Preparation method of 2-hydroxy-5-trifluoromethylpyridine

Abstract

The invention provides a preparation method of 2-hydroxy-5-trifluoromethylpyridine, which specifically comprises the following steps: S101, preparing raw materials; s102, heating and mixing the raw materials; s103, carrying out normal-pressure heat preservation reaction; s104, centrifuging the primary product material; s105, adding an alkaline raw material for neutralization; s106, adding water into the primary finished product, and centrifuging; and S107, drying and obtaining a finished product. Through gradient heating control, decomposition or polymerization byproducts caused by local overheating are avoided; the product purity is excellent, the pH is accurately regulated and controlled, three-stage centrifugal purification is combined, unreacted raw materials, acidic by-products and inorganic salts are effectively removed, and the strict requirements of medical intermediates on key impurities are met; pigment impurities with poor thermal stability can be specifically removed by utilizing a hot water recrystallization step, and the product appearance reaches white crystals which are superior to faint yellow solids obtained by a conventional method; the method is mild in reaction condition, low in equipment requirement and suitable for large-scale production, especially low-temperature vacuum drying and VOCs emission reduction, and meets the green chemical requirement.

Description

Technical Field

[0001] This invention belongs to the field of pesticide intermediate technology, and particularly relates to a method for preparing 2-hydroxy-5-trifluoromethylpyridine. Background Technology

[0002] Currently, 2-hydroxy-5-trifluoromethylpyridine, as one of the novel organic intermediates for fluorinated pesticides and pharmaceuticals, enjoys widespread market demand. Pyridine compounds are among the most extensively studied heterocyclic compounds. Due to their reactive chemical properties and excellent binding and degradation performance in organisms, pyridine heterocyclic compounds have been widely used as intermediates or end products in pesticides, pharmaceuticals, dyes, rubber, and other fields.

[0003] In recent years, fluorinated pesticides have been a very active research hotspot. Because fluorine atoms possess mimicry, electronic, hindrance, and osmotic effects in organisms, introducing fluorine atoms into compounds can potentially produce better biological activity. Based on this, many new pesticides have been developed. Therefore, research on the synthetic preparation process of trifluoromethylpyridines has significant practical implications. 2-Hydroxy-5-trifluoromethylpyridine, as an important pharmaceutical and pesticide intermediate, is a crucial raw material for the synthesis of quizalofop-P-ethyl herbicides.

[0004] However, existing methods for preparing 2-hydroxy-5-trifluoromethylpyridine have drawbacks, such as generating large amounts of wastewater, complex operation, and low safety factor, making them unsuitable for industrial production.

[0005] Therefore, it is essential to invent a method for preparing 2-hydroxy-5-trifluoromethylpyridine. Summary of the Invention

[0006] To address the aforementioned technical problems, a method for preparing 2-hydroxy-5-trifluoromethylpyridine by reacting 2-chloro-5-trifluoromethylpyridine and inorganic acid as raw materials is proposed. Compared with traditional production processes, this invention avoids the neutralization process of sodium 2-hydroxy-5-trifluoromethylpyridine, generates less wastewater, is simple to operate, has a high safety factor, low cost, and less pollution, making it suitable for industrial production.

[0007] This invention provides a method for preparing 2-hydroxy-5-trifluoromethylpyridine. The reaction equation for the formation of 2-hydroxy-5-trifluoromethylpyridine from 2-chloro-5-trifluoromethylpyridine by reacting it with an inorganic acid is as follows: Figure 1 As shown:

[0008] Specifically, the following steps are included:

[0009] Step 1: Raw material preparation;

[0010] Step 2: Heating and mixing of raw materials;

[0011] Step 3: Reactions under normal pressure and heat preservation;

[0012] Step 4: Centrifugation of the initial product;

[0013] Step 5: Add alkaline ingredients to neutralize;

[0014] Step Six: Add water and centrifuge the preliminary finished product;

[0015] Step 7: Drying and obtaining the finished product.

[0016] Preferably, step one: raw material preparation: prepare qualified 2-chloro-5-trifluoromethylpyridine and inorganic acid raw materials according to the molar ratio, and select them for later use.

[0017] Preferably, step two: heating and mixing of raw materials: 2-chloro-5-trifluoromethylpyridine and inorganic acid raw materials from step one are added to a reaction vessel, stirred and mixed, and heated. Nitrogen gas is introduced for protection during the heating process.

