A method for preparing tetrachloropyridine carboxylic acid

Abstract

The present application relates to the field of organic synthesis, in particular to a preparation method of tetrachloropyridine carboxylic acid, which comprises: putting tetrachloro-2-cyanopyridine and water into a reactor, and then adding a catalyst to react, wherein the catalyst comprises a metal oxide catalyst manganese dioxide and a metal inorganic salt catalyst sodium tungstate, the mass ratio of tetrachloro-2-cyanopyridine and water is 1:(1-2.5). The preparation method provided by the present application has a product content of tetrachloropyridine carboxylic acid greater than 98%, a product yield greater than 97%, and the preparation raw material does not include acid or alkali, thereby reducing the pollution to the environment.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of organic synthesis, in particular, to a preparation method of 3,4,5,6-tetrachloropicolinic acid. BACKGROUND

[0002] 3,4,5,6-tetrachloropicolinic acid (CAS: 10469-09-7) is an important intermediate of pyridine herbicides, which can be used to synthesize various pesticide products, including clopyralid and aminopyralid, etc.; these pesticides are widely used in orchard and no-till field weed control.

[0003] The existing preparation and synthesis methods of 3,4,5,6-tetrachloropicolinic acid generally hydrolyze 3,4,5,6-tetrachloro-2-cyanopyridine as raw material under acidic or basic conditions to generate 3,4,5,6-tetrachloropicolinic acid. Specifically, under acidic conditions, free 3,4,5,6-tetrachloropicolinic acid and ammonium salt are obtained, and under basic conditions, sodium 3,4,5,6-tetrachloropicolinic acid and ammonia are obtained. For example, patent document CN115974776A discloses a preparation method of 3,4,5,6-tetrachloropicolinic acid and its application, which mainly uses 3,4,5,6-tetrachloro-2-cyanopyridine as raw material, first reacts with sulfuric acid, and then reacts with nitrosyl sulfuric acid to prepare. However, whether prepared by acid or by base, a large amount of wastewater, waste acid and waste salt will be generated, causing pollution problems.

[0004] Therefore, how to reduce the wastewater and salt discharge in the synthesis process of 3,4,5,6-tetrachloropicolinic acid, while improving the yield of 3,4,5,6-tetrachloropicolinic acid, is a technical problem that the technical personnel in the field have been studying. SUMMARY

[0005] In order to solve the above technical problems, the present application provides a preparation method of 3,4,5,6-tetrachloropicolinic acid, which comprises: under 0-50℃, 3,4,5,6-tetrachloro-2-cyanopyridine and water are put into a reactor, then a catalyst is added for reaction, after the reaction is completed, the catalyst is recovered by filtration, and the obtained filtrate is treated to obtain the product.

[0006] As an implementable case, the catalyst comprises a metal oxide catalyst and a metal inorganic salt catalyst.

[0007] As an implementable case, the metal oxide catalyst comprises one or more of cerium oxide, zirconium oxide, manganese dioxide, silver oxide, copper oxide, platinum oxide, palladium oxide, zinc oxide, iron oxide, and ruthenium oxide.

[0008] Further, the metal oxide catalyst is manganese dioxide (MnO2).

[0009] As an implementable case, the metal inorganic salt catalyst comprises one or more of zirconium sulfate, cerium sulfate, copper sulfate, ferrous sulfate, ferric sulfate, zinc sulfate, ferric chloride, and sodium tungstate.

[0010] Further, the metal inorganic salt catalyst is sodium tungstate (Na2WO4).

[0011] At present, the most common process for synthesizing tetrachloropyridine carboxylic acid is tetrachloro-2-cyanopyridine acidification, but the use of acid in the acidification process will produce a large amount of waste water, waste acid and waste salt, polluting the environment, therefore, the present inventors provide a new synthesis process of tetrachloropyridine carboxylic acid, taking tetrachloro-2-cyanopyridine and water as raw materials, under the compounding of metal oxide catalyst and metal inorganic salt catalyst, especially the compounding of manganese dioxide and sodium tungstate, the target product can be efficiently synthesized, and waste acid water or waste lye discharge is reduced; the present inventors speculate that sodium tungstate may form a composite catalyst with manganese dioxide, the surface properties or active sites of manganese dioxide are changed to improve the catalytic performance thereof, tetrachloro-2-cyanopyridine and water molecules are adsorbed and activated, the activation energy of the reaction is reduced, and the forward rapid progress of the synthesis reaction of tetrachloropyridine carboxylic acid is promoted.

