Preparation method of 2-fluoro-4-nitrobenzoic acid

Abstract

The invention relates to the technical field of organic acids, and particularly discloses a preparation method of 2-fluoro-4-nitrobenzoic acid. The invention relates to a preparation method of 2-fluoro-4-nitrobenzoic acid, which comprises the following steps: by taking polystyrene waste as a raw material, heating concentrated sulfuric acid and concentrated nitric acid to nitrate the polystyrene waste to obtain 4-nitropolystyrene, and oxidizing the 4-nitropolystyrene by taking sodium chlorate as an oxidant, zinc nitrate as a catalyst and concentrated nitric acid as a solvent to obtain 4-nitrobenzoic acid. And finally, by taking iridium acetate as a catalyst and N-fluorobisbenzenesulfonamide as a fluorinating agent, adding potassium fluoride, nitrite and the self-made ligand, and carrying out fluorination reaction to prepare the 2-fluoro-4-nitrobenzoic acid. According to the preparation method disclosed by the invention, efficient utilization of polystyrene waste is realized, the way of recycling polystyrene resources is expanded, and the yield of the prepared 2-fluoro-4-nitrobenzoic acid is high.

Description

Technical Field

[0001] The present application relates to the technical field of organic acids, and more specifically, to a method for preparing 2-fluoro-4-nitrobenzoic acid. Background Art

[0002] Polystyrene is a linear polymer material formed by the polymerization of styrene monomers. It has excellent properties and plays an important role in life and production. It is one of the most widely used types of plastics. Polystyrene products contain a large number of disposable products, and the amount of use and waste is relatively large. Polystyrene products are difficult to degrade under natural conditions, causing serious adverse effects on natural ecology and agricultural production. How to use and treat waste polystyrene has become a common concern of countries around the world. At present, the main methods for recycling polystyrene are solvent recycling as masterbatch. Through simple recycling, waste polystyrene can be made into adhesives, coatings, building materials and other products. In addition, some people have studied thermal degradation, catalytic degradation, and catalytic degradation in supercritical fluids to make waste polystyrene into monomers and oils. Compared with polyester plastics, polystyrene is connected by CC bonds and is more difficult to degrade. However, polystyrene has electron-rich conjugated aromatic ring units and activated benzyl CH bonds for selective depolymerization and conversion, which brings more possibilities for the recycling of polystyrene resources.

[0003] 4-Fluoro-2-nitrobenzoic acid is a common intermediate in organic synthesis. The carboxyl group in the structure can be converted into common active functional groups, such as hydroxyl groups under borane reduction, but the nitro group on the benzene ring is not affected. In addition, there are related literature reports that this carboxyl group can be converted into halogen atoms, such as chlorine, bromine, and iodine under certain conditions. In addition, the carboxyl group can also be removed at high temperature under the action of copper salt to generate a molecule of carbon dioxide.

[0004] The conventional synthesis method of 4-fluoro-2-nitrobenzoic acid is to start from 4-fluoro-2-nitrotoluene or 4-fluoro-2-nitroacetophenone as a raw material, oxidize the methyl group to the carboxyl group under the action of a suitable oxidant, and acidify after the reaction to adjust the reaction system to acidity.

[0005] Polystyrene can be selectively oxidized and efficiently converted into high-value chemical raw material benzoic acid, thereby realizing the resource-based, harmless and high-value utilization of polystyrene. Summary of the invention

[0006] In order to further develop utilization methods of polystyrene waste and realize the value of polystyrene waste, the present application provides a method for preparing 2-fluoro-4-nitrobenzoic acid.

[0007] The present application provides a method for preparing 2-fluoro-4-nitrobenzoic acid, which adopts the following technical scheme:

[0008] A preparation method of 2-fluoro-4-nitrobenzoic acid comprises the following steps: S1, mixing polystyrene waste particles, dichloromethane, concentrated sulfuric acid and concentrated nitric acid in proportion, heating and refluxing, washing and drying to obtain 4-nitropolystyrene; S2, mixing 4-nitropolystyrene, zinc nitrate and concentrated nitric acid, heating to 75-85 DEG C, dripping a saturated aqueous solution of sodium chlorate, ultrasonically reacting for 40-60 minutes, pouring into ice water, filtering and washing, purifying to obtain 4-nitrobenzoic acid; S3, mixing 4-nitrobenzoic acid, iridium acetate, a ligand, N-fluorobisbenzenesulfonamide, nitrite, potassium fluoride and a solvent, stirring at 120-130 DEG C for 20-24 hours, adjusting the pH to 1-2 with an acid, extracting and purifying to obtain 2-fluoro-4-nitrobenzoic acid.

[0009] By adopting the above technical scheme, polystyrene waste is used as raw material, and it is first nitrated by heating with concentrated sulfuric acid and concentrated nitric acid to obtain 4-nitropolystyrene, and then 4-nitropolystyrene is oxidized with sodium chlorate as an oxidant, zinc nitrate as a catalyst, and concentrated nitric acid as a solvent to obtain 4-nitrobenzoic acid. Finally, iridium acetate is used as a catalyst and N-fluorobisbenzenesulfonamide is used as a fluorinating agent, potassium fluoride, nitrite, and a self-made ligand are added to prepare 2-fluoro-4-nitrobenzoic acid through a fluorination reaction, thereby realizing the resource utilization of polystyrene waste.

