Method for preparing 1-(4-chlorphenyl)-3-pyrazole alcohol through air oxidation

Abstract

A method for preparing 1-(4-chlorphenyl)-3-pyrazole alcohol through air oxidation is characterized in that a eutectic solvent is adopted as a solvent and a catalyst, air oxidation reaction of 1-(4-chlorphenyl) pyrazolidine-3-ketone is dissolved and catalyzed to prepare the 1-(4-chlorphenyl)-3-pyrazole alcohol, the mass ratio of the 1-(4-chlorphenyl) pyrazolidine-3-ketone to the eutectic solvent is (1: 20)-(1: 10), and the mass ratio of the 1-(4-chlorphenyl) pyrazolidine-3-ketone to the eutectic solvent is (1: 20)-(1: 10). The method comprises the following steps of: reacting 1-(4-chlorphenyl)-3-pyrazole alcohol for 3-6 hours at the air flow velocity of 10-40L / min at the reaction temperature of 40-70 DEG C, after the reaction is finished, extracting the product 1-(4-chlorphenyl)-3-pyrazole alcohol for three times by using an extracting agent with the same volume as a reaction mixture, combining extracting solutions, and recovering the extracting agent through reduced pressure distillation to obtain the product 1-(4-chlorphenyl)-3-pyrazole alcohol, the yield is 98.2-99.4%, the purity is 98.7-99.5%, the raffinate is a eutectic solvent, and the method is suitable for industrial production. The direct recycling can be realized. The method has the characteristics of mild reaction conditions, simplicity and convenience in operation and high product yield; the eutectic solvent has dual functions of a solvent and a catalyst, can dissolve reaction raw materials and can provide a catalytic active center for the reaction, and the reaction efficiency is improved through the synergistic effect of the solvent and the catalyst; the eutectic solvent is easy to separate from the product, and the active center is not lost and can be repeatedly used.

Description

Technical Field

[0001] The invention relates to the field of fine organic synthesis, and in particular to a method for preparing 1-(4-chlorophenyl)-3-pyrazolol by using a low eutectic solvent as a solvent and a catalyst to dissolve and catalyze the air oxidation reaction of 1-(4-chlorophenyl)pyrazolidine-3-one. Background Art

[0002] Pyraclostrobin is a new type of methoxyacrylate fungicide with low toxicity, low residue, safety to non-target organisms, small dosage and environmental friendliness. 1-(4-chlorophenyl)-3-pyrazolol is a key intermediate in the preparation of pyraclostrobin. It is currently prepared by hydrogen peroxide oxidation, which has the disadvantages of large amount of hydrogen peroxide, high hazard, large amount of wastewater, and inorganic ions in the wastewater are mixed salts, which makes it impossible to prepare high-content by-product salts and difficult to recycle, becoming a bottleneck restricting the production of pyraclostrobin. It can be seen that the optimization of its preparation method is crucial to improving the efficiency of the entire production process and product quality.

[0003] Air is a clean and cheap oxidant. The use of catalytic air to oxidize 1-(4-chlorophenyl)pyrazolidine-3-one to prepare 1-(4-chlorophenyl)-3-pyrazolol can avoid the safety hazards caused by hydrogen peroxide as an oxidant, increase the yield of 1-(4-chlorophenyl)-3-pyrazolol, reduce raw material costs, improve economic benefits, reduce wastewater generation, and achieve clean production. At present, the catalytic air oxidation of 1-(4-chlorophenyl)pyrazolidin-3-one to prepare 1-(4-chlorophenyl)-3-pyrazolol is mostly carried out in alkaline solution. The reason is that the raw material 1-(4-chlorophenyl)pyrazolidin-3-one is soluble in alkaline solution. The oxidation reaction of 1-(4-chlorophenyl)pyrazolidin-3-one is realized in a homogeneous system. This technology has the disadvantages of large alkali consumption and the need for neutralization with acidic substances after the reaction. In addition, under acidic conditions, the product 1-(4-chlorophenyl)-3-pyrazolol is very prone to dehydration side reactions, resulting in low product yield, poor quality, and a large amount of salt-containing wastewater discharge.

