A method for synthesizing 3-methyl-5-trifluoromethylpyrazole

Abstract

This invention belongs to the technical field of pesticides, specifically relating to a method for synthesizing 3-methyl-5-trifluoromethylpyrazole. Trifluoroacetylacetone and hydrazine hydrate are used as reactants, and 3-methyl-5-trifluoromethylpyrazole is synthesized under reaction conditions ① or ②. Reaction condition ① uses water as the reaction solvent and a quaternary ammonium salt as the catalyst; reaction condition ② uses an organic solvent immiscible with water as the reaction solvent and a protic acid as the catalyst. This invention uses water or a water-insoluble organic solvent instead of alcohols or other water-soluble and highly toxic solvents, avoiding problems such as the difficulty in direct crystallization and discharge of the 3-methyl-5-trifluoromethylpyrazole product. Using a quaternary ammonium salt or a protic acid as a catalyst effectively improves the synthesis efficiency of 3-methyl-5-trifluoromethylpyrazole. The method of this invention has simple reaction conditions, readily available raw materials, a yield of over 95%, and a purity of over 92%, making it suitable for industrial scale-up.

Description

Technical Field

[0001] This invention belongs to the technical field of pesticides, specifically relating to a method for synthesizing 3-methyl-5-trifluoromethylpyrazole. Background Technology

[0002] Fluthiazopyrone is the first piperidinylthiazolyl isoxazoline fungicide developed by DuPont. Fluthiazopyrone has a unique site of action against oomycete pathogens and achieves its fungicidal effect by inhibiting oxidized sterol-binding protein (OSBP). It has excellent control efficacy against downy mildew and blight in potatoes, grapes, vegetables and other specialty crops.

[0003] 3-Methyl-5-trifluoromethylpyrazole is an important intermediate in the synthesis of the fungicide fluthiazopyrone. Existing literature reports that methanol or ethanol is used as a solvent in the synthesis of 3-methyl-5-trifluoromethylpyrazole, with trifluoroacetylacetone and hydrazine hydrate as raw materials, via cyclization. However, this method has significant drawbacks: 3-methyl-5-trifluoromethylpyrazole is too soluble in alcohol solvents, making direct crystallization difficult, and water-soluble impurities cannot be removed by separation and washing or filtration. Some researchers have used chloroform as a solvent, but chloroform is volatile and highly toxic, and is rarely used in production.

[0004] Chinese patent application CN115974785A describes the reaction of trifluoroacetylacetone dissolved in tetrahydrofuran with hydrazine hydrate. However, this method has the following drawbacks: tetrahydrofuran is expensive, and it also has the problem of water-soluble impurities that cannot be directly removed. The product must be extracted to remove tetrahydrofuran and water-soluble impurities, and tetrahydrofuran also needs to be recovered from water, making the operation cumbersome. Summary of the Invention

[0005] To address the technical problems of difficulty in direct crystallization and difficulty in removing water-soluble impurities in existing methods for synthesizing 3-methyl-5-trifluoromethylpyrazole, this invention provides a method for synthesizing 3-methyl-5-trifluoromethylpyrazole.

[0006] In a first aspect, the present invention provides a method for synthesizing 3-methyl-5-trifluoromethylpyrazole, the reaction route of which is as follows:

[0007] ;

[0008] Using trifluoroacetylacetone and hydrazine hydrate as reactants and quaternary ammonium salt as catalyst, 3-methyl-5-trifluoromethylpyrazole is generated in water.

[0009] Furthermore, the quaternary ammonium salt is selected from one or more of tetrabutylammonium bromide, benzyltriethylammonium chloride, trioctylmethylammonium chloride, or dodecyltrimethylammonium chloride.

[0010] Furthermore, the molar ratio of trifluoroacetylacetone to hydrazine hydrate is 1:1 to 1.5.

[0011] Furthermore, the molar ratio of trifluoroacetylacetone to quaternary ammonium salt is 1:0.01~0.15.

[0012] Furthermore, the reaction temperature is -15~45℃, preferably 15~35℃.

[0013] Furthermore, after the reaction is complete, the mixture is cooled to crystallize, filtered, and 3-methyl-5-trifluoromethylpyrazole is obtained. Using water as a solvent, the post-treatment process can use filtration instead of solvent removal, simplifying the operation. The wastewater mother liquor contains virtually no product, reducing energy consumption and facilitating scale-up production.

