Study On Synthesis And Kinetics Of Herbicides Picloram

Pyridine herbicides picloram,4-Amino-3,5,6-trichloropicolinicacid, is a systemic herbicides. It has a significant market prospects for its low toxicity, high selectivity, small amount and short cycle of residual in plants and soil and so on.Firstly, our work selected and optimized synthesis process on the basis of current research. We obtained the optimal process conditions through the systematic study of the influent factors, including the material ratio, aqua ammonia concentration, reaction temperature and so on. The optimal process conditions are as follows:the molar ratio of ammonia and 3,4,5,6-tetrachloropicolinicacid is 5; the concentration of aqua ammonia is 6.25%; the temperature is 128℃; the reaction time is 10 hours; the reaction has higher selectivity of the product with a lower temperature and a longer reaction time. The yield of picloram can reach to 82.82% in the above optimal conditions. On this basis, the optimum production conditions were obtained by appropriately increasing the ammonia ratio and the reaction temperature. The ammonia ratio is 8; the concentration of aqua ammonia is 6.25%. The yield of picloram can reach to 81.66% when it reacted at 165℃for 97 min in the above conditions.Secondly, ammonolysis reaction mechanism was also discussed in this paper. It indicated that the reaction of 3,4,5,6-tetrachloropicolinicacid and aqua ammonia is bimolecular nucleophilic substitution (SN2).Finally, our work studied the apparent kinetics of ammonolysis reaction between the 3,4,5,6-tetrachloropicolinicacid and aqua ammonia and established the kinetic model. The content of 4-Amino-3,5,6-trichloropicolinicacid (U),6-Amino-3,4, 5-trichloropicolinicacid (V),4-hydroxy-3,5,6-trichloropicolinicacid (W),3,4,5, 6-tetrachloropicolinicacid were measured at the same materials ratio and aqua ammonia concentration but different reaction temperature conditions so that the kinetics parameters could be determined. By studying a series of the reaction at different reaction temperatures (90℃,110℃,130℃,150℃), determined that the reaction is first order reaction and obtained the kinetic equation and the activation energy.