CN116023271B - Synthesis method of p-fluoroaniline - Google Patents
Synthesis method of p-fluoroaniline Download PDFInfo
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Abstract
The invention provides a method for synthesizing p-fluoroaniline, belonging to the technical field of chemical intermediate preparation; the method efficiently utilizes the byproduct 3, 5-dichloro-4-nitrobenzene, and solves the technical problems of lower yield and higher cost of the existing method for synthesizing the p-fluoroaniline. Respectively adding 3, 5-dichloro-4-fluoronitrobenzene, an active carbon supported nickel-silver catalyst, sodium hydroxide and a solvent into a reaction kettle, wherein the molar ratio of the sodium hydroxide to the 3, 5-dichloro-4-fluoronitrobenzene is 1.9-2.1, and the solvent is C 1 ～C 3 An organic alcohol or an aqueous solution thereof; sealing the reaction kettle, heating the reaction kettle to 130-160 ℃ in a hydrogen atmosphere, then charging hydrogen to 3.0-5.0 MPa in the reaction kettle, starting stirring, maintaining the reaction pressure to 3.0-5.0 MPa, and keeping the reaction temperature to 130-160 ℃ until the pressure in the kettle is not changed; opening the reaction kettle, filtering the reaction liquid to obtain filtrate, rectifying and separating the filtrate, distilling the organic alcohol at normal pressure, removing water from the filtrate, and distilling under reduced pressure at 20mmHg to collect the fraction at 85-86 ℃ to obtain the p-fluoroaniline.
Description
Technical Field
The application relates to the technical field of chemical intermediate preparation, in particular to a method for synthesizing p-fluoroaniline.
Background
Para-fluoroaniline is also called 4-fluoroaniline, CAS number: 371-40-4, molecular formula C 6 H 6 FN, which is a yellowish oily liquid with pungent smell, is an important fine chemical product for medicine, dye and agricultureThe pharmaceutical industry and the like, for example, can be used for synthesizing plant growth regulators, herbicides and various pharmaceutical intermediates. The structural formula is as follows:
the Chinese patent application publication No. CN101624348A discloses a preparation method of p-fluoroaniline: 3, 5-dichloro-4-fluoronitrobenzene and a solvent are mixed to form a reaction solution, the reaction solution is hydrogenated in an autoclave under the action of a catalyst to carry out reduction dechlorination reaction, the reaction pressure is 1.0-4.0 MPa, the reaction temperature is 60-120 ℃, and the reaction time is 2-5 hours; the mass ratio of the catalyst to the 3, 5-dichloro-4-fluoronitrobenzene is 1-40%; after the reaction is finished, collecting a liquid reaction product, filtering, adding an antioxidant into the filtrate, and rectifying to obtain the p-fluoroaniline. The method for preparing the para-fluoroaniline has the characteristics of simple process, high yield and low cost. However, the yield of the p-fluoroaniline is 48-70%, the reaction yield is lower, palladium carbon is used as a catalyst, the current price of the palladium carbon is about 50000 yuan/kg, the price is high, the cost is too high, and the method has no industrial application prospect.
Disclosure of Invention
The invention aims to solve the defects of the technology and provide a method for synthesizing p-fluoroaniline, which efficiently utilizes the byproduct 3, 5-dichloro-4-nitrobenzene, improves the yield of the p-fluoroaniline, reduces the cost and has more industrial value.
The invention provides a method for synthesizing p-fluoroaniline, which comprises the steps of respectively adding 3, 5-dichloro-4-fluoronitrobenzene, an active carbon supported nickel-silver catalyst, sodium hydroxide and a solvent into a reaction kettle, wherein the molar ratio of the sodium hydroxide to the 3, 5-dichloro-4-fluoronitrobenzene is 1.9-2.1, and the solvent is C 1 ～C 3 Or C 1 ～C 3 An aqueous organic alcohol solution of (2); sealing the reaction kettle, heating the reaction kettle to 130-160 ℃ in a hydrogen atmosphere, then charging hydrogen until the pressure in the reaction kettle reaches 3.0-5.0 MPa, starting stirring, maintaining the reaction pressure at 3.0-5.0 MPa in the reaction process, and maintaining the reaction temperature at 13The temperature is kept between 0 and 160 ℃ and the reaction is carried out until the pressure in the kettle is not changed any more and the reaction is finished; opening the reaction kettle, filtering the reaction liquid to obtain a filtrate, rectifying and separating the filtrate, distilling the organic alcohol at normal pressure, removing water from the filtrate, and then distilling under reduced pressure at 20mmHg to collect a fraction at 85-86 ℃ to obtain the p-fluoroaniline.