[0014] Secondly, the present invention also provides a method for synthesizing 3-methyl-5-trifluoromethylpyrazole, the reaction route of which is as follows:

[0015] ;

[0016] Using trifluoroacetylacetone and hydrazine hydrate as reactants and a protic acid as a catalyst, 3-methyl-5-trifluoromethylpyrazole is generated in an organic solvent that is immiscible with water.

[0017] Furthermore, the protic acid is selected from one or more of sulfuric acid, phosphoric acid, and p-toluenesulfonic acid.

[0018] Furthermore, the low-toxicity or non-toxic organic solvent that is immiscible with water is selected from toluene or dichloroethane.

[0019] Furthermore, the molar ratio of trifluoroacetylacetone to hydrazine hydrate is 1:1 to 1.5, preferably 1:1 to 1.1.

[0020] Furthermore, the molar ratio of trifluoroacetylacetone to catalyst is 1:0.01~0.15.

[0021] Furthermore, the reaction temperature is 0~110℃, preferably 60~110℃.

[0022] Furthermore, after the reaction was completed, the mixture was cooled and washed with water to remove the organic phase and obtain 3-methyl-5-trifluoromethylpyrazole.

[0023] The beneficial effects of this invention are as follows:

[0024] This invention uses water or water-insoluble organic solvents instead of alcohols or other water-soluble and highly toxic solvents, thus avoiding the problem of difficulty in direct crystallization and discharge of the product 3-methyl-5-trifluoromethylpyrazole.

[0025] Meanwhile, the present invention creatively uses quaternary ammonium salts or protic acids as catalysts, which effectively improves the synthesis efficiency of 3-methyl-5-trifluoromethylpyrazole.

[0026] The method of this invention has simple reaction conditions, readily available raw materials, a yield of over 95%, and a purity of over 92%, making it suitable for industrial scale-up. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 This is the NMR spectrum of the product from Example 3. Detailed Implementation

[0029] To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions of the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this invention.

[0030] Example 1

[0031] Under stirring, 50 mL of water, 15.4 g (1 eq) of trifluoroacetylacetone, and 0.46 g (0.0143 eq) of tetrabutylammonium bromide were added sequentially to a 100 mL four-necked reaction flask, maintaining the temperature at 20–25 °C. 9.4 g (1.5 eq) of 80% hydrazine hydrate was slowly added dropwise to the system, and the mixture was stirred at 20–25 °C for 5 h. A large amount of solid was formed in the system. A small amount of the reaction solution was extracted with ethyl acetate, and gas chromatography analysis showed complete conversion of the starting material. The mixture was cooled to 0–5 °C for crystallization, maintained at this temperature for 1 h, filtered, and the filter cake was dried to obtain 15.4 g of the product. The HPLC purity was 92.7%, and the yield was 95.1%.

[0032] Example 2

[0033] Add 50 mL of water, 15.4 g (1 eq) of trifluoroacetylacetone, and 0.46 g (0.0143 eq) of tetrabutylammonium bromide sequentially to a 100 mL four-necked reaction flask with stirring, maintaining the temperature at 20–25 °C. Slowly add 8.1 g (1.3 eq) of 80% hydrazine hydrate to the system, maintaining the temperature at 20–25 °C and stirring for 6 h. A large amount of solid is formed in the system. Extract a small amount of the reaction solution with ethyl acetate; gas chromatography analysis showed complete conversion of the starting material. Cool to 0–5 °C for crystallization, maintain at this temperature for 1 h, filter, and dry the filter cake to obtain 15.4 g of product. The HPLC purity was 95.0%, and the yield was 97.5%.

[0034] Example 3

[0035] Add 50 mL of water, 15.4 g (1 eq) of trifluoroacetylacetone, and 0.46 g (0.0143 eq) of tetrabutylammonium bromide sequentially to a 100 mL four-necked reaction flask with stirring, maintaining the temperature at 20–25 °C. Slowly add 6.9 g (1.1 eq) of 80% hydrazine hydrate to the system, maintaining the temperature at 20–25 °C and stirring for 7 h. A large amount of solid is formed in the system. Extract a small amount of the reaction solution with ethyl acetate; gas chromatography analysis showed complete conversion of the starting material. Cool to 0–5 °C for crystallization, maintain at this temperature for 1 h, filter, and dry the filter cake to obtain 14.9 g of product. The HPLC purity was 99.3%, and the yield was 98.6%.

