A method for preparing pyrazoline by internal cyclization of ketone hydrazones using ZSM-5 molecular sieve as catalyst

Abstract

The present application belongs to the field of heterogeneous catalytic preparation of energetic materials, and provides a method for preparing pyrazoline by internal cyclization of ketone hydrazine with ZSM-5 molecular sieve as catalyst. The preparation method is a heterogeneous reaction, which is used to improve the conversion efficiency of acetone hydrazine, solve the problem of difficult separation of catalyst and product, and avoid the technical problem of waste acid catalysis in traditional process. ZSM-5 molecular sieve is a kind of porous material with uniform pore channel, large specific surface area, good thermal stability, high product separation efficiency, easy to control the surface acidity and alkalinity, excellent catalytic selectivity and conversion rate. Compared with the traditional homogeneous acid catalysis of ketone hydrazine internal cyclization to prepare 2-pyrazoline derivatives, the ZSM-5 molecular sieve catalyst not only effectively catalyzes the reaction, but also reduces the post-treatment operation and effectively separates the product. The target product pyrazoline derivative is easy to form a ternary tension ring, which is a key precursor of new high-energy fuel, and has great potential in industrial application.

Description

Technical Field

[0001] This invention belongs to the technical field of heterogeneous catalysis, and particularly relates to a method for preparing pyrazoline by catalytic internal cyclization of ketones using ZSM-5 molecular sieves. Background Technology

[0002] Pyrazolines, as five-membered nitrogen heterocyclic compounds, possess diverse and unique structures. Due to the presence of (C=N-NH-C) functional groups on the pyrazoline ring, they have wide applications in aviation fuels, biomedicine, and fluorescent probes. From an atom utilization perspective, the ketone-azo compound intracyclization method for preparing pyrazoline derivatives is the optimal choice among all methods, as the ketone-azo molecule and the pyrazoline molecule are isomers, achieving 100% atom utilization and offering extremely high economic benefits for industrial production. ZSM-5 molecular sieve is a porous material with uniform channels, a large specific surface area, and excellent thermal stability. Compared to other molecular sieves, its framework structure features characteristic chain-like structural units (Pentasil chains), exhibiting a 10-membered ring wavy network, with further connections between the network layers forming a three-dimensional framework structure. ZSM-5 molecular sieve possesses a framework and ex-framework tri-coordinated aluminum (Al(OH)3, Al(OH)3) 2+ AlOH 3 + and Al 3+ ZSM-5 exhibits abundant Lewis acidic sites, giving it excellent chemoselectivity and easily tunable surface acidity and alkalinity. ZSM-5 has the highest framework density among commonly used molecular sieves. Compared to Y-type molecular sieves, which also contain extra-framework tricoordinated aluminum, ZSM-5 has a higher framework density of 17.9 T / 1000 A3. The higher framework density results in a smaller void volume, which, due to the confinement effect, is more conducive to intramolecular cyclization.

[0003] For the internal cyclization reaction route to prepare pyrazoline derivatives, ketazine is activated by protic acids. Traditional processes commonly use hydrochloric acid, dicarboxylic acid, oxalic acid, and iodine as catalysts to catalyze the conversion of ketazine to 2-pyrazoline. These processes suffer from problems such as complex product post-processing, environmental pollution from waste acid, and uncontrollable acidity corroding equipment, which do not conform to the current green development concept. Our research group has also used Lewis metal salts and ionic liquids to catalyze the internal cyclization of ketazine to prepare pyrazoline compounds. For example, patent publication number CN 115572263 A discloses a method for synthesizing pyrazoline by cyclization of ketazine catalyzed by hydrazine salts. This invention mixes the ketazine compound and the hydrazine salt catalyst and reacts them to obtain the pyrazoline compound. Although these catalysts have achieved excellent results, they still have drawbacks such as difficulty in separating the catalyst from the product, complex synthetic routes, high costs, and sensitivity to water. Therefore, there is an urgent need to develop a catalyst with high product separation efficiency and easily controllable surface acidity.