Preferably, the preparation method of the activated carbon supported nickel-silver catalyst comprises the following steps:
(1) Pretreating active carbon with nitric acid for later use;
(2) Drying and heat-treating the activated carbon treated by the nitric acid in the step (1) in an inert atmosphere, removing water in the activated carbon through drying and heat-treating, and placing the heat-treated activated carbon in a dryer for later use;
(3) Mixing and stirring a proper amount of nickel nitrate aqueous solution, silver nitrate aqueous solution and the activated carbon after the heat treatment in the step (2) uniformly, and refining for 18 hours at room temperature to obtain a precursor;
(4) Putting the precursor obtained in the step (3) into an electrothermal blowing drying box, adjusting the temperature to 130 ℃, and drying for 16 hours; and then placing the mixture into a muffle furnace for burning and cultivating for 5 hours at 500 ℃ to finally obtain the activated carbon supported nickel-silver catalyst.
Preferably, the active carbon supported nickel-silver catalyst is reduced and activated for 2 hours at 400 ℃ in hydrogen atmosphere before being used, and is cooled to room temperature and then is subjected to N 2 And adding the mixture into a reaction kettle under protection.
Preferably, the activated carbon supports a nickel silver catalyst xNi-yiag/AC, wherein the total metal loading is 20wt%, x: y=10:10.
Preferably, C 1 ～C 3 The volume fraction of the organic alcohol in the organic alcohol aqueous solution is 30-80%, wherein C is as follows 1 ～C 3 The organic alcohol is methanol, ethanol, propanol.
Preferably, the organic alcohol is methanol.
Preferably, after the reaction kettle is sealed, nitrogen is firstly filled to replace air in the reaction kettle, and then hydrogen is filled to replace nitrogen in the reaction kettle, so that a hydrogen atmosphere is formed in the reaction kettle.
Preferably, after the heat preservation reaction is finished, the temperature in the reaction kettle is firstly reduced to the room temperature, the exhaust valve is opened for pressure relief, and then the reaction kettle is opened.
The beneficial effects of the invention are as follows: the invention provides a method for synthesizing p-fluoroaniline, which is characterized in that 3, 5-dichloro-4-fluoronitrobenzene is subjected to hydrogenation reduction under the catalysis of an active carbon supported nickel-silver catalyst, p-fluoroaniline and hydrogen chloride are generated by gradual dechlorination in the reduction process, and the generated hydrogen chloride is neutralized by adding alkali to prevent the catalyst from being poisoned. The 3, 5-dichloro-4-fluoronitrobenzene is used for preparing the p-fluoroaniline by using the activated carbon supported nickel-silver catalyst for catalytic hydrogenation dehalogenation under the alkaline condition, so that the cost of raw materials is low, the price of the catalyst is low, the p-fluoroaniline can be recycled, and the yield of the p-fluoroaniline can reach 93.01 percent on the basis of ensuring the efficient utilization of the byproduct 3, 5-dichloro-4-nitrobenzene and not increasing the synthetic route of the p-fluoroaniline, and compared with the prior reported process route, the cost is obviously reduced, the yield is obviously improved, the economic benefit is high, and the p-fluoroaniline has more industrialized value.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings that are required for the embodiments or the description of the prior art will be briefly described below, it being obvious that the drawings in the following description are only some embodiments of the present application, and that other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is a total ion flow diagram of the rectified p-fluoroaniline fraction obtained in example 8 in a positive ion mode using a liquid-mass spectrometer;
fig. 2 is a mass spectrum of a substance in a positive ion mode with a peak time of 1.957min in the total ion flow diagram shown in fig. 1, wherein a peak of 112 in the spectrum is a molecular weight of a compound combined with one hydrogen ion, and a peak of 113 is a molecular weight of a corresponding isotope peak.
