Preparation method of tetrachloropicolinic acid

Abstract

The invention relates to the field of organic synthesis, in particular to a preparation method of tetrachloropicolinic acid. The preparation method of the tetrachloropicolinic acid comprises the following steps: adding tetrachloro-2-cyanopyridine and water into a reactor, and then adding a catalyst to react, thereby obtaining the tetrachloropicolinic acid, wherein the catalyst comprises a metal oxide catalyst manganese dioxide and a metal inorganic salt catalyst sodium tungstate, and the mass ratio of tetrachloro-2-cyanopyridine to water is 1: (1-2.5). According to the preparation method provided by the invention, the content of the prepared tetrachloropicolinic acid product is greater than 98%, the yield of the product is greater than 97%, and the preparation raw materials do not contain acid or alkali, so that the pollution to the environment is reduced.

Description

Technical Field

[0001] The invention relates to the field of organic synthesis, and in particular to a method for preparing tetrachloropyridine carboxylic acid. Background Art

[0002] Tetrachloropyralid (CAS: 10469-09-7) is an important intermediate of pyridine herbicides and can be used to synthesize a variety of pesticide products, including diclopyralid and amiloride; these pesticides are widely used in orchards and no-till weed control.

[0003] The preparation and synthesis methods of tetrachloropyridine carboxylic acid in the prior art are generally as follows: under acidic conditions or alkaline conditions, tetrachloro-2-cyanopyridine is used as a raw material to hydrolyze and generate tetrachloropyridine carboxylic acid. Specifically, free tetrachloropyridine carboxylic acid and ammonium salt are obtained under acidic conditions, and sodium tetrachloropyridine carboxylate and ammonia are obtained under alkaline conditions. For example, patent document CN115974776A discloses a preparation method and application of 3,4,5,6-tetrachloropyridine carboxylic acid, which is mainly prepared by using tetrachloro-2-cyanopyridine as a raw material, first reacting with sulfuric acid, and then reacting with nitrosyl sulfuric acid. However, whether it is prepared by acid or alkali, a large amount of waste water, waste acid and waste salt will be generated, causing pollution problems.

[0004] Therefore, how to reduce the discharge of wastewater and waste salt in the synthesis process of tetrachloropyridine carboxylic acid and improve the yield of tetrachloropyridine carboxylic acid is a technical problem that those skilled in the art have been studying. Summary of the invention

[0005] In order to solve the above technical problems, the present invention provides a method for preparing tetrachloropyridine carboxylic acid, comprising: putting tetrachloro-2-cyanopyridine and water into a reactor at 0-50° C., adding a catalyst to react, filtering and recovering the catalyst after the reaction, and post-treating the obtained filtrate to obtain the obtained product.

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

[0007] As an implementable example, the metal oxide catalyst includes: 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] Furthermore, the metal oxide catalyst is manganese dioxide (MnO2).

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

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

[0011] At present, the most common process for synthesizing tetrachloropyridine carboxylic acid is the acidification of tetrachloro-2-cyanopyridine. However, the use of acid in the acidification process will produce a large amount of waste water, waste acid and waste salt, which pollutes the environment. Therefore, the inventors provide a novel synthesis process of tetrachloropyridine carboxylic acid. With tetrachloro-2-cyanopyridine and water as raw materials, under the condition of compounding of metal oxide catalyst and metal inorganic salt catalyst, especially under the condition of compounding of manganese dioxide and sodium tungstate, the target product can be efficiently synthesized, and the discharge of waste acid water or waste alkali water can be reduced; the inventors speculate that sodium tungstate may form a composite catalyst with manganese dioxide, and improve its catalytic performance by changing the surface properties or active sites of manganese dioxide, adsorb and activate tetrachloro-2-cyanopyridine and water molecules, reduce the activation energy of the reaction, and promote the rapid forward progress of the tetrachloropyridine carboxylic acid synthesis reaction.

[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 example, the amount of the metal oxide catalyst used 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 found that the mass ratio of tetrachloro-2-cyanopyridine to water needs to be further limited to improve the yield of tetrachloropicolinic acid. This is mainly because the reaction for synthesizing tetrachloropicolinic acid is a reversible reaction, that is, the reaction can proceed in the forward reaction direction or in the reverse reaction 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 decrease in the collision frequency between reactant molecules, thereby reducing the reaction rate and yield. Therefore, the present invention preferably sets the mass ratio of tetrachloro-2-cyanopyridine to water to 1: (1-2.5); in addition, the amount of catalyst also has a certain influence on the yield of the reaction. 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 defines that the amount of metal oxide catalyst is 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; only in this way can the yield of the product be improved. In addition, since the catalyst itself does not participate in the reaction and can be recovered after the reaction, the cost of the reaction can be significantly reduced and the discharge of wastewater can be reduced.