[0036] The product was analyzed by HNMR, and the detection data are as follows:

[0037] 1 H NMR (400MHz, CDCl3): δ 9.90-11.08(br, 1H), 6.34(s, 1H), 2.37(s,3H).

[0038] Comparing Examples 1-3, it can be found that when the amount of hydrazine hydrate is 1.1 eq, the reaction results are the best, with the highest purity and yield of the product. At the same time, the reaction time gradually increases as the amount of hydrazine hydrate decreases.

[0039] Example 4

[0040] Add 50 mL of water, 15.4 g (1 eq) of trifluoroacetylacetone, and 0.33 g (0.0143 eq) of benzyltriethylammonium chloride sequentially to a 100 mL four-necked reaction flask with stirring, maintaining the temperature at 20–25 °C. Slowly add 6.9 g (1.1 eq) of 80% hydrazine hydrate to the system, maintaining the temperature at 20–25 °C and stirring for 7 h. A large amount of solid is formed in the system. Extract a small amount of the reaction solution with ethyl acetate; gas chromatography analysis showed complete conversion of the starting material. Cool to 0–5 °C for crystallization, maintain at this temperature for 1 h, filter, and dry the filter cake to obtain 14.4 g of product. The HPLC purity was 98.6%, and the yield was 94.6%.

[0041] Example 5

[0042] Add 50 mL of water, 15.4 g (1 eq) of trifluoroacetylacetone, and 0.58 g (0.0143 eq) of trioctylmethylammonium chloride sequentially to a 100 mL four-necked reaction flask with stirring, maintaining the temperature at 20–25 °C. Slowly add 6.9 g (1.1 eq) of 80% hydrazine hydrate to the system, maintaining the temperature at 20–25 °C and stirring for 7 h. A large amount of solid is formed in the system. Extract a small amount of the reaction solution with ethyl acetate; gas chromatography analysis showed complete conversion of the starting material. Cool to 0–5 °C for crystallization, maintain at this temperature for 1 h, filter, and dry the filter cake to obtain 14.5 g of product. The HPLC purity was 98.5%, and the yield was 95.2%.

[0043] Example 6

[0044] Add 50 mL of water, 15.4 g (1 eq) of trifluoroacetylacetone, and 0.38 g (0.0143 eq) of dodecyltrimethylammonium chloride sequentially to a 100 mL four-necked reaction flask with stirring, maintaining the temperature at 20–25 °C. Slowly add 6.9 g (1.1 eq) of 80% hydrate to the system, maintaining the temperature at 20–25 °C and stirring for 7 h. A large amount of solid is formed in the system. Extract a small amount of the reaction solution with ethyl acetate; gas chromatography analysis showed complete conversion of the starting material. Cool to 0–5 °C for crystallization, maintain at this temperature for 1 h, filter, and dry the filter cake to obtain 14.6 g of product. The HPLC purity was 99.0%, and the yield was 96.3%.

[0045] Examples 3-6 compared the effects of different quaternary ammonium salt catalysts on the reaction results. Tetrabutylammonium bromide, benzyltriethylammonium chloride, trioctylmethylammonium chloride, or dodecyltrimethylammonium chloride all showed good catalytic effects, among which tetrabutylammonium bromide showed the best catalytic effect.

[0046] Comparative Example 1

[0047] Add 50 mL of water, 15.4 g (1 eq) of trifluoroacetylacetone, and 0.23 g (0.00714 eq) of tetrabutylammonium bromide sequentially to a 100 mL four-necked reaction flask with stirring, maintaining the temperature at 20–25 °C. Slowly add 6.9 g (1.1 eq) of 80% hydrazine hydrate to the system, maintaining the temperature at 20–25 °C and stirring for 13 h. A large amount of solid is formed in the system. Extract a small amount of the reaction solution with ethyl acetate; gas chromatography analysis showed complete conversion of the starting material. Cool to 0–5 °C for crystallization, maintain at this temperature for 1 h, filter, and dry the filter cake to obtain 14.5 g of product. The HPLC purity was 99.1%, and the yield was 95.7%.