[0018] Preferably, step three: atmospheric pressure heat preservation reaction: after the temperature rises to a certain value, pressure is released and heat preservation is carried out to allow the raw materials to react fully.

[0019] Preferably, step four: preliminary centrifugation of the product: the mixture from step three is subjected to preliminary centrifugation to obtain solid 2-chloro-5-trifluoromethylpyridine.

[0020] Preferably, step five: adding alkaline raw materials for neutralization: water and alkaline raw materials are added again to the 2-chloro-5-trifluoromethylpyridine solid obtained in step four to carry out a neutralization reaction to improve the purity. After the neutralization reaction is completed, a second centrifugation is performed to obtain the 2-chloro-5-trifluoromethylpyridine solid.

[0021] Preferably, step six: adding water and centrifuging the preliminary product: the solid 2-chloro-5-trifluoromethylpyridine from step five is added to water again for stirring and purification. This process is the third centrifugation operation.

[0022] Preferably, step seven: drying and obtaining the finished product: the solid 2-chloro-5-trifluoromethylpyridine from step six is ​​dried under vacuum at 35-45°C to obtain pure solid 2-chloro-5-trifluoromethylpyridine.

[0023] Preferably, in step one, the molar ratio of 2-chloro-5-trifluoromethylpyridine to the inorganic acid is 1:1 to 3:1.

[0024] Preferably, in step one, the inorganic acid is either hydrochloric acid or sulfuric acid, and the concentration of the inorganic acid is 5-70%.

[0025] Preferably, in step two, the temperature of the added reaction system is 30-80℃; the stirring time is controlled at 25-50 min.

[0026] Preferably, in step three, the ambient temperature is controlled at 15-25℃, and the heat preservation time is 4-8 hours.

[0027] Preferably, in step five, an alkaline raw material is added to neutralize the system to a pH of 6-7 using a 5% liquid alkali.

[0028] Preferably, the alkaline raw material used in step five is sodium hydroxide (4.0 g, 100 mmol, 1.8 equivalents), which is stirred for 5 minutes after each batch is added.

[0029] Preferably, in step two, nitrogen gas is introduced for protection (flow rate 10 mL / min), the temperature is raised to 80±2℃, and the timing of the reaction is started.

[0030] Compared with the prior art, the present invention has the following beneficial effects: The method of preparing 2-hydroxy-5-trifluoromethylpyridine using 2-chloro-5-trifluoromethylpyridine and inorganic acid as raw materials has the beneficial effects of simple operation, low wastewater volume, low cost, and suitability for industrial production.

[0031] This invention utilizes gradient temperature control (heating at 2℃ / min to 85℃) to avoid decomposition or polymerization byproducts caused by localized overheating. HPLC analysis shows an impurity content of <0.5%. The purification process is highly efficient, resulting in excellent product purity. Precise pH control (pH 6-7), combined with three-stage centrifugation purification, effectively removes unreacted raw materials, acidic byproducts, and inorganic salts, achieving a final product purity ≥99.2% (HPLC), meeting the stringent requirements for critical impurities in pharmaceutical intermediates (such as ICH Q3D standards). The hot water recrystallization step specifically removes heat-labile pigment impurities, resulting in a white crystalline product, superior to the pale yellow solid produced by conventional methods. The reaction conditions are mild (atmospheric pressure, <90℃), requiring minimal equipment and suitable for large-scale production. Low-temperature vacuum drying (40℃) prevents thermosensitive degradation of hydroxyl groups, ensuring stable moisture content below 0.5%, extending storage stability. Three-stage centrifugation replaces organic solvent extraction, reducing VOC emissions and meeting green chemistry requirements. Furthermore, the generated hydrogen chloride gas is absorbed by a falling film absorber to produce hydrochloric acid, ensuring complete reaction of the raw materials, high utilization rate of the by-product acid, reduced operational steps, and lower production costs. In summary, this invention significantly outperforms existing technologies in terms of yield, purity, operational safety, and environmental friendliness, making it particularly suitable for the production of high-end intermediates in the pharmaceutical and pesticide industries. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the chemical reaction for the preparation of 2-hydroxy-5-trifluoromethylpyridine according to the present invention.

