A method for synthesizing 2-fluoropyridine-5-formyl chloride
By using phosgene as the acyl chloride reagent and optimizing the reaction conditions, the problem of excessive by-product generation in the synthesis of 2-fluoropyridine-5-carbonyl chloride was solved, and the production of high-yield and high-purity products was achieved. The technology is simple in process, easy to operate, and low in cost.
Patent Information
- Application Number
- CN202411927796.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2024-12-25
- Publication Date
- 2025-10-17
- Estimated Expiration
- 2044-12-25
AI Technical Summary
Existing methods for synthesizing 2-fluoropyridine-5-carbonyl chloride suffer from the problems of high by-product generation, difficulty in separation, and low yield and purity. In particular, when oxalyl chloride or thionyl chloride is used as the chlorination reagent, residual hydrogen chloride gas leads to the formation of by-products.
Phosgene is used as an acyl chloride reagent, and an acyl chloride reaction is carried out by optimizing reaction conditions such as molar ratio, introduction rate, stirring rate, temperature and catalyst usage to prepare 2-fluoropyridine-5-carbonyl chloride. The method includes step S1 of mixing a solution, step S2 of acyl chloride reaction and step S3 of product treatment.
Under room temperature conditions, the yield and purity of 2-fluoropyridine-5-carbonyl chloride were significantly improved, the by-product content was significantly reduced, the product quality was improved to 98.3%-98.9%, and the yield reached 97.0%-99.5%. The process is simple, low-cost, and environmentally friendly.
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Abstract
Description
TECHNICAL FIELD
[0001] The application belongs to the field of organic chemical industry, and relates to a synthesis method of 2-fluoropyridine-5-formyl chloride, in particular to a method for preparing 2-fluoropyridine-5-formyl chloride at room temperature by using phosgene as an acyl chloride reagent. BACKGROUND
[0002] 2-Fluoropyridine-5-formyl chloride is an important chemical intermediate and has important applications in medicines and pesticides. Its main synthesis route is to acylate the carboxyl group in 6-fluoronicotinic acid to obtain 2-fluoropyridine-5-formyl chloride.
[0003] At present, the synthesis methods of 2-fluoropyridine-5-formyl chloride reported in the prior art are mainly divided into two categories according to different acyl chloride reagents, one is to use dichlorosulfoxide as an acyl chloride reagent, and the other is to use oxalyl chloride as an acyl chloride reagent.
[0004] In the existing preparation method, when oxalyl chloride is used as an acyl chloride reagent to prepare 2-fluoropyridine-5-formyl chloride, the reaction formula is as follows:
[0005]
[0006] In the existing preparation method, when dichlorosulfoxide is used as an acyl chloride reagent to prepare 2-fluoropyridine-5-formyl chloride, the reaction formula is as follows:
[0007]
[0008] In the research process of the present inventors, it is found that when 2-fluoropyridine-5-formyl chloride is prepared by using an acyl chloride reagent, especially using oxalyl chloride, dichlorosulfoxide and other acyl chloride reagents, there are a lot of hydrogen chloride gas remaining in the reaction system of the acyl chloride reaction, which can cause the free Cl - can replace the F on the pyridine ring to obtain a by-product 6-chloronicotinyl chloride, and the content of the by-product can reach 1.3%-4.0% under reflux conditions. In addition, since the by-product and the main product have high reactivity in the subsequent reaction and are difficult to separate, effectively inhibiting the by-product and reducing the content of the by-product in the product has important significance for promoting the later application of 2-fluoropyridine-5-formyl chloride.
[0009] SUMMARY
[0010] The technical problem to be solved by the present application is to overcome the shortcomings of the prior art, and to provide a synthesis method of 2-fluoropyridine-5-formyl chloride, which has the advantages of simple process, convenient operation, low cost, mild reaction conditions, high preparation efficiency, high yield, high purity and environmental friendliness.
[0011] To solve the above technical problems, the application adopts the following technical solutions:
[0012] A synthesis method of 2-fluoropyridine-5-formyl chloride, taking 6-fluoronicotinic acid as raw material and taking phosgene as acyl chloride reagent, preparing 2-fluoropyridine-5-formyl chloride through acyl chloride reaction, the reaction formula is as follows:
[0013]
[0014] The synthesis method is further improved and comprises the following steps:
[0015] Step S1, mixing 6-fluoronicotinic acid with a solvent to obtain a mixed solution;
[0016] Step S2, passing phosgene into the mixed solution obtained in step S1 to perform acyl chloride reaction, obtaining a reaction product liquid;
[0017] Step S3, removing phosgene and the solvent in the reaction product liquid obtained in step S2 to obtain 2-fluoropyridine-5-formyl chloride.