[0004] Xiao Yonghou et al. prepared ZSM-5 molecular sieve nanocrystals, which can effectively reduce diffusion pathways, expand specific surface area, increase the exposure of adsorption sites, improve catalytic performance, and also show satisfactory regeneration stability [10.1016 / j.seppur.2022.120698]. The preparation of pyrazoline by ketone azides currently mostly uses protic acid (hydrochloric acid, oxalic acid) catalysis. These reactions are equimolar reactions, the acidity cannot be controlled, and the post-processing is troublesome and easily corrodes the equipment. Some teams have grafted sulfonic acid and solid support together, but sulfonic acid is easy to lose and easily generates waste acid, which does not conform to the current green development concept. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention proposes a method for preparing pyrazoline by intra-azo cyclization of ketones catalyzed by ZSM-5 molecular sieves. This method solves the technical problems of difficulty in separating the catalyst and product during the reaction, as well as the existence of waste acid treatment procedures. The ZSM-5 molecular sieve catalyst can provide suitable Lewis acidic sites for intra-molecular cyclization reactions, exhibiting high selectivity and yield. After the reaction, the catalyst can be recovered through a simple filtration operation, providing a potential technical path for environmentally friendly industries.

[0006] To achieve the above objectives, the technical solution of the present invention is implemented as follows:

[0007] A method for preparing pyrazoline by catalytic internal cyclization of ketazine using ZSM-5 molecular sieve involves mixing a ketazine compound with a ZSM-5 molecular sieve catalyst and reacting the mixture to obtain the pyrazoline compound.

[0008] The structural formula of the ketone azo compound is shown below:

[0009]

[0010] The structural formula of the pyrazoline compound is shown below:

[0011] The pathway for the preparation of pyrazoline via the catalytic intracyclization of ketones using the ZSM-5 molecular sieve catalyst is shown below:

[0012]

[0013] In the formula, R represents an alkane.

[0014] The ketone azide is any one of acetone azide, 2-butanone azide, 2-pentanone azide, methyl isopropyl ketone azide, 2-hexanone azide, 3,3-dimethyl-2-butanone azide, or cyclopropylmethyl ketone azide.

[0015] The pyrazoline compounds are 3,5,5-trimethyl-2-pyrazoline, 3,5-diethyl-5-methyl-2-pyrazoline, 3,5-dipropyl-5-methyl-2-pyrazoline, 3,5-diisopropyl-5-methyl-2-pyrazoline, 3,5-dibutyl-5-methyl-2-pyrazoline, 3,5-diisobutyl-5-methyl-2-pyrazoline, and 3,5-dicyclopropyl-5-methyl-2-pyrazoline.

[0016] The silicon-aluminum ratio in the ZSM-5 molecular sieve catalyst is 30-150; preferably, the silicon-aluminum ratio is 30-70.

[0017] The ZSM-5 molecular sieve catalyst accounts for 0.5-20 wt% of the ketone azide, and the reactor filling ratio is 30%.

[0018] Preferably, the ZSM-5 molecular sieve catalyst accounts for 5-10 wt% of the ketone azo.

[0019] The reaction is carried out at a temperature of 80-250℃ for 1-12 hours.

[0020] The reaction is carried out at a temperature of 140-220℃ for 6-10 hours.

[0021] The reaction is carried out in one or more atmospheres of air, nitrogen, argon, or helium, at atmospheric pressure.

[0022] The beneficial effects of this invention are:

[0023] (1) The reaction of ketone hydrazoline preparation by the ZSM-5 molecular sieve catalyst of the present invention is a heterogeneous reaction, which is used to solve the technical problem of difficult separation of catalyst and product and easy generation of acid wastewater discharge. Moreover, the ZSM-5 molecular sieve catalyst has excellent thermal stability, high separation efficiency, easy control of surface acidity and alkalinity and excellent chemical selectivity, making it suitable for industrial scale-up. After the reaction is completed, the catalyst can be recovered by simple filtration, providing a potential technical path for environmentally friendly industry.