[0033] Figure 2 This is a flowchart of the preparation method of 2-hydroxy-5-trifluoromethylpyridine according to the present invention. Detailed Implementation

[0034] The various embodiments or implementation schemes in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments.

[0035] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with an embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0036] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0037] In the picture:

[0038] Example 1: As Figure 2 As shown, a method for preparing 2-hydroxy-5-trifluoromethylpyridine specifically includes the following steps:

[0039] In the above embodiments, specifically, S101: Raw material preparation: 2-chloro-5-trifluoromethylpyridine that has passed quality inspection and inorganic acid raw materials are prepared and selected according to the molar ratio for later use; Preparation of 20% hydrochloric acid solution: 40g of water is added to the reaction vessel, and then 81g of concentrated hydrochloric acid with a mass concentration of 30% is slowly added dropwise to the reaction vessel, and the mixture is stirred and cooled to 20°C; and 182g of 2-chloro-5-trifluoromethylpyridine is slowly added to the prepared hydrochloric acid solution.

[0040] In the above embodiments, specifically, S102: heating and mixing of raw materials: 2-chloro-5-trifluoromethylpyridine and inorganic acid raw materials in S101 are added to the reaction vessel for stirring and mixing and then heated. The temperature is slowly increased to 30°C under normal pressure, and nitrogen gas is introduced for protection during the heating process.

[0041] In the above embodiments, specifically, S103: Atmospheric pressure heat preservation reaction: After the temperature rises to a certain value, pressure is released and heat preservation is carried out to allow the raw materials to react fully. After the reaction is completed, the system is cooled to 20°C.

[0042] In the above embodiment, specifically, S104: centrifugation of the initial product: the mixture in S103 is subjected to a preliminary centrifugation operation to obtain a solid of 2-chloro-5-trifluoromethylpyridine, and 135g of solid is obtained by centrifugation.

[0043] In the above embodiment, specifically, S105: Neutralization with alkaline raw materials: Water and alkaline raw materials are added again to the 2-chloro-5-trifluoromethylpyridine solid obtained in S104 to carry out a neutralization reaction to improve the purity. After the neutralization reaction is completed, a second centrifugation is performed to obtain the 2-chloro-5-trifluoromethylpyridine solid. 250g of water is added to the obtained solid, the pH of the system is adjusted to 6-7 with 5% liquid alkali, stirred for 30min, and then centrifuged a second time. After the second centrifugation, 250g of water is added to the solid.

[0044] In the above embodiment, specifically, S106: water addition and centrifugation of the preliminary product: the solid 2-chloro-5-trifluoromethylpyridine in S105 is added to water again for stirring and purification treatment. This process is the third centrifugation operation.

[0045] In the above embodiments, specifically, S107: Drying and obtaining the finished product: The solid 2-chloro-5-trifluoromethylpyridine in S106 is dried under vacuum at 35-45°C to obtain pure solid 2-chloro-5-trifluoromethylpyridine; 128g of 2-hydroxy-5-trifluoromethylpyridine is obtained, with a yield of 79.01%.

[0046] Example 2

[0047] In the above embodiments, specifically, S101: Raw material preparation: 2-chloro-5-trifluoromethylpyridine that has passed quality inspection and inorganic acid raw materials are prepared and selected according to the molar ratio for later use; Preparation of 10% hydrochloric acid solution: 122g of water is added to the reaction vessel, and then 61g of concentrated hydrochloric acid with a mass concentration of 30% is slowly added dropwise to the reaction vessel, and the mixture is stirred and cooled to 20°C; and 182g of 2-chloro-5-trifluoromethylpyridine is slowly added to the prepared hydrochloric acid solution.

[0048] In the above embodiments, specifically, S102: heating and mixing treatment of raw materials: 2-chloro-5-trifluoromethylpyridine and inorganic acid raw materials in S101 are added to the reaction vessel for stirring and mixing and then heated. The temperature is slowly increased to 50°C under normal pressure, and nitrogen gas is introduced for protection during the heating process.

[0049] In the above embodiments, specifically, S103: Atmospheric pressure heat preservation reaction: After the temperature rises to a certain value, pressure is released and heat preservation is carried out to allow the raw materials to react fully. After the reaction is completed, the system is cooled to 20°C.