[0018] The synthesis method is further improved, and in step S2, the molar ratio of 6-fluoronicotinic acid to phosgene is 1:1.2-5.0.
[0019] The synthesis method is further improved, and in step S2, the passing speed of phosgene is 120 g / h-200 g / h.
[0020] The synthesis method is further improved, and in step S2, nitrogen is continuously passed into the system during the acyl chloride reaction; the passing rate of the nitrogen is 0.1 L / min-0.3 L / min.
[0021] The synthesis method is further improved, and in step S2, the acyl chloride reaction is performed under stirring at a rotating speed of 50 r / min-220 r / min.
[0022] The synthesis method is further improved, and in step S2, the temperature of the acyl chloride reaction is 25°C-100°C.
[0023] The synthesis method is further improved, and in step S2, the time of the acyl chloride reaction is 2.5 h-8 h.
[0024] The synthesis method is further improved, and in step S1, the mass ratio of 6-fluoronicotinic acid to the solvent is 1:1-8; the solvent is at least one of benzene, xylene, dichloromethane, 1,2-dichloroethane, chloroform, chlorobenzene, and dichlorobenzene.
[0025] The improved synthesis method further comprises adding a catalyst in the mixed solution in step S1; the mass ratio of the 6-fluoronicotinic acid to the catalyst is 100:0.5-3; and the catalyst is N,N-dimethylformamide.
[0026] Compared with the prior art, the method has the advantages that:
[0027] (1) In order to solve the problems of low yield and low purity in the synthesis method, the application creatively provides a synthesis method of 2-fluoropyridine-5-formyl chloride, which uses 6-fluoronicotinic acid as a raw material and phosgene as an acyl chloride reagent, can significantly improve the selectivity of the reaction, and thus can perform the acyl chloride reaction at normal temperature, so that more 6-fluoronicotinic acid is converted into 2-fluoropyridine-5-formyl chloride through the acyl chloride reaction, the generation of by-products (such as 6-chloronicotinyl chloride) is effectively inhibited, the yield of 2-fluoropyridine-5-formyl chloride is further improved, and the content of by-products in the product is reduced, the yield of the product is improved, and higher-quality 2-fluoropyridine-5-formyl chloride is obtained, wherein the content of the product is high, the content is 98.3%-98.9% (gas chromatography, external standard) in terms of mass content, and the yield is high, which is 97.0%-99.5% in terms of 6-fluoronicotinic acid. The synthesis method of 2-fluoropyridine-5-formyl chloride has the advantages of simple process, convenient operation, low cost, mild reaction condition, high preparation efficiency, high yield, high purity, environmental friendliness, and the like, can be used for large-scale preparation of 2-fluoropyridine-5-formyl chloride, and is convenient for industrial application of 2-fluoropyridine-5-formyl chloride.
[0028] (2) In the application, the molar ratio of 6-fluoronicotinic acid to phosgene is 1:1.2-5.0, which can promote the conversion of 6-fluoronicotinic acid into 2-fluoropyridine-5-formyl chloride, and the best yield is obtained. In particular, when the amount of phosgene is small, the yield is low, and when the amount of phosgene is too large, the yield does not change significantly, which not only leads to low utilization rate of phosgene, but also causes difficulty in recovering tail gas.