[0018] As an practicable case, the reaction time of the reaction is 15-30h.

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

[0020] In the present invention, the preferred reaction temperature is 165-195° C., which can ensure that tetrachloropicolinic acid has a higher yield. Too high a reaction temperature may lead to the occurrence of side reactions, and the generation of byproducts trichloro-4-hydroxypyridine acid and trichloro-6-hydroxypyridine acid will reduce the purity and yield of the target product. When the reaction temperature is too low, the activation energy of the reactants is reduced, the reaction rate is slowed down, thereby affecting the yield of the product. In addition, the reaction time will also affect the yield of the product. If the reaction time is too low, the reaction is incomplete, and if the reaction time is too high, the target product tetrachloropicolinic acid may be used as a reaction raw material for further reaction, thereby reducing the yield of the target product. Therefore, the reaction time is preferably 15-30 hours to ensure that the product has a higher yield and content.

[0021] Beneficial Effects

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

[0023] (ii) The present invention selects a combination of a metal oxide catalyst and a metal inorganic salt catalyst as the catalyst, especially in the case of a combination of manganese dioxide and sodium tungstate, which can significantly increase the product content and yield of the product tetrachloropyridine carboxylic acid, and the catalyst can be recovered after use and can be reused, which is beneficial to reducing the cost of the reaction.

[0024] (III) The present invention further stipulates that the amount of metal oxide catalyst is 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; the yield of the target product can be further improved.

[0025] (IV) The present invention limits the reaction temperature to 165-195° C., 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) The inventors found in the actual research and development process that the reaction time would affect the yield of the product, so the reaction time is preferably 15-30h, which can further improve the yield and purity of the target product. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is the HPLC test result spectrum of the tetrachloropyridine carboxylic acid prepared in Example 1. DETAILED DESCRIPTION

[0028] The reaction formulas involved in the following embodiments 1-10 are:

[0029]

