Preparation method of 3, 4, 5, 6-tetrachloropicolinic acid

Abstract

The invention relates to a method for preparing 3, 4, 5, 6-tetrachloropicolinic acid from picloram solid residues. The method comprises the following steps: dissolving picloram solid residues which take 6-amino-3, 4, 5-trichloropicolinic acid and 4-amino-3, 5, 6-trichloropicolinic acid as main components as raw materials in 1, 4-dioxane or other solvents, adding concentrated nitric acid to carry out N-amino nitration, then adding thionyl chloride to carry out sealed heating chlorination, and carrying out post-treatment to obtain 3, 4, 5, 6-tetrachloropicolinic acid. According to the method, picloram solid residues are converted into production raw materials with practical application value, diazotization operation in a traditional method is avoided, and the method has the advantages of being safe and mild in reaction, easy to operate, green and economical.

Description

Technical Field

[0001] This invention belongs to the field of pesticide synthesis, specifically relating to a method for preparing 3,4,5,6-tetrachloropyridinecarboxylic acid. Background Technology

[0002] Atrazine, also known as aminopyridine, has the chemical formula (I) 4-amino-3,5,6-trichloropyridinecarboxylic acid. It is a pyridine-type systemic herbicide. Its main characteristics are low dosage, high selectivity, low toxicity, low residue in soil and plants, and short residual period. It is a high-performance herbicide that is widely used and has a broad market prospect. 3,4,5,6-Tetrachloropyridinecarboxylic acid, represented by formula (II), is mainly used in the pesticide production field and is a key intermediate in the production of herbicides such as atrazine, dichloropyridine, and aminopyridine.

[0003]

[0004] The synthesis of toxicazine generally involves the dechlorination and ammonolysis of 3,4,5,6-tetrachloropyridinecarboxylic acid (as shown in formula (II)) with ammonia. During ammonolysis, the main reaction is the amino substitution of the 4-chlorine group, while side reactions such as amino substitution of the 3, 5, and 6-chlorine groups also occur, with the 6-position substitution being particularly significant. After the toxicazine product is extracted in the subsequent crystallization process, ammonia-chloropyridine acid waste residue is generated. This waste residue mainly contains 4-amino-3,5,6-trichloropyridinecarboxylic acid (as shown in formula (I), 6-amino-3,4,5-trichloropyridinecarboxylic acid (as shown in formula (III), and a small amount of 4,6-diamino-3,5-dichloropyridinecarboxylic acid or its salts (as shown in formula (IV)).

[0005]

[0006] During the production of atrazine, the yield and composition of its solid residue are related to factors such as the production process and the purity of raw materials, estimated to be in the thousands of tons per year. This type of organic waste residue is classified as hazardous waste, subject to strict regulation and continuously soaring disposal costs. Atrazine solid residue contains valuable compounds such as aminochloropyridine acids. Recovering its active ingredients can improve resource utilization, save significant hazardous waste disposal costs, and improve corporate profitability. There are few reports, both domestically and internationally, on how to effectively recycle and treat atrazine solid residue. Treatment methods mainly fall into two categories. The first category involves further purification of the atrazine solid residue. Patents CN104628635A, CN106854178A, and CN118026925A employ different treatment methods to separate and purify the high-value aminochloropyridine acids in the solid residue as much as possible, thus achieving waste residue utilization. The second type of processing method is to transform the solid residue of atrazine into other high-value products through a series of operations. For example, in patent CN104649965A, the solid residue generated during the production of atrazine, which contains atrazine and its isomers, is subjected to diazotization and cuprous chloride (CuCl) chlorination to obtain 3,4,5,6-tetrachloropyridinecarboxylic acid as shown in formula (II).

[0007]

[0008] Patent CN107474013A also employs diazotization and chlorination operations, but differs in that it uses special reaction solvents and conditions. For example, it uses alkyl alcohols as reaction solvents and alkyl nitrite esters as diazotizing reagents to selectively convert the byproduct toxicine isomer 6-amino-3,4,5-trichloropyridine carboxylic acid into 3,4,5,6-tetrachloropyridine carboxylic acid as shown in formula (II). The high-value aminochloropyridine acid in the solid residue is retained, realizing the recycling of toxicine solid residue and improving conversion efficiency.

[0009] In patent CN111909079A, atrazine residue underwent sequential decarboxylation, diazotization, chlorination, and dechlorination steps, ultimately transforming into 2,3,5-trichloropyridine, a product with promising market demand and high economic value, as shown in formula (V). This achieved further efficient utilization of the atrazine residue. However, this process, due to the final dechlorination operation, generates certain 2,5-dichloropyridine byproducts, reducing the purity of the final product.