[0012] As an implementable case, the mass ratio of tetrachloro-2-cyanopyridine to water is 1: (1-2.5).

[0013] As an implementable case, the amount of the metal oxide catalyst is not less than 0.1% of the mass of tetrachloro-2-cyanopyridine.

[0014] As an implementable case, the amount of the metal inorganic salt catalyst is not less than 0.1% of the mass of tetrachloro-2-cyanopyridine.

[0015] As an implementable case, the amount of the metal oxide catalyst is not less than 0.1% of the mass of water.

[0016] As an implementable case, the amount of the metal inorganic salt catalyst is not less than 0.1% of the mass of water.

[0017] The inventors have discovered that further limiting the mass ratio of tetrachloro-2-cyanopyridine to water is necessary to improve the yield of tetrachloropyridinecarboxylic acid. This is mainly because the synthesis of tetrachloropyridinecarboxylic acid is a reversible reaction, meaning the reaction can proceed in either the forward or reverse direction. In this process, water is used as one of the reaction raw materials. However, as the amount of water increases, the organic phase in the reaction system is diluted, resulting in a decrease in the concentration of tetrachloro-2-cyanopyridine and a reduction in the collision frequency between reactant molecules, thereby reducing the reaction rate and yield. Therefore, the present invention preferably uses a mass ratio of tetrachloro-2-cyanopyridine to water of 1:(1-2.5). In addition, the amount of catalyst also has a certain impact on the reaction yield. If the amount of catalyst is too low, it is not conducive to reducing the activation energy of the reaction, thereby reducing the yield of the product. Therefore, the present invention further limits the amount of metal oxide catalyst to not less than 0.1% of the mass of tetrachloro-2-cyanopyridine and the amount of metal inorganic salt catalyst to not less than 0.1% of the mass of tetrachloro-2-cyanopyridine to improve the product yield. In addition, since the catalyst itself does not participate in the reaction, it can be recovered after the reaction, thus significantly reducing the cost of the reaction and reducing the discharge of wastewater.

[0018] As an example of an feasible approach, the reaction time is 15-30 hours.

[0019] As an example of an feasible approach, the reaction temperature is 165-195°C.

[0020] In this invention, the preferred reaction temperature is 165-195℃ to ensure a higher yield of tetrachloropyridinecarboxylic acid. Excessively high reaction temperatures may lead to side reactions, and the formation of byproducts trichloro-4-hydroxypyridine acid and trichloro-6-hydroxypyridine acid will reduce the purity and yield of the target product. Conversely, when the reaction temperature is too low, the activation energy of the reactants decreases, slowing the reaction rate and thus affecting the product yield. Furthermore, the reaction time also affects the product yield. Too short a reaction time results in incomplete reaction, while too long a reaction time may allow the target product, tetrachloropyridinecarboxylic acid, to further react as a reactant, thereby reducing the yield of the target product. Therefore, the preferred reaction time is 15-30 hours to ensure a higher yield and content of the product.

[0021] Beneficial effects

[0022] (i) The preparation process provided by the present invention avoids the use of acids or alkalis, which can further avoid the discharge of highly polluting acid or alkali wastewater, and is beneficial to environmental protection.

[0023] (II) The present invention selects a combination of metal oxide catalyst and metal inorganic salt catalyst as catalyst, especially the combination of manganese dioxide and sodium tungstate, which can significantly improve the product content and yield of tetrachloropyridine carboxylic acid. Furthermore, the catalyst can be recovered and reused after use, which helps to reduce the cost of the reaction.

[0024] (iii) In this invention, the amount of metal oxide catalyst is further specified to be not less than 0.1% of the mass of tetrachloro-2-cyanopyridine, and the amount of metal inorganic salt catalyst is not less than 0.1% of the mass of tetrachloro-2-cyanopyridine; this can further improve the yield of the target product.

[0025] (iv) The present invention limits the reaction temperature to 165-195℃, which can ensure a higher yield of tetrachloropyridine carboxylic acid. Too high or too low a temperature will reduce the yield of the product.

