A process for the preparation of 2-fluoropyridines

Abstract

The application discloses a preparation method of 2-fluoropyridine. 2-amino pyridine is used as raw material, and a diazotization and fluorination reaction is carried out in a fluorine-containing strong acid through a diazotization reagent to obtain 2-fluoropyridine. The fluorine-containing strong acid is tetrafluoroboric acid or hexafluorophosphoric acid, and the diazotization reagent is any one of sodium nitrite, calcium nitrite or tetrafluoroboric acid nitrite. In the application, polysorbate is additionally added in the fluorine-containing strong acid, so that the yield of the method is greatly improved, the stability of the fluoroboric acid diazonium salt in the reaction process is improved, the product is not easy to decompose, and the possibility of side reactions is reduced.

Description

Technical Field

[0001] This invention relates to the field of battery electrolyte technology, and more particularly to a method for preparing an electrolyte additive, specifically a method for preparing 2-fluoropyridine. Background Technology

[0002] Electrolyte additives are small amounts of substances added to the electrolyte to improve its electrochemical performance and enhance cathode deposition quality. While they generally do not participate in the electrode reactions of the electrolysis process, they can improve the electrochemical performance of the electrolyte system, influence ion discharge conditions, and optimize the electrolysis process, making them an indispensable part of the electrolyte system.

[0003] 2-Fluoropyridine is an important intermediate used in the synthesis of antihistamines such as benzyramide and antiarrhythmic drugs such as diisopropyramide. It is also used as a pesticide intermediate in the preparation of pyridinethione insecticides and is an important intermediate in the synthesis of liquid crystal materials. Furthermore, 2-fluoropyridine can be used as an electrolyte additive in the preparation of lithium-ion batteries to improve their electrochemical performance.

[0004] 2-Fluoropyridine has a wide range of applications and can be synthesized through various methods, including denitration fluorination, direct fluorination, halogen exchange, and diazotization. For example, 2-fluoropyridine can be prepared by reacting tetrabutylamine fluoride (TBAF) with 2-nitropyridine. A mixed solution of TBAF and tetrahydrofuran (THF) with two molar amounts of 2-nitropyridine is added to N,N-dimethylformamide (DMF) solvent. Subsequent purification after the reaction yields the target compound. The above denitration fluorination method has mild reaction conditions, yields over 70%, and does not require consideration of the influence of moisture on the reaction; however, it consumes a large amount of organic solvent. Direct fluorination involves introducing fluorine atoms directly onto the pyridine ring using fluorine-containing substances. This typically uses gaseous F2 under specific conditions. However, this method requires harsh reaction conditions, often at -10°C or even -40°C. Furthermore, gaseous F2 is highly toxic and corrosive, posing a significant health hazard. The method also demands sophisticated equipment, hindering its industrial application. Halogen exchange, on the other hand, utilizes fluorine-containing substances to directly replace halogen atoms from the pyridine ring. For the preparation of 2-aminopyridine, this method requires specific phase-transfer catalysts, such as tetraphenylphosphine bromide and S-3-methylpyridine. Commonly used phase-transfer catalysts, such as tetrabutylammonium chloride and tetrabutylammonium bromide, cannot achieve this reaction. Moreover, this reaction often requires temperatures above 200°C, resulting in excessive energy consumption and making it unsuitable for industrial application.

[0005] In contrast, the synthesis of 2-fluoropyridine from 2-aminopyridine via diazotization is more suitable for industrial application due to its milder reaction conditions and simpler operation. However, under current technology, the yield of 2-fluoropyridine obtained by this method is low, generally only around 30%. This is because the diazonium salt of fluoroboronic acid is unstable and easily decomposes during the reaction, leading to numerous side reactions, low yield, and significant difficulty in purification.

[0006] Therefore, a more in-depth study can be conducted on the route of synthesizing 2-fluoropyridine from 2-aminopyridine via diazotization, in order to improve the yield and develop a method for preparing 2-fluoropyridine suitable for industrial production. Summary of the Invention

[0007] The purpose of this invention is to improve and optimize the synthetic route for synthesizing 2-fluoropyridine from 2-aminopyridine via diazotization, so as to improve the yield and purity of 2-aminopyridine.

