A method for preparing 2,4,6-trifluorobenzylamine by catalytic hydrogenation

Abstract

The present invention relates to a method for preparing 2,4,6-trifluorobenzylamine by catalytic hydrogenation, and belongs to the field of fine chemical technology. The method is in a hydroxyl-functionalized ionic liquid (IL-OH), using chloroplatinic acid or a platinum salt to provide a platinum source, first obtaining an ionic liquid catalytic system of highly active zero-valent platinum, and then catalyzing 2,4,6-trifluorobenzonitrile 25-50 DEG C / 0.5-1.5MPa hydrogenolysis reaction to prepare 2,4,6-trifluorobenzylamine. The present invention provides a method that is safer, and has fewer side reactions, higher reaction yields, lighter environmental pollution without using an organic solvent, and is a relatively green and environmentally friendly process.

Description

Technical Field

[0001] The invention relates to a novel method for preparing 2,4,6-trifluorobenzylamine by catalytic hydrogenation, belonging to the technical field of fine chemical industry. Background Art

[0002] 2,4,6-Trifluorobenzylamine is an important pesticide and pharmaceutical intermediate. Its traditional preparation method usually uses 2,4,6-trifluorobenzonitrile as the raw material and is prepared by boron hydrolysis or catalytic hydrogenation in an organic solvent, as shown in the following formula:

[0003]

[0004] The sodium borohydride used in the hydroboration process is a highly explosive and hazardous chemical, subject to strict restrictions on its purchase, storage, and use. Furthermore, the post-processing process generates significant wastewater, resulting in significant environmental pollution. Compared to the hydroboration process, catalytic hydrogenation offers advantages such as faster reaction rates, higher selectivity, higher product purity, reduced waste, waste gas, and catalyst recyclability, and has become a research hotspot in recent years. For example, in 2016, Wen Jianming et al. reported the preparation of 2,4,6-trifluorobenzylamine by hydrogenation reduction using palladium-on-carbon or Raney nickel as catalysts in organic solvents such as ethanol or tetrahydrofuran (Patent CN107778183B). In 2016, our company developed a method for preparing 2,4,6-trifluorobenzylamine by hydrogenation using Raney nickel as a catalyst in an ammonia-methanol system (Patent CN106349083A).

[0005] However, the catalytic hydrogenation process using Raney nickel, platinum carbon or palladium carbon as catalysts has many disadvantages. After the reaction, the catalyst needs to be separated from the reaction liquid. Since Raney nickel, platinum carbon or palladium carbon have the characteristics of spontaneous combustion, there are great safety hazards in the feeding and filtration processes. In addition, since the precious metals of platinum carbon or palladium carbon catalysts are loaded on activated carbon, the probability of the catalytic active center contacting the raw materials during the reaction is small, the activated carbon structure is easily destroyed, the catalyst is lost during separation, and a large amount of organic solvents are used. It is not a relatively green and environmentally friendly process.

[0006] As novel green solvents, ionic liquids offer advantages such as good solubility, near-zero volatility, structural designability, non-flammability, and excellent thermal and chemical stability. They have found widespread application in organic synthesis, catalysis, and extraction separations. Hydroxyl-functionalized ionic liquids, which combine the properties of both organic alcohols and ionic liquids, have been widely used in organic synthesis, nanomaterial preparation, and catalysis. Summary of the Invention

[0007] The object of the present invention is to provide a method for preparing 2,4,6-trifluorobenzylamine by a novel catalytic hydrogenation method. Specifically, the method for preparing 2,4,6-trifluorobenzylamine of the present invention comprises the following steps:

[0008]

[0009] In a hydroxyl-functionalized ionic liquid (IL-OH), chloroplatinic acid or a platinum salt is used as a platinum source to first obtain a highly active zero-valent platinum ionic liquid catalytic system, which then catalyzes the hydrogenolysis reaction of 2,4,6-trifluorobenzonitrile to prepare 2,4,6-trifluorobenzylamine.

[0010] Furthermore, in the above technical solution, the ionic liquid is one or more of 1-hydroxyethyl-3-methylimidazolium tetrafluoroborate, 1-hydroxyethyl-3-methylimidazolium hexafluorophosphate, hydroxyethylpyridinium tetrafluoroborate or hydroxyethylpyridinium hexafluorophosphate.

