A kind of synthetic method of diquat dichloride

Abstract

The present invention discloses a method for synthesizing diquat dichloride, comprising: using an alcohol solvent as a reaction solvent, reacting pyridine and dichloroethane in the presence of a catalyst A to generate a quaternary pyridinium ammonium salt; adding water after the reaction, cooling to room temperature, separating the liquids, and removing the alcohol solvent from the aqueous phase under reduced pressure to obtain an aqueous phase containing the quaternary pyridinium ammonium salt represented by Formula II; adding a catalyst B and a ligand to the aqueous phase containing the quaternary pyridinium ammonium salt, performing a coupling reaction to generate a crude diquat dichloride; filtering the reaction solution, distilling the filtrate under reduced pressure until the diquat dichloride is precipitated, cooling the filtrate to room temperature for crystallization, and filtering to obtain a refined diquat dichloride. The method is simple to operate and reduces the complexity of post-processing; and the second step uses water as a solvent, which is environmentally friendly and greatly reduces the generation of "three wastes". The method significantly reduces the production cost of diquat dichloride and has high industrial application value.

Description

Technical Field

[0001] The invention belongs to the field of pesticide chemicals and relates to a method for synthesizing diquat dichloride. Background Art

[0002] Diquat, also known internationally as diquat and in English as 1,1'-ethyl ene-2,2'-bipyridyldibromide, is a non-active contact herbicide and deoxidizer developed by Syngenta of France. It is currently one of the most widely used herbicides worldwide, second only to glyphosate and paraquat in global sales and demand. As a contact herbicide, diquat is rapidly digested by plant tissue and loses its activity upon contact with soil. Diquat is primarily used for weed control in fields, plantations, non-arable land, and before harvest. It can also be used to induce stem and leaf dryness on potatoes and sweet potatoes. In areas with severe sedge weeds, the combined use of diquat and paraquat is more effective.

[0003] Diquat typically exists as a monohydrated dibromide. Diquat's active ingredient is the cationic moiety; the type of anion has no effect on its herbicidal activity. These ions have equal effects on equimolar amounts of substrate (J. Sci. Food Agric., 1960, 309-315). Changing the diquat anion does not impair its herbicidal activity (US Pat. No. 2,823,987A). Bromine is a precious resource, while chlorine is abundant and inexpensive. The raw material dibromoethane used in traditional diquat dibromide is relatively expensive, more than 10 times that of dichloroethane. Using inexpensive dichloroethane and bipyridine to produce diquat dichloride significantly reduces drug costs without compromising efficacy, thus possessing significant industrial value. Therefore, developing a method for preparing diquat dichloride as an alternative to diquat dibromide is of great economic significance.

[0004] There are several main methods for preparing diquat dichloride:

[0005] 1. Ion Exchange Method: US Patent No. 2823987A discloses a diquat dibromide solution reacted with silver chloride by thorough stirring, followed by filtration to remove the silver bromide and obtain a diquat dichloride solution. This method uses expensive silver chloride as a chloride exchange reagent, resulting in high costs and no industrial application. Alternatively, diquat dichloride can be obtained through ion exchange using ion exchange resins, but this method also lacks industrial application (Brit. J. Industry. Med., 1966, 23, 133).

[0006] CN107573342A reacts 2,2'-bipyridine with ethylene dibromide to produce 1,1'-ethylene-2,2'-bipyridine dibromide. Using an aqueous solution of 1,1'-ethylene-2,2'-bipyridine dibromide as the raw material, a series of post-treatments, including oxidation with an oxidant such as hydrogen peroxide, bromine absorption, and separation, yield a 1,1'-ethylene-2,2'-bipyridine dichloride mother liquor with a cation content of 20-30% and a brominated byproduct. This method has promising industrial applications, but requires the preparation of diquat dibromide, followed by oxidation, bromination, and multiple post-treatment steps to obtain the 1,1'-ethylene-2,2'-bipyridine dichloride mother liquor. This method is lengthy and complex.

[0007] 2. Chloroethanol Cyclization Method: GB1087052A heats 2,2'-bipyridine and 1-chloro-2-ethanol to 130-170°C to produce 1,1'-ethylene-2,2'-bipyridine dichloride and ethylene glycol as a byproduct. The chloroethanol raw material used in this method is relatively expensive, and the byproduct ethylene glycol is difficult to separate and purify.

[0008] 3. CN112500411A uses dichloroethane and 2,2'-bipyridine as raw materials and uses high temperature and high pressure in an autoclave. CN115925707A directly synthesizes diquat dichloride. This method is simple and suitable for industrial production and scale-up.

