Industrial production method of 2,4-difluoronitrobenzene

Abstract

The invention discloses a kind of industrial production method for improving 2,4-difluoronitrobenzene, 1) nitration, 2) nitration post-treatment, 3) fluorination, opening the fluorination kettle feed valve, pumping in the intermediate product, vacuum dehydration until the water content is qualified, then pumping in an appropriate amount of organic solvent, opening the solid injection valve, putting in an appropriate amount of fluorinating agent, secondary vacuum dehydration until the water content is qualified, then filling to normal pressure with nitrogen; at the fluorination temperature, putting in an appropriate amount of catalyst, keeping warm at 80 ℃ to 200 ℃ for a certain time at the fluorination reaction temperature, sampling and detection until the fluorination reaction is complete; 4) fluorination post-treatment, 5) distillation. The present invention is safe and reliable in operation, has high feasibility of process operation, and has high product yield; through industrialized production practice, it is suitable for mass production; the product obtained by distillation of the present invention has high purity, and the main content is ≥99%.

Description

Technical Field

[0001] The invention relates to the technical field of 2,4-difluoronitrobenzene preparation, and in particular to an industrial production method of 2,4-difluoronitrobenzene. Background Art

[0002] 2,4-Difluoronitrobenzene is an important pesticide and pharmaceutical intermediate. It can be used to synthesize: 2,4-difluoro-5-nitrobenzenesulfonic acid, masfilin; synthetic resin-bound 2-arylaminobenzimidazole. In addition, 2,4-difluoronitrobenzene is a reactant for preparing 4-thiazolidinone derivatives as antibacterial agents. 2,4-Difluoronitrobenzene can be hydrogenated to produce 2,4-difluoroaniline, which is also an important pharmaceutical pesticide intermediate.

[0003] CN11153779A involves using m-dichlorobenzene as a raw material, and sequentially undergoing high-temperature chlorination reaction, nitration reaction, and fluorination reaction to obtain 2,4-difluoronitrobenzene. Since the nitration starts from m-dichlorobenzene, although post-treatment is performed during the nitration process, some water is not treated cleanly during the treatment process, resulting in a too long dehydration time during the fluorination process, which also affects the fluorination effect.

[0004] CN114487194A discloses a method for the synthesis, analysis and detection of industrially produced p-fluoronitrobenzene, wherein the raw materials are dehydrated during the production of p-fluoronitrobenzene, mainly by negative pressure dehydration in a reaction kettle, which takes a long time and has a slow effect.

[0005] Therefore, it is urgent to develop an industrial production method for 2,4-difluoronitrobenzene to reduce by-products, improve the degree of reaction completion, and improve production efficiency. Summary of the invention

[0006] The purpose of the present invention is to provide an industrial production method of 2,4-difluoronitrobenzene to solve the problems of long reaction time and poor fluorination effect in the prior art.

[0007] In order to solve the above technical problems, the present invention adopts the following technical solution: an industrial production method of 2,4-difluoronitrobenzene, characterized in that it comprises the following steps:

[0008] 1) Nitration, sulfuric acid is pumped into the workshop sulfuric acid metering tank from the sulfuric acid tank in the tank area by a pump, and nitric acid is pumped into the workshop nitric acid metering tank from the nitric acid tank in the tank area by a pump; the feed valve and the drain valve of the mixed acid kettle are opened, nitric acid from the nitric acid metering tank is added to the mixed acid kettle, sulfuric acid from the sulfuric acid metering tank is added under stirring, circulating water is cooled, and stirring is used for standby; the feed valve and the drain valve of the nitration kettle are opened, and the measured meta-dichlorobenzene is pumped into the nitration kettle for heating; the bottom valve of the mixed acid kettle is opened, the feed valve is adjusted, and the measured mixed acid is dripped into the nitration kettle, and after the dripping is completed, the reaction is kept warm at the nitration reaction temperature, and sampling is performed until the raw materials are completely reacted;

[0009] 2) Post-nitration treatment: the nitration reaction liquid is allowed to stand for stratification, the waste acid is separated, the temperature is maintained, an appropriate amount of water is added, and then the pH is adjusted with a strong alkaline solution, and the pH is re-measured after stirring; after stirring, the intermediate product is allowed to stand for separation to obtain the intermediate product, the intermediate product is barreled for standby use, and the alkaline treatment liquid is recovered for reuse;