Detailed Description
In order to make the technical problems, technical schemes and beneficial effects to be solved by the present application more clear, the present application is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the present application. The method used in the invention is a conventional method unless specified otherwise; the raw materials and devices used, unless otherwise specified, are all conventional commercial products.
Example 1
210g (1 mol) of 3, 5-dichloro-4-fluoronitrobenzene, 21g of active carbon supported nickel silver catalyst xNi-yAg/AC (total metal load is 20wt%, x: y=10:10), 80g (2 mol) of sodium hydroxide and 1470g of 50% methanol water mixed solution (V/V) are added into a reaction kettle, the reaction kettle is sealed, the temperature is raised to 160 ℃ at the inner temperature, the hydrogen is filled to 4.0MPa, stirring is started, the pressure is kept at 3.5-4.0 MPa in the reaction process, and the temperature is kept until the pressure is not changed. And after the heat preservation is finished, cooling the system to room temperature, and opening an exhaust valve to release pressure. The catalyst is filtered and recovered after the kettle is opened to be reserved for the next batch of reaction, the filtrate is rectified and separated, the methanol is distilled off at normal pressure, the water is removed from the filtrate, and then the fraction at 85-86 ℃ is collected by reduced pressure distillation under the pressure of 20mmHg, so that 100.20g of p-fluoroaniline is obtained, the conversion rate is 100%, and the yield is 90.17%.
Example 2
The difference between the method of this example and example 1 is that the reaction temperature is 150 ℃, the other contents are the same, the catalyst is recovered by filtration after opening the kettle and is used as the next batch of reaction, the filtrate is distilled and separated, the methanol is distilled off at normal pressure, the water is removed from the liquid, then the distillation is carried out under reduced pressure at 20mmHg to collect the fraction at 85-86 ℃, 102.61g of p-fluoroaniline is obtained, the conversion rate is 100%, and the yield is 92.34%.
Example 3
The difference between the method of this example and example 1 is that the reaction temperature is 140 ℃, the other contents are the same, the catalyst is recovered by filtration after opening the kettle and is used for the next batch of reaction, the filtrate is rectified and separated, the methanol is distilled off at normal pressure, the water is removed from the liquid, and then the fraction of 85-86 ℃ is collected by reduced pressure distillation under the pressure of 20mmHg, thus 102.44g of p-fluoroaniline is obtained, the conversion rate is 99.11%, and the yield is 92.19%.
Example 4
The difference between the method of this example and example 1 is that the reaction temperature is 130 ℃, the other contents are the same, the catalyst is filtered and recovered after the kettle is opened and is reserved for the next batch of reaction, the filtrate is rectified and separated, the methanol is distilled off at normal pressure, the water is removed from the liquid, and then the fraction of 85-86 ℃ is collected by reduced pressure distillation under the pressure of 20mmHg, thus 102.53g of p-fluoroaniline is obtained, the conversion rate is 96.65%, and the yield is 92.27%.
As is clear from examples 1 to 4, the conversion rate gradually increased with increasing temperature, and the reaction temperature was 130 to 160 ℃.
Example 5
The difference between the method of this example and example 1 is that the addition amount of sodium hydroxide is 84g (2.1 mol), namely the molar ratio of 3, 5-dichloro-4-fluoronitrobenzene to sodium hydroxide is 1:2.1, the other content is the same, the catalyst is recovered by filtration after opening the kettle and is remained for the next reaction, the filtrate is rectified and separated, methanol is distilled off at normal pressure, water is removed from the filtrate, then the distillate at 85-86 ℃ is distilled off under reduced pressure under the pressure of 20mmHg, 103.22g of p-fluoroaniline is obtained, the conversion rate is 100%, and the yield is 92.89%.