[0008] The technical solution adopted in this invention provides a method for preparing 2-fluoropyridine. The key is that 2-aminopyridine is used as a raw material, and diazotization and fluorination reactions are carried out in a fluorinated strong acid by the action of a diazotizing reagent to prepare 2-fluoropyridine. The fluorinated strong acid is tetrafluoroboric acid or hexafluorophosphate, and the diazotizing reagent is any one of sodium nitrite, calcium nitrite or nitrosine tetrafluoroboric acid.

[0009] Furthermore, polysorbate needs to be added to the aforementioned fluorinated strong acid, at a rate of 0.02g to 0.04g per milliliter of fluorinated strong acid.

[0010] Preferably, the diazotization reaction temperature is below 10°C and the reaction time is 40 min to 60 min; the fluorination reaction temperature is 35°C to 45°C and the reaction time is 1.5 h to 2.5 h.

[0011] Optimally, the diazotization reaction temperature is 5°C and the reaction time is 45 min; the fluorination reaction temperature is 40°C and the reaction time is 2 h; the tetrafluoroboric acid mentioned above is either a 40 wt% tetrafluoroboric acid aqueous solution or a 48 wt% tetrafluoroboric acid aqueous solution; and the hexafluorophosphoric acid mentioned above is either a 55 wt% hexafluorophosphoric acid aqueous solution or a 60 wt% hexafluorophosphoric acid aqueous solution.

[0012] Specifically, the above-mentioned diazotization reaction is carried out by dissolving 2-aminopyridine in a fluorinated strong acid, and then adding the diazotizing reagent in batches to control the diazotization reaction temperature and reaction time.

[0013] Specifically, the aforementioned addition of the diazotizing reagent in batches refers to adding the diazotizing reagent to the fluorinated strong acid in 3 to 5 batches, with each addition being 1 / 3 to 1 / 5 of the total amount of the diazotizing reagent.

[0014] More specifically, the above-mentioned dissolution of 2-aminopyridine in a fluorinated strong acid specifically refers to dissolving 1g of 2-aminopyridine in 3.3mL to 4.0mL of a fluorinated strong acid.

[0015] Preferably, the molar ratio of the above-mentioned 2-aminopyridine, fluorinated strong acid and diazotizing reagent is 1:2.4-2.6:1.2-1.5.

[0016] It also includes cooling the reaction solution containing 2-fluoropyridine after the fluorination reaction is completed, adjusting the pH of the reaction solution to neutral, filtering the precipitated salt, extracting the aqueous phase with the organic phase and drying the organic phase with anhydrous magnesium sulfate, and distilling the solvent under normal pressure to obtain the 2-fluoropyridine product.

[0017] The organic phase mentioned above is dichloromethane.

[0018] Compared with the prior art, the present invention has the following advantages:

[0019] This invention optimizes and improves the synthetic route for synthesizing 2-fluoropyridine from 2-aminopyridine via diazotization, increasing the yield to over 55%. Furthermore, this invention uses tetrafluoroboric acid as a solvent and nitrite as the diazotizing agent, and adds polysorbate esters to the reaction system, significantly improving the stability of the diazonium salt of fluoroboric acid during the reaction process. This makes the product less prone to decomposition, reduces the possibility of side reactions, and further improves the yield. More importantly, the prepared product not only has a lower total impurity content but also fewer impurity types, and is free of unknown impurities, facilitating product quality control.

[0020] Furthermore, this invention avoids the use of hydrofluoric acid, as hydrofluoric acid is an extremely strong acid that can severely corrode metals, glass, and silicon-containing materials. Therefore, the use of hydrofluoric acid in production requires specialized equipment. This invention optimizes the preparation route, thereby avoiding the use of specialized production equipment, reducing production costs, and extending the service life of the equipment.