[0010]

[0011] In the first type of recycling process described above, the purification and separation of atrazine solid slag did not resolve the byproducts shown in formulas (III) and (IV) generated during atrazine production. The second type of solid slag conversion methods inevitably involve a diazotization step, and the potential explosive safety risks posed by the instability of diazonium salts make the recycling and disposal of atrazine solid slag challenging. Therefore, developing a safer, more environmentally friendly, and simpler method that can effectively utilize atrazine solid slag is of great significance. Summary of the Invention

[0012] This invention presents a method for preparing 3,4,5,6-tetrachloropyridinecarboxylic acid from atrazine solid residue. This method utilizes the solid residue generated during the ammonolysis step of atrazine production as a raw material to synthesize a practically valuable production feedstock, and the reaction operation is simple and safe.

[0013] A method for preparing 3,4,5,6-tetrachloropyridinecarboxylic acid, specifically comprising the following steps: Using toxic nitrification solid residue with 6-amino-3,4,5-trichloropyridinecarboxylic acid, 4-amino-3,5,6-trichloropyridinecarboxylic acid or their salts as raw materials (the ratio of the two in the toxic nitrification solid residue is not limited), the residue is dissolved in 1,4-dioxane or other solvents, concentrated nitric acid is added for N-amino nitration, followed by the addition of thionyl chloride and sealed heating. After post-treatment, 3,4,5,6-tetrachloropyridinecarboxylic acid is obtained.

[0014] The raw materials are derived from the solid residue produced during the production of chlorpyrifos, or from the waste residue obtained by further purification of chlorpyrifos solid residue.

[0015] The solvent used comprises one or more of 1,2-dichloroethane, N,N-dimethylformamide, 1,4-dioxane, and N,N-dimethylacetamide, preferably 1,4-dioxane, and the raw material concentration is 0.1 mol / L to 1.0 mol / L.

[0016] The amount of concentrated nitric acid used is 1 to 3 times the molar mass of the raw material, preferably 1.5 times.

[0017] The amount of thionyl chloride used is 1 to 3 times the molar mass of the raw material, preferably 2.5 times.

[0018] The heating temperature after adding thionyl chloride is 70~80℃.

[0019] The post-treatment method involves quenching thionyl chloride with water, using ethyl acetate as the organic solvent, extracting 2-3 times, and concentrating the organic phase to obtain 3,4,5,6-tetrachloropyridinecarboxylic acid as shown in formula (II).

[0020]

[0021] In summary, due to the adoption of the above technical solution, compared with patents CN104649965A and CN107474013A, the beneficial effects of this invention are: 1. In this invention, concentrated nitric acid is used for the N-aminonitration of the main components in atrazine solid residue, avoiding the diazotization process with safety risks in traditional methods, thus significantly improving the safety and ease of operation of the production process. 2. In this invention, thionyl chloride, which is inexpensive and readily available, is used instead of cuprous chloride (CuCl) as the chlorination reagent, significantly reducing production costs. Attached Figure Description

[0022] Figure 1 The 1H NMR spectrum of compound (II) in Example 1 ( 1 Results of H NMR spectral analysis; Figure 2 The carbon NMR spectrum of compound (II) in Example 1 ( 13 Results of C NMR spectral analysis; Figure 3 The preparation route for 3,4,5,6-tetrachloropyridinecarboxylic acid is shown. Detailed Implementation

[0023] The beneficial effects of the present invention will be further described through the following embodiments. These embodiments are for illustrative purposes only and do not limit the scope of the present invention. At the same time, obvious changes and modifications made by those skilled in the art according to the present invention are also included within the scope of the present invention. Example 1

[0024] In a 100 mL flask, 15 mL of 1,2-dichloroethane and 5 mL of N,N-dimethylformamide were added, followed by the addition of atrazine residue (483 mg, 2 mmol) and concentrated nitric acid (65%-68%, 171 μL). The mixture was stirred at room temperature for 1 hour, followed by the addition of thionyl chloride (362 μL, 5 mmol). The mixture was then sealed and heated at 70 °C for 2 hours. After the reaction was complete, the mixture was extracted with ethyl acetate, and the organic phase was concentrated to give 267 mg of compound II, with a yield of 51%.

[0025] Structural characterization: 1 H NMR (400 MHz, DMSO- d 6 ) δ 4.48 (s, 1H), 13 C NMR (101 MHz, DMSO- d 6) δ164.48, 147.87, 146.36, 143.92, 132.84, 124.72. Example 2

[0026] In a 100 mL flask, 20 mL of N,N-dimethylformamide was added, followed by the addition of atrazine residue (483 mg, 2 mmol) and concentrated nitric acid (65%-68%, 171 μL). The mixture was stirred at room temperature for 1 hour, followed by the addition of thionyl chloride (362 μL, 5 mmol). The flask was then sealed and heated at 70 °C for 2 hours. After the reaction was complete, the mixture was extracted with ethyl acetate, and the organic phase was concentrated to give 120 mg of compound II, with a yield of 23%. Example 3

[0027] In a 100 mL flask, 20 mL of N,N-dimethylacetamide was added, followed by the addition of atrazine residue (483 mg, 2 mmol) and concentrated nitric acid (65%-68%, 171 μL). The mixture was stirred at room temperature for 1 hour, followed by the addition of thionyl chloride (362 μL, 5 mmol). The flask was then sealed and heated at 70 °C for 2 hours. After the reaction was complete, the mixture was extracted with ethyl acetate, and the organic phase was concentrated to give 99 mg of compound II, with a yield of 19%. Example 4