Example 6
The difference between the method of this example and example 1 is that the addition amount of sodium hydroxide is 76g (1.9 mol), namely the molar ratio of 3, 5-dichloro-4-fluoronitrobenzene to sodium hydroxide is 1:1.9, the other content is the same, the catalyst is recovered by filtration after opening the kettle and is reserved for the next reaction, the filtrate is rectified and separated, methanol is distilled off at normal pressure, water is removed from the liquid, then the liquid is distilled off under reduced pressure at 20mmHg, and the fraction at 85-86 ℃ is collected to obtain 99.47g of p-fluoroaniline, the conversion rate is 98.98%, and the yield is 89.52%.
As is clear from examples 1, 5 and 6, as the equivalent of sodium hydroxide increases, i.e., the molar ratio of 3, 5-dichloro-4-fluoronitrobenzene to sodium hydroxide gradually increases, the conversion and the yield increase first and then decrease, and the molar ratio of 3, 5-dichloro-4-fluoronitrobenzene to sodium hydroxide is 1:1.9-2.1.
Example 7
The difference between the method of this example and example 1 is that hydrogen is charged to 3.0 MPa, the pressure is maintained at 2.5-3.0 MPa during the reaction, the other content is the same, the catalyst is recovered by filtration after opening the kettle and is reserved for the next batch of reaction, the filtrate is rectified and separated, methanol is distilled off under normal pressure, water is removed from the liquid, then the distillate at 85-86 ℃ is collected by reduced pressure distillation under the pressure of 20mmHg, 98.28g of p-fluoroaniline is obtained, the conversion rate is 95.13%, and the yield is 88.44%.
Example 8
The difference between the method of this example and example 1 is that hydrogen is charged to a pressure of 5.0 MPa, the pressure is maintained to be controlled to be 4.5-5.0 MPa in the reaction process, the other content is the same, the catalyst is filtered and recovered after the kettle is opened and is reserved for the next batch of reaction, the filtrate is rectified and separated, methanol is distilled off under normal pressure, water is removed from the liquid, then the distilled liquid is distilled off under reduced pressure under the pressure of 20mmHg to collect the fraction at 85-86 ℃ to obtain 103.35g of p-fluoroaniline, the conversion rate is 100%, and the yield is 93.01%.
As is clear from examples 1, 7 and 8, the conversion and the yield gradually increased with increasing reaction pressure, and the reaction pressure was 3.0 to 5.0 MPa.
Example 9
The difference between the method of this example and example 1 is that the reaction solvent is 80% methanol-water mixed solution (V/V), the other contents are the same, the catalyst is recovered by filtration after opening the kettle and is used as the next batch of reaction, the filtrate is distilled and separated, the methanol is distilled off at normal pressure, the water is removed by liquid separation, then the fraction at 85-86 ℃ is collected by distillation under reduced pressure under the pressure of 20mmHg, 100.09g of p-fluoroaniline is obtained, the conversion rate is 98.79%, and the yield is 90.08%.
Example 10
The difference between the method of this example and example 1 is that the reaction solvent is 30% methanol-water mixed solution (V/V), the other contents are the same, the catalyst is recovered by filtration after opening the kettle and is used for the next batch of reaction, the filtrate is distilled and separated at normal pressure, the methanol is distilled off at first, the water is removed by the liquid, then the fraction at 85-86 ℃ is collected by reduced pressure distillation under the pressure of 20mmHg, 101.16g of p-fluoroaniline is obtained, the conversion rate is 100%, and the yield is 91.04%.
Example 11
The difference between the method of this example and example 1 is that the reaction solvent is methanol, the other content is the same, the catalyst is recovered by filtration after opening the kettle and is used as the next batch of reaction, the filtrate is rectified and separated, the methanol is distilled off at normal pressure, then the distillation is carried out under reduced pressure at 20mmHg, and the fraction at 85-86 ℃ is collected, thus 93.11g of p-fluoroaniline is obtained, the conversion rate is 92.23%, and the yield is 83.79%.
