A method for purifying 2,3-dichloropyridine

Abstract

The present application relates to a kind of 2,3-dichloropyridine purification method.The method of the present application first removes part 2,3,6-trichloropyridine and most other impurities in 2,3-dichloropyridine crude product by water vapor distillation;Subsequently, by means of sweating, 2,3,6-trichloropyridine is further removed from 2,3-dichloropyridine, and 2,3-dichloropyridine with purity above 99.0% is obtained.In the case of need, the material can be further heated and stirred under micro-vacuum environment, so that 2,3,6-trichloropyridine is further removed from 2,3-dichloropyridine in the form of vapor.The method of the present application is simple to operate, and can effectively separate and remove 2,3,6-trichloropyridine from 2,3-dichloropyridine, and the yield of high-purity 2,3-dichloropyridine product is high.

Description

Technical Field

[0001] This invention relates to the field of pesticides, and more specifically, to a method for purifying 2,3-dichloropyridine. Background Technology

[0002] 2,3-Dichloropyridine is an important fine chemical intermediate widely used in the pharmaceutical and pesticide industries. In the pesticide sector, 2,3-dichloropyridine is a key intermediate for the novel insecticides chlorantraniliprole and cyantraniliprole. With the widespread use of chlorantraniliprole both domestically and internationally, the demand for 2,3-dichloropyridine is bound to increase significantly, making its synthesis and purification methods a subject of considerable interest.

[0003] The main synthetic methods for 2,3-dichloropyridine include the synthesis of 2-chloropyridine, 3-chloropyridine, 2-chloro-3-nitropyridine, and 3-aminopyridine, among others. However, most of these methods often simultaneously generate 2,3,6-trichloropyridine impurities during the reaction to produce 2,3-dichloropyridine. Furthermore, 2,3-dichloropyridine and 2,3,6-trichloropyridine have similar physicochemical properties, making them difficult to separate after formation. This significantly affects the purity of the 2,3-dichloropyridine product. In practice, control is generally achieved through two methods: minimizing the formation of 2,3,6-trichloropyridine during the reaction process; and physical separation during post-processing. Because 2,3,6-trichloropyridine is generated during the main reaction, and the reaction process has little room for control, it is particularly important to remove this 2,3,6-trichloropyridine impurity in the post-processing stage to obtain a high-purity 2,3-dichloropyridine product.

[0004] Currently, crude 2,3-dichloropyridine is generally purified by distillation or steam distillation. However, distillation requires sophisticated equipment and involves significant investment, while steam distillation generally yields products with low purity. If high purity is required, the yield is low, and the residual low-purity 2,3-dichloropyridine cannot be recovered and reused.

[0005] Therefore, there is an urgent need to find more effective methods to separate 2,3,6-trichloropyridine from 2,3-dichloropyridine in order to obtain high-purity 2,3-dichloropyridine. Summary of the Invention

[0006] To address the problems existing in the prior art, the present invention provides a method for purifying crude 2,3-dichloropyridine, which can remove most of the 2,3,6-trichloropyridine from the crude 2,3-dichloropyridine to obtain 2,3-dichloropyridine with high purity.

[0007] This invention provides a method for purifying crude 2,3-dichloropyridine, comprising:

[0008] Crude 2,3-dichloropyridine was mixed with water in a reaction vessel and stirred thoroughly. The mixture was then heated for steam distillation. The 2,3-dichloropyridine was distilled off by azeotropic distillation at atmospheric pressure at a vessel temperature below 110°C. The distillate was cooled, filtered, and the solid was collected and dried to constant weight to obtain 2,3-dichloropyridine with a purity of over 95%. The solidified material was then transferred to a sweating container, heated until it melted, and then slowly cooled to solidify. The solidified material was kept at 55–60°C for 0.5–3 hours. The bottom valve was then opened, and the non-solidified material flowed out. The remaining material was cooled to obtain 2,3-dichloropyridine with a purity of over 99.0%.