[0024] (2) The cyclization of ketadiazine to prepare pyrazoline is a complex tandem reaction, prone to side reactions. The target product, pyrazoline, is an unstable product in this tandem reaction. The ZSM-5 molecular sieve catalyst of this application has the characteristics of large specific surface area and abundant Lewis acid sites, which can control the reaction to proceed in the direction of pyrazoline synthesis. The ZSM-5 molecular sieve catalyst used in this application can catalyze a series of ketadiazine compounds, not just a single ketadiazine, and has universal applicability. The ZSM-5 molecular sieve catalyst has a long lifespan, which can avoid the problem of catalyst deactivation during the synthesis process. After the reaction, the ZSM-5 molecular sieve catalyst can be recycled after filtration, and the pyrazoline yield is still considerable after 8 cycles. The preparation method of this invention is a heterogeneous reaction. Compared with the traditional homogeneous acid-catalyzed cyclization of ketadiazine to prepare 2-pyrazoline derivatives, the ZSM-5 molecular sieve catalyst not only effectively catalyzes the reaction, but also reduces post-processing operations and effectively separates the products. Moreover, the target product, pyrazoline derivative, easily forms a ternary strained ring, which is a key precursor for new high-energy fuels and has great potential in industrial applications. Attached Figure Description

[0025] 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, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 XRD patterns of molecular sieves with different Si / Al ratios.

[0027] Figure 2 SEM image of ZSM-5(50).

[0028] Figure 3 This is the BET chart for ZSM-5.

[0029] Figure 4 The image shows the NH3-TPD of ZSM-5.

[0030] Figure 5 This is a diagram of the catalytic activity of ZSM-5.

[0031] Figure 6 The H spectrum of 3,5,5-trimethyl-2-pyrazoline.

[0032] Figure 7 The infrared spectrum of 3,5,5-trimethyl-2-pyrazoline. Detailed Implementation

[0033] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] Preparation of ZSM-5 molecular sieve catalyst:

[0035] A certain amount of aluminum isopropoxide, 7.7 g of tetraethyl orthosilicate, and 10 g of deionized water were stirred at 80 °C for 2 h to obtain a suspension. Then, the suspension was vigorously stirred at room temperature for 4 h, and 10.5 g of TPAOH (tetrapropylammonium hydroxide) was added dropwise to the mixture. The final molar composition of the suspension was 1.0SiO2:X Al2O3:0.349TPAOH:25H2O (X = 0.0334, 0.0557, 0.0891, 0.1447, 0.2004). Finally, the obtained precursor was poured into a 50 mL polytetrafluoroethylene-lined stainless steel autoclave and hydrothermally synthesized in a homogeneous reactor at 170 °C for 72 h. After hydrothermal crystallization, the autoclave was removed and allowed to cool naturally to room temperature. Subsequently, the sample was collected by centrifugation at 12500 rpm for 5 min, washed three times with deionized water, and then dried overnight in an 80 °C oven. After drying, the obtained sample was placed in a muffle furnace and calcined at 550℃ with a heating rate of 2℃ / min. The sample was then calcined in air for 6 hours to remove the template agent, resulting in ZSM-5 molecular sieve catalysts with silicon-to-aluminum ratios of 30, 50, 70, 110, and 150.

[0036] Figure 1 The XRD patterns of molecular sieves with different Si / Al ratios are shown. The diffraction peaks at 14.8°, 23.1°, 23.3°, 23.6°, 23.9° and 24.4° are attributed to the (301), (332), (051), (151), (303) and (133) crystal planes, respectively, corresponding to standard card PDF No. 44-0003. Figure 2 The SEM image is ZSM-5 (45-50), showing a hexagonal blocky morphology with a smooth surface. Figure 3 The BET plot shows that all curves exhibit type IV adsorption-desorption curves and type H4 hysteresis loops, proving that ZSM-5 molecular sieves exhibit mesoporous and microporous structures. Figure 4This is the NH3-TPD spectrum of ZSM-5. The signal peaks from 90-160℃ belong to NH3 adsorbed on Lewis acid sites, which are tricoordinated Al atoms within the ZSM-5 molecular sieve framework. The signal peaks from 160-280℃ belong to Lewis acid sites provided by tricoordinated Al atoms outside the ZSM-5 molecular sieve framework. The signal peaks from 340-530℃ belong to those generated by ≡Si-OH and ≡Al-OH. Acidic sites.