Example 12
The difference between the method of this example and example 1 is that the reaction solvent is ethanol, the other content is the same, the catalyst is recovered by filtration after opening the kettle and is used as the next batch of reaction, the filtrate is rectified and separated, the ethanol is distilled off at normal pressure, then the distillation is carried out under reduced pressure at 20mmHg, the fraction at 85-86 ℃ is collected, 89.95g of para-fluoroaniline is obtained, the conversion rate is 89.93%, and the yield is 80.95%.
As is clear from examples 1, 9, 10, 11 and 12, the conversion and yield are significantly improved by adding water into the reaction system, because the water can dissolve the salt generated by the reaction to prevent the salt from blocking the catalyst pore channels, propanol, like methanol and ethanol, is an organic alcohol solvent with lower boiling point, C 1 ～C 3 The volume fraction of the organic alcohol in the organic alcohol aqueous solution is 30-80%.
Example 13
The method of this example is different from example 1 in that the activated carbon-supported nickel-silver catalyst used is the catalyst used after filtration in example 1, the other content is the same, the filtration and recovery of the catalyst after opening the kettle is continued to carry out the application test, the total application is five times, and the post-treatment operation is the same as in example 1.
99.45g of p-fluoroaniline is obtained after the first application, the conversion rate is 100%, and the yield is 89.50%; 98.89g of p-fluoroaniline is obtained after the second application, the conversion rate is 100%, and the yield is 88.99%; 98.17g of p-fluoroaniline is obtained after the third application, the conversion rate is 100%, and the yield is 88.35%; 97.39g of p-fluoroaniline is obtained after the fourth application, the conversion rate is 100%, and the yield is 87.64%; 96.26g of p-fluoroaniline is obtained in the fifth application, the conversion rate is 100%, and the yield is 86.63%. As can be seen, the catalyst used in example 1 has better stability and higher repeatability.
Comparative example 1
The comparative example was different from example 1 in that the catalyst was xNi-yCu/AC (total metal loading 20wt%, x: y=10:10), the other matters were the same, the catalyst was recovered by filtration after opening the pot and was used as the next reaction, the filtrate was distilled off, methanol was distilled off at normal pressure, water was removed from the filtrate, and then a fraction at 85 to 86 ℃ was collected by distillation under reduced pressure at a pressure of 20mmHg, to give 54.35g of 4-fluoroaniline, a conversion rate of 79.74% and a yield of 48.91%.
Comparative example 2
The comparative example was different from example 1 in that the catalyst was xNi-yCo/AC (total metal loading 20wt%, x: y=10:10), the other matters were the same, the catalyst was recovered by filtration after opening the pot and was used as the next reaction, the filtrate was distilled off, methanol was distilled off at normal pressure, water was removed from the filtrate, and then a fraction at 85 to 86 ℃ was collected by distillation under reduced pressure at a pressure of 20mmHg, to give 67.45g of 4-fluoroaniline, a conversion rate 86.69%, and a yield of 60.70%.
Comparative example 3
The comparative example was different from example 1 in that the catalyst was xNi-yFe/AC (total metal loading 20wt%, x: y=10:10), the other matters were the same, the catalyst was recovered by filtration after opening the pot and was used as the next reaction, the filtrate was distilled off, methanol was distilled off at normal pressure, water was removed from the filtrate, and then a fraction at 85 to 86 ℃ was collected by distillation under reduced pressure at a pressure of 20mmHg, to give 30.83g of 4-fluoroaniline, a conversion rate 55.64%, and a yield of 27.74%.
From example 1 and comparative examples 1 to 3, the metal promoter of the nickel-based catalyst is preferably Ag, i.e., the modified catalyst is preferably xNi-yiag/AC (total metal loading 20wt%, x: y=10:10).