[0021] Furthermore, this invention also reduces the amount of fluorinated strong acid used, lowering the molar ratio of 2-aminopyridine to fluorinated strong acid from approximately 1:3.5 to 1:2.4–2.6, thereby saving production costs from the perspective of production materials.

[0022] In summary, the reaction conditions of this invention are relatively mild, reducing energy consumption in the production of 2-fluoropyridine, avoiding the use of hydrofluoric acid, lowering equipment requirements, and achieving a superior material ratio, thus saving material costs. From the perspectives of production capacity, equipment, and materials, this invention is more suitable for industrial-scale promotion. Furthermore, the 2-fluoropyridine prepared by this invention has higher purity. When used as an electrolyte additive, high-purity 2-fluoropyridine can effectively enhance the environmental safety performance of lithium batteries, improve battery thermal stability, and increase resistance to high temperatures. Attached Figure Description

[0023] Figure 1 This is the 1H NMR spectrum of the sample from this invention.

[0024] Figure 2 This is a gas chromatogram of the sample of this invention.

[0025] Figure 3 This is the gas chromatography-mass spectrum of the sample of this invention. Detailed Implementation

[0026] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0027] Unless otherwise specified in the examples, the procedures can be followed according to conventional conditions; unless the manufacturers of the reagents or instruments used are specified, they are all conventional products that can be purchased commercially.

[0028] Example 1

[0029] S1. Weigh 27.4g of 40wt% tetrafluoroboric acid aqueous solution (approximately 0.125mol), dissolve 5.0g (approximately 0.05mol) of 2-aminopyridine in the above tetrafluoroboric acid aqueous solution, cool to 0℃, and slowly add 4.1g of sodium nitrite (approximately 0.065mol) to the tetrafluoroboric acid aqueous solution in 3 batches, with each addition being 1 / 3 of the total amount of sodium nitrite, to carry out the diazotization reaction, control the reaction temperature at 5℃, and keep the reaction at a constant temperature for 45min after the addition is complete;

[0030] S2. Slowly heat the reaction solution to 40°C to carry out the fluorination reaction, and keep the reaction at a constant temperature for 2 hours.

[0031] S3. After the reaction is complete, cool the temperature to 5°C, adjust the pH of the reaction solution to neutral with saturated sodium carbonate, filter out the precipitated salt, extract the product with dichloromethane in the aqueous phase, dry the organic phase with anhydrous magnesium sulfate, evaporate the solvent at normal pressure and obtain sample 1.

[0032] Example 2

[0033] S1. Weigh 27.4g of 48wt% tetrafluoroboric acid aqueous solution (approximately 0.125mol), add 0.50g of Tween-20 to the weighed tetrafluoroboric acid aqueous solution, and stir until homogeneous;

[0034] S2. Dissolve 5.0 g (approximately 0.05 mol) of 2-aminopyridine in the above tetrafluoroboric acid aqueous solution, cool to 0℃, and slowly add 4.8 g of sodium nitrite (approximately 0.07 mol) to the tetrafluoroboric acid aqueous solution in 3 batches, with each addition being 1 / 3 of the total amount of sodium nitrite, to carry out the diazotization reaction. Control the reaction temperature at 5℃, and after the addition is complete, keep the reaction at a constant temperature for 45 min.

[0035] S3. Slowly heat the reaction solution to 40°C to carry out the fluorination reaction, and keep the reaction at a constant temperature for 2 hours.

[0036] S4. After the reaction is complete, cool the temperature to 6°C, adjust the pH of the reaction solution to neutral with saturated sodium carbonate, filter out the precipitated salt, extract the product with dichloromethane from the aqueous phase, dry the organic phase with anhydrous magnesium sulfate, evaporate the solvent at normal pressure and obtain sample 2.