[0037] Example 1

[0038] A method for synthesizing pyrazoline by ketone nitrogen cyclization catalyzed by ZSM-5 molecular sieve, comprising the following steps:

[0039] 0.25 mol of 2-butanone azide was placed in a 100 mL polytetrafluoroethylene-lined container, followed by the addition of 5 wt% ZS M-5 molecular sieve catalyst with a silica-to-alumina ratio of 30. The container was then placed in a YZPR-250(M) high-pressure reactor manufactured by Shanghai Yanzheng Instrument Co., Ltd., with a stirring speed of 500 rpm. The temperature was raised to 200 °C, and the reaction was stopped and cooled after 7 h. The product was filtered and the liquid phase was collected for analysis. The solid catalyst was washed and recycled. The raw materials and products were analyzed by Agilent gas chromatography using an HP-5 column. The content of each compound was calculated using the internal standard method based on the standard curve. The obtained pyrazoline product was purified by distillation and then subjected to infrared spectroscopy and nuclear magnetic resonance spectroscopy to further confirm the compound structure. The conversion rate of 2-butanone azide was 52.84%, the selectivity of 3,5-diethyl-5-methyl-2-pyrazoline was 97.46%, and the yield was 51.50%.

[0040] Example 2

[0041] The difference from Example 1 is that the reaction time was 8 hours. Catalytic performance evaluation showed a 2-butanone azoconversion rate of 55.89%, a selectivity of 96.78% for 3,5-diethyl-5-methyl-2-pyrazoline, and a yield of 54.09%.

[0042] Example 3

[0043] The difference from Example 1 is that the amount of ZSM-5 molecular sieve catalyst with a silica-to-alumina ratio of 25-30 is 10 wt%. Catalytic performance evaluation showed a 2-butanone azoconversion rate of 59.57%, a 3,5-diethyl-5-methyl-2-pyrazoline selectivity of 96.92%, and a yield of 57.74%.

[0044] Example 4

[0045] The difference from Example 1 is that the reaction temperature was 180°C. Catalytic performance evaluation showed a 47.18% conversion of 2-butanone azohydride, a 96.37% selectivity for 3,5-diethyl-5-methyl-2-pyrazoline, and a yield of 45.47%.

[0046] Example 5

[0047] The difference from Example 1 is that the reactant ketazine was 2-pentanoneazine. Catalytic performance evaluation showed that the conversion of 2-pentanoneazine was 36.04%, the selectivity for 3,5-dipropyl-5-methyl-2-pyrazoline was 95.35%, and the yield was 34.36%.

[0048] Example 6

[0049] 0.25 mol of acetone azide was placed in a 100 mL polytetrafluoroethylene-lined container, followed by the addition of 5 wt% ZSM-5 molecular sieve catalyst with a silica-to-alumina ratio of 50. The mixture was then placed in a YZPR-250(M) high-pressure reactor manufactured by Shanghai Yanzheng Instrument Co., Ltd., with a stirring speed of 500 rpm. The temperature was raised to 200℃, and the reaction was stopped and cooled after 8 hours. The product was filtered and the liquid phase was collected for analysis. The solid catalyst was washed and recycled. The raw materials and products were analyzed by Agilent gas chromatography using an HP-5 column. The content of each compound was calculated using the internal standard method based on the standard curve. The obtained pyrazoline product was purified by distillation and then subjected to infrared spectroscopy and nuclear magnetic resonance spectroscopy to further confirm the compound structure. The conversion rate of acetone azide was 84.64%, the selectivity for 3,5,5-trimethyl-2-pyrazoline was 72.93%, and the yield was 61.73%. Figure 6 and 7 The images show the 1H and IR spectra of 3,5,5-trimethyl-2-pyrazoline, with δ = 2.27 (d, J = 1.1 Hz, 2H, CH2), 1.81 (t, J = 1.0 Hz, 3H, CH3), and 1.11 ppm (s, 6H, CH3); IR (KBr): v = 3288, 2967, 2921, 2852, 1631, 1438, 1365, 1309832 cm⁻¹. -1 .