[0029] (3) In the present application, during the process of acyl chloride reaction, by optimizing the passing speed of phosgene to be 120g / h-200g / h, the contact and reaction of phosgene and 6-fluoronicotinic acid can be promoted, the yield of 2-fluoropyridine-5-formyl chloride can be significantly improved, the generation of hydrogen chloride gas can be inhibited, and the hydrogen chloride gas produced in the system can be removed in time, so that the formation of by-product (6-chloronicotinoyl chloride) can be further inhibited, the content of by-product in the product can be reduced, and the purity of 2-fluoropyridine-5-formyl chloride can be improved. Further, during the process of acyl chloride reaction, nitrogen is continuously passed into the system, and the passing rate of nitrogen is optimized to be 0.1L / min-0.3L / min, so that the hydrogen chloride gas generated in the system can be effectively taken out in time, and at the same time, the content of phosgene taken out can be effectively reduced, the utilization rate of phosgene can be ensured, the hydrogen chloride gas in the system can be effectively removed, the yield of 2-fluoropyridine-5-formyl chloride can be ensured, and the content of by-product can be significantly reduced. More importantly, during the process of acyl chloride reaction, the reaction system is stirred and the stirring speed is controlled to be 50r / min-220r / min, so that the contact of phosgene and 6-fluoronicotinic acid can be increased, and the reaction of the two can be promoted, which is beneficial to the generation of 2-fluoropyridine-5-formyl chloride, and is also helpful to promote the overflow of hydrogen chloride gas, so that the hydrogen chloride gas in the system can be removed in time, and the production of by-product can be avoided. In particular, if the speed is too high, the escape of phosgene will also be increased, and the utilization rate of phosgene will be reduced. It can be seen that in the present application, by optimizing the passing speed of phosgene, the passing speed of nitrogen, and the stirring speed, the generation of 2-fluoropyridine-5-formyl chloride can be promoted, and the generation of by-product can be avoided, so that high-yield and high-purity 2-fluoropyridine-5-formyl chloride product can be finally ensured.
[0030] (4) In the present application, by optimizing the temperature of acyl chloride reaction to be 25℃-100℃, not only the rate of acyl chloride reaction can be improved, but also the occurrence of side reaction can be inhibited, which is beneficial to reduce the content of by-product and improve the purity of product, so that high-quality 2-fluoropyridine-5-formyl chloride product can be quickly prepared. In particular, when the reaction temperature is 25℃, the by-product is the least. However, when the temperature is too high, the occurrence of side reaction will be accelerated, and by-product is easy to be formed, which is not conducive to improving the quality of product.
[0031] (5) In the present application, a catalyst is also added in the mixed solution, and the mass ratio of 6-fluoronicotinic acid to catalyst is 100:0.5-3, and the catalyst is N,N-dimethylformamide, so that the reaction of 6-fluoronicotinic acid and phosgene can be promoted, the yield of product can be improved, and the utilization rate of raw material can be improved. DETAILED DESCRIPTION
[0032] The application will be further described in connection with specific preferred embodiments, but the scope of the application is not limited by the specific embodiments.
[0033] In the following examples of the application, the materials and instruments used are commercially available unless otherwise specified, the equipment used is conventional equipment, and the data obtained are the average values of more than three repeated experiments.
[0034] Example 1
[0035] A method for synthesizing 2-fluoropyridine-5-formyl chloride, using 6-fluoronicotinic acid as a raw material and phosgene as an acyl chloride reagent, to prepare 2-fluoropyridine-5-formyl chloride through an acyl chloride reaction, as shown in the following reaction formula:
[0036]
[0037] In this embodiment, the method for synthesizing 2-fluoropyridine-5-formyl chloride includes the following steps:
[0038] Step S1, 400.0 g (2.84 mol) of 6-fluoronicotinic acid, 2500 mL of toluene and 2.0 g of N,N-dimethylformamide were added to a 5000 mL four-necked flask with a thermometer and a condenser, mechanically stirred, and uniformly mixed to obtain a mixed solution.
[0039] Step S2, under the conditions of a rotation speed of 150 r / min and a temperature of 25℃, phosgene was introduced into the mixed solution obtained in step S1 at a speed of 120 g / h, and the molar ratio of 6-fluoronicotinic acid to phosgene was 1:1.5, the acyl chloride reaction was carried out, the reaction time was 5 h, the reaction liquid became clear, and a reaction product liquid was obtained.
[0040] Step S3, nitrogen was introduced into the reaction product liquid obtained in step S2 to remove phosgene, and then the solvent was removed by reduced pressure treatment to obtain 2-fluoropyridine-5-formyl chloride, the content of the product target product was 97.89%, and the content of 6-chloronicotinoyl chloride was 1.81%.
