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Preparation method of 2,3,5-trichloropyridine
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A technology of trichloropyridine and tetrachloropyridine, which is applied in the field of preparation of 2,3,5-trichloropyridine, achieves the effects of short reaction time, non-corrosion, and reduced treatment cost of three wastes
Active Publication Date: 2018-03-20
ZHEJIANG UNIV OF TECH
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[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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Embodiment 1
[0053] The diaphragm plate frame tank is an electrolytic reactor, the perfluorosulfonic acid membrane is a diaphragm, the lead sheet is a cathode, and the graphite plate is an anode. 1000mL 0.1mol / L 2,3,5,6-tetrachloropyridine (TeCP) (21.8g, GC content 99.1%)+0.3mol / L NH 4 The methanol solution of Cl (16.2g) + 1% vol ammonia water (ammonia content 25% ~ 28%) + 9% vol water is the catholyte; 1000mL0.1mol / L sodiumhydroxideaqueous solution is the anolyte. During the electrolysis process, the temperature is controlled at 45-50°C, and the current density is controlled at 3A / dm 2 , the initial pH of catholyte=8. Stop electrolysis after electrifying for 4.2h (that is, a theoretical electric quantity Q*). GC analysis of the catholyte showed:
[0054] 3,5-Dichloropyridine: 7.671%
[0055] 2,5-Dichloropyridine: 4.238%
[0056] 2,3,5-Trichloropyridine: 60.46%
[0057] 2,3,6-Trichloropyridine: 5.152%
[0058] 2,3,5,6-Tetrachloropyridine: 21.38%
[0059] After distilling the cath...
Embodiment 2
[0062] Same operation with embodiment 1, but change anolyte sodiumhydroxide concentration into 0.15mol / L, the GC analysis of catholyte shows:
[0063] 3,5-Dichloropyridine: 5.405%
[0064] 2,5-Dichloropyridine: 3.139%
[0065] 2,3,5-Trichloropyridine: 56.91%
[0066] 2,3,6-Trichloropyridine: 5.143%
[0067] 2,3,5,6-Tetrachloropyridine: 28.46%
[0068] The products obtained by the comprehensive treatment of the reaction solution are respectively:
[0069] 0.99g of 3,5-dichloropyridine, 0.66g of 2,5-dichloropyridine, 12.11g of 2,3,5-trichloropyridine, 1.03g of 2,3,6-trichloropyridine and unreacted 2,3 , 5,6-tetrachloropyridine 5.96g, in summary, the yield of 2,3,5-trichloropyridine is 55.55%.
Embodiment 3
[0071] Same operation as embodiment 1, but ammoniacal liquor is changed into triethylamine, and the GC analysis of catholyte shows:
[0072] 3-chloropyridine: 5.498%
[0073] 2,5-Dichloropyridine: 3.452%
[0074] 2,3,5-Trichloropyridine: 70.24%
[0075] 2,3,6-Trichloropyridine: 5.795%
[0076] 2,3,5,6-Tetrachloropyridine: 14.43%
[0077] The products obtained by the comprehensive treatment of the reaction solution are respectively:
[0078] 0.83g of 3-chloropyridine, 0.58g of 2,5-dichloropyridine, 14.43g of 2,3,5-trichloropyridine, 1.02g of 2,3,6-trichloropyridine and unreacted 2,3,5, 3.06 g of 6-tetrachloropyridine. In summary, the yield of 2,3,5-trichloropyridine is 66.19%.
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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 titaniummetal material coated with a noble metaloxide 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 zincpowder 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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