Preparation method of 3, 4-dimethylpyrazole and phosphate thereof

Abstract

The invention belongs to the technical field of organic synthesis and fertilizer additives, and particularly relates to a preparation method of 3, 4-dimethyl pyrazole and phosphate thereof, the method comprises the following steps: step 1) formylation reaction; the method comprises the following steps: in the presence of Lewis acid, carrying out formylation reaction on 2-butanone, formate and sodium alkoxide in an alkali solvent to obtain a reaction mixture; (2) cyclization reaction: enabling the reaction mixture obtained in the step (1) to be in contact with hydrazine hydrate for cyclization reaction to obtain the 3, 4-dimethylpyrazole.The preparation method is simple in process, safe, reliable, high in yield and product purity, simple in three-waste treatment and suitable for industrial production, and the solvent can be recycled and reused.

Description

A method for preparing 3,4-dimethylpyrazole and its phosphate Technical Field

[0001] This invention belongs to the field of organic synthesis and fertilizer additive technology, and particularly relates to a method for preparing 3,4-dimethylpyrazole and its phosphate. Background Technology

[0002] 3,4-Dimethylpyrazole phosphate (DMPP) is a nitrification inhibitor toxic to nitrifying bacteria, characterized by high efficiency, non-toxicity, stability, and specificity. It inhibits nitrification by reducing the activity of nitrifying bacteria. Adding DMPP to fertilizers can improve fertilizer utilization, crop quality, and thus increase economic benefits. Therefore, DMPP has received widespread attention since its development and introduction by BASF in Germany, and has been widely applied in agricultural production, showing broad application prospects.

[0003] 3,4-Dimethylpyrazole is not only an important intermediate in the synthesis of 3,4-dimethylpyrazole phosphate, but it is also the main active molecule exerting nitrification inhibition. DMPP, as a precursor to nitrification inhibitors, needs to be converted to 3,4-dimethylpyrazole via urea-dependent hydrolysis in an aqueous soil environment. The latter acts as the active molecule triggering the nitrification inhibition effect. Among the numerous reported synthetic methods for 3,4-dimethylpyrazole, the route using 2-butanone as a starting material, via a 2-methyl-3-oxobutanal metal intermediate, followed by cyclization with hydrazine hydrate, is one of the most commonly used methods.

[0004] In 1955, Walker et al. reported the reaction of 2-butanone, isopropyl formate, and sodium isopropoxide (prepared from sodium and anhydrous isopropanol) to obtain sodium 2-methyl-3-oxobutyraldehyde intermediate. This intermediate was then reacted with hydrazine hydrate under acetic acid catalysis to finally yield 3,4-dimethylpyrazole in 72% yield. The biggest problem with this process is the generation of a large amount of 3-ethylpyrazole byproducts, which often require complex separation processes for removal. Furthermore, the cyclization step of this method requires a relatively high reaction temperature. BASF AG disclosed a method in patent US6022979 using 2-butanone, sodium methoxide, and methyl formate as raw materials, followed by cyclization with hydrazine hydrate in the presence of sulfuric acid to produce 3,4-dimethylpyrazole. This process reduces the generation of 3-ethylpyrazole byproducts by filtering or centrifuging the sodium 2-methyl-3-oxobutyraldehyde intermediate; however, it requires step-by-step operation, the use of large amounts of sulfuric acid increases equipment requirements and the difficulty of waste treatment, and only achieves a 60% yield.

[0005] Therefore, in order to meet the needs of industrial production, there is an urgent need to develop a simple, high-purity, and high-yield method for preparing 3,4-dimethylpyrazole. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for preparing 3,4-dimethylpyrazole and its phosphate. This preparation method is simple, safe and reliable, with high yield and product purity, simple waste treatment, recyclable solvent, and suitable for industrial production.

[0007] The present invention is achieved through the following technical solution: On the one hand, a method for preparing 3,4-dimethylpyrazole is provided, the method comprising the following steps: Step 1) Formylation reaction; in the presence of Lewis acid, 2-butanone, formate ester and sodium alkoxide are subjected to a formylation reaction in an alkaline solvent to obtain a reaction mixture; Step 2) Cyclization reaction; the reaction mixture obtained in Step 1) is contacted with hydrazine hydrate to carry out a cyclization reaction to obtain 3,4-dimethylpyrazole.

[0008] Further, in step 1), the formylation reaction process is as follows: .

[0009] Further, the molar ratio of 2-butanone to formate is 1:1 to 1.5; the molar ratio of 2-butanone to Lewis acid is 1:0.01 to 1; and the molar ratio of 2-butanone to sodium alkoxide is 1:1 to 3.

