Preparation method of N-methyl o-fluoroaniline

Abstract

The invention discloses a preparation method of N-methyl o-fluoroaniline, which is characterized in that o-fluoroaniline is used as a starting raw material, and a target product is efficiently synthesized through three steps of reaction: step 1, in the presence of a solvent and alkali, o-fluoroaniline and acetyl chloride are acetylated at low temperature to generate 2-fluoro-acetanilide, and the product is directly used for the next step after being roughly purified; 2, under the action of a solvent and alkali, carrying out controllable methylation on the 2-fluorine-acetanilide and dimethyl carbonate to obtain 2-fluorine-N-methylacetanilide; and 3, removing acetyl protection through acidic hydrolysis, and adding sodium thiosulfate to prevent oxidation to finally obtain a high-purity product. According to the method, excessive methylation is avoided through an acetyl protection strategy, the process does not need high-risk operations such as ultralow temperature and high pressure, the operation is simple and convenient, the energy consumption is low, and the product purity is gt; the total yield reaches 79.86%, and the method is green, safe and suitable for industrial production.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of pesticides, medicines and chemical industry, and particularly relates to a preparation method of N-methyl-o-fluoroaniline. BACKGROUND

[0002] N-methyl-o-fluoroaniline belongs to fluorine-containing N-alkyl aniline and is widely used in the fields of dyes, plastics, medicines and pesticides, especially in the synthesis of herbicide metazachlor, and its market demand continues to grow, so optimization of the synthesis process has important industrial value.

[0003] There are many deficiencies in the existing synthesis methods of N-methyl-o-fluoroaniline, which are difficult to meet the efficient, green and low-cost requirements of industrial production, and the specific problems are as follows: 1. Direct methylation method: using o-fluoroaniline as raw material, and reacting with dimethyl carbonate, dimethyl sulfate or methyl iodide and other methylating reagents to synthesize N-methyl-o-fluoroaniline by methylation. In this method, if dimethyl carbonate is used, secondary methylation is easy to occur, the yield of the target product N-methyl-o-fluoroaniline is low, and a large amount of N,N-dimethyl-o-fluoroaniline is generated; if dimethyl sulfate is used, it needs to be carried out at a low temperature of-78℃ and under anhydrous and anaerobic conditions, and dimethyl sulfate is a highly toxic product, which has great safety hazards; if methyl iodide is used, the cost of raw materials is high, and dangerous reagents such as sodium hydride need to be used, which is difficult to industrialize; 2. Catalytic hydrogenation method: the existing technology discloses a method for synthesizing N-methyl-o-fluoroaniline by catalytic hydrogenation of o-fluoroaniline and paraformaldehyde after enamine reaction. In this method, the preparation of N-methylene-o-fluoroaniline is difficult, and the hydrogenation process needs a high-pressure reactor, which has high requirements for equipment, and a large amount of by-products may be generated, resulting in low purity and yield of the intermediate, and difficult separation and purification in the subsequent process; 3. Diazotization-aminolysis method: the existing technology discloses a method for synthesizing N-methyl-o-fluoroaniline by reacting o-fluoroaniline with methylamine aqueous solution after diazotization reaction. In this method, the diazotization reaction is a high-risk process, a large amount of concentrated hydrochloric acid is used, the reaction temperature control is harsh, high temperature is easy to produce organic tar, and a large amount of high-salinity acidic wastewater is generated, which has high treatment cost, the intermediate has poor stability, and the yield and product quality of the subsequent reaction are affected.

[0004] In summary, the existing synthesis process of N-methyl-o-fluoroaniline generally has problems such as poor selectivity, many by-products, harsh reaction conditions, great safety hazards, difficult treatment of three wastes or high cost, and therefore, it is urgent to develop a simple operation, high selectivity, green and safe synthesis method suitable for industrial production. SUMMARY

[0005] In view of the deficiencies of the above-mentioned existing preparation method of N-methyl o-fluoroaniline, the application provides a preparation method of N-methyl o-fluoroaniline, which uses o-fluoroaniline as a starting material, generates 2-fluoro-acetanilide through acetylation reaction, obtains 2-fluoro-N-methyl acetanilide through methylation reaction, and finally generates N-methyl o-fluoroaniline through hydrolysis reaction. The application has multiple advantages such as high yield, high purity, strong safety, low pollution and easy operation, and has significant industrial application value and promotion prospect.