[0010] 3) Fluorination, open the feed valve of the fluorination reactor, pump in the intermediate product, vacuum dehydrate until the water content is qualified, pump in the organic solvent, open the solid injection valve, add the fluorinating agent, vacuum dehydrate again until the water content is qualified, and then fill it to normal pressure with nitrogen; at the fluorination temperature, add the catalyst, keep the temperature at the fluorination reaction temperature and reflux the reaction, and take samples for detection until the fluorination reaction is complete;

[0011] 4) Post-fluorination treatment: distill the solvent until no more liquid is discharged, then add 1000-3000L of water to the kettle and stir, then let it stand to separate into layers, the organic layer goes to the distillation tower, and the water layer is treated to recover by-products;

[0012] 5) Distillation: After the product and the organic solvent enter the distillation kettle, the temperature is raised to 80℃~180℃ under negative pressure to evaporate the fraction, collect the front fraction, continue distillation to collect the main fraction with a content of ≧99%, and pack it into barrels.

[0013] As a preferred technical solution, the mixed acid in step 1) is one of a mixture of 98% nitric acid and 98% sulfuric acid and a mixture of 65% nitric acid and 98% sulfuric acid.

[0014] As a preferred technical solution, in the step 1), the measured m-dichlorobenzene is pumped into the nitration kettle and heated to 30-90°C; the nitration temperature is 30-90°C; the insulation temperature at the nitration reaction temperature is 30-90°C; the insulation reaction temperature is 1-12 hours.

[0015] As a preferred technical solution, in step 2), the temperature is maintained at 30-80° C.; the strong alkaline solution is one of potassium carbonate, potassium bicarbonate, potassium pyrophosphate, potassium tripolyphosphate and potassium hydroxide; and the pH is adjusted to 9 in step 2).

[0016] As a preferred technical solution, the organic solvent in step 3) is one of dimethyl sulfoxide, N,N-dimethylformamide, N-methylpyrrolidone, n-hexane and xylene.

[0017] As a preferred technical solution, in step 3), an auxiliary dehydration activator is added at the same time as the organic solvent is added; the auxiliary dehydration activator is one of methanol, ethanol, n-butanol and isopropanol.

[0018] As a preferred technical solution, the fluorinating agent in step 3) is one of potassium fluoride and potassium bifluoride.

[0019] As a preferred technical solution, the catalyst in step 3) is one of polyethylene glycol, tetrabutylammonium bromide, 1-ethyl-3-methylimidazolium tetrafluoroborate, tetrabutylammonium chloride and tetrabutylammonium fluoride.

[0020] As a preferred technical solution, the vacuum dehydration time in step 3) is 1 to 3 hours; and the qualified moisture content after dehydration is ≤0.5%.

[0021] As a preferred technical solution, in the step 3), the fluorination reaction temperature is kept at 80°C to 200°C for 12 to 72 hours under reflux.

[0022] Specifically, the chemical reaction formula involved is as follows:

[0023]

[0024] Advantages of the present invention:

[0025] 1. The industrial production method of 2,4-difluoronitrobenzene provided by the present invention has safe and reliable operation, high process operation feasibility and high product yield;

[0026] 2. The byproducts of the nitrification post-treatment and the fluorination post-treatment of the present invention are both potassium salts, which can be used as fertilizers after treatment, effectively reducing the cost and difficulty of byproduct treatment;

[0027] 3. The product obtained by the distillation of the present invention has high purity. After testing by gas chromatography-mass spectrometry, the content of 2,4-difluoronitrobenzene is ≥99%;

[0028] 4. The nitration reaction of the present invention is good, the fluorination reaction is controllable, and the fluorination catalyst has high selectivity and a wide variety;

[0029] The present invention has been put into industrial production practice and is suitable for mass production;

[0030] 5. The auxiliary dehydration activator used in the present invention can form an azeotrope with the water contained in the raw material during the dehydration process, which is helpful to clean the water in the raw material; the fluoride can be activated during the dehydration process to enhance the activity of the fluoride, so that the raw material can be fluorinated more thoroughly, the fluorination conversion rate can be improved, and the fluorination time can be significantly reduced; the auxiliary dehydration activator used has a low boiling point and does not participate in the reaction, so it will not affect the fluorination process, and effectively ensures the normal progress of fluorination. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is a process flow chart of Example 1 of the present invention;

[0032] Figure 2 The mass spectrum of the final product of Example 1 of the present invention;

[0033] Figure 3 It is the gas chromatogram of the product of Example 4 of the present invention. DETAILED DESCRIPTION

[0034] The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention. Without departing from the spirit and substance of the present invention, modifications or substitutions made to the methods, steps or conditions of the present invention are within the scope of the present invention.