[0048] Comparative Example 2

[0049] Add 50 mL of water and 15.4 g (1 eq) of trifluoroacetylacetone sequentially to a 100 mL four-necked reaction flask with stirring, maintaining the temperature at 20–25 °C. Slowly add 6.9 g (1.1 eq) of 80% hydrazine hydrate to the system, maintaining the temperature at 20–25 °C and stirring for 7 h. A large amount of solid is formed in the system. Extract a small amount of the reaction solution with ethyl acetate; gas chromatography analysis showed that 16.7% of the raw material remained. Continue to maintain the temperature for 3 h; gas chromatography analysis showed that the remaining raw material remained essentially unchanged. Cool to 0–5 °C for crystallization, maintain this temperature for 1 h, filter, recrystallize the filter cake with one part 50% ethanol, and dry to obtain 8.1 g of product. The HPLC purity was 99.0%, and the yield was 53.4%. Analysis showed that approximately 20% of the yield was lost in the filtrate.

[0050] After determining the optimal dosage of hydrazine hydrate and the type of quaternary ammonium salt catalyst, the dosage of quaternary ammonium salt catalyst was studied. According to the reaction results of Example 3 and Comparative Examples 1 and 2, it can be seen that when the dosage of quaternary ammonium salt is too small (<0.01eq) or not used, the conversion rate of the raw materials slows down and the reaction time is prolonged, which is not conducive to industrial scale-up production. This indicates that quaternary ammonium salt has a positive effect on improving the conversion rate of raw materials.

[0051] Comparative Example 3

[0052] Under stirring, 50 mL of ethanol, 15.4 g (1 eq) of trifluoroacetylacetone, and 0.46 g (0.0143 eq) of tetrabutylammonium bromide were added sequentially to a 100 mL four-necked reaction flask, maintaining the temperature at 25–30 °C. 6.9 g (1.1 eq) of 80% hydrazine hydrate was slowly added dropwise to the system, and the mixture was stirred at 25–30 °C for 6 h. A large amount of solid was formed in the system. A small amount of the reaction solution was extracted with ethyl acetate, and gas chromatography analysis showed complete conversion of the starting material. The mixture was cooled to 0–5 °C for crystallization, maintained at this temperature for 1 h, filtered, and the filter cake was dried to obtain 15.0 g of the product. The HPLC purity was 98.3%, and the yield was 98.2%.

[0053] Example 3 and Comparative Example 3 employed different post-processing techniques, demonstrating that 3-methyl-5-trifluoromethylpyrazole was prepared using ethanol as a solvent. The reaction solution was not washed with water, and the water-soluble impurities tetrabutylammonium bromide and excess hydrazine hydrate affected the product content and yield.

[0054] Example 7

[0055] Toluene (100 mL), trifluoroacetylacetone (15.4 g, 1 eq), and p-toluenesulfonic acid monohydrate (1.9 g, 0.1 eq) were added sequentially to a 250 mL four-necked reaction flask equipped with a water separator under stirring. The mixture was stirred and dissolved at room temperature. After complete dissolution, 80% hydrazine hydrate (6.9 g, 1.1 eq) was slowly added dropwise. After the addition was complete, the temperature was raised to 84-85 °C and reflux was initiated. Water was carried out by the water separator. When the temperature in the reaction flask reached the boiling point of toluene (110-111 °C), reflux was continued for 2 hours until no water evaporated from the water separator. A gas chromatography sample was taken for analysis, confirming complete conversion of the raw materials. The mixture was cooled to room temperature, washed with 90 mL of water, and toluene was separated. The toluene phase was washed twice more with water until the pH was neutral. The toluene was removed by vacuum distillation to obtain 14.9 g of the product. The HPLC purity was 99.3%, and the yield was 98.6%.

[0056] The product was analyzed by HNMR, and the detection data are as follows:

[0057] 1H NMR (400MHz, CDCl3): δ9.87-11.07(br, 1H), 6.34(s, 1H), 2.37(s,3H).

[0058] Example 8

[0059] Toluene (100 mL), trifluoroacetylacetone (15.4 g, 1 eq), and p-toluenesulfonic acid monohydrate (1.0 g, 0.05 eq) were added sequentially to a 250 mL four-necked reaction flask equipped with a water separator under stirring. The mixture was stirred and dissolved at room temperature. After complete dissolution, 6.9 g (1.1 eq) of 80% hydrazine hydrate was slowly added dropwise. After the addition was complete, the temperature was raised to 84-85 °C and reflux was initiated. Water was carried out by the water separator. When the temperature in the reaction flask reached the boiling point of toluene (110-111 °C), reflux was continued for 2 hours until no water evaporated from the water separator. A gas chromatography sample was taken for analysis, confirming complete conversion of the raw materials. The mixture was cooled to room temperature, washed with 90 mL of water, and toluene was separated. The toluene phase was washed twice more with water until the pH was neutral. The toluene was removed by vacuum distillation to obtain 14.8 g of the product. The HPLC purity was 99.8%, and the yield was 98.4%.