[0006] The technical scheme adopted by the application to achieve the above-mentioned purposes is as follows: A preparation method of N-methyl o-fluoroaniline, comprising the following steps: S1, acetylation reaction of o-fluoroaniline and acetyl chloride in the presence of a solvent and a base to generate 2-fluoro-acetanilide, and the reaction formula is as follows: ; S2, methylation reaction of 2-fluoro-acetanilide and a methylating agent in the presence of a solvent and a base to generate 2-fluoro-N-methyl acetanilide, and the reaction formula is as follows: ; S3, hydrolysis reaction of 2-fluoro-N-methyl acetanilide under acidic conditions to remove the acetyl protecting group to generate N-methyl o-fluoroaniline, and the reaction formula is as follows: .

[0007] Further, the specific preparation method of the step S1 is as follows: o-fluoroaniline, a solvent and a base are uniformly mixed to obtain a mixed solution, the mixed solution is cooled to -5-5 ℃, and then acetyl chloride is slowly added into the mixed solution, the temperature of the system is controlled to be -5-5 ℃ during the adding process of acetyl chloride, after the adding is completed, the temperature is increased to 20-30 ℃, and the reaction is continued at 20-30 ℃ for 2-4 h, after the reaction is completed, the obtained mixed product is subjected to crude purification to obtain a solvent phase containing 2-fluoro-acetanilide, and the next step reaction is directly performed.

[0008] Further, the solvent is a low-polarity aromatic hydrocarbon solvent, preferably toluene, xylene, mesitylene and the like, the base is at least one of sodium bicarbonate, potassium carbonate, sodium carbonate and sodium hydroxide, and the molar ratio of the o-fluoroaniline, acetyl chloride and base is 1.0:1-2:1-2.

[0009] Further, the method for crude purification of the mixed product is as follows: Concentrated ammonia water is added into the obtained mixed product, the mixture is uniformly stirred and then is left to stand to be separated into layers, the organic phase is extracted with water and is separated, the organic phase is extracted with dilute hydrochloric acid and is separated, and a solvent phase containing 2-fluoro-acetanilide is obtained.

[0010] Further, the step S2 is specifically prepared as follows: If the solid 2-fluoro-acetanilide is directly used, the solid 2-fluoro-acetanilide needs to be dissolved in a solvent to obtain a 2-fluoro-acetanilide solution; The base is added to the solvent phase of 2-fluoro-acetanilide or the 2-fluoro-acetanilide solution and mixed uniformly, the temperature of the system is controlled to be not more than 40°C during the process of adding the base, then the temperature is lowered to 25-35°C, then the methylating agent is added dropwise, after the dropwise addition is completed, the temperature is raised to 70-80°C, the reaction is continued at 70-80°C for 2-5h, after the reaction is completed, the obtained mixed product is purified to obtain 2-fluoro-N-methylacetanilide.

[0011] Further, the solvent is a low-polarity aromatic hydrocarbon solvent, preferably toluene, xylene, mesitylene, etc., the base is at least one of sodium hydroxide, potassium hydroxide and cesium carbonate, the methylating agent is at least one of dimethyl carbonate, dimethyl sulfate, chloromethane and bromomethane, the molar ratio of 2-fluoro-acetanilide, base and methylating agent is 1.0:1.5-2.5:0.5-1.5.

[0012] Further, the method for purifying the mixed product is as follows: The obtained mixed product is cooled to room temperature, then water is added thereto, after stirring uniformly, the phases are separated, the organic phase is extracted with dilute hydrochloric acid and the phases are separated, the organic phase is subjected to reduced pressure distillation to remove the solvent to obtain 2-fluoro-N-methylacetanilide.

[0013] Further, the step S3 is specifically prepared as follows: 2-fluoro-N-methylacetanilide and the acid are mixed uniformly, the temperature is raised to 100-110°C, reflux is carried out at 100-110°C for 7-10h, after the reaction is completed, the obtained mixed product is purified to obtain N-methyl-o-fluoroaniline.

[0014] Further, the acid is 20-35wt% concentrated hydrochloric acid, the molar ratio of 2-fluoro-N-methylacetanilide, HCl and sodium thiosulfate is 1.0:2-3:0.05-0.2.

[0015] Further, the method for purifying the mixed product is as follows: The obtained mixed product is cooled to room temperature, then sodium thiosulfate is added thereto and mixed uniformly, then sodium hydroxide is added dropwise to adjust the pH of the system to 10-11, the phases are separated, the organic phase is dried to remove water, and filtration is carried out to obtain N-methyl-o-fluoroaniline.