[0041] Example 2
[0042] A method for synthesizing 2-fluoropyridine-5-formyl chloride, using 6-fluoronicotinic acid as a raw material and phosgene as an acyl chloride reagent, to prepare 2-fluoropyridine-5-formyl chloride through an acyl chloride reaction, as shown in the following reaction formula:
[0043]
[0044] In this embodiment, the method for synthesizing 2-fluoropyridine-5-formyl chloride includes the following steps:
[0045] Step S1, 400.0 g (2.84 mol) of 6-fluoronicotinic acid, 2500 mL of toluene and 2.0 g of N,N-dimethylformamide were added into a 5000 mL four-necked flask with a thermometer and a condenser, mechanically stirred, mixed uniformly to obtain a mixed solution.
[0046] Step S2, under the conditions of a rotation speed of 150 r / min and a temperature of 25℃, the phosgene was introduced into the mixed solution obtained in step S1 at a speed of 170 g / h, the molar ratio of 6-fluoronicotinic acid to phosgene was 1:1.5, the acyl chloride reaction was carried out, nitrogen was continuously introduced into the reaction liquid surface at a flow rate of 0.2 L / min, the reaction time was 5 h, the reaction liquid became clear, and the reaction product liquid was obtained.
[0047] In step S2, the acyl chloride reaction also includes taking heat preservation measures to ensure that the reaction is carried out at low temperature. At the same time, nitrogen is continuously introduced into the reaction liquid surface to bubble during the acyl chloride reaction to carry away hydrogen chloride gas. In this embodiment, by taking heat preservation measures, the reaction can be ensured to be carried out at low temperature, which can effectively avoid the generation of by-products, and at the same time, by carrying away hydrogen chloride gas through nitrogen, the by-products are reduced, and the product quality is improved.
[0048] Step S3, nitrogen was introduced into the reaction product liquid obtained in step S2 to remove phosgene, and then the solvent was removed by reduced pressure treatment to obtain 2-fluoropyridine-5-carbonyl chloride.
[0049] In this embodiment, the effects of different molar ratios of 6-fluoronicotinic acid to phosgene on product purity and yield and by-products were also investigated, and other conditions were the same as in Example 2, and the results are shown in Table 1.
[0050] Table 1 Comparison of product purity and yield and by-product data under different molar ratios of 6-fluoronicotinic acid to phosgene
[0051] Molar ratio of 6-fluoronicotinic acid to phosgene Product yield (%) Product purity (%) Content of 6-chloronicotinoyl chloride (%) 1∶1 70.5 77.5 0.5 1∶1.5 97.5 98.6 0.9 1∶2 97.6 98.8 0.9 1∶3 97.2 98.2 0.9 1∶5 96.8 97.8 0.8
[0052] As shown in Table 1, when the molar ratio of 6-fluoronicotinic acid to phosgene is 1:1.5-5.0, 2-fluoropyridine-5-carbonyl chloride with high yield and high purity can be prepared, and the content of by-products is very low, which shows that by optimizing the molar ratio of 6-fluoronicotinic acid to phosgene to 1:1.2-5.0 in the present application, the conversion of 6-fluoronicotinic acid to 2-fluoropyridine-5-carbonyl chloride can be promoted, and the best yield can be obtained. In particular, when the amount of phosgene introduced is small, the yield is low, and when the amount of phosgene introduced is too much, the yield does not change significantly, which not only leads to low utilization rate of phosgene, but also causes difficulty in recovering tail gas.
[0053] In this embodiment, the effects of different acyl chloride reaction temperatures on product purity and yield and by-products were also investigated, and other conditions were the same as in Example 2, and the results are shown in Table 2.
[0054] Table 2 Product purity and yield, byproduct data comparison under different acyl chloride reaction temperature conditions
[0055] Reaction temperature of acyl chloride (°C) Product yield (%) Product purity (%) Content of 6-chloronicotinoyl chloride (%) 25 97.5 98.6 0.9 50 97.6 98.1 1.2 90 97.2 97.7 1.5 110 97.0 96.9 2.0
[0056] As shown in Table 2, when the acyl chloride reaction temperature is 25-100°C, high yield and high purity 2-fluoropyridine-5-carbonyl chloride can be prepared, and the content of byproducts is very low. This shows that by optimizing the acyl chloride reaction temperature to 25-100°C in the present application, not only the acyl chloride reaction rate is improved, but also the occurrence of side reactions is inhibited, which is conducive to reducing the content of byproducts and improving the purity of the product. Thus, high-quality 2-fluoropyridine-5-carbonyl chloride product can be quickly prepared. In particular, when the reaction temperature is 25°C, the byproduct is the least. However, when the temperature is too high, the occurrence of side reactions is accelerated, and byproducts are easily formed, which is not conducive to improving the quality of the product.