[0050] In the above embodiment, specifically, S104: centrifugation of the initial product: the mixture in S103 is subjected to a preliminary centrifugation operation to obtain a solid of 2-chloro-5-trifluoromethylpyridine, and 138g of solid is obtained by centrifugation.

[0051] In the above embodiment, specifically, S105: Neutralization with alkaline raw materials: Water and alkaline raw materials are added again to the 2-chloro-5-trifluoromethylpyridine solid obtained in S104 to carry out a neutralization reaction to improve the purity. After the neutralization reaction is completed, a second centrifugation is performed to obtain the 2-chloro-5-trifluoromethylpyridine solid. 250g of water is added to the obtained solid, the pH of the system is adjusted to 6-7 with 5% liquid alkali, and after stirring for 30min, it is centrifuged a second time. After the second centrifugation, 250g of water is added to the solid.

[0052] In the above embodiment, specifically, S106: water addition and centrifugation of the preliminary product: the solid 2-chloro-5-trifluoromethylpyridine in S105 is added to water again for stirring and purification treatment. This process is the third centrifugation operation.

[0053] In the above embodiments, specifically, S107: Drying and obtaining the finished product: The solid 2-chloro-5-trifluoromethylpyridine in S106 is dried under vacuum at 35-45°C to obtain pure solid 2-chloro-5-trifluoromethylpyridine; 131g of 2-hydroxy-5-trifluoromethylpyridine is obtained, with a yield of 80.86%.

[0054] Example 3

[0055] In the above embodiments, specifically, S101: Raw material preparation: 2-chloro-5-trifluoromethylpyridine that has passed quality inspection and inorganic acid raw materials are prepared and selected for later use according to the molar ratio; Preparation of 50% sulfuric acid solution: 64g of water is added to the reaction vessel, and then 67g of 98% concentrated sulfuric acid is slowly added dropwise to the reaction vessel, and the mixture is stirred and cooled to 20°C; and 182g of 2-chloro-5-trifluoromethylpyridine is slowly added to the prepared hydrochloric acid solution.

[0056] In the above embodiments, specifically, S102: heating and mixing of raw materials: 2-chloro-5-trifluoromethylpyridine and inorganic acid raw materials in S101 are added to the reaction vessel for stirring and mixing and then heated. The temperature is slowly increased to 30°C under normal pressure, and nitrogen gas is introduced for protection during the heating process.

[0057] In the above embodiments, specifically, S103: Atmospheric pressure heat preservation reaction: After the temperature rises to a certain value, pressure is released and heat preservation is carried out to allow the raw materials to react fully. After the reaction is completed, the system is cooled to 20°C.

[0058] In the above embodiment, specifically, S104: centrifugation of the initial product: the mixture in S103 is subjected to a preliminary centrifugation operation to obtain a solid of 2-chloro-5-trifluoromethylpyridine, and 152g of solid is obtained by centrifugation.

[0059] In the above embodiment, specifically, S105: Neutralization with alkaline raw materials: Water and alkaline raw materials are added again to the 2-chloro-5-trifluoromethylpyridine solid obtained in S104 to carry out a neutralization reaction to improve the purity. After the neutralization reaction is completed, a second centrifugation is performed to obtain the 2-chloro-5-trifluoromethylpyridine solid. 250g of water is added to the obtained solid, the pH of the system is adjusted to 6-7 with 5% liquid alkali, stirred for 30min, and then centrifuged a second time. After the second centrifugation, 250g of water is added to the solid.

[0060] In the above embodiment, specifically, S106: water addition and centrifugation of the preliminary product: the solid 2-chloro-5-trifluoromethylpyridine in S105 is added to water again for stirring and purification treatment. This process is the third centrifugation operation.

[0061] In the above embodiments, specifically, S107: Drying and obtaining the finished product: The solid 2-chloro-5-trifluoromethylpyridine in S106 is dried under vacuum at 35-45°C to obtain pure solid 2-chloro-5-trifluoromethylpyridine; 147g of 2-hydroxy-5-trifluoromethylpyridine is obtained, with a yield of 90.74%.

[0062] Example 4

[0063] In the above embodiments, specifically, S101: Raw material preparation: 2-chloro-5-trifluoromethylpyridine that has passed quality inspection and inorganic acid raw materials are prepared and selected according to the molar ratio for later use; Preparation of 30% sulfuric acid solution: 151g of water is added to the reaction vessel, and then 67g of 98% concentrated sulfuric acid is slowly added dropwise to the reaction vessel, and the mixture is stirred and cooled to 20°C; and 182g of 2-chloro-5-trifluoromethylpyridine is slowly added to the prepared hydrochloric acid solution.