[0004] A low eutectic solvent is a green and environmentally friendly solvent or catalyst, which is characterized by easy acquisition of the required raw materials, a simple preparation process, and properties that can be adjusted as needed. In addition, the low eutectic solvent is easy to separate and recover from the reaction system and has good reusability. Therefore, the present invention applies for a method for preparing 1-(4-chlorophenyl)-3-pyrazolol by air oxidation, that is, a method for preparing 1-(4-chlorophenyl)-3-pyrazolol by using a low eutectic solvent as a solvent and a catalyst to dissolve and catalyze the air oxidation reaction of 1-(4-chlorophenyl)pyrazolidine-3-one. In the reaction of preparing 1-(4-chlorophenyl)-3-pyrazolol by air oxidation of 1-(4-chlorophenyl)-pyrazolidine-3-one, the low eutectic solvent can directly dissolve the raw material 1-(4-chlorophenyl)-pyrazolidine-3-one, which is convenient for realizing the rapid oxidation of the raw material in a homogeneous system. At the same time, the metal active sites in the low eutectic solvent are more likely to contact with the raw material in a homogeneous system, providing more reaction sites for the oxidation reaction. The synergistic effect of the two improves the efficiency of the reaction; in addition, the low eutectic solvent is easy to separate from the product after the reaction and can be reused. The present invention has important academic significance and potential application prospects for the technical innovation of the green production process of 1-(4-chlorophenyl)-3-pyrazolol. Summary of the invention

[0005] The purpose of the present invention is to replace the preparation method of 1-(4-chlorophenyl)-3-pyrazolol in the traditional oxidant hydrogen peroxide system, develop a method for preparing 1-(4-chlorophenyl)-3-pyrazolol by oxidation under mild reaction conditions using air as an oxidant, and solve the problems of consuming a large amount of reducing agent to reduce excess hydrogen peroxide after the reaction of the traditional oxidant hydrogen peroxide system, large amount of wastewater discharge, and inability to reuse the catalyst.

[0006] A method for preparing 1-(4-chlorophenyl)-3-pyrazolol by air oxidation, characterized in that a low eutectic solvent is used as a solvent and a catalyst to dissolve and catalyze the air oxidation reaction of 1-(4-chlorophenyl)pyrazolidine-3-one to prepare 1-(4-chlorophenyl)-3-pyrazolol, the mass ratio of 1-(4-chlorophenyl)pyrazolidine-3-one to the low eutectic solvent is 20:1-10:1, the air flow rate is 10-40 L / min, the reaction temperature is 40-70°C, the reaction time is 3-6 hours, and after the reaction is completed, the product 1-(4-chlorophenyl)-3-pyrazolol is extracted three times using an extractant with an equal volume to the reaction mixture, and the extracted products are combined. After taking the liquid and recovering the extractant by vacuum distillation, the product 1-(4-chlorophenyl)-3-pyrazolol is obtained, and the yield is 98.2% to 99.4%, the purity is 98.7% to 99.5%, and the raffinate is a low eutectic solvent, which can be directly recycled. The preparation method of the low eutectic solvent is to use ferric chloride, ferrous chloride, manganese acetate, cobalt chloride or cobalt acetate as a hydrogen bond acceptor, urea, glycerol, ethylene glycol or choline chloride as a hydrogen bond donor, and react at 60 to 80° C. for 4 to 6 hours under the condition that the molar ratio of the hydrogen bond acceptor to the hydrogen bond donor is 2:1 to 1:2; the extractant is one of acetone, methyl isobutyl ketone or tetrahydrofuran.

[0007] The present invention solves this technical problem through the following technical solutions:

[0008] The specific technical scheme is illustrated by taking a low eutectic solvent prepared by using cobalt acetate as a hydrogen bond acceptor and ethylene glycol (EG) as a hydrogen bond donor in a molar ratio of 1:1 as an example, in which the catalyst is named [(CH3COO)2Co][EG], and the naming method of other low eutectic solvents is similar.