[0010] Further, the sodium alkoxide is selected from any one of sodium methoxide, sodium ethoxide, and sodium isopropoxide; or, the Lewis acid is one or more of nickel fluoride (cobalt, magnesium, iron, zinc, copper, or aluminum), nickel chloride (cobalt, magnesium, iron, zinc, copper, or aluminum), nickel bromide (cobalt, magnesium, iron, zinc, copper, or aluminum), nickel iodide (cobalt, magnesium, iron, zinc, copper, or aluminum), nickel acetate (cobalt, magnesium, iron, zinc, copper, or aluminum), and magnesium sulfate (cobalt, magnesium, iron, zinc, copper, or aluminum); or, the formate ester is one of methyl formate, ethyl formate, and isopropyl formate.

[0011] Furthermore, the alkaline solvent is selected from one or more of methanol, ethanol, and isopropanol.

[0012] Further, in step 2), the cyclization reaction process is as follows: .

[0013] Furthermore, the molar ratio of 2-butanone to hydrazine hydrate is 1:1 to 1.5.

[0014] Another method for preparing 3,4-dimethylpyrazole phosphate is provided. This method is based on the 3,4-dimethylpyrazole prepared by the above method, and the 3,4-dimethylpyrazole is reacted with phosphoric acid in methanol to generate 3,4-dimethylpyrazole phosphate. The synthetic route is as follows: .

[0015] Preferably, the solvent is selected from methanol, ethanol, and water.

[0016] Finally, a 3,4-dimethylpyrazole phosphate prepared by the above method is provided.

[0017] Beneficial effects: By adding inexpensive and readily available Lewis acids, this invention not only improves the regioselectivity of the formylation reaction of 2-butanone with formate, but also lowers the temperature of the cyclization reaction and avoids the use of acids. High-purity 3,4-dimethylpyrazole phosphate can be obtained in high yield without the need for complex distillation and recrystallization methods, with a total yield of up to 90% and a product purity of up to 99%.

[0018] This invention uses readily available and inexpensive raw materials such as industrial-grade 2-butanone and sodium methoxide, and employs a one-pot continuous reaction process to integrate the traditional multi-step synthesis process (formylation and cyclization) into a single reaction system. This method eliminates the need for intermediate product separation and purification steps, thus shortening the process flow.

[0019] The reaction conditions of this invention are mild. Compared with the high temperature and high pressure conditions required by traditional processes, this not only significantly reduces the pressure and temperature resistance requirements of the equipment but also significantly improves operational safety. At the same time, the mild reaction conditions effectively reduce the occurrence of side reactions, improve product selectivity, and provide a simpler and more economical process solution for industrial-scale production.

[0020] The solvent of this invention is recyclable and the waste treatment is simple, which is beneficial for industrial production. Attached Figure Description

[0021] Figure 1 shows the content ratio of 3,4-dimethylpyrazole to 3-ethylpyrazole in Example 1 of the present invention; Figure 2 shows the content ratio of 3,4-dimethylpyrazole to 3-ethylpyrazole in Example 9 of the present invention. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0023] Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this invention. Experimental methods in the following embodiments that do not specify specific conditions are generally performed under conventional conditions or as recommended by the manufacturer. Unless otherwise stated, all percentages, ratios, proportions, or parts are by weight.

[0024] Unless otherwise specified, the reagents and raw materials used in the embodiments and comparative examples of this invention are commercially available.

[0025] In Example 1, under nitrogen protection, a sodium methoxide methanol solution (1000 ml, 5.0 mol, 2.0 eq) and nickel chloride (65 g, 0.5 mol, 0.1 eq) were added to a 5 L reaction vessel. The mixture was then cooled to 0 °C, and 2-butanone (180 g, 2.5 mol) and methyl formate (170 ml, 2.75 mol, 1.1 eq) were slowly added dropwise. The reaction mixture was then reacted at 50 °C for 12 hours. The mixture was then cooled to 0 °C, and hydrazine hydrate (197 ml, 3.25 mol, 1.3 eq) was slowly added dropwise. The reaction mixture was then reacted at 25 °C for 4 hours. The reaction was quenched with water, and the aqueous phase was extracted with ethyl acetate. The organic phases were combined and dried over anhydrous sodium sulfate. Finally, the solvent was removed under reduced pressure to obtain crude 3,4-dimethylpyrazole in oily form. The 1H NMR spectrum of the crude product is shown in Figure 1, where the ratio of 3,4-dimethylpyrazole to 3-ethylpyrazole is 1:0.05.