[0011] Furthermore, in the above technical solution, the platinum source is one or more of chloroplatinic acid, potassium chloroplatinate, sodium chloroplatinate, ammonium chloroplatinate, and platinum dichloride.

[0012] Furthermore, in the above technical solution, the preparation temperature of the high-activity platinum catalyst system is 70-150°C, preferably 90-120°C.

[0013] Furthermore, in the above technical solution, the preparation time of the high-activity platinum catalyst system is 1-6 hours, preferably 3-5 hours.

[0014] Furthermore, in the above technical solution, the mass ratio of the platinum source to the ionic liquid is 1:100-280, preferably 1:150-200; the mass ratio of the platinum source to 2,4,6-trifluorobenzonitrile is 1:1000-2000, preferably 1:1000-1500.

[0015] Furthermore, in the above technical solution, the hydrogenolysis reaction temperature is 25-50°C, preferably 40-50°C; the hydrogenolysis reaction pressure is 0.5-1.5 MPa, preferably 0.5-1.0 MPa.

[0016] Furthermore, in the above technical solution, the typical reaction operation is as follows:

[0017] 1) Adding a hydroxyl-functionalized ionic liquid and a platinum source to a reaction kettle in sequence, heating the reaction kettle to 90-120° C., stirring the mixture for 3-5 hours, and cooling the mixture to 20-25° C. to obtain a reaction solution.

[0018] 2) adding 2,4,6-trifluorobenzonitrile and the reaction solution obtained in 1) to a high-pressure hydrogenation reactor in sequence, slowly heating to the reaction temperature, maintaining the temperature while stirring, charging with hydrogen, and maintaining a certain pressure to carry out the hydrogenation reaction until the reaction is completed;

[0019] 3) The reaction solution obtained in 2) is evaporated under reduced pressure to remove the product to obtain 2,4,6-trifluorobenzylamine product.

[0020] Advantageous Effects of the Invention

[0021] 1. The present invention overcomes the problems of the prior art, such as the flammable catalyst, poor operational safety, harsh reaction conditions, complicated post-reaction treatment, catalyst recovery loss and deactivation, and serious environmental pollution.

[0022] 2. The method provided by the present invention has readily available raw materials, relatively mild reaction conditions, simple operation, easy recycling, safer operation, fewer side reactions, higher reaction yield, and less environmental pollution without the use of organic solvents. It provides a feasible method for the preparation of 2,4,6-trifluorobenzylamine and has potential industrial prospects. DETAILED DESCRIPTION

[0023] The following non-limiting examples may enable those skilled in the art to more fully understand the present invention, but are not intended to limit the present invention in any way.

[0024] Unless otherwise specified, the experimental methods described in the following examples are conventional methods; the reagents and materials described are all commercially available unless otherwise specified.

[0025] Comparative Example

[0026] In a 1000mL autoclave, 50g of 2,4,6-trifluorobenzonitrile, 5g of Raney-Ni, 85g of 25% aqueous ammonia, and 500g of methanol were added. The temperature was controlled at 80-90°C, and hydrogen was introduced at a pressure of 1.0 MPa for approximately 8 hours until the reaction was complete. The catalyst was filtered, and methanol was distilled from the filtrate. After distillation, dichloromethane was added for extraction. The extract was concentrated under normal pressure, and then the product was distilled under reduced pressure to obtain 43.6g of 2,4,6-trifluorobenzylamine. The HPLC assay was 99%, and the yield based on 2,4,6-trifluorobenzonitrile was 85%.

[0027] Example 1

[0028] ① Catalyst preparation

[0029] Add 0.1 mmol (0.027 g) of sodium chloroplatinate to 5 mL of 1-hydroxyethyl-3-methylimidazolium tetrafluoroborate, react in an oil bath at 120°C for 3 h with magnetic stirring to obtain a black suspension.