[0037] Example 3

[0038] S1. Weigh 31.8g of 55wt% hexafluorophosphate aqueous solution (approximately 0.12mol), add 0.58g of Tween-60 to the weighed hexafluorophosphate aqueous solution, and stir until homogeneous;

[0039] S2. Dissolve 5.0 g (approximately 0.05 mol) of 2-aminopyridine in the above aqueous solution of hexafluorophosphate, cool it by 2°C, and slowly add 9.2 g of calcium nitrite (approximately 0.07 mol) to the aqueous solution of hexafluorophosphate in 5 batches, with each addition being 1 / 5 of the total amount of calcium nitrite, to carry out the diazotization reaction. Control the reaction temperature at 8°C, and after the addition is complete, keep the reaction at a constant temperature for 40 min.

[0040] S3. Slowly heat the reaction solution to 35°C to carry out the fluorination reaction, and keep the reaction at a constant temperature for 2.5 hours.

[0041] S4. After the reaction is complete, cool the temperature to 4℃, adjust the pH of the reaction solution to neutral with saturated sodium carbonate, filter out the precipitated salt, extract the product with dichloromethane in the aqueous phase, dry the organic phase with anhydrous magnesium sulfate, evaporate the solvent at normal pressure and obtain sample 3.

[0042] Example 4

[0043] S1. Weigh 31.6g of 60wt% hexafluorophosphate aqueous solution (approximately 0.13mol), add 0.38g of Tween-80 to the weighed hexafluorophosphate aqueous solution, and stir until homogeneous;

[0044] S2. Dissolve 5.0 g (approximately 0.05 mol) of 2-aminopyridine in the above aqueous solution of hexafluorophosphate, cool to 0°C, and slowly add 8.8 g of nitrite tetrafluoroborate (approximately 0.075 mol) to the aqueous solution of hexafluorophosphate in 4 batches, with each addition being 1 / 4 of the total amount of nitrite tetrafluoroborate, to carry out the diazotization reaction. Control the reaction temperature at 5°C, and after the addition is complete, keep the reaction at a constant temperature for 45 min.

[0045] S3. Slowly heat the reaction solution to 40°C to carry out the fluorination reaction, and keep the reaction at a constant temperature for 2.0 h;

[0046] S4. After the reaction is complete, cool the temperature to 5°C, adjust the pH of the reaction solution to neutral with saturated sodium carbonate, filter out the precipitated salt, extract the product with dichloromethane in the aqueous phase, dry the organic phase with anhydrous magnesium sulfate, evaporate the solvent at normal pressure and obtain sample 4.

[0047] Example 5

[0048] S1. Dissolve 5.0 g (approximately 0.05 mol) of 2-aminopyridine in the above aqueous solution of hexafluorophosphate, cool down by 1°C, and slowly add 7.0 g of nitrite tetrafluoroborate (approximately 0.06 mol) to the aqueous solution of hexafluorophosphate in 4 batches, with each addition being 1 / 4 of the total amount of nitrite tetrafluoroborate, to carry out the diazotization reaction. Control the reaction temperature at 2°C, and after the addition is complete, keep the reaction at a constant temperature for 55 min.

[0049] S2. Slowly heat the reaction solution to 42°C to carry out the fluorination reaction, and keep the reaction at a constant temperature for 2 hours.

[0050] S3. After the reaction is complete, cool the temperature to 4°C, adjust the pH of the reaction solution to neutral with saturated sodium carbonate, filter out the precipitated salt, extract the product with dichloromethane in the aqueous phase, dry the organic phase with anhydrous magnesium sulfate, evaporate the solvent at normal pressure and obtain sample 5.

[0051] Comparative Example 1

[0052] The implementation method is the same as in Example 1, except that in "S1, step", the solution weighed is not a 40wt% tetrafluoroboric acid aqueous solution, but 43.3g (about 0.175mol) of a 40wt% hydrogen fluoride pyridine aqueous solution. The batch of sodium nitrite added is controlled according to the temperature of the reaction system and the intensity of the reaction, and control product 1 is prepared.

