A process for the preparation of 2,3-dichloropyridine

Abstract

The application discloses a preparation method of 2,3-dichloropyridine. In a solvent of C1-C4 aliphatic carboxylic acid, 2,3,6-trichloropyridine is dechlorinated under the catalysis of a non-noble metal to obtain a target product. The preparation method provided by the application uses cheap and readily available C1-C4 aliphatic carboxylic acid as a solvent, and uses a non-noble metal as a catalyst, greatly improves the reaction safety, and greatly reduces the material cost.

Description

Technical Field

[0001] This application relates to the field of organic synthesis, and in particular to a method for preparing 2,3-dichloropyridine. Background Technology

[0002] 2,3-Dichloropyridine is an important synthetic intermediate in pesticides and pharmaceuticals, primarily used in the synthesis of chlorantraniliprole. Therefore, with the gradual promotion of chlorantraniliprole, the demand for 2,3-dichloropyridine has increased significantly.

[0003] Currently, known methods for synthesizing 2,3-dichloropyridine require high-pressure hydrogenation or the use of noble metals as catalysts, resulting in high costs and demanding synthesis conditions. For example, Chinese patents CN110759859A, CN112592313A, and CN106518755A provide methods for obtaining 2,3-dichloropyridine from 2,3,6-trichloropyridine or 2,3,4,6-tetrachloropyridine via high-pressure hydrogenation. These methods require ligands, acid-binding agents, catalysts, and high-pressure hydrogenation, and suffer from drawbacks such as low reaction safety and poor selective elimination. Chinese patent CN106518754A provides a method for synthesizing 2,3-dichloropyridine. Although this method does not use high-pressure hydrogenation, it uses 2,3,6-trichloropyridine as a raw material and 10% Pd / C noble metal and menthol as catalysts to react in methanol solution to obtain the target product. This method uses noble metals for catalysis, which has disadvantages such as high cost and low selective elimination effect.

[0004] Therefore, given the shortcomings of the existing methods for synthesizing 2,3-dichloropyridine, it is crucial to provide a low-cost method for synthesizing 2,3-dichloropyridine with safer reaction conditions. Summary of the Invention

[0005] In view of the problems existing in the prior art mentioned above, this application provides a method for preparing 2,3-dichloropyridine, wherein 2,3,6-trichloropyridine is dechlorinated in a solvent of C1-C4 aliphatic carboxylic acids under the catalysis of non-precious metals to obtain the target product.

[0006] By adopting the above-described technical solution, the preparation method provided in this application uses C1-C4 aliphatic carboxylic acids as solvents and non-precious metals as catalysts. Compared with the high-pressure hydrogenation conditions used in existing technologies, this method greatly improves reaction safety. Furthermore, compared with existing methods using Pd / C precious metals and menthol as catalysts, the preparation method of this application significantly reduces material costs. Moreover, under the reaction conditions of this application, the chlorine atom at the C-6 position of 2,3,6-trichloropyridine can be removed more precisely, accurately yielding the target product 2,3-dichloropyridine with a high yield. This provides a new approach for the preparation of 2,3-dichloropyridine and achieves excellent results.

[0007] Preferably, the C1-C4 fatty carboxylic acids are one or more of formic acid, acetic acid, propionic acid and butyric acid.

[0008] In the above technical solution, formic acid, acetic acid, propionic acid and butyric acid are all common short-chain fatty carboxylic acids on the market. Compared with long-chain fatty carboxylic acids, short-chain fatty carboxylic acids are cheaper, more readily available and have stable performance, thus saving costs, achieving safe production, and being particularly easy to industrialize.

[0009] Preferably, the non-precious metal is one or more of zinc powder, iron powder, and copper powder.

[0010] By adopting the above technical solution, compared with the prior art, the preparation method of this application abandons precious metals and uses non-precious metals as catalysts. Zinc powder, iron powder and copper powder are commonly available on the market, which greatly reduces the production cost.

[0011] Preferably, the ratio of 2,3,6-trichloropyridine, non-precious metals and C1-C4 aliphatic carboxylic acids is 4.3g:(3-5)g:(30-50)mL.

[0012] Preferably, the reaction temperature is 130–150°C.

[0013] Preferably, the reaction time is 6 to 18 hours.