[0028] In a 100 mL flask, 20 mL of 1,4-dioxane was added, followed by the addition of atrazine solid residue (483 mg, 2 mmol) and concentrated nitric acid (65%-68%, 171 μL). The mixture was stirred at room temperature for 1 hour, followed by the addition of thionyl chloride (362 μL, 5 mmol). The flask was then sealed and heated at 70 °C for 2 hours. After the reaction was complete, the mixture was extracted with ethyl acetate, and the organic phase was concentrated to give 496 mg of compound II, with a yield of 95%. Example 5

[0029] In a 100 mL flask, 10 mL of 1,4-dioxane was added, followed by atrazine residue (483 mg, 2 mmol) and concentrated nitric acid (65%-68%, 171 μL). The mixture was stirred at room temperature for 1 hour, and then thionyl chloride (362 μL, 5 mmol) was added. The flask was sealed and heated at 70 °C for 2 hours. After the reaction was complete, the mixture was extracted with ethyl acetate, and the organic phase was concentrated to give 434 mg of compound II, with a yield of 83%. Example 6

[0030] In a 100 mL flask, 10 mL of 1,4-dioxane was added, followed by 4-amino-3,5,6-trichloropyridinecarboxylic acid (483 mg, 2 mmol) as shown in formula (I), and concentrated nitric acid (65%-68%, 171 μL). The mixture was stirred at room temperature for 1 hour, followed by the addition of thionyl chloride (362 μL, 5 mmol). The mixture was then sealed and heated at 70 °C for 2 hours. After the reaction was complete, the mixture was extracted with ethyl acetate, and the organic phase was concentrated to give 519 mg of compound II, with a yield of 99%. Example 7

[0031] In a 100 mL flask, 10 mL of 1,4-dioxane was added, followed by 6-amino-3,4,5-trichloropyridinecarboxylic acid (483 mg, 2 mmol) as shown in formula (III), and concentrated nitric acid (65%-68%, 171 μL). The mixture was stirred at room temperature for 1 hour, followed by the addition of thionyl chloride (362 μL, 5 mmol). The mixture was then sealed and heated at 70 °C for 2 hours. After the reaction was complete, the mixture was extracted with ethyl acetate, and the organic phase was concentrated to give 519 mg of compound II, with a yield of 88%. Example 8

[0032] In a 500 mL flask, 200 mL of 1,4-dioxane was added, followed by the addition of atrazine residue (10.00 g, 41.4 mmol) and concentrated nitric acid (65%-68%, 2.85 mL). The mixture was stirred at room temperature for 1 hour, and then thionyl chloride (7.5 mL, 104 mmol) was added. The mixture was sealed and heated at 70 °C for 2 hours. After the reaction was complete, the mixture was extracted with ethyl acetate, and the organic phase was concentrated to give 14.58 g of compound II, with a yield of 89%.

Claims

1. A method for preparing 3,4,5,6-tetrachloropyridinecarboxylic acid, characterized in that, The specific method includes the following steps: Using atrazine solid residue containing 6-amino-3,4,5-trichloropyridinecarboxylic acid, 4-amino-3,5,6-trichloropyridinecarboxylic acid or their salts as raw material, with no limit on the ratio of the two in the atrazine solid residue, it is dissolved in 1,4-dioxane or other solvents, N-aminonitration is carried out by adding concentrated nitric acid, followed by chlorination by adding thionyl chloride and heating in a sealed environment, and after post-treatment, 3,4,5,6-tetrachloropyridinecarboxylic acid is obtained.

2. The preparation method according to claim 1, characterized in that, The raw materials are derived from the solid residue produced during the production of chlorpyrifos, or from the waste residue obtained by further purification of chlorpyrifos solid residue.

3. In the preparation method according to claim 1, the characteristic is that, The solvent used comprises one or more of 1,2-dichloroethane, N,N-dimethylformamide, 1,4-dioxane, and N,N-dimethylacetamide, preferably 1,4-dioxane, and the raw material concentration is 0.1 mol / L to 1.0 mol / L.

4. In the preparation method according to claim 1, the characteristic is that, The N-aminonitrifying agent is concentrated nitric acid, and the amount used is 1 to 3 times the molar mass of the raw material, preferably 1.5 times.

5. The preparation method according to claim 1, characterized in that, The chlorination reagent is thionyl chloride, and the amount used is 1 to 3 times the molar mass of the raw material, preferably 2.5 times.

6. In the preparation method according to claim 1, the characteristic is that, The heating temperature after adding thionyl chloride is 70~80℃.

7. The preparation method according to claim 1, characterized in that, The post-treatment method involves quenching thionyl chloride with water, using ethyl acetate as the organic solvent, extracting 2-3 times, and concentrating the organic phase to obtain 3,4,5,6-tetrachloropyridinecarboxylic acid.

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