Selective Electrocatalytic Dechlorination Of 2,3,5,6-tetrachloropyridine

The compounds containing pyridine structure are the main products in pesticide synthesis area.For example,2,3,5-trichloropyridine?2,3,5-TCP?is one of the key intermediate for the synthesis of pesticide,and has broad market application prospects,so the synthesis of pyridyl chloride has always been a hot spot in chemical industry.Based on the research of the synthesis of 2,3,5-TCP,the electro-catalytic dechlorination of 2,3,5,6-tetrachloropyridine?2,3,5,6-TeCP?used as a model reaction in this thesis,and the electro-catalytic behavior and reaction mechanism were studied on the silver electrode.The reductive dechlorination of 2,3,5,6-TeCP was investigated by constant current electrolysis and potentiostatic electrolysis,and the influence of electrode materials and electrode surface structure was on the dechlorination performance of 2,3,5,6-TeCP explored.In the first part,the electrochemical reductive dechlorination process of2,3,5,6-TeCP was studied by cyclic voltammetry.The cleavage order of C-Cl bonds at four positions of 2,3,5,6-TeCP was analyzed through the electrochemical reductive dechlorination of different chloropyridine compounds?2,3,5,6-TeCP,2,3,5-TCP and2,3,6-TCP?.The relationship between peak currents and scan rates showed that the electrochemical dechlorination of 2,3,5,6-TeCP was controlled by diffusion process,and the coefficient of diffusion was 4.06×10^-7 cm²/s.The adsorption phenomenon and catalytic activity of 2,3,5,6-TeCP on the silver electrode surface was analyzed through linear voltammetry on the electrolysis process,and the apparent activation energy was6.893 KJ/mol.Finally,the electrolysis conditions of 2,3,5,6-TeCP were optimized by potentiostatic electrolysis.The results showed the yield of 2,3,5-TCP was 53%,and the selectivity is 54%after electrolyzing for 6 h with 0.02 M 2,3,5,6-TeCP and 0.1 M TBAP as catholyte,0.5 M NaOH solution as anolyte at 1.7 V and 30?.In the second part,two kinds of ionic liquids based on the framework of imidazole and piperidine were synthesized,and the electrochemical properties were compared between the synthesized ionic liquids and the traditional electrolytes.The results showed that the two kinds of ionic liquids have higher conductivity and wider electrochemical windows than lithium perchlorate and tetrabutyl ammonium perchlorate.Then the electrolysis conditions of 2,3,5,6-TeCP electrode chlorination were optimized by constant current electrolysis.The results showed that the yield of2,3,5-TCP was 60%,and the selectivity was 63%after electrolysis for 6 h at a current density of 7 mA/cm² and 30?.The surface roughness of the silver electrode was increased and the activity was activated through chronoamperometry.The surface roughness of the silver electrode could be controlled by changing the activation current and activation time.The results showed that the yield of 2,3,5-TCP was 68%,and the selectivity was 69%under the optimized electrolysis conditions on the roughed silver electode which was activated with a current of 19.2 mA for 10 min.