[0030] Example 1

[0031] This example provides a method for preparing tetrachloropyridine carboxylic acid, comprising: at 30°C, putting 250g of tetrachloro-2-cyanopyridine with a mass content of 98% and 250g of tap water into an autoclave, then adding 250mg of manganese dioxide and 280mg of sodium tungstate, heating to 195°C, maintaining the pressure in the autoclave at 1.4Mpa, and then keeping the temperature for reaction for 15h; after the reaction is completed, filtering and recovering the catalyst, which can be reused. The filtrate is post-treated to obtain 263g of tetrachloropyridine carboxylic acid, with a content 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: at 30°C, putting 250g of tetrachloro-2-cyanopyridine with a mass content of 98% and 250g of tap water into an autoclave, then adding 250mg of manganese dioxide and 280mg of sodium tungstate, heating to 185°C, maintaining the pressure in the autoclave at 1.1Mpa, and then keeping the temperature to react for 18h; after the reaction is completed, filtering and recovering the catalyst, which can be reused. After post-treatment of the filtrate, 263g of tetrachloropyridine carboxylic acid is obtained, with a content 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: at 30°C, putting 250g of tetrachloro-2-cyanopyridine with a mass content of 98% and 250g of tap water into an autoclave, then adding 250mg of manganese dioxide and 280mg of sodium tungstate, heating to 165°C, maintaining the pressure in the autoclave at 0.7Mpa, and then keeping the temperature to react for 20h; after the reaction is completed, filtering and recovering the catalyst, which can be reused. After post-treatment of the filtrate, 263.5g of tetrachloropyridine carboxylic acid is obtained, with a content 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: at 30°C, putting 250g of tetrachloro-2-cyanopyridine with a mass content of 98% and 750g of tap water into an autoclave, then adding 250mg of manganese dioxide and 280mg of sodium tungstate, heating to 165°C, maintaining the pressure in the autoclave at 0.7Mpa, and then keeping the temperature for reaction for 20h; after the reaction is completed, filtering and recovering the catalyst, which can be reused. After post-treatment of the filtrate, 262g of tetrachloropyridine carboxylic acid is obtained, with a content 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: at 30°C, putting 250g of tetrachloro-2-cyanopyridine with a mass content of 98% and 875g of tap water into an autoclave, then adding 250mg of manganese dioxide and 280mg of sodium tungstate, heating to 165°C, maintaining the pressure in the autoclave at 0.7Mpa, and then keeping the temperature to react for 30h; after the reaction is completed, filtering and recovering the catalyst, which can be reused. The filtrate is post-treated to obtain 255g of tetrachloropyridine carboxylic acid, with a content 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: at 30°C, putting 250g of tetrachloro-2-cyanopyridine with a mass content of 98% and 250g of tap water into an autoclave, then adding 100mg of manganese dioxide and 280mg of sodium tungstate, heating to 165°C, maintaining the pressure in the autoclave at 0.7Mpa, and then keeping the temperature to react for 30h; after the reaction is completed, filtering and recovering the catalyst, which can be reused. The filtrate is post-treated to obtain 255g of tetrachloropyridine carboxylic acid, with a content 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: at 30°C, putting 250g of tetrachloro-2-cyanopyridine with a mass content of 98% and 250g of tap water into an autoclave, then adding 250mg of manganese dioxide and 100mg of sodium tungstate, heating to 165°C, maintaining the pressure in the autoclave at 0.7Mpa, and then keeping the temperature for reaction for 45h; after the reaction is completed, filtering and recovering the catalyst, which can be reused. The filtrate is post-treated to obtain 243g of tetrachloropyridine carboxylic acid, with a content 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: at 30°C, putting 250g of tetrachloro-2-cyanopyridine with a mass content of 98% and 250g of tap water into an autoclave, then adding 100mg of manganese dioxide and 280mg of sodium tungstate, heating to 185°C, maintaining the pressure in the autoclave at 1.1Mpa, and then keeping the temperature for reaction for 25h; after the reaction is completed, filtering and recovering the catalyst, which can be reused. After post-treatment of the filtrate, 246g of tetrachloropyridine carboxylic acid is obtained, with a content 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: at 30°C, putting 250g of tetrachloro-2-cyanopyridine with a mass content of 98% and 250g of tap water into an autoclave, then adding 250mg of manganese dioxide and 280mg of sodium tungstate, heating to 200°C, maintaining the pressure in the autoclave at 1.6Mpa, and then keeping the temperature to react for 10h; after the reaction is completed, filtering and recovering the catalyst, which can be reused. After post-treatment of the filtrate, 251g of tetrachloropyridine carboxylic acid is obtained, with a content 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: at 30°C, putting 250g of tetrachloro-2-cyanopyridine with a mass content of 98% and 250g of tap water into an autoclave, then adding 250mg of manganese dioxide and 280mg of sodium tungstate, heating to 150°C, maintaining the pressure in the autoclave at 0.48Mpa, and then keeping the temperature for reaction for 36h; after the reaction is completed, filtering and recovering the catalyst, which can be reused. The filtrate is post-treated to obtain 238g of tetrachloropyridine carboxylic acid, with a content of 97.20%, and a product yield of 87.13%.

[0050] The materials used for the raw materials, reaction conditions, and product contents and yields of Examples 1-10 are detailed in Table 1.

[0051] Table 1

[0052]

[0053] It can be seen from Examples 1-3 that the reaction described in the present invention is feasible in the temperature range of 165-195°C, and the reaction yield is basically at the same level, greater than 97%. It can be seen from Examples 8-9 that the reaction temperature must be strictly controlled in the range of 165-195°C. Too low or too high a temperature has a great influence on the yield of the target product.

[0054] Comparative Examples 3, 4 and 5 show that the amount of water used should not exceed 3 times the amount of tetrachloro-2-cyanopyridine fed, otherwise the yield of the target product will decrease to a certain extent.

[0055] Comparative Examples 3, 6 and 7 show that the amount of manganese dioxide and sodium tungstate is at least controlled to be one thousandth or more of the amount of water or tetrachloro-2-cyanopyridine, otherwise the yield of the target product will also decrease to a certain extent.

[0056] Performance Testing

[0057] 1. HPLC test

[0058] Test object: tetrachloropyridine carboxylic acid prepared in Example 1.