[0014] Preferably, the reaction time is 6 to 8 hours.

[0015] By adopting the above technical solution, under the above reaction conditions, the catalytic effect can be achieved at a better level. In particular, when the reaction time is 6 to 8 hours, not only is the yield higher, but the reaction process is also safer, and the short reaction time greatly reduces production costs.

[0016] Preferably, the non-precious metal is a mixture of copper powder and zinc powder, wherein the mass ratio of copper powder to zinc powder is (1-3):1.

[0017] Preferably, the C1-C4 fatty carboxylic acids are a mixed solvent of propionic acid and acetic acid, and the volume ratio of propionic acid to acetic acid is (2-3):1.

[0018] By adopting the above technical solution, under the above ratio, and in a mixed acid solvent, using a mixed non-precious metal as a catalyst, the reaction can be made more complete, and the chlorine atom at the C-6 position of 2,3,6-trichloropyridine can be removed more accurately, thereby resulting in a higher yield and accurate acquisition of the target product 2,3-dichloropyridine.

[0019] In summary, this application has the following beneficial effects:

[0020] 1. The preparation method provided in this application uses C1-C4 aliphatic carboxylic acids as solvents and non-precious metals as catalysts. Compared with the high-pressure hydrogenation conditions used in the prior art, this method greatly improves the safety of the reaction. Furthermore, compared with the prior art using Pd / C precious metals and menthol as catalysts, this method greatly reduces the production cost.

[0021] 2. The preparation method provided in this application can more accurately remove the chlorine atom at the C-6 position of 2,3,6-trichloropyridine, precisely obtain the target product 2,3-dichloropyridine, and achieve a higher yield. Detailed Implementation

[0022] Example

[0023] The following examples illustrate the preparation method of 2,3-dichloropyridine.

[0024] Example 1

[0025] A method for preparing 2,3-dichloropyridine: In a 250 mL three-necked flask, 30 mL of formic acid was first added, followed by 4.3 g of 2,3,6-trichloropyridine and 3 g of zinc powder. After mixing, the temperature was raised to 130 °C and the reaction was carried out for 6 h. After the reaction was completed, 30 mL of toluene was added and stirred after cooling to room temperature. The mixture was filtered, and the filter cake was washed with toluene until the blue-green color of the product in the filter cake disappeared and became colorless. The filtrate was dried with anhydrous sodium sulfate, filtered, and the organic solvent was removed by rotary evaporation under reduced pressure to obtain 1.71 g of white powder 2,3-dichloropyridine. The yield and purity are shown in Table 1.

[0026] Example 2

[0027] The difference between Example 2 and Example 1 is that 3g of zinc powder was replaced with 3g of copper powder. Everything else was the same as in Example 1. 1.92g of white powder 2,3-dichloropyridine was obtained. The yield and purity are shown in Table 1.

[0028] Example 3

[0029] The difference between Example 3 and Example 1 is that 30 mL of formic acid was replaced with 30 mL of acetic acid. Otherwise, the same as in Example 1 was obtained, yielding 2.41 g of white powder 2,3-dichloropyridine. The yield and purity are shown in Table 1.

[0030] Example 4

[0031] The difference between Example 4 and Example 3 is that 3g of zinc powder was replaced with 3g of iron powder. Everything else was the same as in Example 3. 2.12g of white powder 2,3-dichloropyridine was obtained. The yield and purity are shown in Table 1.

[0032] Example 5

[0033] The difference between Example 5 and Example 3 is that 3g of zinc powder was replaced with 3g of copper powder. Everything else was the same as in Example 3. 2.59g of white powder 2,3-dichloropyridine was obtained. The yield and purity are shown in Table 1.

[0034] Example 6

[0035] The difference between Example 6 and Example 1 is that 30 mL of formic acid was replaced with 30 mL of propionic acid. Otherwise, the same as in Example 1 was obtained, yielding 3.03 g of white powder 2,3-dichloropyridine. The yield and purity are shown in Table 1.

[0036] Example 7

[0037] The difference between Example 7 and Example 6 is that 3g of zinc powder was replaced with 3g of copper powder. Otherwise, the same as in Example 6 was obtained, yielding 3.40g of white powder 2,3-dichloropyridine. The yield and purity are shown in Table 1.