[0009] In one embodiment, the crude 2,3-dichloropyridine contains 95% or less of 2,3-dichloropyridine, preferably 94% or less, or 93%, 92%, 91%, or 90% or less. The crude 2,3-dichloropyridine contains 4.5% or more of 2,3,6-trichloropyridine, preferably 5%, 6%, 7%, 8%, 9%, or 10% or more.

[0010] In one embodiment, the mass ratio of crude 2,3-dichloropyridine to water is 1:1 to 10, preferably 1:2 to 5.

[0011] In one embodiment, during steam distillation, the kettle temperature is 90–100°C and the top temperature is 90–95°C. Preferably, the kettle temperature is 96–100°C and the top temperature is 93–94°C.

[0012] In one embodiment, the 2,3-dichloropyridine obtained by steam distillation has a purity of 96% or higher, or 96.5% or higher, or 97% or higher. The content of 2,3-dichloropyridine is 4% or lower, or 3.5% or lower, or 3% or lower.

[0013] In a preferred embodiment, the method further includes:

[0014] Steam distillation is carried out at a vessel temperature below 110°C until there is almost no flow. The vessel temperature is then raised to 120–130°C to continue distillation. Low-purity 2,3-dichloropyridine is distilled off by azeotropic distillation at atmospheric pressure. The collected distillate can be added to the next batch of steam distillation.

[0015] Preferably, low-purity 2,3-dichloropyridine here refers to a purity of less than 95%, or less than 90% or less than 85%.

[0016] In one implementation scheme, during sweating, the temperature is first raised to 75-80°C to melt, and then slowly cooled at a rate of 1.5-2.5°C / hour, and kept at 58-60°C for 1-2 hours. The bottom valve is then opened, and the non-condensable material flows out.

[0017] Preferably, the cooling rate is 2℃ / hour.

[0018] In one embodiment, the 2,3-dichloropyridine obtained through sweating has a purity of 99.1% or higher, or 99.2% or higher, or 99.3% or higher. The content of 2,3-dichloropyridine is 0.8% or lower, or 0.7% or lower, or 0.6% or lower.

[0019] In a preferred embodiment of the present invention, the method further includes:

[0020] 2,3-Dichloropyridine with a purity of over 99.0% obtained by sweating is placed in a vacuum container and heated to 69-75°C to melt the material. Then, it is stirred under micro-vacuum for 1-5 hours to obtain 2,3-Dichloropyridine with a purity of over 99.6%.

[0021] In one implementation, the material is heated to approximately 70°C to melt it.

[0022] In one embodiment, the microvacuum refers to a vacuum environment with a vacuum level below -0.05 MPa. Preferably, the vacuum level is -0.02 to -0.03 MPa. Here, -0.05 MPa means an absolute pressure 0.05 MPa below standard atmospheric pressure, and -0.02 to -0.03 MPa means a pressure 0.02 to 0.03 MPa below standard atmospheric pressure.

[0023] In one embodiment, stirring under microvacuum yields 2,3-dichloropyridine with a purity of over 99.7%, wherein the content of 2,3,6-trichloropyridine is less than 0.1%.

[0024] In this invention, unless otherwise specified, all percentages refer to mass percentages.

[0025] Beneficial effects:

[0026] This invention provides a method for purifying crude 2,3-dichloropyridine. The method first removes some 2,3,6-trichloropyridine and most of other impurities from the crude 2,3-dichloropyridine by steam distillation. While steam distillation is simple and convenient for large-scale processing of raw materials, it cannot completely separate 2,3,6-trichloropyridine, resulting in a high concentration of 2,3-dichloropyridine. Subsequently, this invention utilizes a sweating process to further remove 2,3,6-trichloropyridine from the crude 2,3-dichloropyridine, yielding 2,3-dichloropyridine with a purity of over 99.0%. Because the crude 2,3-dichloropyridine not only contains excessively high levels of 2,3,6-trichloropyridine but also many other impurities, directly using sweating of the crude product not only fails to yield high-purity 2,3-dichloropyridine but also significantly reduces the yield. In this invention, if necessary, the material can be further heated and stirred in a micro-vacuum environment, so that 2,3,6-trichloropyridine can be further removed from 2,3-dichloropyridine in vapor form. This method is particularly suitable for the removal of small amounts of 2,3,6-trichloropyridine.