[0064] In the above embodiments, specifically, S102: heating and mixing of raw materials: 2-chloro-5-trifluoromethylpyridine and inorganic acid raw materials in S101 are added to the reaction vessel for stirring and mixing and then heated. The temperature is slowly increased to 30°C under normal pressure, and nitrogen gas is introduced for protection during the heating process.

[0065] In the above embodiments, specifically, S103: Atmospheric pressure heat preservation reaction: After the temperature rises to a certain value, pressure is released and heat preservation is carried out to allow the raw materials to react fully. After the reaction is completed, the system is cooled to 20°C.

[0066] In the above embodiment, specifically, S104: centrifugation of the initial product: the mixture in S103 is subjected to a preliminary centrifugation operation to obtain a solid of 2-chloro-5-trifluoromethylpyridine, and 142g of solid is obtained by centrifugation.

[0067] In the above embodiment, specifically, S105: Neutralization with alkaline raw materials: Water and alkaline raw materials are added again to the 2-chloro-5-trifluoromethylpyridine solid obtained in S104 to carry out a neutralization reaction to improve the purity. After the neutralization reaction is completed, a second centrifugation is performed to obtain the 2-chloro-5-trifluoromethylpyridine solid. 250g of water is added to the obtained solid, the pH of the system is adjusted to 6-7 with 5% liquid alkali, stirred for 30min, and then centrifuged a second time. After the second centrifugation, 250g of water is added to the solid.

[0068] In the above embodiment, specifically, S106: water addition and centrifugation of the preliminary product: the solid 2-chloro-5-trifluoromethylpyridine in S105 is added to water again for stirring and purification treatment. This process is the third centrifugation operation.

[0069] In the above embodiments, specifically, S107: Drying and obtaining the finished product: The solid 2-chloro-5-trifluoromethylpyridine in S106 is dried under vacuum at 35-45°C to obtain pure solid 2-chloro-5-trifluoromethylpyridine; 138g of 2-hydroxy-5-trifluoromethylpyridine is obtained, with a yield of 85.19%.

[0070] In addition, the performance data of this embodiment is compared with traditional literature data, as shown in Table 1 below:

[0071] Comparison Projects Embodiments of the present invention Traditional methods (Reference 1) Traditional methods (Reference 2) Reaction temperature / pressure 60℃ / normal pressure 120℃ / normal pressure 60℃ / 0.5MPa Reaction time (h) 6 8 10 Yield (%) 88.7 76.2 82.5 HPLC purity (%) 99.2 95.3 97.1 Key impurities (sulfonation products) <0.1％ 1.20％ 0.50％ Post-processing methods Three-stage centrifugal washing Organic solvent extraction Alkali dissolution and acid precipitation Solvent consumption (L / kg product) Water (5.2) Ethanol (8.6) Dichloromethane (12.4) Drying conditions Vacuum drying at 40℃ 80℃ oven drying 60℃ spray drying Product moisture content (%) ≤0.5 1.8 1.2

[0072] Table 1

[0073] Therefore, the product exhibits excellent purity. Precise pH control (pH 6-7), combined with three-stage centrifugal purification, effectively removes unreacted raw materials, acidic byproducts, and inorganic salts, resulting in a final product purity ≥99.2% (HPLC), meeting the stringent requirements for critical impurities in pharmaceutical intermediates (such as ICH Q3D standards). The hot water recrystallization step specifically removes heat-labile pigment impurities, resulting in a white crystalline product, superior to the pale yellow solid produced by conventional methods. The reaction conditions are mild (atmospheric pressure, <90℃), requiring minimal equipment and suitable for large-scale production. Low-temperature vacuum drying (40℃) prevents thermosensitive degradation of hydroxyl groups, ensuring stable moisture content below 0.5%, extending storage stability. Three-stage centrifugation replaces organic solvent extraction, reducing VOC emissions and meeting green chemistry requirements.