[0016] Compared with the prior art, the advantages and beneficial effects of the present application are as follows: 1、The step-by-step strategy of acetyl protection-selective methylation-hydrolytic deprotection of the application effectively avoids the excessive methylation side reaction caused by direct methylation, the product purity is greater than 99%, the total yield of three steps reaches 79.86%, which is significantly better than the direct methylation method (the yield is about 5%).

[0017] 2、The acetylation reaction is used for acetyl protection in the first step of the application, the reaction can be carried out at room temperature, and the product only needs to be extracted and purified to obtain the solvent phase for the next step reaction, which reduces the solvent transfer and purification steps, greatly shortens the production cycle, makes the operation more simple, reduces the energy consumption, further reduces the production cost, and is more in line with the requirements of industrial production.

[0018] 3、In the hydrolytic deacetylation step of the application, sodium thiosulfate is added as an antioxidant, which effectively prevents the oxidative degradation of the product, ensures the color and quality of the product, and reduces the waste caused by oxidative degradation of the product.

[0019] 4、The process of the application does not need ultra-low temperature, high pressure hydrogenation or diazotization and other high-risk operations, and also avoids the use of dangerous reagents such as sodium hydride and n-butyllithium. Carbon dioxide is effectively reduced by controllable drop and temperature management, and the residual carbon dioxide is decomposed by adding water in the post-processing, which further ensures the operation safety and is more in line with the requirements of industrial production.

[0020] 5、The post-processing of each step of the application mainly uses extraction, layering and conventional distillation, without complex purification operations such as column chromatography and high vacuum distillation, which simplifies the purification operation and reduces the purification cost. DETAILED DESCRIPTION

[0021] In order to facilitate those skilled in the art to understand and implement the application, the application will be further described in detail below in combination with examples, and it should be understood that the implementation examples described herein are only used to illustrate and explain the application, and are not used to limit the application.

[0022] Example 1 1. Acetylation Into a reaction kettle, 30 L of water was added, and 11.35 kg (135.10 mol, 1.5 eq) of sodium bicarbonate was added under stirring until completely dissolved, then 10 kg (90.00 mol, 1 eq) of o-fluoroaniline and 80 L of toluene (solvent) were sequentially added into the reaction kettle, and after mixing, the temperature was lowered to 0°C. Then 9.55 kg (121.66 mol, 1.35 eq) of acetyl chloride was slowly added dropwise into the reaction kettle, and the temperature was maintained at 0-5°C during the dropwise addition, after the dropwise addition was completed, the temperature was raised to 25°C, and the reaction was continued at 25°C for 2 h. HPLC detection showed that the content of o-fluoroaniline was <0.3%, at which time the reaction was completed. 1.13 kg of concentrated ammonia water (28 wt%) was added to the obtained mixed product, and after stirring uniformly, it was allowed to stand and separate into layers, the aqueous phase was discarded, and the organic phase was extracted with 15 L of water and 1 wt% dilute hydrochloric acid, respectively, to obtain a toluene phase containing 2-fluoroacetanilide, which was directly used in the next step.

[0023] 2. Methylation Into a reaction kettle, 30 L of water was added, and 11.35 kg (135.10 mol, 1.5 eq) of sodium bicarbonate was added under stirring until completely dissolved, then 10 kg (90.00 mol, 1 eq) of o-fluoroaniline and 80 L of toluene (solvent) were sequentially added into the reaction kettle, and after mixing, the temperature was lowered to 0°C. Then 9.55 kg (121.66 mol, 1.35 eq) of acetyl chloride was slowly added dropwise into the reaction kettle, and the temperature was maintained at 0-5°C during the dropwise addition, after the dropwise addition was completed, the temperature was raised to 25°C, and the reaction was continued at 25°C for 2 h. HPLC detection showed that the content of o-fluoroaniline was <0.3%, at which time the reaction was completed. 1.13 kg of concentrated ammonia water (28 wt%) was added to the obtained mixed product, and after stirring uniformly, it was allowed to stand and separate into layers, the aqueous phase was discarded, and the organic phase was extracted with 15 L of water and 1 wt% dilute hydrochloric acid, respectively, to obtain a toluene phase containing 2-fluoroacetanilide, which was directly used in the next step.