[0053] Comparative Example 2

[0054] The implementation method is the same as in Example 1, except that in "S1, step", the solution weighed is not a 40wt% tetrafluoroboric acid aqueous solution, but 21.7g (about 0.175mol) of 80wt% pyridine hydrogen fluoride aqueous solution. The batch of sodium nitrite added is controlled according to the temperature and intensity of the reaction system to prepare control product 2.

[0055] Comparative Example 3

[0056] The implementation method is the same as in Example 1, except that in "S1, step", the solution weighed is not a 40wt% tetrafluoroboric acid aqueous solution, but 40.4g of hydrogen fluoride-40% pyridine solution (of which, hydrogen fluoride is about 0.175mol). The batch of sodium nitrite added is controlled according to the temperature of the reaction system and the intensity of the reaction, and control product 3 is prepared.

[0057] Comparative Example 4

[0058] The implementation method is the same as in Example 1, except that in "S1, Step", the solution weighed is not a 40wt% tetrafluoroboric acid aqueous solution, but a 40.4g solution of hydrogen fluoride-40% pyridine (of which, hydrogen fluoride is about 0.175mol), and the mass of sodium nitrite added is 20g. The batch of sodium nitrite added is controlled according to the temperature of the reaction system and the intensity of the reaction, and control product 4 is prepared.

[0059] Analysis and Testing

[0060] The samples from the examples were analyzed by 1H NMR and HPLC-MS / MS. The resulting sample structures were consistent with those of 2-fluoropyridine. The results are shown in the appendix. Figure 1 and attached Figure 2 .

[0061] The yields of the samples and reference standards were calculated, and the purity of the test samples was detected using high-performance gas chromatography. The results are shown in Tables 1 to 3. The test chromatogram of sample 1 is shown in Appendix. Figure 3 .

[0062] Yield calculation formula:

[0063] Yield = Actual weight (g) of the obtained sample or reference standard / Theoretical yield (g) calculated based on the amount of 2-aminopyridine used × 100%.

[0064] Table 1: Summary of Sample Yield and Purity Test Results

[0065] Sample number Yield (%) purity(%) Sample 1 55.8 99.4 Sample 2 63.2 99.6 Sample 3 75.6 99.5 Sample 4 81.2 99.7 Sample 5 78.6 99.7 Reference Standard 1 10.7 81.5 Reference Standard 2 15.6 84.6 Reference Standard 3 17.3 86.3 Reference Standard 4 35.6 91.6

[0066] Table 2: Gas chromatogram peaks of sample 1

[0067]

[0068] Table 3: Impurity Analysis of Samples and Reference Standards

[0069]

[0070]

[0071] As shown in Tables 1-3, the use of tetrafluoroboric acid as a solvent in this invention significantly improves the yield and product purity, while avoiding the use of hydrofluoric acid, reducing the requirements for production equipment, and extending the equipment's service life. Using a higher concentration of tetrafluoroboric acid helps improve the yield, but the effect is not significant. However, using hexafluorophosphoric acid as a solvent, combined with nitrosotetrafluoroboric acid as a diazotizing agent, can greatly improve the stability of the diazonium salt of fluoroboric acid, thereby increasing the reaction yield and product purity. The prepared product not only contains fewer types of impurities but also does not contain any unknown impurities.

[0072] In addition, the addition of polysorbate to the reaction system also helps to improve the stability of diazonium fluoroborate, which in turn helps to increase the yield of the product.

[0073] Application testing

[0074] Sample 1, reference standard 4, and commercially available 2-fluoropyridine (purity 98%) were added sequentially as electrolyte additives to the lithium battery electrolyte. The electrolyte without added 2-fluoropyridine was used as a blank example. The amount of electrolyte additive added was 1% of the total mass of the electrolyte. At the same time, a lithium battery with a capacity of 1000mAh was made using these electrolytes and battery electrical safety test and battery environmental safety test were conducted.