[0009] 4. Patent US3803147A uses bipyridinium dibromide to couple with sodium amalgam in a solvent. The resulting 1,1'-ethylene-2,2'-bipyridinium dibromide is oxidized in dilute hydrochloric acid and air to produce 1,1'-ethylene-2,2'-bipyridinium dichloride. This method has a long reaction process and a complex operation. Furthermore, the reaction involves the use of flammable and explosive sodium and the highly toxic mercury. Therefore, it is not suitable for industrial application.

[0010] In summary, 2,2'-bipyridine is used as the starting material in the synthesis of diquat dichloride. There are usually two synthetic routes for 2,2'-bipyridine:

[0011] Synthesis Route 1: CN112457239A uses 2-chloropyridine as the raw material and reacts at high temperature in the presence of a catalyst to produce 2,2'-bipyridine. This method uses relatively high-cost 2-chloropyridine, and a large amount of catalyst waste residue remains during the reaction.

[0012]

[0013] Synthesis Route 2: CN106380444A uses pyridine as the starting material. A high-temperature, high-pressure reaction under a catalyst results in a coupling reaction to obtain 2,2'-bipyridine. This method is energy-intensive and requires advanced process technology.

[0014] Summary of the Invention

[0015] The purpose of the present invention is to provide a new synthesis route of diquat dichloride in view of the shortcomings of the prior art.

[0016] The purpose of the present invention is achieved through the following technical solutions:

[0017] A method for synthesizing diquat dichloride, the synthetic route is as follows:

[0018]

[0019] include:

[0020] Step (1), using an alcohol solvent as a reaction solvent, in the presence of a catalyst A, pyridine and dichloroethane react to form a pyridine quaternary ammonium salt. After the reaction is completed, water is added, the mixture is cooled to room temperature, the liquid is separated, and the alcohol solvent is removed from the aqueous phase under reduced pressure to obtain an aqueous phase containing the pyridine quaternary ammonium salt (Formula II);

[0021] Step (2), adding catalyst B and ligand to the aqueous phase containing pyridinium quaternary ammonium salt obtained in step (1), coupling reaction to generate crude diquat dichloride, filtering the reaction solution, and distilling the filtrate under reduced pressure to precipitate diquat dichloride, cooling to room temperature for crystallization, and filtering to obtain a refined diquat dichloride.

[0022] In step (1), the molar ratio of pyridine to dichloroethane is 1:1.1 to 1:3, preferably 1:1.5 to 1:2.

[0023] The alcohol solvent is one or a combination of methanol, ethanol, propanol, isopropanol, n-butanol, and isobutanol, preferably methanol.

[0024] The mass ratio of the alcohol solvent to dichloroethane is 1:1 to 5:1, preferably 1:1 to 1.5:1.

[0025] The mass ratio of water to dichloroethane is 2:1 to 5:1, preferably 2:1 to 3.5:1.

[0026] The water can be purified water.

[0027] The catalyst A is one or a combination of cupric chloride, cuprous chloride, cupric iodide, cuprous iodide, ferrous chloride, and ferric chloride, preferably one or a combination of cupric chloride, cuprous chloride, cupric iodide, and cuprous iodide.

[0028] The molar ratio of the catalyst A to pyridine is 0.01:1 to 0.05:1, preferably 0.05:1.

[0029] The reaction was carried out under a nitrogen atmosphere.

[0030] The reaction temperature is 120-230° C., preferably 160-180° C.; the reaction pressure is 1-5 MPa, preferably 2-3 MPa.

[0031] In step (2), the catalyst B is one or a combination of nickel, nickel chloride, nickel acetate, palladium carbon, palladium chloride, and palladium acetate.

[0032] The molar ratio of the catalyst B to pyridine is 0.01:1 to 0.05:1, preferably 0.03:1.

[0033] The ligand is triphenylphosphine.

[0034] The molar ratio of the ligand to the catalyst B is 1.1:1.

[0035] The coupling reaction was carried out under a nitrogen atmosphere.

[0036] The temperature of the coupling reaction is 120-180° C., preferably 150-160° C.; the pressure of the coupling reaction is 2-6 MPa, preferably 4-5 MPa.

[0037] Beneficial effects of the present invention:

[0038] The invention adopts pyridine which is easy to obtain and cheap as a starting raw material, which can greatly reduce the cost of raw materials and reduce the use cost for farmers in weeding cultivated land.

[0039] The invention uses pyridine as a starting material, first reacts with dichloroethane through a quaternary ammonium salt to produce a pyridine quaternary ammonium salt, and then catalytically couples the reaction to produce diquat dichloride. The two-step reaction is carried out in one reactor, which is simple to operate and reduces the trouble of post-processing. In addition, water is used as a solvent in the second step, which is green and environmentally friendly and greatly reduces the generation of "three wastes".