[0009] 0.1 mol (CH3COO)2Co and 0.1 mol EG were reacted at 70°C for 5 h to obtain [(CH3COO)2Co][EG].

[0010] Put [(CH3COO)2Co][EG]15g and 1g of 1-(4-chlorophenyl)pyrazolidin-3-one into a reactor equipped with a magnetic stirrer, a thermometer and a gas distributor. When the materials in the reactor are heated to 60°C, air is introduced at a flow rate of 20L / min, and the reaction is stirred and kept warm for 4 hours. After the reaction, the reactor is quickly cooled to room temperature in a water bath, and the product 1-(4-chlorophenyl)-3-pyrazolol is extracted three times with an extractant methyl isobutyl ketone in an amount equal to the volume of the reaction mixture. The extracts are combined and the extractant is recovered by vacuum distillation to obtain the product 1-(4-chlorophenyl)-3-pyrazolol with a yield of 99.4% and a purity of 99.5%. The raffinate is a low eutectic solvent and can be directly recycled.

[0011] Compared with the traditional method, the present invention has the following characteristics:

[0012] 1. Mild reaction conditions, simple operation and high product yield.

[0013] 2. Low eutectic solvents can dissolve the reaction raw materials and provide catalytic active centers for the reaction. The synergistic effect of the two improves the efficiency of the reaction.

[0014] 3. The low eutectic solvent is easy to separate from the product, the active center is not lost and it can be reused. Specific implementation methods

[0016] The method of the present invention is further described below in conjunction with embodiments, which are not intended to limit the present invention.

[0017] Example 1: 0.1 mol (CH3COO)2Co and 0.1 mol ethylene glycol (EG) were reacted at 70°C for 5 h to obtain [(CH3COO)2Co][EG].

[0018] [(CH3COO)2Co][EG]10g and 1g of 1-(4-chlorophenyl)pyrazolidin-3-one were put into a reactor equipped with a magnetic stirrer, a thermometer and a gas distributor. When the materials in the reactor were heated to 60°C, air was introduced at a flow rate of 10L / min, and the reaction was stirred and kept warm for 4 hours. After the reaction, the reactor was quickly cooled to room temperature in a water bath, and the product 1-(4-chlorophenyl)-3-pyrazolol was extracted 3 times with an extractant methyl isobutyl ketone in an amount equal to the volume of the reaction mixture. The extracts were combined and the extractant was recovered by vacuum distillation to obtain the product 1-(4-chlorophenyl)-3-pyrazolol with a yield of 99.4% and a purity of 99.5%. The raffinate was a low eutectic solvent and could be directly recycled.

[0019] Comparative Example 1: This comparative example provides a method for preparing 1-(4-chlorophenyl)-3-pyrazolol. The difference between the comparative example and the embodiment is that the comparative example does not use a low eutectic solvent as a solvent and a catalyst, but uses formic acid as a solvent and ferric chloride as a catalyst. The specific amounts are as follows: 90 g of formic acid is added to a reactor, and 20 g of 1-(4-chlorophenyl)pyrazolidine-3-one and 1.6 g of ferric chloride are added under stirring. The temperature is raised to 90°C and air is passed to react. After 6 hours, most of the solvent is removed under reduced pressure, water is added and stirred, a large amount of product is precipitated, and the pH value is adjusted to 5 with sodium hydroxide solution. Stirring is continued for 1 hour, and 19.68 g of 1-(4-chlorophenyl)-3-pyrazolol is obtained by filtration. The product yield is 96.3% and the purity is 98.6%. The synthetic route of the comparative example is consistent with that of the embodiment.

[0020] Comparative Example 2: In this comparative example, only the hydrogen bond acceptor (CH3COO)2Co was added. 20g of (CH3COO)2Co and 1g of 1-(4-chlorophenyl)pyrazolidin-3-one were put into a reaction kettle equipped with a magnetic stirrer, a thermometer and a gas distributor. It was found that both were solid at room temperature. When the materials in the kettle were heated to 60°C, it was found that both were still solid and no reaction occurred.