[0024] 3. Hydrolysis Into a reaction kettle, 10 kg (59.81 mol, 1 eq) of 2-fluoro-N-methylacetanilide and 18 kg (containing HCl 147.56 mol, 2.5 eq) of 30 wt% hydrochloric acid were added, and after mixing, the temperature was raised to 102°C, and the reaction was continued at 102°C for 7 h. Gas chromatography detection showed that the content of 2-fluoro-N-methylacetanilide was <1%, at which time the reaction was completed, and the temperature was cooled to room temperature. Into the obtained mixed product, 1 kg (6.32 mol, 0.11 eq) of sodium thiosulfate was added, then 30 wt% sodium hydroxide was added dropwise to adjust the pH to 10, and the organic phase was dried with anhydrous sodium sulfate, and was filtered under suction to obtain 6.62 kg of yellowish oily N-methyl-o-fluoroaniline (yield 88.5%, purity >99%).

[0025] 1 H NMR (400 MHz, CDCl3) δ 7.06 – 6.89 (m, 2H), 6.62 (dddd, J = 11.0,7.6, 6.5, 5.2 Hz, 2H), 3.90 (s, 1H), 2.85 (s, 3H)。

[0026] Example 2 1. Acetylation Into a reaction kettle, 21 L of water was added, and 9.0 kg (107.13 mol, 1.5 eq) of sodium bicarbonate was added under stirring until completely dissolved, followed by sequentially adding 7.93 kg (71.33 mol, 1 eq) of o-fluoroaniline and 50 L of toluene (solvent) into the reaction kettle, and after mixing, the temperature was lowered to 2°C. Then, 7.57 kg (96.44 mol, 1.35 eq) of acetyl chloride was slowly added dropwise into the reaction kettle, and during the dropwise addition, the temperature was maintained at 0-5°C. After the dropwise addition was completed, the temperature was raised to 30°C, and the reaction was continued at 30°C for 3 h. HPLC detection showed that the content of o-fluoroaniline was <0.3%, at which time the reaction was completed. To the obtained mixed product, 0.90 kg of concentrated ammonia water (28 wt%) was added, and after stirring uniformly, it was allowed to stand and separate into layers, and the aqueous phase was discarded, and the organic phase was extracted with 12 L of water and 1 wt% dilute hydrochloric acid, respectively, to obtain a toluene phase containing 2-fluoroacetanilide, which was directly used in the next step.

[0027] 2. Methylation Into the reaction kettle, the toluene phase containing 2-fluoroacetanilide was added, followed by sequentially adding 5.71 kg (142.75 mol, 2.0 eq) of sodium hydroxide in batches into the reaction kettle, and during the addition of sodium hydroxide, the temperature of the system was controlled to be not more than 40°C. After the addition of sodium hydroxide was completed, the temperature was lowered to 29°C, and then 5.78 kg (64.17 mol, 0.9 eq) of dimethyl carbonate was added dropwise. After the dropwise addition was completed, the temperature was raised to 75°C, and the reaction was continued at 75°C for 4 h. HPLC detection showed that the content of 2-fluoroacetanilide was <1%, at which time the reaction was completed, and it was cooled to room temperature. To the obtained mixed product, 12 L of water was added to separate the phases, and after stirring uniformly, the phases were separated, and the aqueous phase was discarded, and the organic phase was extracted with 1 wt% dilute hydrochloric acid, and the aqueous phase was discarded, and the organic phase was transferred into a distillation kettle, and heated to 80°C for distillation under reduced pressure (-0.1 MPa) to remove toluene, to obtain 12.1 kg of light yellow 2-fluoro-N-methylacetanilide (two-step yield 90.53%).

[0028] 3. Hydrolysis Into a reactor, add 9.5 kg (56.82 mol, 1 eq) of 2-fluoro-N-methylacetanilide, 17 kg (containing 140.12 mol, 2.47 eq) of 30 wt% hydrochloric acid, mix well, and then heat to 105°C. Reflux at 105°C for 6 h. The content of 2-fluoro-N-methylacetanilide is <1% as detected by gas chromatography. At this time, the reaction is complete, and the temperature is cooled to room temperature. Into the resulting mixture, add 1 kg (6.32 mol, 0.11 eq) of sodium thiosulfate, and then add 30 wt% sodium hydroxide dropwise to adjust the pH to 10. Separate the phases, dry the organic phase with anhydrous sodium sulfate, and filter under suction to obtain 6.22 kg of N-methyl-o-fluoroaniline in the form of a light yellow oil (yield 87.48%, purity >99%).