[0050] Example 7

[0051] The difference from Example 6 is that the amount of ZSM-5 molecular sieve catalyst with a silica-to-alumina ratio of 45-50 is 10 wt%. Catalytic performance evaluation showed an acetone azoconversion rate of 85.59%, a 3,5,5-trimethyl-2-pyrazoline selectivity of 71.40%, and a yield of 61.11%.

[0052] Example 8

[0053] The difference from Example 6 is that the reaction time was 7 hours. Catalytic performance evaluation showed that the acetone azoconversion rate was 83.38%, the selectivity for 3,5,5-trimethyl-2-pyrazoline was 75.27%, and the yield was 62.76%.

[0054] Example 9

[0055] The difference from Example 6 is that the reaction temperature was 180°C. Catalytic performance evaluation showed an acetone azoconversion rate of 82.84%, a 3,5,5-trimethyl-2-pyrazoline selectivity of 97.91%, and a yield of 81.11%.

[0056] Comparative Example 1

[0057] 0.25 mol of acetone hydrazine was placed in a 100 mL polytetrafluoroethylene liner, followed by the addition of 5 wt% MCM-41 molecular sieve catalyst. The mixture was then placed in a YZPR-250(M) high-pressure reactor manufactured by Shanghai Yanzheng Instrument Co., Ltd., with the stirring speed set to 500 rpm. The temperature was raised to 180℃, and the reaction was stopped and cooled after 8 h. The product was filtered and the liquid phase was taken for analysis. The catalytic performance evaluation is shown in Table 1.

[0058] Comparative Example 2

[0059] 0.25 mol of acetone hydrazine was placed in a 100 mL polytetrafluoroethylene liner, followed by the addition of 5 wt% montmorillonite catalyst. The mixture was then placed in a YZPR-250(M) high-pressure reactor manufactured by Shanghai Yanzheng Instrument Co., Ltd., with the stirring speed set to 500 rpm. The temperature was raised to 180℃, and the reaction was stopped and cooled after 8 h. The product was filtered and the liquid phase was taken for analysis. The catalytic performance evaluation is shown in Table 1.

[0060] Comparative Example 3

[0061] 0.25 mol of acetone hydrazine was placed in a 100 mL polytetrafluoroethylene liner, followed by the addition of 5 wt% SBA-15 catalyst. The mixture was then placed in a YZPR-250(M) high-pressure reactor manufactured by Shanghai Yanzheng Instrument Co., Ltd., with the stirring speed set to 500 rpm. The temperature was raised to 180℃, and the reaction was stopped and cooled after 8 h. The product was filtered and the liquid phase was taken for analysis. The catalytic performance evaluation is shown in Table 1.

[0062] Comparative Example 4

[0063] 0.25 mol of acetone hydrazine was placed in a 100 mL polytetrafluoroethylene liner, followed by the addition of 5 wt% Y-type molecular sieve catalyst. The mixture was then placed in a YZPR-250(M) high-pressure reactor manufactured by Shanghai Yanzheng Instrument Co., Ltd., with the stirring speed set to 500 rpm. The temperature was raised to 180℃, and the reaction was stopped and cooled after 8 h. The product was filtered and the liquid phase was taken for analysis. The catalytic performance evaluation is shown in Table 1.

[0064] Table 1. Molecular sieve-catalyzed synthesis of 3,5,5-trimethyl-2-pyrazoline a

[0065]

[0066] a Reaction conditions: acetone azo (28 g, 0.25 mol), catalyst (5 wt%), 8 h, 180 °C.

[0067] b The conversion rate was determined by gas chromatography using n-heptane as an internal standard.