[0059] Test content: After drying the product in Example 1, it was dissolved in a small amount of acetonitrile, and acetonitrile and 0.5% phosphoric acid aqueous solution were used as mobile phases. An Agilent C8 chromatographic column and an ultraviolet or diode array detector were used to separate the amide, tetrachloropyralidic acid, pentachloropyridine, and related impurities in the sample by reverse phase high performance liquid chromatography at a wavelength of 294 nm.

[0060] Test method:

[0061] Weigh 0.05 g (accurate to 0.0001 g) of tetrachloropyralid acid reference substance into a 100 mL volumetric flask and add 20 mL

[0062] Shake with acetonitrile to dissolve, dilute to scale with 50% (v / v) acetonitrile, shake well, and filter to obtain.

[0063] Weigh 0.05 g (accurate to 0.0001 g) of the dried sample, place it in a 100 mL volumetric flask, add 20 mL of acetonitrile and shake to dissolve it, dilute it to the scale with 50% (v / v) acetonitrile, shake well, and filter.

[0064] After the instrument is stable under the above operating conditions, 50% acetonitrile is used as the blank solution. After two consecutive injections of blank solution have the same peak, several injections of reference solution are continuously injected until the relative change in the peak area of ​​two adjacent injections of tetrachloropyralid is less than 1.0%. Then, the determination is carried out in the order of reference solution, sample solution, sample solution, and reference solution.

[0065] Collect the HPLC liquid phase data of the sample and calculate the content of tetrachloropyridine carboxylic acid.

[0066] The HPLC test spectrum is shown in Figure 1 The peak retention time of each component is shown in Table 2.

[0067]

[0068]

[0069] 2. Stability test

[0070] Experimental process (taking stability experiment 1 as an example): At 30°C, 250g of tetrachloro-2-cyanopyridine with a mass content of 98% and 250g of tap water were put into an autoclave, and then 250mg of manganese dioxide and 280mg of sodium tungstate were added, and the temperature was raised to 190°C, and the pressure in the autoclave was maintained at 1.32Mpa, and then the reaction was kept warm for 16 hours; after the reaction was completed, the catalyst was filtered and recovered, and the catalyst was reused for the next batch. After post-treatment of the filtrate, 266.95g of tetrachloropyridine carboxylic acid was obtained, with a content of 98.53%, and a product yield of 98.01%.

[0071] Test method: HPLC test.

[0072] Test object: tetrachloropyridine carboxylic acid prepared in Example 1-3. Specific test results are shown 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 product quality obtained by the process provided by the invention is stable and qualified, without waste water and waste solids, with 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 tetrachloropyridine carboxylic acid, characterized in that, include: At 0-50°C, tetrachloro-2-cyanopyridine and water are placed in a reactor, and a catalyst is added to react. After the reaction is completed, the catalyst is filtered and recovered, and the filtrate is post-treated to obtain the product; The catalyst includes metal oxide catalyst and metal inorganic salt catalyst.

2. The method for preparing tetrachloropyralid according to claim 1, characterized in that: The metal oxide catalyst includes 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.

3. The method for preparing tetrachloropyridine carboxylic acid according to claim 1, characterized in that: The metal inorganic salt catalyst includes: one or more of zirconium sulfate, cerium sulfate, copper sulfate, ferrous sulfate, ferrous sulfate, zinc sulfate, ferric chloride, and sodium tungstate.

4. The method for preparing tetrachloropyralidone according to claim 1, characterized in that: The amount of the metal oxide catalyst is not less than 0.1% of the mass of tetrachloro-2-cyanopyridine.

5. The method for preparing tetrachloropyridine carboxylic acid according to claim 1, characterized in that: The amount of the metal inorganic salt catalyst is not less than 0.1% of the mass of tetrachloro-2-cyanopyridine.

6. The method for preparing tetrachloropyridine carboxylic acid according to any one of claims 1 to 5, characterized in that: The mass ratio of tetrachloro-2-cyanopyridine to water is 1:(1-2.5).

7. The method for preparing tetrachloropyridine carboxylic acid according to claim 1, characterized in that: The reaction time of the reaction is 15-40h.

8. The method for preparing tetrachloropyridine carboxylic acid according to any one of claims 1 to 7, characterized in that: The reaction temperature of the reaction is 165-195°C.

9. The method for preparing tetrachloropyridine carboxylic acid according to claim 1, characterized in that: The amount of the metal oxide catalyst is not less than 0.1% of the mass of water.

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

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