[0021] Comparative Example 3: In this comparative example, only hydrogen bond donor EG was added, and 20 g of EG and 1 g of 1-(4-chlorophenyl)pyrazolidine-3-one were put into a reaction kettle equipped with a magnetic stirrer, a thermometer and a gas distributor. It was found that 1-(4-chlorophenyl)pyrazolidine-3-one could not be dissolved in EG; when the materials in the kettle were heated to 60°C, it was found that 1-(4-chlorophenyl)pyrazolidine-3-one could not be dissolved in EG; air was introduced at a flow rate of 10 L / min, and the reaction was stirred and kept warm for 4 hours. After the reaction was completed, the solid was basically not reduced, and liquid chromatography analysis showed that no reaction occurred.

[0022] Example 2: 0.1 mol (CH3COO)2Co and 0.2 mol EG were reacted at 60°C for 6 h to obtain [(CH3COO)2Co][EG]2.

[0023] 215 g of [(CH3COO)2Co][EG] and 1 g of 1-(4-chlorophenyl)pyrazolidin-3-one were put into a reactor equipped with a magnetic stirrer, a thermometer and a gas distributor. When the materials in the reactor were heated to 40°C, air was introduced at a flow rate of 20 L / min, and the reaction was stirred and kept warm for 3 hours. After the reaction, the reactor was quickly cooled to room temperature in a water bath, and the product 1-(4-chlorophenyl)-3-pyrazolol was extracted 3 times with an extractant of methyl isobutyl ketone in an amount equal to the volume of the reaction mixture. The extracts were combined and the extractant was recovered by vacuum distillation to obtain the product 1-(4-chlorophenyl)-3-pyrazolol with a yield of 99.3% and a purity of 99.1%. The raffinate was a low eutectic solvent and could be directly recycled.

[0024] Example 3: 0.2 mol (CH3COO)2Co and 0.1 mol EG were reacted at 80°C for 4 h to obtain [(CH3COO)2Co]2[EG].

[0025] [(CH3COO)2Co]2[EG]15g and 1g of 1-(4-chlorophenyl)pyrazolidin-3-one were put into a reactor equipped with a magnetic stirrer, a thermometer and a gas distributor. When the materials in the reactor were heated to 50°C, air was introduced at a flow rate of 30L / min, and the reaction was stirred and kept warm for 5 hours. After the reaction, the reactor was quickly cooled to room temperature in a water bath, and the product 1-(4-chlorophenyl)-3-pyrazolol was extracted 3 times with an extractant acetone having an equal volume to the reaction mixture. The extracts were combined and the extractant was recovered by vacuum distillation to obtain the product 1-(4-chlorophenyl)-3-pyrazolol with a yield of 99.0% and a purity of 99.0%. The raffinate was a low eutectic solvent and could be directly recycled.

[0026] Example 4: 0.1 mol CoCl2 and 0.1 mol EG were reacted at 70°C for 5 h to obtain [CoCl2][EG].

[0027] Put 20g of [CoCl2][EG] and 1g of 1-(4-chlorophenyl)pyrazolidin-3-one into a reactor equipped with a magnetic stirrer, a thermometer and a gas distributor. When the materials in the reactor are heated to 70°C, air is introduced at a flow rate of 40L / min, and the reaction is stirred and kept warm for 6 hours. After the reaction, the reactor is quickly cooled to room temperature in a water bath, and the product 1-(4-chlorophenyl)-3-pyrazolol is extracted 3 times with an extractant of tetrahydrofuran equal to the volume of the reaction mixture. The extracts are combined and the extractant is recovered by vacuum distillation to obtain the product 1-(4-chlorophenyl)-3-pyrazolol with a yield of 99.1% and a purity of 99.0%. The raffinate is a low eutectic solvent and can be directly recycled.

[0028] Example 5: 0.1 mol CoCl2 and 0.2 mol glycerol (Glycerin) were reacted at 60°C for 6 h to obtain [CoCl2][Glycerin]2.