[0027] The method of this invention is simple to operate, makes full use of the differences in physical properties between 2,3-dichloropyridine and 2,3,6-trichloropyridine, and improves the purification effect by organically combining different purification methods. It can effectively separate and remove 2,3,6-trichloropyridine from 2,3-dichloropyridine, making full use of 2,3-dichloropyridine and achieving a high yield of high-purity 2,3-dichloropyridine product. Detailed Implementation

[0028] The following will describe preferred embodiments of the invention in detail. These embodiments are provided to better illustrate the invention and are not intended to limit the invention to these examples. Non-essential improvements and adjustments to the embodiments based on the invention's description still fall within the scope of the invention.

[0029] Unless otherwise specified, the experimental methods in the following embodiments are conventional methods. Where specific techniques or conditions are not specified in the embodiments, they should be performed in accordance with the techniques or conditions described in the literature in this field, or in accordance with the product instructions.

[0030] Example 1:

[0031] 1 kg of crude 2,3-dichloropyridine (86% 2,3-dichloropyridine and 10% 2,3,6-trichloropyridine) was mixed with 3 kg of water in a reaction vessel and stirred thoroughly. The mixture was then heated for steam distillation. The vessel temperature was set at 96–98 °C and the top temperature at 93–94 °C. 2,3-dichloropyridine was distilled off by azeotropic distillation at atmospheric pressure until almost no flow was observed. The distillate was cooled to room temperature, filtered, and the solid was collected and dried to constant weight to obtain 851 g of 97.0% 2,3-dichloropyridine with a 2.7% 2,3,6-trichloropyridine content. The vessel temperature was then raised to approximately 125 °C and distillation continued, azeotropically distilling off lower-purity 2,3-dichloropyridine. This collected azeotropically distilled 2,3-dichloropyridine could be added to the next batch of steam distillation.

[0032] The obtained 97.0% 2,3-dichloropyridine was poured into a sweating container, heated to 75-80℃ to melt, and then slowly cooled at a rate of 2℃ / hour. The mixture was then kept at 59-60℃ for 2 hours. The bottom valve was opened, and the non-condensable material flowed out. After cooling, 826g of 2,3-dichloropyridine with a purity of 99.3% and a 2,3,6-trichloropyridine content of 0.5% were obtained.

[0033] The 2,3-dichloropyridine with a purity of 99.3% was placed in a vacuum container and heated to about 70°C until it was almost melted. The mixture was then stirred for 2 to 3 hours under a micro-vacuum of -0.02 to -0.03 MPa to obtain 821 g of 2,3-dichloropyridine with a purity of 99.7% and a 2,3,6-trichloropyridine content of <0.1%.

[0034] Example 2:

[0035] 5 kg of crude 2,3-dichloropyridine (86% 2,3-dichloropyridine and 10% 2,3,6-trichloropyridine) was mixed with 15 kg of water in a reaction vessel and stirred thoroughly. The mixture was then heated for steam distillation. The vessel temperature was set at 97–99 °C and the top temperature at 93–94 °C. 2,3-dichloropyridine was distilled off by azeotropic distillation at atmospheric pressure until almost no flow was observed. The distillate was cooled to room temperature, filtered, and the solid was collected and dried to constant weight, yielding 4.27 kg of 97.1% 2,3-dichloropyridine with a 2.6% 2,3,6-trichloropyridine content. The vessel temperature was then raised to approximately 125 °C to continue distillation, azeotropically distilling off lower-purity 2,3-dichloropyridine, which was collected and added to the next batch of steam distillation.