[0075] Battery electrical safety test

[0076] 1. External short circuit at room temperature

[0077] After fully charging the battery, place it in an environment of 20℃±5℃. After the battery surface temperature reaches 20℃±5℃, leave it for another 30 minutes. Then connect the positive and negative terminals of the battery with wires and ensure that all external resistances are 80mΩ±20mΩ. Monitor the battery temperature change during the test. The battery should not catch fire or explode, and the maximum temperature should not exceed 150℃.

[0078] 2. High-temperature external short circuit

[0079] After fully charging the battery, place it in an environment of 55℃±5℃. After the battery surface temperature reaches 55℃±5℃, leave it for another 30 minutes. Then connect the positive and negative terminals of the battery with wires and ensure that all external resistances are 80mΩ±20mΩ. Monitor the battery temperature change during the test. The battery should not catch fire or explode, and the maximum temperature should not exceed 150℃.

[0080] 3. Overcharging

[0081] After the battery is fully discharged, charge it with a constant current of 3CA to a test voltage of 4.6V, and then charge it with the same test voltage. The battery should not catch fire or explode.

[0082] 4. Forced discharge

[0083] After the battery is fully discharged, it should be reverse-charged at a current of 1CA for 90 minutes. The battery should not catch fire or explode.

[0084] The test results for battery electrical safety are shown in Table 4:

[0085] Table 4: Test Results of Battery Electrical Safety

[0086] sample External short circuit at room temperature High temperature external short circuit overcharge Forced discharge Sample 1 normal normal normal normal Reference Standard 4 normal normal normal normal Commercially available samples normal normal normal normal Blank example fire Temperature exceeding 150℃ fire ——

[0087] As shown in Table 4, the addition of 2-fluoropyrimidine to the lithium battery electrolyte can effectively enhance the electrical safety performance of the lithium battery.

[0088] Battery environmental safety testing:

[0089] 1. Low air pressure

[0090] After fully charging the battery, place it in a vacuum chamber at 20°C, evacuate the chamber to reduce the pressure to 11.6 kPa, and maintain this pressure for 6 hours. The battery should not catch fire, explode, or leak.

[0091] 2. Temperature Cycling

[0092] After fully charging the battery, place it in a temperature-controlled chamber at 20℃±5℃ and perform the following steps:

[0093] a) Place the sample in an experimental chamber at a temperature of 75℃±2℃ for 6 hours;

[0094] b) Then the temperature of the experimental chamber is reduced to -40℃±2℃ and maintained for 6 hours, with the temperature transition time not exceeding 30 minutes;

[0095] c) Raise the temperature of the experimental chamber to 75℃±2℃ again, with a temperature transition time not exceeding 30 minutes.

[0096] d) Repeat steps a) to c) for a total of 10 cycles;

[0097] The battery should not catch fire, explode, or leak.

[0098] 3. Acceleration impact

[0099] After fully charging the battery, it was fixed on the impact platform and subjected to a half-sine pulse impact test. The minimum average acceleration was 75g in the first 3ms. n Peak acceleration is 150g n ±25g n The pulse duration is 6ms ± 1ms. The battery is subjected to three acceleration impacts in each direction. The battery should not catch fire, explode, or leak.

[0100] 4. Fall

[0101] After fully charging the battery, drop it freely from a height of 1 meter onto a concrete slab. Perform four drop tests in total. The battery should not catch fire or explode.

[0102] 5. Extrusion

[0103] After fully charging the battery, place it in two planes and press it perpendicular to the plates. Apply a pressing force of 13.0kN±0.78kN between the two plates. Stop the pressing test once the pressure reaches the maximum value. The battery must not experience an external short circuit during the test.

[0104] 6. Heat abuse

[0105] After fully charging the battery, place it in a test chamber. The test chamber is heated at a rate of (5±2)℃ / min. When the temperature inside the chamber reaches 130℃±2℃, it is kept constant for 30 minutes. The battery should not catch fire or explode.