[0029] 210 g of [CoCl2][Glycerin] and 1 g of 1-(4-chlorophenyl)pyrazolidine-3-one were put into a reactor equipped with a magnetic stirrer, a thermometer and a gas distributor. When the materials in the reactor were heated to 70°C, air was introduced at a flow rate of 40 L / min, and the reaction was stirred and kept warm for 3 hours. After the reaction, the reactor was quickly cooled to room temperature in a water bath, and the product 1-(4-chlorophenyl)-3-pyrazolol was extracted 3 times with an extractant acetone having an equal volume to the reaction mixture. The extracts were combined and the extractant was recovered by vacuum distillation to obtain the product 1-(4-chlorophenyl)-3-pyrazolol with a yield of 98.5% and a purity of 98.9%. The raffinate was a low eutectic solvent and could be directly recycled.

[0030] Example 6: 0.2 mol (CH3COO)2Mn and 0.1 mol urea (Urea) were reacted at 80°C for 4 h to obtain [(CH3COO)2Mn]2[Urea].

[0031] [(CH3COO)2Mn]2[Urea]15g and 1g of 1-(4-chlorophenyl)pyrazolidin-3-one were put into a reactor equipped with a magnetic stirrer, a thermometer and a gas distributor. When the materials in the reactor were heated to 60°C, air was introduced at a flow rate of 30L / min, and the reaction was stirred and kept warm for 4 hours. After the reaction, the reactor was quickly cooled to room temperature in a water bath, and the product 1-(4-chlorophenyl)-3-pyrazolol was extracted 3 times with an extractant methyl isobutyl ketone in an amount equal to the volume of the reaction mixture. The extracts were combined and the extractant was recovered by vacuum distillation to obtain the product 1-(4-chlorophenyl)-3-pyrazolol with a yield of 98.6% and a purity of 98.9%. The raffinate was a low eutectic solvent and could be directly recycled.

[0032] Example 7: 0.1 mol (CH3COO)2Mn and 0.1 mol choline chloride (ChCl) were reacted at 70°C for 5 h to obtain [(CH3COO)2Mn][ChCl].

[0033] [(CH3COO)2Mn][ChCl]15g and 1g of 1-(4-chlorophenyl)pyrazolidin-3-one were put into a reactor equipped with a magnetic stirrer, a thermometer and a gas distributor. When the materials in the reactor were heated to 50°C, air was introduced at a flow rate of 20L / min, and the reaction was stirred and kept warm for 5 hours. After the reaction, the reactor was quickly cooled to room temperature in a water bath, and the product 1-(4-chlorophenyl)-3-pyrazolol was extracted 3 times with an extractant methyl isobutyl ketone in an amount equal to the volume of the reaction mixture. The extracts were combined and the extractant was recovered by vacuum distillation to obtain the product 1-(4-chlorophenyl)-3-pyrazolol with a yield of 99.0% and a purity of 99.0%. The raffinate was a low eutectic solvent and could be directly recycled.

[0034] Example 8: 0.1 mol FeCl2 and 0.2 mol glycerol (Glycerin) were reacted at 60°C for 6 h to obtain [FeCl2][Glycerin]2.

[0035] 220 g of [FeCl2][Glycerin] and 1 g of 1-(4-chlorophenyl)pyrazolidin-3-one were put into a reactor equipped with a magnetic stirrer, a thermometer and a gas distributor. When the materials in the reactor were heated to 40°C, air was introduced at a flow rate of 10 L / min, and the reaction was stirred and kept warm for 6 hours. After the reaction, the reactor was quickly cooled to room temperature in a water bath, and the product 1-(4-chlorophenyl)-3-pyrazolol was extracted 3 times with an extractant of tetrahydrofuran equal to the volume of the reaction mixture. The extracts were combined and the extractant was recovered by vacuum distillation to obtain the product 1-(4-chlorophenyl)-3-pyrazolol with a yield of 98.6% and a purity of 98.9%. The raffinate was a low eutectic solvent and could be directly recycled.

