弱碱体系中电化学合成3,6-二氯吡啶甲酸

Preparation 3,6-dichloropicolinic acid by electrochemical reduction dechlorination of 3,4,5,6-tetrachloropicolinic acid in Na_2CO_3 alkalescent system

测定了弱碱性Na_2CO_3水溶液中3,4,5,6-四氯吡啶甲酸(3,4,5,6-TeCP)在粗糙化银电极上的还原脱氯历程:3,4,5,6-TeCP=>3,5,6-三氯吡啶甲酸(3,5,6-TrCP)=>3,6-二氯吡啶甲酸(3,6-DCP).并研究了以3,4,5,6-TeCP为原料在弱碱水溶液中电解合成3,6-DCP的新工艺,结果表明:当以粗糙化银为阴极,电流密度为500 A/m^2,RITT为阳极,控制电解温度为(70+273)K,控制第二步反应pH≥13时,产品收率可达96%,产品纯度>98%.此外探究了Cl^-对该体系合成3,6-DCP的影响,结果表明Cl^-不利于产物收率和电流效率的提高.

The reduction of 3,4,5,6,tetrachloropicolinic acid on the surface of roughened silver electrode in 0.5 mol/L Na2 CO3 aqueous solution was determined to be a stepwise dechlorination as follows： 3,4, 5,6-tetrachloropicolinic acid= 〉3,5,6-trichloropicolinic acid= 〉3,6-dichloropicolinic acid （3,6-DCP）. In addition, 3,6-DCP was electrocatalytic synthesized at roughened silver electrode from 3,4,5,6- tetrachloropicolinic acid in Na2COs system. Experimental results showed the product yield was about 96 % and the purity is above 98 % if suitable conditions were controlled： temperature was （70 ± 273） K, current density was 500 A/m2, anode electrode was RITT, pH value of dechlorination of 3, 5, 6-trichloropicolinic acid into 3, 6-DCP was over 13. Furthermore, we investigated the influence of the chloride ion generated from the dechlorination reaction on the electrosynthesis of 3, 6-DCP： it could reduce the current efficiency and the product yield of electrolysis reaction.