[0035] Example 1

[0036] (1) Nitration:

[0037] Pump sulfuric acid from the 98% sulfuric acid tank in the tank area to the 900kg sulfuric acid metering tank in the workshop, and pump nitric acid from the 65% nitric acid tank in the tank area to the 900kg nitric acid metering tank in the workshop; open the feed valve and drain valve of the mixed acid kettle, add nitric acid from the nitric acid metering tank to the mixed acid kettle, add sulfuric acid from the sulfuric acid metering tank under stirring (circulating water cooling), and stir for standby; open the feed valve and drain valve of the nitrification kettle, pump 1500kg of measured meta-dichlorobenzene into the nitrification kettle and heat it to 80°C; open the bottom valve of the mixed acid kettle, adjust the feed valve, and then drip the measured mixed acid into the kettle at a temperature of about 80°C, keep it warm at 80°C for 5h after the dripping is completed, take samples to detect the raw material content = 0.5%, and the reaction is complete;

[0038] (2) Post-nitrification treatment:

[0039] The nitration reaction liquid was allowed to stand for stratification and waste acid was separated. The temperature was maintained at 80°C, 600L of water was added, and then 88kg of 50% potassium pyrophosphate solution was used to adjust the pH to 9. After stirring for 30 minutes, the pH was retested to be 9; after stirring for 1 hour, the solution was allowed to stand for 1 hour to separate the intermediate product, which was barreled for use in the next fluorination reaction. The alkali treatment solution was recovered and reused.

[0040] (3) Fluorination:

[0041] Open the feed valve of the fluorination reactor, pump in 1000L of the intermediate product, and vacuum dehydrate until the water content is qualified. Then pump in 2000L of dimethyl sulfoxide, add 10L of methanol as an activated dehydrating agent, open the solid injection valve, put in 800kg of potassium fluoride, and vacuum dehydrate for 1h. Test the water content = 0.45%, which is qualified. Then fill it with nitrogen to normal pressure. Heat to 180℃, put in 10kg of catalyst tetrabutylammonium fluoride, keep warm at 180℃ for reflux reaction for 36h, take samples to test the 2,4-difluoronitrobenzene content = 85.99%, and the reaction is good.

[0042] (4) Fluorination post-treatment:

[0043] After the fluorination reaction is qualified, negative pressure is applied and the solvent is distilled at 80°C until no more liquid is discharged. Then 3000L of water is added to the kettle and stirred. After that, the kettle is allowed to stand and the layers are separated. The organic layer is sent to the distillation tower and the water layer is used for processing and recovery of by-products.

[0044] (5) Distillation:

[0045] After the organic layer enters the distillation kettle, it is heated to 140°C under negative pressure to evaporate the fraction, collect the front fraction, and test the content of the rear fraction, which shows 2,4-difluoronitrobenzene = 99.47%. The rear fraction is collected and barreled.

[0046] The final mass spectrum of the product is as follows Figure 2 As shown in the figure, this spectrum is a high-resolution mass spectrum, which can directly test the precise relative molecular mass; the horizontal axis is the mass-to-charge ratio (the ratio of the mass number of charged particles to the charge number (m / z)), and the vertical axis is the relative intensity (i.e. the intensity of the particle flow, unit: %). It can be seen from the figure that the peak with a mass-to-charge ratio (m / z) of 159 is both a base peak (a peak with a relative intensity of 100%) and a molecular ion peak. This mass-to-charge ratio is the same as the relative molecular mass of 2,4-difluoronitrobenzene (the precise relative molecular mass of 2,4-difluoronitrobenzene is 159.013).