[0106] 7. Combustion Injection

[0107] After fully charging the battery, place it on the wire mesh of the test fixture. If the battery slips during the test, a single metal wire can be used to fix the battery sample to the wire mesh. If this does not happen, the battery should not be tied up. Heat the battery with a flame. Stop heating when any of the following three situations occur: a) the battery explodes; b) the battery burns completely; c) heating continues for 30 minutes, but the battery does not catch fire or explode. After the test, the components of the battery (except for dust products) or the battery as a whole must not penetrate the aluminum mesh.

[0108] The test results for battery environmental safety are shown in Table 5:

[0109] Table 5: Test Results of Battery Environmental Safety Test

[0110] sample low pressure Temperature Cycling Acceleration impact fall extrusion Heat abuse Combustion jet Sample 1 normal normal normal normal normal No change normal Reference Standard 4 normal normal normal normal normal fire fire Commercially available samples normal normal normal normal normal No change fire Blank example normal Leakage Leakage normal Short circuit explode explode

[0111] As can be seen from the results in Table 5, adding 2-fluoropyridine to the lithium battery electrolyte can effectively enhance the environmental safety performance of the lithium battery. The addition of the pure 2-fluoropyridine prepared in this invention can improve the thermal stability of the battery and enhance its resistance to high temperatures.

Claims

1. A method for preparing 2-fluoropyridine, characterized in that, 2-Fluoropyridine is prepared by diazotization and fluorination reactions in a fluorinated strong acid with the aid of a diazotizing agent. The fluorinated strong acid is tetrafluoroboric acid or hexafluorophosphate, and the diazotizing agent is any one of sodium nitrite, calcium nitrite, or nitrite tetrafluoroboric acid. The fluorinated strong acid also requires the addition of polysorbate, at a rate of 0.02 g to 0.04 g per milliliter of fluorinated strong acid; The diazotization reaction temperature is below 10℃, and the reaction time is 40 min to 60 min; the fluorination reaction temperature is 35℃ to 45℃, and the reaction time is 1.5 h to 2.5 h. The specific operation of the diazotization reaction is as follows: 2-aminopyridine is dissolved in a fluorinated strong acid, and then the diazotizing reagent is added in batches to control the diazotization reaction temperature and reaction time.

2. The method for preparing 2-fluoropyridine according to claim 1, characterized in that, The diazotization reaction temperature is 5℃ and the reaction time is 45 min; the fluorination reaction temperature is 40℃ and the reaction time is 2 h; the tetrafluoroboric acid is either a 40 wt% tetrafluoroboric acid aqueous solution or a 48 wt% tetrafluoroboric acid aqueous solution; and the hexafluorophosphoric acid is either a 55 wt% hexafluorophosphoric acid aqueous solution or a 60 wt% hexafluorophosphoric acid aqueous solution.

3. The method for preparing 2-fluoropyridine according to claim 1, characterized in that, The aforementioned batch addition of the diazotizing reagent specifically refers to adding the diazotizing reagent to the fluorine-containing strong acid in 3 to 5 batches, with each addition being 1 / 3 to 1 / 5 of the total amount of the diazotizing reagent.

4. The method for preparing 2-fluoropyridine according to claim 1, characterized in that, The dissolution of 2-aminopyridine in a fluorinated strong acid specifically refers to dissolving 1 g of 2-aminopyridine in 3.3 mL to 4.0 mL of a fluorinated strong acid.

5. The method for preparing 2-fluoropyridine according to claim 1, characterized in that, The molar ratio of the 2-aminopyridine, the fluorinated strong acid, and the diazotizing reagent is 1:2.4-2.6:1.2-1.

5.

6. The method for preparing 2-fluoropyridine according to claim 1, characterized in that, After the fluorination reaction is completed, the reaction solution containing 2-fluoropyridine is cooled, the pH of the reaction solution is adjusted to neutral, the precipitated salt is filtered, the aqueous phase is extracted with the organic phase and the organic phase is dried with anhydrous magnesium sulfate, and the solvent is distilled at atmospheric pressure to obtain the 2-fluoropyridine product.

7. The method for preparing 2-fluoropyridine according to claim 6, characterized in that, The organic phase is dichloromethane.

Images