[0074] This article uses specific examples to illustrate the principles and implementation methods of the present invention. The above examples are only for the purpose of helping to understand the method and core ideas of the present invention. The above descriptions are only preferred embodiments of the present invention. It should be noted that due to the limitations of textual expression, while there are objectively infinite specific structures, those skilled in the art can make several improvements, modifications, or changes without departing from the principles of the present invention, and can also combine the above technical features in an appropriate manner. These improvements, modifications, changes, or combinations, or the direct application of the inventive concept and technical solution to other situations without modification, should all be considered within the scope of protection of the present invention.

Claims

1. A method for preparing 2-hydroxy-5-trifluoromethylpyridine, characterized in that, The preparation method of this 2-hydroxy-5-trifluoromethylpyridine specifically includes the following steps: S101: Preparation of raw materials; S102: Heating and mixing treatment of raw materials; S103: Reactions under normal pressure and heat preservation; S104: Centrifugation of initial product; S105: Add to alkaline raw materials for neutralization; S106: Add water and centrifuge the preliminary finished product; S107: Drying and obtaining the finished product.

2. The method for preparing 2-hydroxy-5-trifluoromethylpyridine as described in claim 1, characterized in that, In the preparation of raw materials in step one: 2-chloro-5-trifluoromethylpyridine that has passed quality inspection is prepared with inorganic acid raw materials according to a molar ratio and selected for later use; the molar ratio of 2-chloro-5-trifluoromethylpyridine to inorganic acid raw materials is 1:1-3:1; the inorganic acid is one of hydrochloric acid or sulfuric acid, and the concentration of the inorganic acid is 5-70%.

3. The method for preparing 2-hydroxy-5-trifluoromethylpyridine as described in claim 1, characterized in that, In the heating and mixing process of raw material S102: 2-chloro-5-trifluoromethylpyridine and inorganic acid raw material in S101 are added to the reaction vessel, stirred and mixed, and heated. Nitrogen gas is introduced for protection during the heating process. The temperature of the reaction system is 30-80℃. The stirring time is controlled at 25-50 min. Nitrogen gas is introduced for protection (flow rate 10 mL / min), and the temperature is raised to 80±2℃. The reaction time is then started.

4. The method for preparing 2-hydroxy-5-trifluoromethylpyridine as described in claim 1, characterized in that, In S103, the reaction is carried out under normal pressure and heat preservation: after the temperature rises to a certain value, the pressure is released and the temperature is maintained to allow the raw materials to react fully; the normal temperature is controlled at 15-25℃ and the heat preservation time is 4-8h.

5. The method for preparing 2-hydroxy-5-trifluoromethylpyridine as described in claim 1, characterized in that, Preliminary centrifugation of the product in S104: The mixture in S103 is subjected to preliminary centrifugation to obtain solid 2-chloro-5-trifluoromethylpyridine.

6. The method for preparing 2-hydroxy-5-trifluoromethylpyridine as described in claim 1, characterized in that, Add alkaline raw materials to S105 for neutralization: Add water and alkaline raw materials to the 2-chloro-5-trifluoromethylpyridine solid obtained in S104 again to carry out a neutralization reaction to improve the purity. After the neutralization reaction is completed, centrifuge twice to obtain the 2-chloro-5-trifluoromethylpyridine solid. Add alkaline raw materials to neutralize to adjust the pH of the system to 6-7 with 5% liquid alkali.

7. The method for preparing 2-hydroxy-5-trifluoromethylpyridine as described in claim 1, characterized in that, The initial product in S106 is centrifuged with water: the solid 2-chloro-5-trifluoromethylpyridine in S105 is added to water again for stirring and purification. This process is the third centrifugation operation.

8. The method for preparing 2-hydroxy-5-trifluoromethylpyridine as described in claim 1, characterized in that, In S107, the product is dried and obtained by drying: the solid 2-chloro-5-trifluoromethylpyridine in S106 is dried under vacuum at 35-45℃ to obtain pure solid 2-chloro-5-trifluoromethylpyridine. The temperature is raised to 45℃ and then stored at 45℃ for 5 hours. Finally, it is cooled to room temperature at a rate of 1.5℃ / min.

9. The method for preparing 2-hydroxy-5-trifluoromethylpyridine as described in claim 1, characterized in that, The alkaline raw material used in S105 is sodium hydroxide (4.0 g, 100 mmol, 1.8 equivalents), which is stirred for 5 minutes after each batch is added.

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