[0026] The 3,4-dimethylpyrazole obtained in the previous step was dissolved in methanol, and then 85% phosphoric acid (256 ml, 2.88 mol, 1.15 eq) was slowly added dropwise. The reaction solution was then reacted at 45 °C for 1 hour. After the reaction was completed, the reaction system was cooled to -20 °C and stirred at this temperature for 4 hours. After filtration and drying, 436 g of 3,4-dimethylpyrazole phosphate was obtained, with a yield of 90%.

[0027] In Example 2, under nitrogen protection, sodium ethoxide (340 g, 5.0 mol, 2.0 eq), ethanol (1000 ml), and nickel bromide (11 g, 0.05 mol, 0.01 eq) were added to a 5 L reactor. The mixture was then cooled to 0 °C, and 2-butanone (180 g, 2.5 mol) and ethyl formate (225 ml, 2.75 mol, 1.1 eq) were slowly added dropwise. The reaction mixture was then reacted at 0 °C for 1 hour. The mixture was then cooled to 0 °C, and hydrazine hydrate (151 ml, 2.5 mol, 1.0 eq) was slowly added dropwise. The reaction mixture was then reacted at -10 °C for 0.5 hours. The reaction was quenched with water, and the aqueous phase was extracted with ethyl acetate. The organic phases were combined and dried over anhydrous sodium sulfate. Finally, the solvent was removed under reduced pressure to obtain crude 3,4-dimethylpyrazole in oil form.

[0028] The 3,4-dimethylpyrazole obtained in the previous step was dissolved in methanol, and then 85% phosphoric acid (256 ml, 2.88 mol, 1.15 eq) was slowly added dropwise. The reaction solution was then reacted at 45 °C for 1 hour. After the reaction was completed, the reaction system was cooled to -20 °C and stirred at this temperature for 4 hours. After filtration and drying, 339 g of 3,4-dimethylpyrazole phosphate was obtained, with a yield of 70%.

[0029] In Example 3, under nitrogen protection, sodium isopropoxide (410 g, 5.0 mol, 2.0 eq), isopropanol (1000 ml), and cobalt acetate (22 g, 0.125 mol, 0.05 eq) were added to a 5 L reactor. The mixture was then cooled to 0 °C, and 2-butanone (180 g, 2.5 mol) and isopropyl formate (274 ml, 2.75 mol, 1.1 eq) were slowly added dropwise. The reaction mixture was then reacted at 60 °C for 1 hour. The mixture was then cooled to 0 °C, and hydrazine hydrate (181 ml, 3 mol, 1.2 eq) was slowly added dropwise. The reaction mixture was then reacted at 60 °C for 20 hours. The reaction was quenched with water, and the aqueous phase was extracted with ethyl acetate. The organic phases were combined and dried over anhydrous sodium sulfate. Finally, the solvent was removed under reduced pressure to obtain crude 3,4-dimethylpyrazole in oil form.

[0030] The 3,4-dimethylpyrazole obtained in the previous step was dissolved in methanol, and then 85% phosphoric acid (256 ml, 2.88 mol, 1.15 eq) was slowly added dropwise. The reaction solution was then reacted at 45 °C for 1 hour. After the reaction was completed, the reaction system was cooled to -20 °C and stirred at this temperature for 4 hours. After filtration and drying, 426 g of 3,4-dimethylpyrazole phosphate was obtained, with a yield of 88%.

[0031] In Example 4, under nitrogen protection, a sodium methoxide methanol solution (500 ml, 2.5 mol, 1.0 eq) and copper sulfate (159 g, 1.0 mol, 0.2 eq) were added to a 5 L reaction vessel. The mixture was then cooled to 0 °C, and 2-butanone (180 g, 2.5 mol) and methyl formate (155 ml, 2.5 mol, 1.0 eq) were slowly added dropwise. The reaction mixture was then reacted at 50 °C for 20 hours. The mixture was then cooled to 0 °C, and hydrazine hydrate (212 ml, 3.5 mol, 1.4 eq) was slowly added dropwise. The reaction mixture was then reacted at 25 °C for 4 hours. The reaction was quenched with water, and the aqueous phase was extracted with ethyl acetate. The organic phases were combined and dried over anhydrous sodium sulfate. Finally, the solvent was removed under reduced pressure to obtain crude 3,4-dimethylpyrazole in oily form.