[0029] Comparative Example 1 1. Acetylation Into a reactor, add 30 L of water, and then add 11.35 kg (135.10 mol, 1.5 eq) of sodium bicarbonate under stirring until completely dissolved. Then, add 10 kg (90.00 mol, 1 eq) of o-fluoroaniline and 80 L of toluene (solvent) into the reactor in sequence, mix well, and then cool to 10°C. Then, slowly add 9.55 kg (121.66 mol, 1.35 eq) of acetyl chloride into the reactor, and maintain the temperature of the system at 10-15°C during the dropwise addition. After the dropwise addition is completed, heat to 25°C, and continue to react at 25°C for 2 h. The content of o-fluoroaniline is <0.3% as detected by HPLC. At this time, the reaction is complete. Into the resulting mixture, add 1.13 kg of concentrated ammonia water (28 wt%), mix well under stirring, and then separate the phases by standing. Discard the aqueous phase, and retain the organic phase. Extract the organic phase with 15 L of water and 1 wt% dilute hydrochloric acid in sequence to obtain a toluene phase containing 2-fluoro-acetanilide, which is directly used in the next step.

[0030] The amino group of o-fluoroaniline is highly active. If the temperature of the dropwise addition of acetyl chloride is >5°C, the local reaction of acetyl chloride will be intense, which will cause an excessive acetylation side reaction. If the temperature is <-5°C, the activity of acetyl chloride will decrease sharply, and the conversion of the raw material will not be complete.

[0031] 2. Methylation According to the method and the feeding operation of Example 1, 10.1 kg of 2-fluoro-N-methylacetanilide is obtained (two-step yield 67.8%).

[0032] 3. Hydrolysis According to the method and the feeding operation of Example 1, 5.23 kg of N-methyl-o-fluoroaniline is obtained (yield 70.3%, purity 97.8%, containing 1.5% of unknown by-products).

[0033] Comparative Example 2 1. Acetylation According to the method and the feeding operation of Example 1, a toluene phase containing 2-fluoro-acetanilide is obtained.

[0034] 2. Methylation Into a reactor, 2-fluoro-acetanilide in toluene phase was charged, then 7.21 Kg (180.25 mol, 2.0 eq) sodium hydroxide was charged into the reactor in batches, and the temperature of the system was controlled to be no more than 40°C during the addition of sodium hydroxide. After the addition of sodium hydroxide was completed, the temperature was lowered to 30°C, then 7.30 kg (81.04 mol, 0.9 eq) dimethyl carbonate was added dropwise, after the dropwise addition was completed, the temperature was raised to 60°C, and the reaction was continued at 60°C for 3 h. HPLC detection showed that the content of 2-fluoro-acetanilide was 8.5%, at which point the reaction was completed, and the temperature was cooled to room temperature. 12 L water was added to the obtained mixed product to separate the phases, after stirring, the aqueous phase was discarded and the organic phase was retained. The organic phase was extracted with 1 wt% dilute hydrochloric acid to separate the phases, the aqueous phase was discarded and the organic phase was retained. The organic phase was transferred into a distillation kettle, heated to 80°C, and distilled under reduced pressure (-0.1 MPa) to remove toluene, thereby obtaining 10.2 kg of light yellow 2-fluoro-N-methylacetanilide (two-step yield 68.7%).

[0035] The activity of dimethyl carbonate was moderate at 70-80°C, and the reaction was efficient; the activity was insufficient when the temperature was <70°C, and the residual 2-fluoro-acetanilide was >5%; when the temperature was >80°C, dimethyl carbonate was decomposed, and the side reaction of ester exchange was initiated, and the byproduct increased by more than 3%.

[0036] 3. Hydrolysis According to the method and the feeding operation of Example 1, 4.89 kg of N-methyl-o-fluoroaniline was obtained (yield 65.2%, purity 97.2%, containing 2.1% unreacted intermediate).

Claims

1. A process for the preparation of N-methyl-o-fluoroaniline, characterized in that The method comprises the following steps: S1, acetylation reaction of o-fluoroaniline and acetyl chloride in the presence of a solvent and a base to generate 2-fluoro-acetanilide, and the reaction formula is as follows: ； S2, methylation reaction of 2-fluoro-acetanilide and a methylating agent in the presence of a solvent and a base to generate 2-fluoro-N-methylacetanilide, and the reaction formula is as follows: ； S3, hydrolysis reaction of 2-fluoro-N-methylacetanilide under acidic conditions to remove an acetyl protecting group to generate N-methyl-o-fluoroaniline, and the reaction formula is as follows: 。 2. The process for the preparation of N-methylaniline-o-fluoride according to claim 1, characterized in that The specific preparation method of the step S1 is as follows: The o-fluoroaniline, the solvent and the base are uniformly mixed to obtain a mixed solution, the mixed solution is cooled to-5-5 ℃, then acetyl chloride is slowly added into the mixed solution, the temperature of the system is controlled to be-5-5 ℃ during the adding process of the acetyl chloride, after the adding process is completed, the temperature is increased to 20-30 ℃, the reaction is continuously carried out at 20-30 ℃ for 2-4 h, after the reaction is completed, the obtained mixed product is subjected to crude purification to obtain a solvent phase containing 2-fluoro-acetanilide, and the next step reaction is directly carried out.