[0036] Example 9: 0.2 mol FeCl2 and 0.1 mol urea (Urea) were reacted at 80°C for 4 h to obtain [FeCl2]2[Urea].

[0037] [FeCl2]2[Urea]10g and 1-(4-chlorophenyl)pyrazolidin-3-one1g were put into a reactor equipped with a magnetic stirrer, a thermometer and a gas distributor. When the materials in the reactor were heated to 40°C, air was introduced at a flow rate of 30L / min, and the reaction was stirred and kept warm for 6 hours. After the reaction, the reactor was quickly cooled to room temperature in a water bath, and the product 1-(4-chlorophenyl)-3-pyrazolol was extracted 3 times with an extractant of tetrahydrofuran equal to the volume of the reaction mixture. The extracts were combined and the extractant was recovered by vacuum distillation to obtain the product 1-(4-chlorophenyl)-3-pyrazolol with a yield of 99.1% and a purity of 99.0%. The raffinate was a low eutectic solvent and could be directly recycled.

[0038] Example 10: 0.1 mol FeCl3 and 0.1 mol choline chloride (ChCl) were reacted at 70°C for 5 h to prepare [FeCl3][ChCl].

[0039] Put [FeCl3][ChCl]15g and 1g of 1-(4-chlorophenyl)pyrazolidin-3-one into a reactor equipped with a magnetic stirrer, a thermometer and a gas distributor. When the materials in the reactor are heated to 50°C, air is introduced at a flow rate of 10L / min, and the reaction is stirred and kept warm for 5 hours. After the reaction, the reactor is quickly cooled to room temperature in a water bath, and the product 1-(4-chlorophenyl)-3-pyrazolol is extracted three times with an extractant methyl isobutyl ketone in an amount equal to the volume of the reaction mixture. The extracts are combined and the extractant is recovered by reduced pressure distillation to obtain the product 1-(4-chlorophenyl)-3-pyrazolol with a yield of 99.1% and a purity of 98.6%. The raffinate is a low eutectic solvent and can be directly recycled.

[0040] Example 11: 0.1 mol FeCl3 and 0.2 mol glycerol (Glycerin) were reacted at 60°C for 6 h to obtain [FeCl3][Glycerin]2.

[0041] 215 g of [FeCl3][Glycerin] and 1 g of 1-(4-chlorophenyl)pyrazolidine-3-one were put into a reactor equipped with a magnetic stirrer, a thermometer and a gas distributor. When the materials in the reactor were heated to 60°C, air was introduced at a flow rate of 40 L / min, and the reaction was stirred and kept warm for 4 hours. After the reaction, the reactor was quickly cooled to room temperature in a water bath, and the product 1-(4-chlorophenyl)-3-pyrazolol was extracted 3 times with an extractant acetone having an equal volume to the reaction mixture. The extracts were combined and the extractant was recovered by vacuum distillation to obtain the product 1-(4-chlorophenyl)-3-pyrazolol with a yield of 98.9% and a purity of 99.0%. The raffinate was a low eutectic solvent and could be directly recycled.

[0042] Example 12: 0.2 mol FeCl3 and 0.1 mol urea (Urea) were reacted at 80°C for 4 h to obtain [FeCl3]2[Urea].

[0043] 20 g of [FeCl3]2[Urea] and 1 g of 1-(4-chlorophenyl)pyrazolidin-3-one were put into a reactor equipped with a magnetic stirrer, a thermometer and a gas distributor. When the materials in the reactor were heated to 70°C, air was introduced at a flow rate of 20 L / min, and the reaction was stirred and kept warm for 3 hours. After the reaction, the reactor was quickly cooled to room temperature in a water bath, and the product 1-(4-chlorophenyl)-3-pyrazolol was extracted 3 times with an extractant methyl isobutyl ketone in an amount equal to the volume of the reaction mixture. The extracts were combined and the extractant was recovered by reduced pressure distillation to obtain the product 1-(4-chlorophenyl)-3-pyrazolol with a yield of 99.0% and a purity of 98.9%. The raffinate was a low eutectic solvent and could be directly recycled.

