylpyridine,electrochemical reduction steps were faster than other steps,and the smaller the particle size of silver,better catalytic effect.