As the modified nickel-based catalyst, the preparation method of the activated carbon supported nickel-silver catalyst can be used in the prior art, and the following preparation method can also be adopted: the active carbon is pretreated by nitric acid, dilute nitric acid or concentrated nitric acid can be used, and the residual metal ions are usually washed off by adopting the dilute nitric acid for standby. And (3) carrying out controlled oxidation and heat treatment under inert atmosphere on the activated carbon treated by nitric acid, and placing the activated carbon subjected to heat treatment in a dryer for standby. Weighing a proper amount of nickel nitrate aqueous solution, silver nitrate aqueous solution and heat-treated activated carbon, mixing and stirring uniformly, and refining at room temperature for 18 hours to obtain a precursor. The precursor is firstly put into an electrothermal blowing drying box, and the temperature is adjusted to 130 ℃ for drying for 16 hours; and then placing the mixture into a muffle furnace for burning and cultivating for 5 hours at 500 ℃ to finally prepare the activated carbon supported nickel-silver catalyst expressed as xNi-yAg/AC, wherein the molar ratio of x to y can guide the addition of the nickel nitrate aqueous solution, the silver nitrate aqueous solution and the activated carbon after heat treatment according to actual production requirements. The activated carbon used in examples 1-13 supported nickel silver catalysts, expressed as xNi-yiag/AC, where the total metal loading was 20wt%, x: y=10:10 (molar ratio).
The preparation method of the modified nickel-based catalyst in the above comparative examples 1 to 3 is the same as the preparation method of the activated carbon-supported nickel-silver catalyst, except that the silver nitrate aqueous solution is replaced with a copper nitrate aqueous solution, a cobalt nitrate aqueous solution, and an aqueous solution of an aqueous nitrate, respectively, expressed as: xNi-yCu/AC, xNi-yCo/AC, xNi-yFe/AC, where the total metal loading is 20wt%, x: y=10:10 (molar ratio).
The modified nickel-based catalyst is reduced and activated for 2 hours at 400 ℃ by hydrogen (usually 20 ml/min and flowmeter value) before being used, cooled to room temperature in a hydrogen stream, and then treated with N 2 The catalyst is added into the reaction liquid under the protection, and the operation of the catalyst after reduction is carried out under the anaerobic condition.
Sampling and sending the rectified p-fluoroaniline fraction obtained in the example 8 to a liquid-mass spectrometer for combined use, wherein the total ion flow diagram under the positive ion mode is shown in figure 1; then the instrument automatically carries out mass spectrum detection on the main substance with the peak time of 1.957min in the figure 1, and the mass spectrum of the main substance in the positive ion mode is shown in figure 2.
From FIG. 1, it can be seen that the main substance in the test sample is a substance of 1.957 min; as shown in fig. 2, the mass spectrum detection result of the substance of 1.957min in fig. 1 is compared with the molecular weight of the possible products of the reaction one by one, and the obtained result is: the molecular weight of the structure of the compound combined with one hydrogen ion detected in the positive ion mode is 112 (113 in a mass spectrum is an isotope peak), so that the molecular weight of the corresponding compound is 111 and is matched with the accurate molecular weight 111.05 of the p-fluoroaniline; and finally determining the sample to be measured as p-fluoroaniline. From the data of the mass spectrum in fig. 2 and the possible structural correspondence of the reaction, the product was determined to be p-fluoroaniline.
In examples 1 to 13 and comparative examples 1 to 3, the method for forming the hydrogen atmosphere in the reaction vessel was as follows: after the reaction kettle is sealed, firstly filling nitrogen to replace air in the reaction kettle, and then filling hydrogen to replace nitrogen in the reaction kettle, so that a hydrogen atmosphere is formed in the reaction kettle. In addition, after the air in the reaction kettle is replaced by the nitrogen, the hydrogen can be directly filled into the reaction kettle, so that the reaction pressure of the hydrogen atmosphere in the reaction kettle can be reached.
The invention provides a method for synthesizing p-fluoroaniline, which is characterized in that 3, 5-dichloro-4-fluoronitrobenzene is subjected to hydrogenation reduction under the catalysis of an active carbon supported nickel-silver catalyst, p-fluoroaniline and hydrogen chloride are generated by gradual dechlorination in the reduction process, and the generated hydrogen chloride is neutralized by adding alkali to prevent the catalyst from being poisoned. The 3, 5-dichloro-4-fluoronitrobenzene is used for carrying the nickel silver catalyst to catalyze and hydrodehalogenating under the alkaline condition to prepare the p-fluoroaniline, so that the cost of raw materials is low, the price of the catalyst is lower, the catalyst can be recycled, the yield of the p-fluoroaniline can reach 93.01 percent, and compared with the prior reported process route, the cost is obviously reduced, the yield is obviously improved, the economic benefit is high, and the method has more industrialized value.