[0044] Example 13: The [(CH3COO)2Co][EG] low eutectic solvent recovered in Example 1 was directly used for recycling. 10 g of [(CH3COO)2Co][EG] and 1 g of 1-(4-chlorophenyl)pyrazolidin-3-one were put into a reactor equipped with a magnetic stirrer, a thermometer and a gas distributor. When the materials in the reactor were heated to 60°C, air was introduced at a flow rate of 10 L / min, and the reaction was stirred and kept warm for 4 hours. After the reaction was completed, the reactor was quickly cooled to room temperature in a water bath. The product 1-(4-chlorophenyl)-3-pyrazolol was extracted three times with methyl isobutyl ketone in an amount equal to the volume of the reaction mixture. The extracts were combined and the extract was distilled under reduced pressure to recover the extract, thereby obtaining the product 1-(4-chlorophenyl)-3-pyrazolol. After [(CH3COO)2Co][EG] was used repeatedly for 5 times, the yield of the obtained product was 99.1% and the purity was 99.2%. After [(CH3COO)2Co][EG] was used repeatedly for 10 times, the yield of the obtained product was 98.8% and the purity was 99.0%.

[0045] Example 14: The [(CH3COO)2Co][EG]2 low eutectic solvent recovered in Example 2 was directly used for recycling. [(CH3COO)2Co][EG]215g and 1g of 1-(4-chlorophenyl)pyrazolidin-3-one were put into a reactor equipped with a magnetic stirrer, a thermometer and a gas distributor. When the materials in the reactor were heated to 40°C, air was introduced at a flow rate of 20L / min, and the reaction was stirred and kept warm for 3h. After the reaction was completed, the reactor was quickly cooled to room temperature in a water bath. The product 1-(4-chlorophenyl)-3-pyrazolol was extracted three times with methyl isobutyl ketone in an amount equal to the volume of the reaction mixture. The extracts were combined and the extract was distilled under reduced pressure to recover the extract, thereby obtaining the product 1-(4-chlorophenyl)-3-pyrazolol. After [(CH3COO)2Co][EG]2 was used repeatedly for 5 times, the yield of the obtained product was 99.1% and the purity was 99.0%. After [(CH3COO)2Co][EG]2 was used repeatedly for 10 times, the yield of the obtained product was 98.8% and the purity was 98.7%.

Claims

1. A method for preparing 1-(4-chlorophenyl)-3-pyrazolol by air oxidation, characterized in that A low eutectic solvent is used as a solvent and a catalyst to dissolve and catalyze the air oxidation reaction of 1-(4-chlorophenyl)pyrazolidine-3-one to prepare 1-(4-chlorophenyl)-3-pyrazolol, the mass ratio of 1-(4-chlorophenyl)pyrazolidine-3-one to the low eutectic solvent is 1:20-1:10, the air flow rate is 10-40 L / min, the reaction temperature is 40-70°C, the reaction time is 3-6h, and after the reaction is completed, the product 1-(4-chlorophenyl)-3-pyrazolol is extracted 3 times with an extractant having an equal volume to the reaction mixture, and the extracts are combined and the extractant is recovered by vacuum distillation to obtain the product The product 1-(4-chlorophenyl)-3-pyrazolol has a product yield of 98.2% to 99.4% and a purity of 98.7% to 99.5%. The raffinate is a low eutectic solvent and can be directly recycled. The preparation method of the low eutectic solvent is to use ferric chloride, ferrous chloride, manganese acetate, cobalt chloride or cobalt acetate as a hydrogen bond acceptor, urea, glycerol, ethylene glycol or choline chloride as a hydrogen bond donor, and react at 60 to 80° C. for 4 to 6 hours under the condition that the molar ratio of the hydrogen bond acceptor to the hydrogen bond donor is 2:1 to 1:2; the extractant is one of acetone, methyl isobutyl ketone or tetrahydrofuran.