[0032] The 3,4-dimethylpyrazole obtained in the previous step was dissolved in methanol, and then 85% phosphoric acid (256 ml, 2.88 mol, 1.15 eq) was slowly added dropwise. The reaction solution was then reacted at 45 °C for 1 hour. After the reaction was completed, the reaction system was cooled to -20 °C and stirred at this temperature for 4 hours. After filtration and drying, 368 g of 3,4-dimethylpyrazole phosphate was obtained, with a yield of 76%.

[0033] In Example 5, under nitrogen protection, a sodium methoxide methanol solution (750 ml, 3.75 mol, 1.5 eq) and zinc iodide (159 g, 0.5 mol, 0.1 eq) were added to a 5 L reaction vessel. The mixture was then cooled to 0 °C, and 2-butanone (180 g, 2.5 mol) and methyl formate (185 ml, 3 mol, 1.2 eq) were slowly added dropwise. The reaction mixture was then reacted at 50 °C for 12 hours. The mixture was then cooled to 0 °C, and hydrazine hydrate (227 ml, 3.75 mol, 1.5 eq) was slowly added dropwise. The reaction mixture was then reacted at 25 °C for 4 hours. The reaction was quenched with water, and the aqueous phase was extracted with ethyl acetate. The organic phases were combined and dried over anhydrous sodium sulfate. Finally, the solvent was removed under reduced pressure to obtain crude 3,4-dimethylpyrazole in oily form.

[0034] The 3,4-dimethylpyrazole obtained in the previous step was dissolved in methanol, and then 85% phosphoric acid (256 ml, 2.88 mol, 1.15 eq) was slowly added dropwise. The reaction solution was then reacted at 45 °C for 1 hour. After the reaction was completed, the reaction system was cooled to -20 °C and stirred at this temperature for 4 hours. After filtration and drying, 407 g of 3,4-dimethylpyrazole phosphate was obtained, with a yield of 84%.

[0035] In Example 6, under nitrogen protection, a sodium methoxide methanol solution (1250 ml, 6.25 mol, 2.5 eq) and magnesium fluoride (312 g, 5.0 mol, 1.0 eq) were added to a 5 L reaction vessel. The mixture was then cooled to 0 °C, and 2-butanone (180 g, 2.5 mol) and methyl formate (212 ml, 3.44 mol, 1.5 eq) were slowly added dropwise. The reaction mixture was then reacted at 50 °C for 12 hours. The mixture was then cooled to 0 °C, and hydrazine hydrate (197 ml, 3.25 mol, 1.3 eq) was slowly added dropwise. The reaction mixture was then reacted at 25 °C for 4 hours. The reaction was quenched with water, and the aqueous phase was extracted with ethyl acetate. The organic phases were combined and dried over anhydrous sodium sulfate. Finally, the solvent was removed under reduced pressure to obtain crude 3,4-dimethylpyrazole in oily form.

[0036] The 3,4-dimethylpyrazole obtained in the previous step was dissolved in methanol, and then 85% phosphoric acid (256 ml, 2.88 mol, 1.15 eq) was slowly added dropwise. The reaction solution was then reacted at 45 °C for 1 hour. After the reaction was completed, the reaction system was cooled to -20 °C and stirred at this temperature for 4 hours. After filtration and drying, 388 g of 3,4-dimethylpyrazole phosphate was obtained, with a yield of 80%.

[0037] In Example 7, under nitrogen protection, a sodium methoxide methanol solution (1500 ml, 7.5 mol, 3.0 eq) and aluminum chloride (67 g, 0.5 mol, 0.1 eq) were added to a 5 L reaction vessel. The mixture was then cooled to 0 °C, and 2-butanone (180 g, 2.5 mol) and methyl formate (170 ml, 2.75 mol, 1.1 eq) were slowly added dropwise. The reaction mixture was then reacted at 50 °C for 12 hours. The mixture was then cooled to 0 °C, and hydrazine hydrate (197 ml, 3.25 mol, 1.3 eq) was slowly added dropwise. The reaction mixture was then reacted at 25 °C for 4 hours. The reaction was quenched with water, and the aqueous phase was extracted with ethyl acetate. The organic phases were combined and dried over anhydrous sodium sulfate. Finally, the solvent was removed under reduced pressure to obtain crude 3,4-dimethylpyrazole in oil form.