The foregoing description of the preferred embodiments of the present application is not intended to be limiting, but is intended to cover any and all modifications, equivalents, and alternatives falling within the spirit and principles of the present application.
Claims (8)
1. A method for synthesizing p-fluoroaniline is characterized in that 3, 5-dichloro-4-fluoronitrobenzene, an active carbon supported nickel-silver catalyst, sodium hydroxide and a solvent are respectively added into a reaction kettle, wherein the molar ratio of the sodium hydroxide to the 3, 5-dichloro-4-fluoronitrobenzene is 1.9-2.1, and the solvent is C 1 ～C 3 Or C 1 ～C 3 An aqueous organic alcohol solution of (2); sealing the reaction kettle, heating the reaction kettle to 130-160 ℃ in a hydrogen atmosphere, and then filling hydrogen until the pressure in the reaction kettle reachesStarting stirring until the pressure reaches 3.0-5.0 MPa, maintaining the reaction pressure at 3.0-5.0 MPa in the reaction process, maintaining the reaction temperature at 130-160 ℃, and performing heat preservation reaction until the pressure in the kettle is not changed any more, and ending the heat preservation reaction; opening the reaction kettle, filtering the reaction liquid to obtain a filtrate, rectifying and separating the filtrate, distilling the organic alcohol at normal pressure, removing water from the filtrate, and then distilling under reduced pressure at 20mmHg to collect a fraction at 85-86 ℃ to obtain the p-fluoroaniline.
2. The method for synthesizing p-fluoroaniline according to claim 1, wherein the method for preparing the activated carbon supported nickel-silver catalyst comprises the following steps:
(1) Pretreating active carbon with nitric acid for later use;
(2) Drying and heat-treating the activated carbon treated by the nitric acid in the step (1) in an inert atmosphere, and placing the heat-treated activated carbon in a dryer for standby;
(3) Mixing and stirring a proper amount of nickel nitrate aqueous solution, silver nitrate aqueous solution and the activated carbon after the heat treatment in the step (2) uniformly, and refining for 18 hours at room temperature to obtain a precursor;
(4) Putting the precursor obtained in the step (3) into an electrothermal blowing drying box, adjusting the temperature to 130 ℃, and drying for 16 hours; and then placing the mixture into a muffle furnace for burning and cultivating for 5 hours at 500 ℃ to finally obtain the activated carbon supported nickel-silver catalyst.
3. The method for synthesizing p-fluoroaniline according to claim 2, wherein the activated carbon supported nickel-silver catalyst is subjected to reduction activation for 2 hours at 400 ℃ in a hydrogen atmosphere before being used, and after being cooled to room temperature, is subjected to reduction activation for N 2 And adding the mixture into a reaction kettle under protection.
4. The method for synthesizing p-fluoroaniline according to claim 1, wherein the activated carbon supported nickel silver catalyst is xNi-yiag/AC, wherein the total metal loading is 20wt%, x: y=10:10.
5. The method for synthesizing p-fluoroaniline according to claim 1, wherein said C 1 ～C 3 The volume fraction of the organic alcohol in the organic alcohol aqueous solution is 30-80%.
6. The method for synthesizing p-fluoroaniline according to claim 5 wherein the organic alcohol is methanol.
7. The method for synthesizing para-fluoroaniline according to claim 1, wherein after the reaction kettle is sealed, nitrogen is firstly filled to replace air in the reaction kettle, and then hydrogen is filled to replace nitrogen in the reaction kettle, so that a hydrogen atmosphere is formed in the reaction kettle.
8. The method for synthesizing p-fluoroaniline according to claim 1, wherein after the heat preservation reaction is finished, the temperature in the reaction kettle is reduced to room temperature, the exhaust valve is opened for pressure relief, and then the reaction kettle is opened.
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