Process for preparing symmetric tetrachloro pyridine

Abstract

The process of preparing symmetric tetrachloro pyridine includes the chlorination reaction of chloro pyridine containing 1-3 chlorine atoms and chlorine at 170-250 deg.c in the presence of iron powder or Lewis acid as catalyst for 8-48 hr. The preparation process uses chlorine in the liquid phase chlorination reaction to chlorinate chloropyridine, dichloropyridine, trichloropyridine, etc, and has single pass conversion rate up to 97 %, simple technological process, low production cost and excellent industrial application value.

Description

(1) Technical field [0001] The invention relates to a preparation method of symmetrical tetrachloropyridine. (2) Background technology [0002] Symmetrical tetrachloropyridine, also known as 2,3,5,6-tetrachloropyridine, has a molecular structure as shown in the figure below: [0003] [0004] Due to the presence of multiple electron-withdrawing groups in its molecular structure, the chlorine at the 2-position has a relatively high reactivity and becomes a commercially valuable pyridine derivative, which can be used in the synthesis of herbicides, fungicides and insecticides . Because symmetric tetraclopyridine can be used as an important starting material for the highly efficient, low-toxicity, broad-spectrum insecticide "chlorpyrifos", which ranks first in terms of sales volume and sales in the world, so far, domestic and foreign industry insiders have little interest in this chemical. A large amount of research has been done in the preparation, and multiple preparatio...

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Problems solved by technology

[0005] Chinese patent CN1421436 introduces the use of pentachloropyridine as a starting material, and in the presence of inorganic ammonium salts, it is reduced to tetrachloropyridine with zinc or iron powder in a solvent, because pentachloropyridine is obtained by reacting pyridine or polychloropyridine with chlorine gas Compared with directly making symmetrical tetrachloropyridine with pyridine or polychloropyridine and chlorine, it is obviously uneconomical from the perspective of raw material utilization, which will inevitably lead to excessive production costs of products

Chinese patent CN1421435 discloses the production technique that uses pyridine and chlorine as starting raw material to prepare symmetrical tetrachloropyridine, but the reaction product that obtains is the mixture of tetrachloropyridine (about 60%) and pentachloropyridine (about 38%) or The mixture with pentachloropyridine as the main component still needs to undergo reduction reaction to obtain tetrachloropyridine. In addition, the reaction temperature of this preparation method is too high (270-500 ° C), which also increases the difficulty of practical application.

But there is not high (81.21%) that causes the total yield of symmetric tetrachloropyridine because of the longer process route, and the deficiency that content is on the low side (93%)

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