[0030] ②Catalytic hydrogenation

[0031] In a 250 mL autoclave, 50 g of 2,4,6-trifluorobenzonitrile and the homemade catalyst were added. The temperature was maintained at 40-50°C, and hydrogen was introduced at a pressure of 0.5 MPa for approximately 2 hours. The reaction was then completed, and the product was then distilled under reduced pressure to yield 47.2 g of 2,4,6-trifluorobenzylamine. The HPLC assay was 99%, and the yield based on 2,4,6-trifluorobenzonitrile was 92%.

[0032] Example 2

[0033] Into a 250 mL autoclave, 50 g of 2,4,6-trifluorobenzonitrile and the still residue from Example 1 (containing a homemade catalyst) were added. The temperature was controlled at 35-45°C, and hydrogen was introduced at a pressure of 0.8 MPa for approximately 2.5 hours. The reaction was then completed, and the product was distilled under reduced pressure to yield 46.2 g of 2,4,6-trifluorobenzylamine. The HPLC content was 99%, and the yield based on 2,4,6-trifluorobenzonitrile was 90%.

[0034] Example 3

[0035] ① Catalyst preparation

[0036] Add 0.1 mmol (0.03 g) of platinum chloride to 5 mL of hydroxyethylpyridinium tetrafluoroborate, react in an oil bath at 100°C for 3 h with magnetic stirring to obtain a black suspension.

[0037] ②Catalytic hydrogenation

[0038] In a 250 mL autoclave, 50 g of 2,4,6-trifluorobenzonitrile and the homemade catalyst were added. The temperature was maintained at 40-45°C, and hydrogen was introduced at a pressure of 0.6 MPa for approximately 3 hours. The reaction was then completed, and the product was then distilled under reduced pressure to yield 48.7 g of 2,4,6-trifluorobenzylamine. The HPLC assay indicated a 99% yield based on 2,4,6-trifluorobenzonitrile.

[0039] The above embodiments illustrate the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions are merely intended to explain the principles of the present invention. Various changes and improvements may be made to the present invention without departing from the scope of the present invention, and all such changes and improvements fall within the scope of protection of the present invention.

Claims

1. A method for preparing 2,4,6-trifluorobenzylamine by catalytic hydrogenation of a catalyst system, characterized in that: The steps include: ； In a hydroxyl-functionalized ionic liquid, chloroplatinic acid or a platinum salt is used as a platinum source to first obtain a zero-valent platinum ionic liquid catalytic system, which then catalyzes the hydrogenolysis reaction of 2,4,6-trifluorobenzonitrile to prepare 2,4,6-trifluorobenzylamine; the hydroxyl-functionalized ionic liquid is one or more of 1-hydroxyethyl-3-methylimidazolium tetrafluoroborate, 1-hydroxyethyl-3-methylimidazolium hexafluorophosphate, hydroxyethylpyridinium tetrafluoroborate, or hydroxyethylpyridinium hexafluorophosphate.

2. The method for preparing 2,4,6-trifluorobenzylamine by catalytic hydrogenation of the catalyst system according to claim 1, characterized in that: The platinum source is one or more of chloroplatinic acid, potassium chloroplatinate, sodium chloroplatinate, ammonium chloroplatinate, and platinum dichloride.

3. The method for preparing 2,4,6-trifluorobenzylamine by catalytic hydrogenation of the catalyst system according to claim 1, characterized in that: The preparation temperature of the zero-valent platinum ionic liquid catalytic system is 70-150°C.

4. The method for preparing 2,4,6-trifluorobenzylamine by catalytic hydrogenation of the catalyst system according to claim 1, characterized in that: The preparation time of the zero-valent platinum ionic liquid catalytic system is 1-6 hours.

5. The method for preparing 2,4,6-trifluorobenzylamine by catalytic hydrogenation of the catalyst system according to claim 1, characterized in that: The mass ratio of the platinum source to the hydroxyl functionalized ionic liquid is 1:100-280; the mass ratio of the platinum source to 2,4,6-trifluorobenzonitrile is 1:1000-2000.

6. The method for preparing 2,4,6-trifluorobenzylamine according to claim 1, wherein: The hydrogenolysis reaction temperature is 25-50°C; the hydrogenolysis reaction pressure is 0.5-1.5 MPa.

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