[0038] The 3,4-dimethylpyrazole obtained in the previous step was dissolved in methanol, and then 85% phosphoric acid (256 ml, 2.88 mol, 1.15 eq) was slowly added dropwise. The reaction solution was then reacted at 45 °C for 1 hour. After the reaction was completed, the reaction system was cooled to -20 °C and stirred at this temperature for 4 hours. After filtration and drying, 397 g of 3,4-dimethylpyrazole phosphate was obtained, with a yield of 82%.

[0039] In Example 8, under nitrogen protection, a sodium methoxide methanol solution (1000 ml, 5.0 mol, 2.0 eq) and ferric sulfate (200 g, 0.5 mol, 0.1 eq) were added to a 5 L reaction vessel. The mixture was then cooled to 0 °C, and 2-butanone (180 g, 2.5 mol) and methyl formate (170 ml, 2.75 mol, 1.1 eq) were slowly added dropwise. The reaction mixture was then reacted at 50 °C for 12 hours. The mixture was then cooled to 0 °C, and hydrazine hydrate (197 ml, 3.25 mol, 1.3 eq) was slowly added dropwise. The reaction mixture was then reacted at 25 °C for 4 hours. The reaction was quenched with water, and the aqueous phase was extracted with ethyl acetate. The organic phases were combined and dried over anhydrous sodium sulfate. Finally, the solvent was removed under reduced pressure to obtain crude 3,4-dimethylpyrazole in oily form.

[0040] The 3,4-dimethylpyrazole obtained in the previous step was dissolved in methanol, and then 85% phosphoric acid (256 ml, 2.88 mol, 1.15 eq) was slowly added dropwise. The reaction solution was then reacted at 45 °C for 1 hour. After the reaction was completed, the reaction system was cooled to -20 °C and stirred at this temperature for 4 hours. After filtration and drying, 383 g of 3,4-dimethylpyrazole phosphate was obtained, with a yield of 79%.

[0041] Comparative Example 1 is a comparative example of Example 8, mainly examining the effect of Lewis acid on the reaction. Therefore, except for the absence of Lewis acid, the reaction conditions in this example are the same as those in Example 8.

[0042] Under nitrogen protection, a sodium methoxide methanol solution (1000 ml, 5.0 mol, 2.0 eq) was added to a 5 L reaction vessel, and the mixture was cooled to 0 °C. 2-Butanone (180 g, 2.5 mol) and methyl formate (170 ml, 2.75 mol, 1.1 eq) were slowly added dropwise. The reaction mixture was then incubated at 50 °C for 12 hours. The mixture was then cooled to 0 °C, and hydrazine hydrate (197 ml, 3.25 mol, 1.3 eq) was slowly added dropwise. The reaction mixture was then incubated at 25 °C for 4 hours. The reaction was quenched with water, and the aqueous phase was extracted with ethyl acetate. The organic phases were combined and dried over anhydrous sodium sulfate. Finally, the solvent was removed under reduced pressure to obtain crude 3,4-dimethylpyrazole in oil form.

[0043] The 3,4-dimethylpyrazole obtained in the previous step was dissolved in methanol, and then 85% phosphoric acid (256 ml, 2.88 mol, 1.15 eq) was slowly added dropwise. The reaction solution was then reacted at 45 °C for 1 hour. After the reaction was completed, the reaction system was cooled to -20 °C and stirred at that temperature for 4 hours. After filtration and drying, no target product was formed.

[0044] In Comparative Example 2, under nitrogen protection, 180 g (2.5 mol) of 2-butanone and methyl formate (170 ml, 2.75 mol, 1.1 eq) were slowly added sequentially to a sodium methoxide methanol solution (500 ml, 2.5 mol, 1.0 eq). The mixture was stirred at 30 °C for 2 hours. Then, a sodium methoxide methanol solution (150 ml, 0.75 mol, 0.3 eq) and methyl formate (46 ml, 0.75 mol, 1.1 eq) were added sequentially. The reaction mixture was stirred at room temperature for 16 hours. The solvent was removed under reduced pressure, and the resulting solid was dissolved in water (1000 ml). Concentrated sulfuric acid (105 g, 1.1 mol) and hydrazine hydrate (84 g, 1.65 mol) were then added sequentially to this aqueous solution. The mixture was stirred at room temperature for 16 hours. The pH of the reaction solution was adjusted to 8.1 using an aqueous sodium hydroxide solution. The aqueous phase was then extracted with ethyl acetate, the organic phases were combined, and dried over anhydrous sodium sulfate. Finally, the solvent was removed under reduced pressure to obtain crude 3,4-dimethylpyrazole in oil form. The 1H NMR spectrum of the crude product is shown in Figure 2, where the ratio of 3,4-dimethylpyrazole to 3-ethylpyrazole is 1:0.085.

