Study On The Synthesis Of 2,3,5-trichloropyridine

2,3,5-trichloropyridine is an important intermediate for the production of herbicidal or pesticidal active substance such as 3,5-dichloro-2-pyridinol and isoxapyrifop.Through comparing different methods of preparation,we found that the way of the preparation which used pentachloropyridine and zinc as initial reactant to be more suitable at last.In such way, the material could be gained easily and t-he process was short .By orthogonal experiment,it was confirmed that the opti-mum reaction condition:The reaction temperature was 75oC; The reaction time was 5 hours;the concentration of sodium hydroxy was 8 mol/L;the mole ratio of zinc to pentachloropyridine was 3.5 to 1.Under the conditions,the yield of 2,3,5-trichloropyridine was about 66%,which was higher about 3% than the previous literature.From the reaction mechanism,this paper established macrokinetics of synth-esis of 2,3,5-trichloropyridine by pentachloropyridine and zinc.The parameter of the reaction kinetics model was estimated with the Matlab program and simple method.The model result agreed well with experimental datal.The model was re-liable inexperimental scope, which could reflect the truth of experiment.From the activation energy,we could conclude that the lower temperature could impr-ove the yield of 2,3,5-trichloropyridine.It provided theory direction for the indu-strial reactor scaleup and the optimization.In the presence of phase transfer catalyst,it could obviously quiken the rateof reaction.First,we studied the theory of synthesis of 2,3,5-trichloropyridine by phase transfer catalyst.Then we optimize the process: The reaction temperature was 50oC;The reaction time was 6 hours;The concentration of sodium hydroxy was 8 mol/L;the mole ratio of zinc to pentachloropyridine to tetramethylammo-nium bromide was 3～3.5 to 1 to 0.05.Under the conditions, the yield of 2,3,5-trichloropyridine was above 73%. The reaction time was shortened and the mole ratio was reduced.The yield of this new method was improved about 10% co-mpared with the literature method.