[0060] Example 9

[0061] Toluene (100 mL), trifluoroacetylacetone (15.4 g, 1 eq), and p-toluenesulfonic acid monohydrate (0.6 g, 0.03 eq) were added sequentially to a 250 mL four-necked reaction flask equipped with a water separator under stirring. The mixture was stirred and dissolved at room temperature. After complete dissolution, 6.9 g (1.1 eq) of 80% hydrazine hydrate was slowly added dropwise. After the addition was complete, the temperature was raised to 84-85 °C and reflux was initiated. Water was carried out by the water separator. When the temperature in the reaction flask reached the boiling point of toluene (110-111 °C), reflux was continued for 2 hours until no water evaporated from the water separator. A gas chromatography sample was taken for analysis, confirming complete conversion of the raw materials. The mixture was cooled to room temperature, washed with 90 mL of water, and toluene was separated. The toluene phase was washed twice more with water until the pH was neutral. The toluene was removed by vacuum distillation to obtain 14.8 g of the product. The HPLC purity was 99.7%, and the yield was 98.3%.

[0062] According to the experimental data in Examples 7-9, when p-toluenesulfonic acid monohydrate is used as a catalyst and the catalyst dosage is 0.03-0.1 eq, the product purity can reach over 99% and the yield can reach over 98%.

[0063] Example 10

[0064] Toluene (100 mL), trifluoroacetylacetone (15.4 g, 1 eq), and p-toluenesulfonic acid monohydrate (0.6 g, 0.03 eq) were added sequentially to a 250 mL four-necked reaction flask equipped with a water separator under stirring. The mixture was stirred and dissolved at room temperature. After complete dissolution, 80% hydrazine hydrate (6.6 g, 1.06 eq) was slowly added dropwise. After the addition was complete, the temperature was raised to 84-85 °C and reflux was initiated. Water was carried out in the water separator. When the temperature in the reaction flask reached the boiling point of toluene (110-111 °C), reflux was continued for 2 hours until no water evaporated from the water separator. Gas chromatography analysis showed complete conversion of the raw materials. The mixture was cooled to room temperature, washed with 90 mL of water, and toluene was separated. The toluene phase was washed twice more with water until the pH was neutral. Toluene was removed by vacuum distillation to obtain 14.9 g of the product. The HPLC purity was 99.5%, and the yield was 98.8%.

[0065] Example 11

[0066] Toluene (100 mL), trifluoroacetylacetone (15.4 g, 1 eq), and p-toluenesulfonic acid monohydrate (0.6 g, 0.03 eq) were added sequentially to a 250 mL four-necked reaction flask equipped with a water separator under stirring. The mixture was stirred and dissolved at room temperature. After complete dissolution, 80% hydrazine hydrate (6.3 g, 1 eq) was slowly added dropwise. After the addition was complete, the temperature was raised to 84-85 °C and reflux was initiated. Water was carried out by the water separator. When the temperature in the reaction flask reached the boiling point of toluene (110-111 °C), reflux was continued for 2 hours until no water evaporated from the water separator. Gas chromatography analysis confirmed complete conversion of the raw materials. The mixture was cooled to room temperature, washed with 90 mL of water, and toluene was separated. The toluene phase was washed twice more with water until the pH was neutral. The toluene was removed by vacuum distillation to obtain 14.9 g of the product. The HPLC purity was 99.6%, and the yield was 98.9%.

[0067] According to the experimental data from Examples 9 to 11, when the hydrazine hydrate ratio is 1 to 1.1 eq, the purity is maintained above 99% and the yield is maintained above 98%.

[0068] Example 12

[0069] Toluene (100 mL), trifluoroacetylacetone (15.4 g, 1 eq), and 98 wt% concentrated sulfuric acid (0.3 g, 0.03 eq) were added sequentially to a 250 mL four-necked reaction flask equipped with a water separator under stirring. The mixture was stirred and dissolved at room temperature. After complete dissolution, 80% hydrazine hydrate (6.3 g, 1 eq) was slowly added dropwise. After the addition was complete, the temperature was raised to 84-85 °C and reflux was initiated. Water was carried out by the water separator. When the temperature in the reaction flask reached the boiling point of toluene (110-111 °C), reflux was continued for 2 hours until no more water evaporated from the water separator. A gas chromatography sample was taken for analysis, confirming complete conversion of the raw materials. The mixture was cooled to room temperature, washed with 90 mL of water, and toluene was separated. The toluene phase was washed twice more with water until the pH was neutral. The toluene was removed by vacuum distillation to obtain 14.8 g of the product. The HPLC purity was 99.9%, and the yield was 98.5%.