[0068] Example 10

[0069] The difference from Example 6 is that the reaction temperature was 220°C, and the amount of ZSM-5 molecular sieve catalyst with a silicon-to-aluminum ratio of 50 was 10 wt%. Catalytic performance evaluation showed that the acetone azoconversion rate was 86.67%, the selectivity for 3,5,5-trimethyl-2-pyrazoline was 68.89%, and the yield was 59.71%.

[0070] Example 11

[0071] The difference from Example 6 is that the reactant ketazine was selected as cyclopropylmethyl ketazine. Catalytic performance evaluation showed that the conversion rate of cyclopropylmethyl ketazine was 38.14%, the selectivity for 3,5-dicyclopropyl-5-methyl-2-pyrazoline was 94.83%, and the yield was 36.17%.

[0072] Example 12

[0073] The difference from Example 6 is that the reactant ketazine was 2-hexanone azine. Catalytic performance evaluation showed that the conversion of 2-hexanone azine was 41.57%, the selectivity for 3,5-dibutyl-5-methyl-2-pyrazoline was 93.04%, and the yield was 38.68%.

[0074] Example 13

[0075] 0.25 mol of acetone azide was placed in a 100 mL polytetrafluoroethylene-lined container, followed by the addition of 5 wt% ZSM-5 molecular sieve catalyst with a silica-to-alumina ratio of 70. The mixture was then placed in a YZPR-250(M) high-pressure reactor manufactured by Shanghai Yanzheng Instrument Co., Ltd., with a stirring speed of 500 rpm. The temperature was raised to 160℃, and the reaction was stopped and cooled after 8 hours. The product was filtered and the liquid phase was collected for analysis. The solid catalyst was washed and recycled. The raw materials and products were analyzed by Agilent gas chromatography using an HP-5 column. The content of each compound was calculated using the internal standard method based on the standard curve. The obtained pyrazoline product was purified by distillation and then subjected to infrared spectroscopy and nuclear magnetic resonance spectroscopy to further confirm the compound structure. The conversion rate of acetone azide was 57.93%, the selectivity for 3,5,5-trimethyl-2-pyrazoline was 97.63%, and the yield was 56.56%.

[0076] Example 14

[0077] The difference from Example 13 is that the reactant ketazine was 2-butanone azine. Catalytic performance evaluation showed that the conversion of 2-butanone azine was 34.68%, the selectivity for 3,5-diethyl-5-methyl-2-pyrazoline was 95.84%, and the yield was 33.24%.

[0078] Example 15

[0079] The difference from Example 13 is that the reaction temperature was 180°C, the catalyst was ZSM-5 molecular sieve with a silica-to-alumina ratio of 110, and the amount of catalyst used was 10 wt%. Catalytic performance evaluation showed that the acetone azoconversion rate was 52.64%, the selectivity for 3,5,5-trimethyl-2-pyrazoline was 96.16%, and the yield was 50.62%.

[0080] Example 16

[0081] The difference from Example 15 is that the reactant ketazine was 2-pentanoneazine. Catalytic performance evaluation showed that the conversion of 2-pentanoneazine was 29.81%, the selectivity for 3,5-dipropyl-5-methyl-2-pyrazoline was 94.25%, and the yield was 28.10%.

[0082] Example 17

[0083] The difference from Example 13 is that the reaction temperature was 180°C, the reaction time was 9 h, and the catalyst was a ZSM-5 molecular sieve catalyst with a silicon-to-aluminum ratio of 150. Catalytic performance evaluation showed that the acetone azoconversion rate was 47.84%, the selectivity for 3,5,5-trimethyl-2-pyrazoline was 96.31%, and the yield was 46.07%.

[0084] Example 18

[0085] The difference from Example 17 is that the reactant ketazine was selected as methyl isopropyl ketazine, and the reaction temperature was 200°C. Catalytic performance evaluation showed that the conversion rate of methyl isopropyl ketazine was 22.69%, the selectivity for 3,5-diisopropyl-5-methyl-2-pyrazoline was 95.42%, and the yield was 21.65%.