[0057] In this example, the effects of different phosgene feeding speeds on product purity and yield, byproducts during the acyl chloride reaction process were also investigated, and other conditions were the same as those in Example 2. The results are shown in Table 3.
[0058] Table 3 Product purity and yield, byproduct data comparison under different phosgene feeding speed conditions during the acyl chloride reaction process
[0059] Different phosgene feeding rate Product yield (%) Product purity (%) Content of 6-chloronicotinoyl chloride (%) 100 g / h 96.5 97.0 1.8 120 g / h 96.8 97.3 1.5 150 g / h 97.3 98.6 1.0 170 g / h 97.5 98.6 0.9 200 g / h 97.8 98.7 0.9
[0060] As shown in Table 3, when the phosgene feeding speed is 120-200 g / h, high yield and high purity 2-fluoropyridine-5-carbonyl chloride can be prepared, and the content of byproducts is very low. This shows that by optimizing the phosgene feeding speed to 120-200 g / h in the present application, the contact and reaction of phosgene and 6-fluoronicotinic acid can be promoted, and the yield of 2-fluoropyridine-5-carbonyl chloride can be significantly improved. At the same time, the generation of hydrogen chloride gas can be inhibited, and the hydrogen chloride gas produced in the system can be removed in time, thereby further inhibiting the formation of byproducts (6-chloronicotinyl chloride), reducing the content of byproducts in the product, and improving the purity of 2-fluoropyridine-5-carbonyl chloride.
[0061] In this example, the effects of different nitrogen feeding speeds on product purity and yield, byproducts during the acyl chloride reaction process were also investigated, and other conditions were the same as those in Example 2. The results are shown in Table 4.
[0062] Table 4 Product purity and yield, byproduct data comparison under different nitrogen feeding speed conditions during the acyl chloride reaction process
[0063] Different nitrogen feeding rate Product yield (%) Product purity (%) Content of 6-chloronicotinoyl chloride (%) 0.1 L / min 97.3 98.0 1.2 0.2 L / min 97.5 98.6 0.9 0.25 L / min 98.6 99.1 0.6 0.3 L / min 99.0 99.1 0.5
[0064] As shown in Table 4, when the nitrogen gas flow rate is 0.1 L / min to 0.3 L / min, 2-fluoropyridine-5-formyl chloride with high yield and high purity can be prepared, and the content of by-products is very low, which shows that, in the process of the acyl chloride reaction, by continuously feeding nitrogen gas into the system and optimizing the nitrogen gas flow rate to 0.1 L / min to 0.3 L / min, the generated hydrogen chloride gas can be effectively carried out of the system, at the same time, the content of the carried-out phosgene can be effectively reduced, the high utilization rate of phosgene is ensured, and the content of by-products can be significantly reduced while ensuring the high yield of 2-fluoropyridine-5-formyl chloride.
[0065] In this embodiment, the effects of different stirring speeds on the purity and yield of the product, and by-products in the process of the acyl chloride reaction are also investigated, and other conditions are the same as those in Example 2, and the results are shown in Table 5.
[0066] Table 5 Comparison of data of different stirring speeds on the purity and yield of the product, and by-products in the process of the acyl chloride reaction
[0067] Different stirring rate Product yield (%) Product purity (%) Content of 6-chloronicotinoyl chloride (%) 50 r / min 97.3 97.8 1.2 100 r / min 97.4 98.1 1.1 150 r / min 97.5 98.6 0.9 180 r / min 97.8 98.7 0.9 220 r / min 97.5 98.7 0.9
[0068] As shown in Table 5, when the stirring speed is 50 r / min to 220 r / min, 2-fluoropyridine-5-formyl chloride with high yield and high purity can be prepared, and the content of by-products is very low, which shows that, in the process of the acyl chloride reaction, by stirring the reaction system and controlling the stirring speed to 50 r / min to 220 r / min, the contact between phosgene and 6-fluoronicotinic acid can be increased, and thus the reaction of the two can be promoted, which is conducive to the generation of 2-fluoropyridine-5-formyl chloride, and also helps to promote the overflow of hydrogen chloride gas, so that the hydrogen chloride gas in the system can be removed in time, and thus the production of by-products can be avoided. In particular, if the stirring speed is too high, the escape of phosgene will also be increased, and thus the utilization rate of phosgene will be reduced.