3. Process for the preparation of N-methylaniline-o-fluoride according to claim 1 or 2, characterized in that: The solvent is a low-polarity aromatic hydrocarbon solvent, the base is at least one of sodium bicarbonate, potassium carbonate, sodium carbonate and sodium hydroxide, and the molar ratio of the o-fluoroaniline, the acetyl chloride and the base is 1.0:1-2:1-2.

4. The process for the preparation of N-methylaniline-o-fluoride according to claim 2, characterized in that The method for the crude purification of the mixed product is as follows: Concentrated ammonia water is added into the obtained mixed product, the mixed product is uniformly stirred and then is allowed to stand to be separated into layers, the collected organic phase is extracted with water and is separated into phases, the organic phase is extracted with dilute hydrochloric acid and is separated into phases to obtain a solvent phase containing 2-fluoro-acetanilide.

5. The process for the preparation of N-methyl o-fluoroaniline according to claim 1 or 2, characterized in that The specific preparation method of the step S2 is as follows: If the solid 2-fluoro-acetanilide is directly used, the solid 2-fluoro-acetanilide needs to be dissolved in a solvent to obtain a 2-fluoro-acetanilide solution; The base is added into the solvent phase of the 2-fluoro-acetanilide or the 2-fluoro-acetanilide solution and is uniformly mixed, the temperature of the system is controlled to be not higher than 40 ℃ during the adding process of the base, then the system is cooled to 25-35 ℃, then the methylating agent is slowly added, after the adding process is completed, the temperature is increased to 70-80 ℃, the reaction is continuously carried out at 70-80 ℃ for 2-5 h, after the reaction is completed, the obtained mixed product is purified to obtain 2-fluoro-N-methylacetanilide.

6. The process for the preparation of N-methylaniline-o-fluoride according to claim 5, characterized in that: The solvent is a low-polarity aromatic hydrocarbon solvent, the methylating agent is at least one of dimethyl carbonate, dimethyl sulfate, chloromethane and bromomethane, the base is at least one of sodium hydroxide, potassium hydroxide and cesium carbonate, and the molar ratio of the 2-fluoro-acetanilide, the base and the methylating agent is 1.0:1.5-2.5:0.5-1.

5.

7. The process for the preparation of N-methylaniline-o-fluoride according to claim 5, characterized in that The method for the purification of the mixed product is as follows: The obtained mixed product is cooled to room temperature, then water is added into the mixed product, the mixed product is uniformly stirred and then is separated into phases, the organic phase is extracted with dilute hydrochloric acid and is separated into phases, and the organic phase is subjected to reduced-pressure distillation to remove the solvent to obtain 2-fluoro-N-methylacetanilide.

8. The process for the preparation of N-methylaniline-o-fluoride according to claim 1, characterized in that The specific preparation method of the step S3 is as follows: The 2-fluoro-N-methylacetanilide and the acid are uniformly mixed, the temperature is increased to 100-110 ℃, the system is refluxed at 100-110 ℃ for 7-10 h, after the reaction is completed, the obtained mixed product is purified to obtain N-methyl-o-fluoroaniline.

9. The process for the preparation of N-methylaniline-o-fluoride according to claim 8, characterized in that: The acid is 20-35 wt% concentrated hydrochloric acid, the molar ratio of 2-fluoro-N-methylacetanilide, HCl and sodium thiosulfate is 1.0:2-3:0.05-0.

2.

10. The process for the preparation of N-methylaniline-o-fluoride according to claim 8, characterized in that The method for purifying the mixed product is: The obtained mixed product is cooled to room temperature, then sodium thiosulfate is added thereto and mixed, then sodium hydroxide is added dropwise to adjust the pH of the system to 10-11, the phases are separated, the organic phase is dried to remove water, and filtration is performed to obtain N-methyl o-fluoroaniline.

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