[0070] Example 13

[0071] Toluene (100 mL), trifluoroacetylacetone (15.4 g, 1 eq), and 75 wt% phosphoric acid (0.4 g, 0.03 eq) were added sequentially to a 250 mL four-necked reaction flask equipped with a water separator under stirring. The mixture was stirred and dissolved at room temperature. After complete dissolution, 80% hydrazine hydrate (6.3 g, 1 eq) was slowly added dropwise. After the addition was complete, the temperature was raised to 84-85 °C and reflux was initiated. Water was carried out by the water separator. When the temperature in the reaction flask reached the boiling point of toluene (110-111 °C), reflux was continued for 2 hours until no more water evaporated from the water separator. A gas chromatography sample was taken for analysis, indicating complete conversion of the raw materials. The mixture was cooled to room temperature, washed with 90 mL of water, and toluene was separated. The toluene phase was washed twice more with water until the pH was neutral. The toluene was removed by vacuum distillation to obtain 14.8 g of the product. The HPLC purity was 99.5%, and the yield was 98.1%.

[0072] According to the experimental data from Examples 11-13, the yield and content of using sulfuric acid or phosphoric acid as catalysts are basically the same as those using p-toluenesulfonic acid monohydrate as catalysts.

[0073] Comparative Example 4

[0074] 100 mL of toluene and 15.4 g (1 eq) of trifluoroacetylacetone were added sequentially to a 250 mL four-necked reaction flask equipped with a water separator under stirring. The mixture was stirred and dissolved at room temperature. After complete dissolution, 6.3 g (1 eq) of 80% hydrazine hydrate was slowly added dropwise. After the addition was complete, the temperature was raised to 84-85 °C and reflux was initiated. Water was carried out by the water separator. When the temperature in the reaction flask reached the boiling point of toluene (110-111 °C), reflux was continued for 2 hours until no water evaporated from the water separator. A gas chromatography sample was taken, and 13% of the raw material remained. Reflux was continued for 6 hours, and a gas chromatography sample was taken again, showing that the raw material had not been significantly converted. The mixture was cooled to room temperature, washed with 90 mL of water, and toluene was separated. The toluene phase was washed twice with water until the pH was neutral. Toluene was removed by vacuum distillation. The crude product was crystallized from 50% ethanol to obtain 12.7 g of the product. The HPLC purity was 94.3%, and the yield was 79.8%.

[0075] The experimental data from Comparative Example 4 show that without a catalyst, the conversion of the raw materials is incomplete, and the yield and content are both low.

[0076] Although the present invention has been described in detail with reference to the accompanying drawings and preferred embodiments, the present invention is not limited thereto. Various equivalent modifications or substitutions can be made to the embodiments of the present invention by those skilled in the art without departing from the spirit and essence of the invention, and such modifications or substitutions should all be within the scope of the present invention. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should also be covered within the protection scope of the present invention.

Claims

1. A method for synthesizing 3-methyl-5-trifluoromethylpyrazole, characterized in that, The reaction route is as follows: ； Using trifluoroacetylacetone and hydrazine hydrate as reactants and quaternary ammonium salt as catalyst, 3-methyl-5-trifluoromethylpyrazole is generated in water.

2. The synthesis method according to claim 1, characterized in that, The quaternary ammonium salt is selected from one or more of tetrabutylammonium bromide, benzyltriethylammonium chloride, trioctylmethylammonium chloride, or dodecyltrimethylammonium chloride.

3. The synthesis method as described in claim 1 or 2, characterized in that, The molar ratio of trifluoroacetylacetone to hydrazine hydrate is 1:1 to 1.

5.

4. The synthesis method according to claim 1 or 2, characterized in that, The molar ratio of trifluoroacetylacetone to quaternary ammonium salt is 1:0.01~0.

15.

5. The synthesis method as described in claim 1 or 2, characterized in that, The reaction temperature is -15~45℃.

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