Study On Electrochemical Dechlorination Of Polychlorinated Pyridine Compounds

4-amino-3,6-dichloropicolinic acid?4-N-3,6-DCP?is a new efficient,low-toxic hormonal herbicide with broad market application prospects.At present,the relevant technical parameters of electrochemical synthesis of 4-N-3,6-DCP are still blank in the domestic industrialization.And the related patents will be expired several years later.Once expired,the enterprises who master the relevant production technologies can quickly win the market.In addition,the described electrochemical synthesis methods are susceptible to hydroxylation and oxidation of the amino group,and the product purity is only 90%.The first part work of this paper is based on the above problems to improve the process.We use H-type diaphragm cell instead of non-diaphragm cell,roughened silver electrode as the cathode and graphite as the anode.The raw materials dissolved in the alkaline solution.Cyclic voltammetry?CV?is used to study the electrochemical performance of silver electrodes in aqueous solutions containing 4-amino-3,5,6-trichloropicolinic acid?4-N-3,5,6-TCP?.Electrochemical synthesis of4-N-3,6-DCP has been optimized by galvanostatic electrolysis technique.The product has been characterized and analyzed.Experimental results show that under the optimized electrolysis conditions---0.1M 4-N-3,5,6-TCP and 1M NaOH as catholyte,1M NaOH as anolyte,the temperature is 30?,the current density is 125 A·m^-2,rotating speed is 800r/min,4-N-3,5,6-TCP can be selectively dehydrochlorinated into4-N-3,6-DCP with high selectivity.The rate of conversion?98%,yield?85%,current efficiency?40%and the purity of product is about 95%.The yield of4-N-3,6-DCP increased about 10%compared with the recorded in the literature,and the purity of the product increased from 90.6%to 95%.The silver electrode exhibits good dehydrochlorination stability in electrolysis experiments.The second part of this paper explores the feasibility of electrochemically selective dehydrochlorination of 2,3,5,6-tetrachloropyridine?2,3,5,6-TeCP?to2,3,5-trichloropyridine?2,3,5-TCP?.2,3,5-TCP has many important applications in synthesis of efficient and green pesticides,such as acaroid mites and schizophyllan.The electrochemical dechlorination performances of 2,3,5,6-TeCP on different electrodes have been compared using cyclic voltammetry.The electroreduction dechlorination process was optimized by galvanostatic electrolysis.The electrolysis conditions are as follow:Pb as the cathode,methanol solution containing 0.1M 2,3,5,6-TeCP,0.3M NH₄Cl,10%?V%?water and 2.5%?V%??C₂H₅?₃N as catholyte,the current density is 62.5 A·m^-2.Experimental results show that the yield of 2,3,5-TCP can achieve 62.47%,and the current efficiency is 60.39%.Compared with 63%of the 2,3,5-TCP yield in the literature,the electrolytic synthesis method effectively avoids the production of zinc containing wastewater and reduction the reaction temperature about 25?.