[0036] The obtained 97.1% 2,3-dichloropyridine was poured into a sweating container, heated to 75-80℃ to melt, and then slowly cooled at a rate of 2℃ / hour. The mixture was then kept at 59-60℃ for 2 hours. The bottom valve was opened, and the non-condensable material flowed out. After cooling, 4.14 kg of 2,3-dichloropyridine with a purity of 99.4% and a 2,3,6-trichloropyridine content of 0.5% were obtained.

[0037] The 2,3-dichloropyridine with a purity of 99.4% was placed in a vacuum container and heated to about 70°C until it was almost melted. The mixture was then stirred for 2-3 hours under a micro-vacuum of -0.02 to -0.03 MPa to obtain 4.10 kg of 2,3-dichloropyridine with a purity of 99.8% and a 2,3,6-trichloropyridine content of <0.1%.

[0038] Finally, it should be noted that the above preferred embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail through the above preferred embodiments, those skilled in the art should understand that various changes can be made to it in form and detail without departing from the scope defined by the claims of the present invention.

Claims

1. A method for purifying crude 2,3-dichloropyridine, comprising: Crude 2,3-dichloropyridine was mixed with water in a reaction vessel and stirred thoroughly. The mixture was then heated for steam distillation. The 2,3-dichloropyridine was distilled off by azeotropic distillation at atmospheric pressure at a vessel temperature below 110°C. The distillate was cooled, filtered, and the solid was collected and dried to constant weight to obtain 2,3-dichloropyridine with a purity of over 95%. Pour it into a sweating container, heat it until it melts, and then slowly cool it down to solidify the material. Keep it at 55~60℃ for 0.5~3 hours, open the bottom valve, and the non-solidified material flows out. Cool the remaining material to obtain 2,3-dichloropyridine with a purity of over 99.0%.

2. The purification method according to claim 1, characterized in that, The crude 2,3-dichloropyridine contains less than 95% 2,3-dichloropyridine and more than 4.5% 2,3,6-trichloropyridine.

3. The purification method according to claim 1, characterized in that, The mass ratio of crude 2,3-dichloropyridine to water is 1:1~10.

4. The purification method according to claim 3, characterized in that, The mass ratio of crude 2,3-dichloropyridine to water is 1:2~5.

5. The purification method according to claim 1, characterized in that, During steam distillation, the kettle temperature is 90~100℃ and the top temperature is 90~95℃.

6. The purification method according to claim 5, characterized in that, During steam distillation, the kettle temperature is 96~100℃ and the top temperature is 93~94℃.

7. The purification method according to claim 1, characterized in that, The 2,3-dichloropyridine obtained by steam distillation has a purity of over 96% and a content of less than 4%.

8. The purification method according to claim 1, characterized in that, Steam distillation is carried out at a vessel temperature below 110°C until there is almost no flow. The vessel temperature is then raised to 120-130°C to continue distillation. Low-purity 2,3-dichloropyridine is distilled off by azeotropic distillation at atmospheric pressure and collected and added to the next batch of steam distillation.

9. The purification method according to claim 1, characterized in that, When sweating, first heat to 75~80℃ to melt, then slowly cool down at a rate of 2℃ / hour, keep at 58~60℃ for 1~2 hours, then open the bottom valve and the non-condensable material flows out.

10. The purification method according to claim 1, characterized in that, The 2,3-dichloropyridine obtained through sweating has a purity of over 99.1% and a content of less than 0.8%.

11. The purification method according to claim 1, characterized in that, The method further includes: 2,3-Dichloropyridine with a purity of over 99.0% obtained by sweating is placed in a vacuum container and heated to 69-75°C to melt the material. Then, it is stirred under micro-vacuum for 1-5 hours to obtain 2,3-Dichloropyridine with a purity of over 99.6%.

12. The purification method according to claim 11, characterized in that, The microvacuum refers to a vacuum environment with a vacuum level below -0.05 MPa.