[0026] (v) In the actual research and development process, the inventors found that the reaction time would affect the yield of the product. Therefore, the preferred reaction time is 15-30h, which can further improve the yield and purity of the target product. Attached Figure Description

[0027] Figure 1 The image shows the HPLC chromatogram of tetrachloropyridine carboxylic acid prepared in Example 1. Detailed Implementation

[0028] The reaction equations for the reactions involved in Examples 1-10 below are as follows:

[0029]

[0030] Example 1

[0031] This example provides a method for preparing tetrachloropyridine carboxylic acid, comprising: adding 250g of tetrachloro-2-cyanopyridine (98% by mass) and 250g of tap water to a high-pressure reactor at 30°C, then adding 250mg of manganese dioxide and 280mg of sodium tungstate, raising the temperature to 195°C, maintaining the pressure inside the reactor at 1.4 MPa, and then holding the reaction at this temperature for 15 hours; after the reaction is completed, filtering and recovering the catalyst, which can be reused. The filtrate, after post-treatment, yields 263g of tetrachloropyridine carboxylic acid with a purity of 98.43%, and a product yield of 96.46%.

[0032] Example 2

[0033] This example provides a method for preparing tetrachloropyridine carboxylic acid, comprising: adding 250g of tetrachloro-2-cyanopyridine (98% by mass) and 250g of tap water to a high-pressure reactor at 30°C, then adding 250mg of manganese dioxide and 280mg of sodium tungstate, raising the temperature to 185°C, maintaining the pressure inside the reactor at 1.1 MPa, and then holding the reaction at this temperature for 18 hours; after the reaction is completed, filtering and recovering the catalyst, which can be reused. The filtrate, after post-treatment, yields 263g of tetrachloropyridine carboxylic acid with a purity of 98.48%, and a product yield of 97.80%.

[0034] Example 3

[0035] This example provides a method for preparing tetrachloropyridine carboxylic acid, comprising: adding 250g of tetrachloro-2-cyanopyridine (98% by mass) and 250g of tap water to a high-pressure reactor at 30°C, then adding 250mg of manganese dioxide and 280mg of sodium tungstate, raising the temperature to 165°C, maintaining the pressure inside the reactor at 0.7MPa, and then holding the reaction at this temperature for 20 hours; after the reaction is completed, filtering and recovering the catalyst, which can be reused. The filtrate, after post-treatment, yields 263.5g of tetrachloropyridine carboxylic acid with a purity of 98.51%, and a product yield of 98.31%.

[0036] Example 4

[0037] This example provides a method for preparing tetrachloropyridine carboxylic acid, comprising: adding 250g of tetrachloro-2-cyanopyridine (98% purity) and 750g of tap water to a high-pressure reactor at 30°C, then adding 250mg of manganese dioxide and 280mg of sodium tungstate; raising the temperature to 165°C, maintaining the pressure inside the reactor at 0.7MPa, and then holding the reaction at this temperature for 20 hours; after the reaction is completed, filtering and recovering the catalyst, which can be reused. The filtrate, after post-treatment, yields 262g of tetrachloropyridine carboxylic acid with a purity of 98.50%, and a product yield of 97.20%.

[0038] Example 5

[0039] This example provides a method for preparing tetrachloropyridine carboxylic acid, comprising: adding 250g of tetrachloro-2-cyanopyridine (98% purity) and 875g of tap water to a high-pressure reactor at 30°C, then adding 250mg of manganese dioxide and 280mg of sodium tungstate; raising the temperature to 165°C, maintaining the pressure inside the reactor at 0.7MPa, and then holding the reaction at this temperature for 30 hours; after the reaction is completed, filtering and recovering the catalyst, which can be reused. The filtrate, after post-treatment, yields 255g of tetrachloropyridine carboxylic acid with a purity of 98.12%, and a product yield of 94.24%.

[0040] Example 6

[0041] This example provides a method for preparing tetrachloropyridine carboxylic acid, comprising: adding 250g of tetrachloro-2-cyanopyridine (98% by mass) and 250g of tap water to a high-pressure reactor at 30°C, then adding 100mg of manganese dioxide and 280mg of sodium tungstate, raising the temperature to 165°C, maintaining the pressure inside the reactor at 0.7MPa, and then holding the reaction at this temperature for 30h; after the reaction is completed, filtering and recovering the catalyst, which can be reused. The filtrate, after post-treatment, yields 255g of tetrachloropyridine carboxylic acid with a purity of 98.12%, and a product yield of 94.24%.