[0045] The 3,4-dimethylpyrazole obtained in the previous step was dissolved in methanol, and then 85% phosphoric acid (256 ml, 2.88 mol, 1.15 eq) was slowly added dropwise. The reaction solution was then reacted at 45 °C for 1 hour. After the reaction was completed, the reaction system was cooled to -20 °C and stirred at this temperature for 4 hours. After filtration and drying, 271 g of 3,4-dimethylpyrazole phosphate was obtained, with a yield of 56%.

[0046] Therefore, the results of Example 8, Comparative Example 1, and Comparative Example 2 show that the addition of Lewis acids is crucial to the reaction. In this invention, Lewis acids mainly play the following roles: 1) coordinating with the carbon group in 2-butanone, further altering the acidity of the α-position hydrogen of the carbon group, thereby regulating the reaction activity and selectivity; 2) coordinating with the carbon group in methyl formate, making it more susceptible to attack by enol anions; 3) coordinating with the two carbon groups in the sodium 3-oxo-2-methylbutyraldehyde intermediate, improving the stability of the intermediate; 4) catalyzing the cyclization reaction of the sodium 3-oxo-2-methylbutyraldehyde intermediate with hydrazine hydrate. In other words, by adding inexpensive and readily available Lewis acids, this invention not only improves the regioselectivity of the formylation reaction of 2-butanone with formate, but also lowers the cyclization reaction temperature and avoids the use of acids. It achieves high-purity 3,4-dimethylpyrazole phosphate in high yield without the need for complex distillation and recrystallization methods, with a total yield as high as 90% and a product purity as high as 99%.

[0047] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing 3,4-dimethylpyrazole, characterized in that, The method includes the following steps: Step 1) Formylation reaction; 2-Butanone, formate ester and sodium alkoxide are subjected to formylation reaction in an alkaline solvent in the presence of Lewis acid to obtain a reaction mixture; Step 2) Cyclization reaction; The reaction mixture obtained in Step 1) is contacted with hydrazine hydrate to carry out cyclization reaction to obtain 3,4-dimethylpyrazole.

2. The method for preparing 3,4-dimethylpyrazole according to claim 1, characterized in that, In step 1), the formylation reaction process is as follows: 。 3. The method for preparing 3,4-dimethylpyrazole according to claim 2, characterized in that, The molar ratio of 2-butanone to formate is 1:1 to 1.5; the molar ratio of 2-butanone to Lewis acid is 1:0.01 to 1; and the molar ratio of 2-butanone to sodium alkoxide is 1:1 to 3.

4. The method for preparing 3,4-dimethylpyrazole according to claim 3, characterized in that, The sodium alkoxide is selected from any one of sodium methoxide, sodium ethoxide, and sodium isopropoxide; or, the Lewis acid is one or more of nickel fluoride (cobalt, magnesium, iron, zinc, copper, or aluminum), nickel chloride (cobalt, magnesium, iron, zinc, copper, or aluminum), nickel bromide (cobalt, magnesium, iron, zinc, copper, or aluminum), nickel iodide (cobalt, magnesium, iron, zinc, copper, or aluminum), nickel acetate (cobalt, magnesium, iron, zinc, copper, or aluminum), and magnesium sulfate (cobalt, magnesium, iron, zinc, copper, or aluminum); or, the formate ester is one of methyl formate, ethyl formate, and isopropyl formate.

5. The method for preparing 3,4-dimethylpyrazole according to claim 1, characterized in that, The alkaline solvent is selected from one or more of methanol, ethanol, and isopropanol.

6. The method for preparing 3,4-dimethylpyrazole according to claim 1, characterized in that, In step 2), the cyclization reaction process is as follows: 。 7. The method for preparing 3,4-dimethylpyrazole according to claim 6, characterized in that, The molar ratio of 2-butanone to hydrazine hydrate is 1:1 to 1.

5.

8. A method for preparing 3,4-dimethylpyrazole phosphate, characterized in that, This method is based on 3,4-dimethylpyrazole prepared by the method according to any one of claims 1-7. The 3,4-dimethylpyrazole is reacted with phosphoric acid in methanol to generate 3,4-dimethylpyrazole phosphate. The synthetic route is as follows: 。 9. The method for preparing 3,4-dimethylpyrazole phosphate according to claim 8, characterized in that, The solvent is selected from methanol, ethanol, and water.

10. A 3,4-dimethylpyrazole phosphate prepared by the method of claim 8 or 9.

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