[0040] The method of the present invention greatly reduces the production cost of diquat dichloride and has high industrial application value. DETAILED DESCRIPTION

[0041] The technical solution of the present invention is further described below in conjunction with specific embodiments, but the protection scope of the present invention is not limited thereto.

[0042] Examples 1 to 7 are the preparation of quaternary pyridinium ammonium salts, and Examples 8 to 12 are the preparation of diquat dichloride.

[0043] The room temperature is 25℃±5℃.

[0044] Example 1

[0045] 7.9 g (0.1 mol) of pyridine, 14.85 g (0.15 mol) of ethylene dichloride, 14.85 g of methanol and 0.495 g (0.005%) of cuprous chloride were added to a 200 mL autoclave. The gas in the autoclave was replaced with nitrogen, the temperature was raised to 160° C., and the reaction was maintained for 8 hours. The pressure was controlled at 3 MPa during the reaction (if overpressure, the pressure was released). After the reaction, the slurry was filtered to remove cuprous chloride, and 45 g of purified water was added with stirring. The mixture was cooled to room temperature and separated. The aqueous phase contained methanol, and the methanol was removed under reduced pressure to obtain an aqueous phase containing a pyridine quaternary ammonium salt for standby use. The liquid phase detection showed a pyridine conversion rate of 98.5%, and a yield of the product pyridine quaternary ammonium salt of 93% (based on pyridine).

[0046] Example 2

[0047] 7.9 g (0.1 mol) of pyridine, 14.85 g (0.15 mol) of dichloroethane, 14.85 g of anhydrous ethanol and 0.495 g (0.005%) of cuprous chloride were added to a 200 mL autoclave. The gas in the autoclave was replaced with nitrogen, the temperature was raised to 160° C., and the reaction was maintained for 8 hours. The pressure was controlled at 3 MPa during the reaction (if overpressure, the pressure was released). After the reaction, the slurry was filtered to remove cuprous chloride, and 45 g of purified water was added and stirred to dissolve. The mixture was cooled to room temperature and separated. The aqueous phase contained ethanol, and the ethanol was removed under reduced pressure to obtain an aqueous phase containing a pyridine quaternary ammonium salt, which was set aside. The liquid phase detection showed a pyridine conversion rate of 93%, and a product pyridine quaternary ammonium salt yield of 86% (based on pyridine).

[0048] Example 3

[0049] 7.9 g (0.1 mol) of pyridine, 14.85 g (0.15 mol) of dichloroethane, 14.85 g of methanol, and 0.95 g (0.005%) of cuprous iodide were added to a 200 mL autoclave. The gas in the autoclave was replaced with nitrogen, the temperature was raised to 170° C., and the reaction was maintained for 8 hours. The pressure was controlled at 4 MPa during the reaction (if overpressure, the pressure was released). After the reaction, the slurry was filtered to remove cuprous iodide, and 45 g of purified water was added with stirring. The mixture was cooled to room temperature and separated. The aqueous phase contained methanol, and the methanol was removed under reduced pressure and set aside. The liquid phase detection showed a pyridine conversion rate of 96.3%, and the yield of the product pyridine quaternary ammonium salt was 92.4% (based on pyridine).

[0050] Example 4

[0051] 7.9 g (0.1 mol) of pyridine, 14.85 g (0.15 mol) of dichloroethane, 14.85 g of methanol, and 0.81 g (0.005%) of ferric chloride were added to a 200 mL autoclave, and the gas in the autoclave was replaced with nitrogen. The temperature was raised to 160° C. and the reaction was kept warm for 8 hours. The pressure during the reaction was controlled at 3 MPa (if overpressure, the pressure was released). After the reaction, 45 g of purified water was added to the slurry with stirring, cooled to room temperature, and separated. The aqueous phase contained methanol, and the methanol was removed under reduced pressure and set aside. The liquid phase detection showed a pyridine conversion rate of 23.5%, and the yield of the product pyridine quaternary ammonium salt was 21% (based on pyridine).

[0052] Example 5

[0053] 7.9 g (0.1 mol) of pyridine, 14.85 g (0.15 mol) of dichloroethane, 14.85 g of methanol, and 0.495 g (0.005%) of cuprous chloride were added to a 200 mL autoclave. The gas in the autoclave was replaced with nitrogen, the temperature was raised to 180° C., and the reaction was maintained for 8 hours. The pressure was controlled at 5 MPa during the reaction (if overpressure, the pressure was released). After the reaction, the slurry was filtered to remove cuprous chloride, and 45 g of purified water was added with stirring. The mixture was cooled to room temperature and separated. The aqueous phase contained methanol, and the methanol was removed under reduced pressure and set aside. The liquid phase detection showed a pyridine conversion rate of 99%, and the yield of the product pyridine quaternary ammonium salt was 85% (based on pyridine).