[0042] Example 7

[0043] This example provides a method for preparing tetrachloropyridine carboxylic acid, comprising: adding 250g of tetrachloro-2-cyanopyridine (98% by mass) and 250g of tap water to a high-pressure reactor at 30°C, then adding 250mg of manganese dioxide and 100mg of sodium tungstate, raising the temperature to 165°C, maintaining the pressure inside the reactor at 0.7MPa, and then holding the reaction at this temperature for 45h; after the reaction is completed, filtering and recovering the catalyst, which can be reused. The filtrate, after post-treatment, yields 243g of tetrachloropyridine carboxylic acid with a purity of 98.02%, and a product yield of 89.71%.

[0044] Example 8

[0045] This example provides a method for preparing tetrachloropyridine carboxylic acid, comprising: adding 250g of tetrachloro-2-cyanopyridine (98% by mass) and 250g of tap water to a high-pressure reactor at 30°C, then adding 100mg of manganese dioxide and 280mg of sodium tungstate, raising the temperature to 185°C, maintaining the pressure inside the reactor at 1.1 MPa, and then holding the reaction at this temperature for 25 hours; after the reaction is completed, filtering and recovering the catalyst, which can be reused. The filtrate, after post-treatment, yields 246g of tetrachloropyridine carboxylic acid with a purity of 98.05%, and a product yield of 90.85%.

[0046] Example 9

[0047] This example provides a method for preparing tetrachloropyridine carboxylic acid, comprising: adding 250g of tetrachloro-2-cyanopyridine (98% by mass) and 250g of tap water to a high-pressure reactor at 30°C, then adding 250mg of manganese dioxide and 280mg of sodium tungstate, raising the temperature to 200°C, maintaining the pressure inside the reactor at 1.6 MPa, and then holding the reaction at this temperature for 10 hours; after the reaction is completed, filtering and recovering the catalyst, which can be reused. The filtrate, after post-treatment, yields 251g of tetrachloropyridine carboxylic acid with a purity of 98.15%, and a product yield of 92.79%.

[0048] Example 10

[0049] This example provides a method for preparing tetrachloropyridine carboxylic acid, comprising: adding 250g of tetrachloro-2-cyanopyridine (98% by mass) and 250g of tap water to a high-pressure reactor at 30°C, then adding 250mg of manganese dioxide and 280mg of sodium tungstate, raising the temperature to 150°C, maintaining the pressure inside the reactor at 0.48 MPa, and then holding the reaction at this temperature for 36 hours; after the reaction is completed, filtering and recovering the catalyst, which can be reused. The filtrate, after post-treatment, yields 238g of tetrachloropyridine carboxylic acid with a purity of 97.20%, and a product yield of 87.13%.

[0050] The raw materials, reaction conditions, and product content and yield of Examples 1-10 are detailed in Table 1.

[0051] Table 1

[0052]

[0053] As can be seen from Examples 1-3, the reaction described in this invention is feasible in the temperature range of 165-195℃, and the reaction yield is basically at the same level, greater than 97%. As can be seen from Examples 8-9, the reaction temperature must be strictly controlled in the range of 165-195℃. Too low or too high a temperature will have a great impact on the yield of the target product.

[0054] Comparing Examples 3, 4 and 5, it can be seen that the amount of water used should not exceed three times the amount of tetrachloro-2-cyanopyridine added; otherwise, the yield of the target product will decrease to some extent.

[0055] Comparing Examples 3, 6, and 7, it was found that the amount of manganese dioxide and sodium tungstate used must be controlled at least one-thousandth or more of the amount of water or tetrachloro-2-cyanopyridine used; otherwise, the yield of the target product will also decrease to some extent.

[0056] Performance testing

[0057] 1. HPLC test

[0058] Test subject: Tetrachloropyridinecarboxylic acid prepared in Example 1.