[0069] As shown in the results in Tables 3 to 5, in the present application, by optimizing the phosgene flow rate, the nitrogen gas flow rate, and the stirring speed, the generation of 2-fluoropyridine-5-formyl chloride can be promoted, and the generation of by-products can be avoided, and finally 2-fluoropyridine-5-formyl chloride with high yield and high purity can be obtained.
[0070] The above results show that, compared with the conventional method, the synthesis method of 2-fluoropyridine-5-formyl chloride can significantly improve the selectivity of the reaction by using 6-fluoronicotinic acid as a raw material and phosgene as an acyl chloride reagent, so that the acyl chloride reaction can be carried out at normal temperature and pressure, more 6-fluoronicotinic acid can be converted into 2-fluoropyridine-5-formyl chloride through the acyl chloride reaction, the generation of by-products (such as 6-chloronicotinyl chloride) can be effectively inhibited, the yield of 2-fluoropyridine-5-formyl chloride can be further improved, and the content of by-products in the product can be reduced, so that higher-quality 2-fluoropyridine-5-formyl chloride can be obtained while the yield of the product is improved, wherein the content of the product is high, the content is 98.3% to 98.9% (gas chromatography, external standard) in terms of mass content, and the yield is high, which is 97.0% to 99.5% in terms of 6-fluoronicotinic acid. The synthesis method of 2-fluoropyridine-5-formyl chloride has the advantages of simple process, convenient operation, low cost, mild reaction conditions, high preparation efficiency, high yield, high purity, environmental friendliness, and the like, and can be used for large-scale preparation of 2-fluoropyridine-5-formyl chloride, so that the industrial application of 2-fluoropyridine-5-formyl chloride can be realized.
[0071] The above examples are only preferred embodiments of the present application, and the protection scope of the present application is not limited to the above examples. Any technical solution falling within the concept of the present application belongs to the protection scope of the present application. It should be pointed out that, for ordinary skilled persons in the technical field, improvements and refinements without departing from the principles of the present application should also be considered as the protection scope of the present application.
Claims
1. A method for synthesizing 2-fluoropyridine-5-carbonyl chloride, characterized in that: 2-Fluoropyridine-5-carbonyl chloride is prepared by acyl chlorination reaction using 6-fluoronicotinic acid as raw material and phosgene as acyl chlorination reagent. The reaction formula is as follows: , including the following steps: Step S1, mixing 6-fluoronicotinic acid with a solvent to obtain a mixed solution; Step S2, introducing phosgene into the mixed solution obtained in step S1 to carry out an acyl chlorination reaction to obtain a reaction product liquid; the phosgene introduction rate is 120 g / h to 200 g / h; nitrogen is continuously introduced into the system during the acyl chlorination reaction; the nitrogen introduction rate is 0.1 L / min to 0.3 L / min; Step S3: removing phosgene and solvent from the reaction product liquid obtained in step S2 to obtain 2-fluoropyridine-5-carbonyl chloride.
2. The synthesis method according to claim 1, wherein In step S2, the molar ratio of 6-fluoronicotinic acid to phosgene is 1:1.2-5.
0.
3. The synthesis method according to claim 2, characterized in that In step S2, the acyl chloride reaction is carried out under stirring conditions at a rotation speed of 50 r / min to 220 r / min.
4. The synthesis method according to any one of claims 1 to 3, characterized in that In step S2, the temperature of the acyl chlorination reaction is 25°C to 100°C.
5. The synthesis method according to claim 4, characterized in that In step S2, the acyl chlorination reaction time is 2.5h to 8h.
6. The synthesis method according to any one of claims 1 to 3, characterized in that In step S1, the mass ratio of the 6-fluoronicotinic acid to the solvent is 1:1-8; the solvent is at least one of benzene, xylene, dichloromethane, 1,2-dichloroethane, chloroform, chlorobenzene, and dichlorobenzene.
7. The synthesis method according to claim 6, characterized in that In step S1, a catalyst is further added to the mixed solution; the mass ratio of the 6-fluoronicotinic acid to the catalyst is 100:0.5-3; and the catalyst is N,N-dimethylformamide.
Citation Information
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