[0054] Example 6

[0055] 7.9 g (0.1 mol) of pyridine, 14.85 g (0.15 mol) of dichloroethane, 22.28 g of methanol, and 0.495 g (0.005%) of cuprous chloride were added to a 200 mL autoclave. The gas in the autoclave was replaced with nitrogen, the temperature was raised to 170° C., and the reaction was maintained for 8 hours. The pressure was controlled at 4 MPa during the reaction (if overpressure, the pressure was released). After the reaction, the slurry was filtered to remove cuprous chloride, and 45 g of purified water was added and stirred. The mixture was cooled to room temperature. The aqueous phase contained methanol, and the methanol was removed under reduced pressure and set aside. The liquid phase detection showed a pyridine conversion rate of 99%, and the yield of the product pyridine quaternary ammonium salt was 94% (based on pyridine).

[0056] Example 7

[0057] 7.9 g (0.1 mol) of pyridine, 14.85 g (0.15 mol) of dichloroethane, 14.85 g of methanol, and 0.297 g (0.003%) of cuprous chloride were added to a 200 mL autoclave. The gas in the autoclave was replaced with nitrogen, the temperature was raised to 160° C., and the reaction was maintained for 8 hours. The pressure was controlled at 3 MPa during the reaction (if overpressure, the pressure was released). After the reaction, the slurry was filtered to remove cuprous chloride, and 45 g of purified water was added with stirring. The mixture was cooled to room temperature and separated. The aqueous phase contained methanol, and the methanol was removed under reduced pressure and set aside. The liquid phase detection showed a pyridine conversion rate of 87%, and the yield of the product pyridine quaternary ammonium salt was 84% (based on pyridine).

[0058] Example 8

[0059] The aqueous phase containing the pyridinium quaternary ammonium salt of Example 1 was used as the reaction solution, 0.86 g (0.0033 mol) of triphenylphosphine and 0.39 g (0.003 mol) of nickel chloride were added, the gas in the autoclave was replaced with nitrogen, the temperature was raised to 150° C., and the reaction was kept warm for 5 hours. The reaction pressure was controlled at 4 MPa. The reaction solution was filtered to obtain a solid, and the mixture was distilled under reduced pressure to precipitate a solid diquat dichloride. The mixture was cooled to room temperature for crystallization and filtered to obtain a solid diquat dichloride (yield 85.2%, based on pyridine). The filtrate was used mechanically.

[0060] Example 9

[0061] The aqueous phase containing the pyridinium quaternary ammonium salt of Example 1 was used as the reaction solution, 0.86 g (0.0033 mol) of triphenylphosphine and 0.53 g (0.003 mol) of palladium chloride were added, the gas in the autoclave was replaced with nitrogen, the temperature was raised to 150° C., and the reaction was kept warm for 5 hours. The reaction pressure was controlled at 4 MPa. The reaction solution was filtered to obtain a solid, and the mixture was distilled under reduced pressure to precipitate a diquat dichloride solid. The mixture was cooled to room temperature for crystallization and filtered to obtain a diquat dichloride solid (yield 91.2%, based on pyridine).

[0062] Example 10

[0063] The aqueous phase containing the quaternary ammonium salt of pyridinium in Example 1 was used as the reaction solution, 0.86 g (0.0033 mol) of triphenylphosphine and 0.68 g (0.003 mol) of palladium acetate were added, the gas in the autoclave was replaced with nitrogen, the temperature was raised to 150° C., and the reaction was kept warm for 5 hours. The reaction pressure was controlled at 4 MPa. The reaction solution was filtered to obtain a solid, and the solution was distilled under reduced pressure to precipitate a diquat dichloride solid. The solution was cooled to room temperature for crystallization and filtered to obtain a diquat dichloride solid (yield 92.6%, based on pyridine).

[0064] Example 11

[0065] The aqueous phase containing the pyridinium quaternary ammonium salt of Example 1 was used as the reaction solution, 0.86 g (0.0033 mol) of triphenylphosphine and 0.68 g (0.003 mol) of palladium acetate were added, the gas in the autoclave was replaced with nitrogen, the temperature was raised to 180° C., the reaction was kept warm for 5 hours, the reaction pressure was controlled at 5 MPa, the reaction solution was filtered for solid, and the mixture was distilled under reduced pressure to precipitate diquat dichloride solid. The mixture was cooled to room temperature for crystallization and filtered to obtain diquat dichloride solid (yield 95%, based on pyridine).