[0047] Example 2

[0048] (1) Nitration:

[0049] Pump sulfuric acid from the 98% sulfuric acid tank in the tank area to the 650kg sulfuric acid metering tank in the workshop, and pump nitric acid from the 98% nitric acid tank in the tank area to the 650kg nitric acid metering tank in the workshop; open the feed valve and drain valve of the mixed acid kettle, add nitric acid from the nitric acid metering tank to the mixed acid kettle, add sulfuric acid from the sulfuric acid metering tank under stirring (circulating water cooling), and stir for standby; open the feed valve and drain valve of the nitrification kettle, pump 1500kg of measured meta-dichlorobenzene into the nitrification kettle and heat it to 50°C; open the bottom valve of the mixed acid kettle, adjust the feed valve, and then drip the measured mixed acid into the kettle at a temperature of about 50°C, keep warm at 50°C for 3h after the dripping is completed, take samples to detect the raw material content = 0.9%, and the reaction is complete;

[0050] (2) Post-nitrification treatment:

[0051] The nitration reaction liquid was allowed to stand for stratification and waste acid was separated. The temperature was maintained at 50°C, 600L of water was added, and then 40kg of 50% potassium carbonate solution was used to adjust the pH to 9. After stirring for 30 minutes, the pH was retested to be 9; after stirring for 1 hour, the solution was allowed to stand for 1 hour to separate the intermediate product, which was stored in barrels for use in the next fluorination reaction. The alkali treatment solution was recovered and reused.

[0052] (3) Fluorination:

[0053] Open the feed valve of the fluorination reactor, pump in 1000L of the intermediate product, and vacuum dehydrate until the water content is qualified. Then pump in 2000L of n-hexane, add 10L of ethanol as an activated dehydrating agent, open the solid injection valve, put in 700kg of potassium fluoride, and vacuum dehydrate for 1.5h for the second time. The moisture content is tested to be 0.31%, and the moisture content is qualified. Then fill it with nitrogen to normal pressure. Heat to 80℃, put in 20kg of catalyst 1-ethyl-3-methylimidazolium tetrafluoroborate, keep warm at 80℃ for reflux reaction for 60h, take samples to detect the 2,4-difluoronitrobenzene content = 86.76%, and the reaction is good.

[0054] (4) Fluorination post-treatment:

[0055] After the fluorination reaction is qualified, negative pressure is applied and the solvent is distilled at 40°C until no more liquid is discharged. Then 3000L of water is added to the kettle and stirred. After that, it is allowed to stand and separate into layers. The organic layer is sent to the distillation tower, and the water layer is used for processing and recovery of by-products.

[0056] (5) Distillation:

[0057] After the organic layer enters the distillation kettle, it is heated to 150°C under negative pressure to evaporate the fraction, collect the front fraction, and test the content of the rear fraction, which shows 2,4-difluoronitrobenzene = 99.18%. The rear fraction is collected and barreled.

[0058] Example 3

[0059] (1) Nitration:

[0060] Pump sulfuric acid from the 98% sulfuric acid tank in the tank area to the 1000kg sulfuric acid metering tank in the workshop, and pump nitric acid from the 98% nitric acid tank in the tank area to the 500kg nitric acid metering tank in the workshop; open the feed valve and drain valve of the mixed acid kettle, add nitric acid from the nitric acid metering tank to the mixed acid kettle, add sulfuric acid from the sulfuric acid metering tank under stirring (circulating water cooling), and stir for standby; open the feed valve and drain valve of the nitrification kettle, pump 1500kg of measured meta-dichlorobenzene into the nitrification kettle and heat it to 70°C; open the bottom valve of the mixed acid kettle, adjust the feed valve, and then drip the measured mixed acid into the kettle at a temperature of about 70°C, keep it warm at 70°C for 2h after the dripping is completed, take samples to detect the raw material content = 0.4%, and the reaction is complete;

[0061] (2) Post-nitrification treatment:

[0062] The nitration reaction liquid was allowed to stand for stratification and waste acid was separated. The temperature was maintained at 70°C, 600L of water was added, and then 27kg of 30% potassium bicarbonate solution was used to adjust the pH to 9. After stirring for 30 minutes, the pH was retested to be 9; after stirring for 1 hour, the solution was allowed to stand for 1 hour to separate the intermediate product, which was barreled for use in the next fluorination reaction. The alkali treatment solution was recovered and reused.

