Preparation method of 2,3,5-trichloropyridine

Abstract

The invention discloses a preparation method of 2,3,5-trichloropyridine. The preparation method comprises the following steps: dissolving 2,3,5,6-tetrachloropyridine as an initial raw material in a weakly alkaline solvent; carrying out an electrolytic reaction in an electrolytic cell taking a conductive material as a cathode and a chemically inertial conductive material or a titanium metal material coated with a noble metal oxide as an anode, wherein the temperature is 20-50 DEG C and the current density is 1-5A / dm<2>; in the reaction process, stabilizing the pH value of the cathode solution by proportion of an anode solution, wherein the pH is 9; and after reaction for 0.5Q*-2Q*, carrying separation and purification to obtain the 2,3,5-trichloropyridine. According to the method disclosedby the invention, the pH of the cathode solution can be controlled in a range from 8-9, so that the problem of excessive dechloridation, low selectivity, more byproducts and the like as the pH is unstable when the inertial conductive material is used for preparing 2,3,5-trichloropyridine is solved; a lot zinc containing waste water in reduction of 2,3,5,6-tetrachloropyridine zinc powder is avoided, so that the treatment cost of three wastes is lowered; an electrode material is cheap, easily available and stable; electrolysis can be carried out at normal temperature; the selectivity of synthesizing 2,3,5-trichloropyridine is greater than 80%, and the yield is higher than 60%.

Description

technical field [0001] The invention relates to a preparation method of 2,3,5-trichloropyridine, in particular to the preparation of 2,3,5- Triclopyridine method. Background technique [0002] 2,3,5-Trichloropyridine is an important pesticide intermediate, which is widely used in herbicides and insecticides. 2,3,5-Trichloropyridine can be used to prepare a series of pesticides such as insecticidal mite and chlorpyrifos. It is an important intermediate of the new herbicide oxafefen. After fluorination, it can be used to prepare the important pesticide intermediate 2,3,5-difluoro -5-chloropyridine (US244586). [0003] The synthesis process of 2,3,5-trichloropyridine was first proposed by Sell et al. in 1888. It was prepared by mixing pyridine and phosphorus pentachloride in a sealed test tube and reacting at 210-220°C. Existing methods mainly include three categories: 1. direct chlorination method, mainly including gas-phase chlorination represented by U.S. patent US4108856...

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Problems solved by technology

[0004] The technical problem to be solved by the present invention is to provide a method for controlling the small-scale fluctuation of the pH value of the catholyte by using the alkaline ratio of the anolyte, which can avoid the pH of the electrochemical reduction to prepare 2,3,5-trichloropyridine. The problem of excessive dechlorination, low selectivity, and many by-products caused by instability, the use of this method for electrocatalytic reactions has the advantages of cheap and easy-to-obtain electrode materials, low preparation costs, simple process flow, high product yield, less three wastes, and more efficient production. Advantages of safety

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