[0066] Example 12

[0067] The aqueous phase containing the pyridinium quaternary ammonium salt of Example 1 was used as the reaction solution, 1.44 g (0.0055 mol) of triphenylphosphine and 1.125 g (0.005 mol) of palladium acetate were added, the gas in the autoclave was replaced with nitrogen, the temperature was raised to 150° C., and the reaction was kept warm for 5 hours. The reaction pressure was controlled at 4 MPa, the reaction solution was filtered to obtain a solid, and the mixture was distilled under reduced pressure to precipitate a diquat dichloride solid. The mixture was cooled to room temperature for crystallization and filtered to obtain a diquat dichloride solid (yield 87%, based on pyridine).

Claims

1. A method for synthesizing diquat dichloride, characterized in that: The synthetic route is as follows: include: Step (1), using an alcohol solvent as a reaction solvent, in the presence of a catalyst A, pyridine and dichloroethane react to generate a pyridine quaternary ammonium salt, adding water after the reaction, cooling to room temperature, separating the liquids, and removing the alcohol solvent from the aqueous phase under reduced pressure to obtain an aqueous phase containing the pyridine quaternary ammonium salt shown in Formula II; wherein the molar ratio of the pyridine to the dichloroethane is 1:1.1 to 1:3; the catalyst A is one or a combination of cupric chloride, cuprous chloride, cupric iodide, cuprous iodide, ferrous chloride, and ferric chloride; the reaction temperature is 120 to 230° C., and the reaction pressure is 1 to 5 MPa; Step (2), adding catalyst B and ligand to the aqueous phase containing pyridinium quaternary ammonium salt obtained in step (1), coupling reaction to generate crude diquat dichloride, filtering the reaction solution, distilling the filtrate under reduced pressure until diquat dichloride is precipitated, cooling to room temperature for crystallization, filtering, and obtaining fine diquat dichloride; wherein the catalyst B is one or a combination of several of nickel, nickel chloride, nickel acetate, palladium carbon, palladium chloride, and palladium acetate; the ligand is triphenylphosphine; the temperature of the coupling reaction is 120-180° C., and the pressure of the coupling reaction is 2-6 MPa.

2. The method for synthesizing diquat dichloride according to claim 1, wherein: In step (1), the mass ratio of water to dichloroethane is 2:1 to 5:

1.

3. The method for synthesizing diquat dichloride according to claim 2, wherein: In step (1), the molar ratio of pyridine to dichloroethane is 1:1.5 to 1:2; and the mass ratio of water to dichloroethane is 2:1 to 3.5:

1.

4. The method for synthesizing diquat dichloride according to claim 1, wherein: In step (1), the alcohol solvent is one or a combination of methanol, ethanol, propanol, isopropanol, n-butanol, and isobutanol.

5. The method for synthesizing diquat dichloride according to claim 4, characterized in that: In step (1), the alcohol solvent is methanol.

6. The method for synthesizing diquat dichloride according to claim 1 or 4, characterized in that: In step (1), the mass ratio of the alcohol solvent to dichloroethane is 1:1 to 5:

1.

7. The method for synthesizing diquat dichloride according to claim 6, wherein: In step (1), the mass ratio of the alcohol solvent to dichloroethane is 1:1 to 1.5:

1.

8. The method for synthesizing diquat dichloride according to claim 1, wherein: In step (1), the molar ratio of the catalyst A to pyridine is 0.01:1 to 0.05:

1.

9. The method for synthesizing diquat dichloride according to claim 8, characterized in that: In step (1), the molar ratio of the catalyst A to pyridine is 0.05:

1.

10. The method for synthesizing diquat dichloride according to claim 1, characterized in that: In step (1), the reaction temperature is 160-180° C.; the reaction pressure is 2-3 MPa.

11. The method for synthesizing diquat dichloride according to claim 1, characterized in that: In step (2), the molar ratio of the catalyst B to pyridine is 0.01:1 to 0.05:

1.

12. The method for synthesizing diquat dichloride according to claim 11, characterized in that: In step (2), the molar ratio of the catalyst B to pyridine is 0.03:

1.

13. The method for synthesizing diquat dichloride according to claim 1, wherein: In step (2), the molar ratio of the ligand to the catalyst B is 1.1:

1.

14. The method for synthesizing diquat dichloride according to claim 1, characterized in that: In step (2), the temperature of the coupling reaction is 150-160° C.; the pressure of the coupling reaction is 4-5 MPa.

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