[0063] (3) Fluorination:

[0064] Open the feed valve of the fluorination reactor, pump in 1000L of the intermediate product, and vacuum dehydrate until the water content is qualified. Then pump in 1500L of N-methylpyrrolidone, add 10L of n-propanol as an activated dehydrating agent, open the solid injection valve, put in 900kg of potassium bifluoride, vacuum dehydrate for 2h, test the water content = 0.11%, and the water content is qualified. Then fill it with nitrogen to normal pressure. Heat to 200℃, put in 60kg of catalyst polyethylene glycol, keep warm at 200℃ for reflux reaction for 48h, take samples to detect the 2,4-difluoronitrobenzene content = 88.61%, and the reaction is good.

[0065] (4) Fluorination post-treatment:

[0066] After the fluorination reaction is qualified, negative pressure is applied and the solvent is distilled at 100°C until no more liquid is discharged. Then 3000L of water is added to the kettle and stirred. After that, it is allowed to stand and separate into layers. The organic layer is sent to the distillation tower, and the water layer is used for processing and recovery of by-products.

[0067] (5) Distillation:

[0068] After the organic layer enters the distillation kettle, it is heated to 160°C under negative pressure to evaporate the fraction, and the front fraction is collected. After testing, the content of 2,4-difluoronitrobenzene in the rear fraction is 99.27%, and the rear fraction is collected and barreled.

[0069] Example 4

[0070] (1) Nitration:

[0071] Pump sulfuric acid from the 98% sulfuric acid tank in the tank area to the 1000kg sulfuric acid metering tank in the workshop, and pump nitric acid from the 65% nitric acid tank in the tank area to the 1000kg nitric acid metering tank in the workshop; open the feed valve and drain valve of the mixed acid kettle, add nitric acid from the nitric acid metering tank to the mixed acid kettle, add sulfuric acid from the sulfuric acid metering tank under stirring (circulating water cooling), and stir for standby; open the feed valve and drain valve of the nitrification kettle, pump 1500kg of measured meta-dichlorobenzene into the nitrification kettle and heat it to 60°C; open the bottom valve of the mixed acid kettle, adjust the feed valve, and then drip the measured mixed acid into the kettle at a temperature of about 60°C, keep it warm at 60°C for 5h after the dripping is completed, take samples to detect the raw material content = 0.23%, and the reaction is complete;

[0072] (2) Post-nitrification treatment:

[0073] The nitration reaction liquid was allowed to stand for stratification and waste acid was separated. The temperature was maintained at 70°C, 600L of water was added, and then 10kg of 50% potassium tripolyphosphate solution was used to adjust the pH to 9. After stirring for 30 minutes, the pH was retested to be 9; after stirring for 1 hour, the solution was allowed to stand for 1 hour, and the intermediate product was separated and barreled for use in the next fluorination reaction. The alkali treatment solution was recovered and reused.

[0074] (3) Fluorination:

[0075] Open the feed valve of the fluorination reactor, pump in 1000L of the intermediate product, and vacuum dehydrate until the water content is qualified. Then pump in 1500L of DMF, add 10L of isopropanol as an activated dehydrating agent, open the solid injection valve, put in 900kg of potassium bifluoride, and vacuum dehydrate for 1.5h. Test the water content = 0.47%, which is qualified. Then fill it with nitrogen to normal pressure. Heat to 150℃, put in 45kg of catalyst tetrabutylammonium bromide, keep warm and reflux at 150℃ for 48h, take samples to detect the 2,4-difluoronitrobenzene content = 86.79%, and the reaction is good.

[0076] (4) Fluorination post-treatment:

[0077] After the fluorination reaction is qualified, negative pressure is applied and the solvent is distilled at 70°C until no more liquid is discharged. Then 3000L of water is added to the kettle and stirred. After that, it is allowed to stand and separate into layers. The organic layer is sent to the distillation tower, and the water layer is used for processing and recovery of by-products.

[0078] (5) Distillation:

[0079] After the organic layer enters the distillation kettle, it is heated to 130°C under negative pressure to evaporate the fraction, collect the front fraction, and test the content of the rear fraction, which shows 2,4-difluoronitrobenzene = 99.36%. The rear fraction is collected and barreled.