[0038] Example 8

[0039] The difference between Example 8 and Example 1 is that 30 mL of formic acid was replaced with 30 mL of butyric acid. Otherwise, the same as in Example 1 was obtained, yielding 2.68 g of white powder 2,3-dichloropyridine. The yield and purity are shown in Table 1.

[0040] Example 9

[0041] The difference between Example 9 and Example 8 is that 3g of zinc powder was replaced with 3g of copper powder. Otherwise, the same as in Example 8 was obtained, yielding 2.89g of white powder 2,3-dichloropyridine. The yield and purity are shown in Table 1.

[0042] Example 10

[0043] The difference between Example 10 and Example 7 is that 3g of copper powder was replaced with a mixture of 1.5g of copper powder and 1.5g of zinc powder. Otherwise, it was the same as Example 7, and 3.43g of white powder 2,3-dichloropyridine was obtained. The yield and purity are shown in Table 1.

[0044] Example 11

[0045] The difference between Example 11 and Example 7 is that 3g of copper powder was replaced with a mixture of 2g of copper powder and 1g of zinc powder. Otherwise, it was the same as Example 7, and 3.41g of white powder 2,3-dichloropyridine was obtained. The yield and purity are shown in Table 1.

[0046] Example 12

[0047] The difference between Example 12 and Example 7 is that 3g of copper powder was replaced with a mixture of 2.25g of copper powder and 0.75g of zinc powder. Otherwise, it was the same as Example 7, and 3.45g of white powder 2,3-dichloropyridine was obtained. The yield and purity are shown in Table 1.

[0048] Example 13

[0049] The difference between Example 13 and Example 7 is that 30 mL of propionic acid was replaced with a mixture of 20 mL of propionic acid and 10 mL of acetic acid. Otherwise, the same as in Example 7 was obtained, yielding 3.42 g of white powder 2,3-dichloropyridine. The yield and purity are shown in Table 1.

[0050] Example 14

[0051] The difference between Example 14 and Example 7 is that 30 mL of propionic acid was replaced with a mixture of 22.5 mL of propionic acid and 7.5 mL of acetic acid. Otherwise, the same as in Example 7 was obtained, yielding 3.44 g of white powder 2,3-dichloropyridine. The yield and purity are shown in Table 1.

[0052] Example 15

[0053] The difference between Example 15 and Example 7 is that the mass of copper powder is 5g, while the rest is the same as in Example 7. 3.39g of white powder 2,3-dichloropyridine was obtained. The yield and purity are shown in Table 1.

[0054] Example 16

[0055] The difference between Example 16 and Example 7 is that the mass of copper powder is 4g, while the rest is the same as in Example 7. 3.43g of white 2,3-dichloropyridine powder was obtained. The yield and purity are shown in Table 1.

[0056] Example 17

[0057] The difference between Example 17 and Example 7 is that the amount of propionic acid is 40 mL, while the rest is the same as in Example 7. 3.41 g of white powder 2,3-dichloropyridine was obtained. The yield and purity are shown in Table 1.

[0058] Example 18

[0059] The difference between Example 18 and Example 7 is that the amount of propionic acid is 50 mL, while the rest is the same as in Example 7. 3.39 g of white powder 2,3-dichloropyridine was obtained. The yield and purity are shown in Table 1.

[0060] Example 19

[0061] The difference between Example 19 and Example 7 is that the reaction temperature is 140°C, while the rest is the same as in Example 7. 3.46 g of white powder 2,3-dichloropyridine was obtained. The yield and purity are shown in Table 1.

[0062] Example 20

[0063] The difference between Example 20 and Example 7 is that the reaction temperature is 150°C, while the rest is the same as in Example 7. 3.38 g of white powder 2,3-dichloropyridine was obtained. The yield and purity are shown in Table 1.

[0064] Example 21

[0065] The difference between Example 21 and Example 7 is that the reaction time is 18 hours, while the rest is the same as in Example 7. 3.23 g of white powder 2,3-dichloropyridine was obtained. The yield and purity are shown in Table 1.

[0066] Example 22

[0067] The difference between Example 22 and Example 7 is that the reaction time is 12 hours, while the rest is the same as in Example 7. 3.31 g of white powder 2,3-dichloropyridine was obtained. The yield and purity are shown in Table 1.