[0059] Test content: After drying the product in Example 1, it was dissolved in a small amount of acetonitrile. Using acetonitrile and 0.5% phosphoric acid aqueous solution as the mobile phase, reversed-phase high-performance liquid chromatography was performed at a wavelength of 294 nm using an Agilent C8 column and a UV or diode array detector to separate amides, tetrachloropyridine acid, pentachloropyridine, and related impurities in the sample.

[0060] Test method:

[0061] Weigh 0.05 g (accurate to 0.0001 g) of tetrachloropyridine acid reference standard and place it in a 100 mL volumetric flask. Add 20 mL of the solution.

[0062] Dissolve the acetonitrile by shaking, dilute with 50% (v / v) acetonitrile to the mark, shake well, and filter to obtain the final product.

[0063] Weigh 0.05 g (accurate to 0.0001 g) of the dried sample and place it in a 100 mL volumetric flask. Add 20 mL of acetonitrile and shake to dissolve. Dilute to the mark with 50% (v / v) acetonitrile and shake well. Filter.

[0064] Under the above operating conditions, after the instrument stabilizes, 50% acetonitrile is used as a blank solution. After two consecutive blank solutions produce consistent peaks, several reference solutions are injected continuously until the relative change in peak area between two adjacent tetrachloropyridine acid solutions is less than 1.0%. Then, the determination is performed in the order of reference solution, sample solution, sample solution, and reference solution.

[0065] The HPLC data of the sample were collected, and the content of tetrachloropyridine carboxylic acid was calculated.

[0066] For detailed chromatograms from HPLC testing, please refer to [link / reference]. Figure 1 The retention times of each component are shown in Table 2.

[0067]

[0068]

[0069] 2. Stability test

[0070] Experimental procedure (taking stability experiment 1 as an example): At 30℃, 250g of tetrachloro-2-cyanopyridine (98% purity) and 250g of tap water were added to a high-pressure reactor, followed by 250mg of manganese dioxide and 280mg of sodium tungstate. The temperature was raised to 190℃, and the pressure inside the reactor was maintained at 1.32MPa. The reaction was then carried out at this temperature for 16 hours. After the reaction was completed, the catalyst was recovered by filtration and reused in the next batch. The filtrate was post-treated to obtain 266.95g of tetrachloropyridinecarboxylic acid with a purity of 98.53%, and the product yield was 98.01%.

[0071] Test method: HPLC test.

[0072] Test subject: Tetrachloropyridinecarboxylic acid prepared in Examples 1-3. The specific test results are detailed in Table 3.

[0073] Table 3

[0074] Product content Yield Stability experiment 1 98.53％ 98.01％ Stability experiment 2 98.50％ 97.84％ Stability experiment 3 98.56％ 97.72％ Average value 98.53％ 97.86％

[0075] The process provided by this invention produces products with stable and qualified quality, with no wastewater or solid waste, an average content of 98.53%, and an average yield of 97.86%, which is at the leading level in China.

Claims

1. A method for preparing tetrachloropyridinecarboxylic acid, characterized by, The application relates to a method for preparing 2-cyanopyridine by using a catalyst. The catalyst comprises a metal oxide catalyst and a metal inorganic salt catalyst. The metal oxide catalyst is manganese dioxide. The metal inorganic salt catalyst is sodium tungstate. The reaction temperature is 165-195 DEG C. The metal oxide catalyst is not less than 0.1% of the mass of 2-cyanopyridine.

2. The method of preparing tetrachloropyridinecarboxylic acid according to claim 1, characterized in that, The metal inorganic salt catalyst is not less than 0.1% of the mass of 2-cyanopyridine.

3. The method for preparing tetrachloropyridinecarboxylic acid according to claim 1, characterized in that, The mass ratio of 2-cyanopyridine to water is 1: (1-2.5).

4. The process for the preparation of tetrachloropyridinecarboxylic acid according to any one of claims 1 to 3, characterized in that, The reaction time is 15-40 h.

5. The method for preparing tetrachloropyridinecarboxylic acid according to claim 1, characterized in that, The metal oxide catalyst is not less than 0.1% of the mass of water.

6. The method for preparing tetrachloropyridinecarboxylic acid according to claim 1, characterized in that, The metal inorganic salt catalyst is not less than 0.1% of the mass of water.

7. The method for preparing tetrachloropyridinecarboxylic acid according to claim 1, characterized in that, ​

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