[0080] The gas chromatogram of the final product is shown in Figure 3 As shown, by taking the nitration raw material m-dichlorobenzene, the possible nitration products 2,6-dichloronitrobenzene and 2,4-dichloronitrobenzene, the possible fluorination intermediates 2-chloro-4-fluoronitrobenzene and 4-chloro-2-fluoronitrobenzene, the possible fluorination products 2,6-difluoronitrobenzene and 2,4-difluoronitrobenzene, the above substances are used as standard samples to formulate the gas chromatography peak area normalization method for testing the purity of 2,4-difluoronitrobenzene. Table 1 Data compiled from Figure 3 From the data, we can see that the compound with a retention time of 4.398 min is 2,4-difluoronitrobenzene, and the peak area is 99.36249%, which reflects that the purity of the substance is 99.36%, which meets the use requirements of 2,4-difluoronitrobenzene industrial products (2,4-difluoronitrobenzene purity ≥ 99%).

[0081] Table 1 Gas chromatogram of distillation product of Example 4

[0082] Retention time / min Compound Name Peak area% 4.171 m-Dichlorobenzene 0.02114 4.248 2,6-Difluoronitrobenzene 0.10043 4.398 2,4-Difluoronitrobenzene 99.36249 5.330 2-Chloro-4-fluoronitrobenzene 0.00000 5.547 4-Chloro-2-fluoronitrobenzene 0.00000 6.482 2,6-Dichloronitrobenzene 0.00000 6.582 2,4-Dichloronitrobenzene 0.00000

[0083] Example 5

[0084] (1) Nitration:

[0085] Pump sulfuric acid from the 98% sulfuric acid tank in the tank area to the 650kg sulfuric acid metering tank in the workshop, and pump nitric acid from the 98% nitric acid tank in the tank area to the 650kg nitric acid metering tank in the workshop; open the feed valve and drain valve of the mixed acid kettle, add nitric acid from the nitric acid metering tank to the mixed acid kettle, add sulfuric acid from the sulfuric acid metering tank under stirring (circulating water cooling), and stir for standby; open the feed valve and drain valve of the nitrification kettle, pump 1500kg of measured meta-dichlorobenzene into the nitrification kettle and heat it to 30°C; open the bottom valve of the mixed acid kettle, adjust the feed valve, and then drip the measured mixed acid into the kettle at a temperature of about 30°C, keep warm at 30°C for 10h after the dripping is completed, take samples to detect the raw material content = 0.35%, and the reaction is complete;

[0086] (2) Post-nitrification treatment:

[0087] The nitration reaction liquid was allowed to stand for stratification and waste acid was separated. The temperature was maintained at 30°C, 600L of water was added, and then 10kg of 30% potassium hydroxide solution was used to adjust the pH to 9. After stirring for 30 minutes, the pH was retested to be 9; after stirring for 1 hour, the solution was allowed to stand for 1 hour, and the intermediate product was separated and barreled for use in the next fluorination reaction. The alkali treatment solution was recovered and reused.

[0088] (3) Fluorination:

[0089] Open the feed valve of the fluorination reactor, pump in 1000L of the intermediate product, and vacuum dehydrate until the water content is qualified. Then pump in 1500L of xylene, add 10L of n-butanol as an activated dehydrating agent, open the solid injection valve, put in 700kg of potassium fluoride, and vacuum dehydrate for 1.5h. Test the water content = 0.25%, the water content is qualified, and then fill it with nitrogen to normal pressure. Heat to 140℃, put in 35kg of catalyst tetrabutylammonium chloride, keep warm at 140℃ for reflux reaction for 55h, take samples to test the 2,4-difluoronitrobenzene content = 87.67%, the reaction is good.

[0090] (4) Fluorination post-treatment:

[0091] After the fluorination reaction is qualified, negative pressure is applied and the solvent is distilled at 80°C until no more liquid is discharged. Then 3000L of water is added to the kettle and stirred. After that, the kettle is allowed to stand and the layers are separated. The organic layer is sent to the distillation tower and the water layer is used for processing and recovery of by-products.

[0092] (5) Distillation:

[0093] After the organic layer enters the distillation kettle, it is heated to 120°C under negative pressure to evaporate the fraction, and the front fraction is collected. After testing, the content of 2,4-difluoronitrobenzene in the rear fraction is 99.91%, and the rear fraction is collected and barreled.