[0068] Example 23

[0069] The difference between Example 23 and Example 7 is that the reaction time is 8 hours, while the rest is the same as in Example 7. 3.40 g of white powder 2,3-dichloropyridine was obtained. The yield and purity are shown in Table 1.

[0070] Table 1. Summary of the yield and purity of 2,3-dichloropyridine in Examples 1-23

[0071]

[0072]

[0073] By comparing the above Examples 1-9, it can be found that using formic acid, acetic acid, propionic acid and butyric acid as solvents, and zinc powder, iron powder and copper powder as catalysts, the yield reaches more than 49% and the purity reaches more than 85%. In particular, the system using propionic acid as solvent and copper powder as catalyst achieves a yield of 97.42% and a purity of 95.02%, which is quite excellent.

[0074] By comparing Examples 7 and 10-12, it can be found that when a mixed metal, copper powder and zinc powder, are used in a mass ratio of (1-3):1, a better catalytic effect is obtained than that of a single catalyst. It can remove the chlorine atom at the C-6 position of 2,3,6-trichloropyridine more accurately, resulting in a yield of 98.85% and a purity of 98.13%.

[0075] By comparing Examples 7 and 13-14, it can be found that when using mixed acid, the volume ratio of propionic acid and acetic acid is (2-3):1, a better catalytic effect is obtained than that of a single solvent, resulting in a yield of 98.57% and a purity of 97.89%.

[0076] By comparing Examples 7 and 15-20, it can be found that the amount of catalyst, the volume of solvent, and the reaction temperature have a certain impact on the entire reaction system, and the yield and purity are improved to a certain extent. In particular, when the reaction temperature is around 140℃, the yield reaches 99.14% and the purity reaches 97.67%.

[0077] By comparing Examples 7 and 21-23, it can be found that the reaction time has a certain impact on the entire reaction system. When the reaction time is 12-18 hours, the reaction can be left overnight, but the yield and purity of the reaction decrease to some extent. In order to obtain not only a high yield and purity but also to ensure safe production, this application considers a reaction time of 6-8 hours as the optimal reaction condition.

[0078] The above comparison reveals that this application achieves superior reaction results when using C1-C4 aliphatic carboxylic acids as solvents and non-precious metals as catalysts, particularly when using mixed acids as solvents and mixed metals as catalysts. Furthermore, this application avoids the use of precious metals and high-pressure hydrogenation conditions. The solvents and catalysts used are inexpensive and readily available, significantly reducing production costs. It also avoids harsh reaction conditions, greatly improving production safety. Simultaneously, it achieves high yields and selectivity, precisely removing the chlorine atom at the C-6 position of 2,3,6-trichloropyridine to accurately obtain the target product, 2,3-dichloropyridine. This application demonstrates excellent performance and is suitable for industrial production.

[0079] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A method for preparing 2,3-dichloropyridine, characterized in that, In a solvent of C2–C4 aliphatic carboxylic acids, 2,3,6-trichloropyridine is dechlorinated under the catalysis of a non-precious metal to give the target product; The C2-C4 aliphatic carboxylic acids are propionic acid, butyric acid, or a mixture of propionic acid and acetic acid. The non-precious metal is iron powder, copper powder, or a mixture of copper powder and zinc powder.

2. The preparation method according to claim 1, characterized in that, The ratio of 2,3,6-trichloropyridine, non-precious metals, and C2-C4 aliphatic carboxylic acids is 4.3 g: (3-5) g: (30-50) mL.

3. The preparation method according to claim 1, characterized in that, The reaction temperature is 130~150℃. o C.

4. The preparation method according to claim 1, characterized in that, The reaction time is 6 to 18 hours.

5. The preparation method according to claim 1, characterized in that, The reaction time is 6-8 hours.

6. The preparation method according to claim 1, characterized in that, The non-precious metal is a mixture of copper powder and zinc powder, wherein the mass ratio of copper powder to zinc powder is (1~3):

1.

7. The preparation method according to claim 1, characterized in that, The C2-C4 aliphatic carboxylic acids are a mixed solvent of propionic acid and acetic acid, and the volume ratio of propionic acid to acetic acid is (2-3):1.

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