[0086] Example 19

[0087] The difference from Example 9 is that the catalyst is a ZSM-5 molecular sieve with a silica-to-alumina ratio of 30, and the catalytic activity is shown in [reference needed]. Figure 5 .

[0088] Example 20

[0089] The difference from Example 9 is that the catalyst is a ZSM-5 molecular sieve with a silica-to-alumina ratio of 70, and the catalytic activity is shown in [reference needed]. Figure 5 .

[0090] Example 21

[0091] The difference from Example 9 is that the catalyst is a ZSM-5 molecular sieve with a silica-to-alumina ratio of 110, and the catalytic activity is shown in [reference needed]. Figure 5 .

[0092] Example 22

[0093] The difference from Example 9 is that the catalyst is a ZSM-5 molecular sieve with a silica-to-alumina ratio of 150, and the catalytic activity is shown in [reference needed]. Figure 5 .

[0094] Figure 5 The graph shows the catalytic activity of ZSM-5, with the horizontal axis corresponding to Examples 19, 9, 20, 21, and 22, respectively. The selectivity for the preparation of 2-pyrazoline from acetone hydrazoline via molecular sieve catalysis is close to 100%, and the highest conversion rate for pyrazoline preparation from acetone hydrazoline reaches 82.8%.

[0095] Catalyst recycling times

[0096] The ZSM-5 molecular sieve catalyst in Example 9 was filtered after reaction, and the solid was washed 2-3 times with anhydrous ethanol and dried in a forced-air drying oven at 60°C for 12 hours to obtain a reusable ZSM-5 molecular sieve catalyst. After being reused 8 times, it still exhibited high catalytic activity, with a yield of 67.38% for 3,5,5-trimethyl-2-pyrazoline.

[0097] Table 2 Effect of catalyst cycle number on acetone pyrazoline yield

[0098] Loop count 2 4 6 8 yield 82.84％ 77.30％ 71.80％ 67.38％

[0099] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. 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 pyrazoline by catalytic intracyclization of ketones using ZSM-5 molecular sieve, characterized in that, The ketazine compound was reacted with a ZSM-5 molecular sieve catalyst to obtain a pyrazoline compound. The ketone azide is any one of acetone azide, 2-butanone azide, 2-pentanone azide, methyl isopropyl ketone azide, 2-hexanone azide, 3,3-dimethyl-2-butanone azide or cyclopropylmethyl ketone azide; The pyrazoline compound is 3,5,5-trimethyl-2-pyrazoline, 3,5-diethyl-5-methyl-2-pyrazoline, 3,5-dipropyl-5-methyl-2-pyrazoline, 3,5-diisopropyl-5-methyl-2-pyrazoline, 3,5-dibutyl-5-methyl-2-pyrazoline, 3,5-diisobutyl-5-methyl-2-pyrazoline, or 3,5-dicyclopropyl-5-methyl-2-pyrazoline; The silicon-aluminum ratio in the ZSM-5 molecular sieve catalyst is 30-150; The ZSM-5 molecular sieve catalyst accounts for 0.5-20 wt% of the ketazine.

2. The method for preparing pyrazoline by catalytic ketone azobination using ZSM-5 molecular sieve according to claim 1, characterized in that, The ZSM-5 molecular sieve catalyst accounts for 5-10 wt% of the ketazine.

3. The method for preparing pyrazoline by catalytic ketone azobination using ZSM-5 molecular sieve according to claim 1, characterized in that: The reaction is carried out at a temperature of 80-250 °C for 1-12 h.

4. The method for preparing pyrazoline by catalytic ketone azobination using ZSM-5 molecular sieve according to claim 3, characterized in that, The reaction is carried out at a temperature of 140-220 °C for 6-10 h.

5. The method for preparing pyrazoline by catalytic ketone azobination using ZSM-5 molecular sieve according to claim 4, characterized in that: The reaction is carried out in one or more atmospheres of air, nitrogen, argon, or helium, at atmospheric pressure.

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