[0094] The above shows and describes the basic principles, main features and advantages of the present invention. It should be understood by those skilled in the art that the present invention is not limited to the above embodiments. The above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which fall within the scope of the present invention. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. An industrial production method of 2,4-difluoronitrobenzene, characterized in that: The following steps are involved: 1) Nitration: Sulfuric acid is pumped from the sulfuric acid tank in the tank area to the sulfuric acid metering tank in the workshop, and nitric acid is pumped from the nitric acid tank in the tank area to the nitric acid metering tank in the workshop; the feed valve and drain valve of the mixed acid kettle are opened, nitric acid from the nitric acid metering tank is added to the mixed acid kettle, sulfuric acid from the sulfuric acid metering tank is added under stirring, circulating water is used to cool down, and stirring is performed for standby; the feed valve and drain valve of the nitration kettle are opened, and the measured m-dichlorobenzene is pumped into the nitration kettle to increase the temperature; the bottom valve of the mixed acid kettle is opened, the feed valve is adjusted, and the measured mixed acid is dripped into the nitration kettle. After the dripping is completed, the mixture is kept warm at the nitration reaction temperature, and samples are taken for testing until the raw materials react completely; 2) Post-nitration treatment: let the nitration reaction liquid stand for stratification, separate the waste acid, maintain the temperature, add an appropriate amount of water, and then use a strong alkaline solution to adjust the pH. After stirring, re-measure the pH. After stirring, let it stand for separation to obtain the intermediate product, which is barreled for standby use, and the alkaline treatment liquid is recovered for reuse; 3) Fluorination: open the feed valve of the fluorination reactor, pump in the intermediate product, vacuum dehydrate until the water content is qualified, pump in the organic solvent, open the solid injection valve, add the fluorinating agent, vacuum dehydrate again until the water content is qualified, and then fill it to normal pressure with nitrogen; at the fluorination temperature, add the catalyst, keep the temperature at the fluorination reaction temperature and reflux the reaction, and take samples for testing until the fluorination reaction is complete; 4) Post-fluorination treatment: distill the solvent until no more liquid is discharged, then add 1000-3000L of water to the kettle and stir, then let it stand to separate into layers, the organic layer goes to the distillation tower, and the water layer is treated to recover by-products; 5) Distillation: After the organic layer enters the distillation kettle, it is heated to 80℃~180℃ under negative pressure to evaporate the fraction, collect the front fraction, continue distillation to collect the main fraction with a content of ≥99%, and barrel it; In step 1), the mixed acid is one of a mixture of 98% nitric acid and 98% sulfuric acid and a mixture of 65% nitric acid and 98% sulfuric acid; In the step 1), the measured m-dichlorobenzene is pumped into the nitration kettle and heated to 30-90°C; the nitration temperature is 30-90°C; the insulation temperature at the nitration reaction temperature is 30-90°C; the insulation temperature at the nitration reaction temperature is 2-10 hours, and the pH value is adjusted to 9 in the step 2); In the step 2), the temperature is maintained at 30-80° C.; the strong alkaline solution is one of potassium carbonate, potassium bicarbonate, potassium pyrophosphate, potassium tripolyphosphate and potassium hydroxide; In step 3), the organic solvent is one of N-methylpyrrolidone, n-hexane and xylene; In the step 3), an auxiliary dehydration activator is added at the same time as the organic solvent is added; the auxiliary dehydration activator is one of ethanol, n-butanol and isopropanol; In the step 3), the catalyst is one of polyethylene glycol and 1-ethyl-3-methylimidazolium tetrafluoroborate.

2. The industrial production method of 2,4-difluoronitrobenzene according to claim 1, characterized in that: In the step 3), the fluorinating agent is one of potassium bifluoride and potassium fluoride.

3. The industrial production method of 2,4-difluoronitrobenzene as claimed in claim 1, characterized in that: The vacuum dehydration time in step 3) is 1 to 3 hours; the qualified moisture content after dehydration is ≤0.5%.

4. The industrial production method of 2,4-difluoronitrobenzene according to claim 1, characterized in that: In the step 3), the fluorination reaction temperature is kept at 80°C to 200°C for 12 to 72 hours under reflux.

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