The Study Of Dechlorination Of Tetrachloropyridine And Dichloropicolinic Acid

Pyridine Derivative 2,3,5,6 - tetrachloro-pyridine is a very important pesticide intermediates,it can be used to prepare a variety of potential insecticides and herbicides.At present,the most common synthesis method is prepared by the dechlorination of pentachloropyridine.Based on the domestic and foreign research at present,we chose the Zn/Ag bimetallic system to dechlorinate pentachloropyridine to prepare tetrachlorpyridine.And we studied the effect of initial pH of the system, amount of catalyst and reaction temperature on the reaction.And the reaction mechanism of this bimetallic system was investigated.The results showed that:the zinc powder could be used to reductively dechlorinate pentachloropyridine to tetrachloropyridine with its yield about 20%.Under the catalytic effect of silver,the dechlorination efficiency of pentachloropyridine was greatly improved.When the initial pH was about 5,the concentration of silver nitrate was 10 g·L^-1,the yield of tetrachloropyridine could be above 60%.The reaction took place on the bimetal surface in a first order reaction,and the rate constant was 0.0097 min^-1.Another pyridine derivative 3,4,5,6 - tetrachloro-pyridine carboxylic acid is a very active plant growth regulator,it has broad market prospect.Electrolytic reduction method is the most effective preparation method of 3,6 - dichloro-picolinic acid. 3,4,5,6 - tetrachloro-pyridine carboxylic acid on silver electrode in the synthesis of 3,6-dichloro-picolinic acid has been industrialized,but there will be a bubble situation and the slow feeding,long reaction time in the actual production process. And because of the low solubility of thetetrachlorophthalic in the reaction solution and the low one time output rate,which will cause difficult post-processing such as extraction with dichloromethane consumed in large quantities,and the high energy consumption,waste treatment capacity.This paper,based on this technology to make the raw material dissolved in weak basic solution instead of being dissolved in the strong alkaline solution before,using cyclic voltammetry,chronocoulometry and potential-controlled electrolysis,studied the electrochemical reduction behavior of 3,4,5,6 -tetrachloro-pyridine carboxylic acid on silver electrode.The results showed that:（1）:In the weak alkaline solution,at tetrachlorophthalic on rough silver electrode for the dechlorination reaction is not reversible,controlled by diffusion of 3,4,5,6-tetrachloropyridine carboxylic acid,moderately increasing the temperature can significantly accelerate the reaction diffusion steps.（2）:In the weak alkaline solution,the hydroxylation rate is still very low even at high temperature（60～80℃）,but the solubility is increased from 2%in the strong alkaline solution and at the ambient temperature to 13～18%.And there is not any bubble generated.All of the above problems are solved.（3）:The electrolysis process does not have any other by-products in the electrolysis of tetrachlorophthalic at weak basic solution of ph 9,10,11,which proved the feasibility of the study.（4）:It can reach the maximum solubility and the maximum space-time yield under the condition of ph 11.