[0010] Preferably, the usage ratio of the polystyrene waste particles, dichloromethane, concentrated sulfuric acid and concentrated nitric acid in S1 is: (10-12) g: (70-80) mL: (10.2-11.3) mL: (13.5-14.8) g; the mass concentration of concentrated sulfuric acid is 90-98 g / mL; and the mass concentration of concentrated nitric acid is 65-68 g / mL.

[0011] Preferably, the heating temperature in S1 is 70-80° C., and the reflux time is 2-3 h.

[0012] By adopting the above technical solution, the 4-nitrostyrene prepared at this ratio has a high yield and a high purity.

[0013] Preferably, the dosage ratio of 4-nitropolystyrene, zinc nitrate, concentrated nitric acid, and saturated aqueous solution of sodium chlorate in S2 is: (5-7) g: (0.08-0.1) g: (10-15) mL: (20-30) mL; the mass fraction of the concentrated nitric acid is 95-98%.

[0014] By adopting the above technical scheme, the 4-nitrobenzoic acid prepared under this ratio has good quality and high yield.

[0015] Preferably, the dosage ratio of 4-nitrobenzoic acid, iridium acetate, ligand, N-fluorobisbenzenesulfonamide, nitrite, potassium fluoride, and solvent in S3 is 1 mol: (0.08-0.1) mol: (0.16-0.2) mol: (2-2.5) mol: (2-2.5) mol: (1-1.2) mol: (50-60) mL.

[0016] By adopting the above technical scheme, the ligand can form active coordination with iridium acetate, and under the action of potassium fluoride and nitrite, with N-fluorobisbenzenesulfonamide as the fluorination reagent, it has high selectivity for the ortho position of 4-nitrobenzoic acid, realizes the ortho-monofluorination of 4-nitrobenzoic acid, and obtains 2-fluoro-4-nitrobenzoic acid with a high yield.

[0017] Preferably, the ligand in S3 is prepared by the following method: 4-hydroxy-5-nitronicotinic acid, toluene, 4-amino-2-trifluoromethylbenzonitrile and N,N-diisopropylethylamine are mixed in proportion, heated under reflux at 100-110° C. for 10-12 h, extracted and dried, and purified to obtain the ligand.

[0018] Preferably, the usage ratio of 4-hydroxy-5-nitronicotinic acid, toluene, 4-amino-2-trifluoromethylbenzonitrile, and N,N-diisopropylethylamine is (1.1-1.2) mol: (50-80) mL: 1.0 mol: (0.5-0.6) mL.

[0019] By adopting the above technical scheme, 4-hydroxy-5-nitronicotinic acid and 4-amino-2-trifluoromethylbenzonitrile undergo an amidation reaction under the alkaline condition of N,N-diisopropylethylamine to obtain a ligand with a specific structure.

[0020] Preferably, the solvent in S3 is one or more of n-pentane, cyclohexane, n-heptane, chloroform and carbon tetrachloride.

[0021] By adopting the technical scheme, the yield of the obtained 2-fluoro-4-nitrobenzoic acid is high.

[0022] Preferably, the nitrite includes one or more of sodium nitrite, potassium nitrite, calcium nitrite, and cerium nitrite.

[0023] By adopting the technical scheme, the yield of the obtained 2-fluoro-4-nitrobenzoic acid is high.

[0024] Preferably, the acid in S3 is a 1-2 mol / L hydrochloric acid solution.

[0025] In summary, this application has the following beneficial effects:

[0026] 1. The present application uses polystyrene waste as raw material, first nitrates it by heating it with concentrated sulfuric acid and concentrated nitric acid to obtain 4-nitrostyrene, then uses sodium chlorate as an oxidant, zinc nitrate as a catalyst, and concentrated nitric acid as a solvent to oxidize 4-nitrostyrene to obtain 4-nitrobenzoic acid, and finally uses iridium acetate as a catalyst and N-fluorobisbenzenesulfonamide as a fluorinating agent, and adds potassium fluoride, nitrite, and a homemade ligand to prepare 2-fluoro-4-nitrobenzoic acid through a fluorination reaction, thereby realizing the resource utilization of polystyrene waste.

[0027] 2. In the present application, 4-hydroxy-5-nitronicotinic acid and 4-amino-2-trifluoromethylbenzocyanide are used as raw materials, toluene is used as solvent, and a ligand is prepared under the action of N,N-diisopropylethylamine. The ligand can form an active coordination with iridium acetate, and under the action of potassium fluoride and nitrite, N-fluorobisbenzenesulfonamide is used as a fluorination reagent, which has high selectivity for the ortho position of 4-nitrobenzoic acid, realizes the ortho-monofluorination of 4-nitrobenzoic acid, and obtains 2-fluoro-4-nitrobenzoic acid with a yield of up to 72.5%.

[0028] 3. The yield of 2-fluoro-4-nitrobenzoic acid prepared by the preparation method of the present application is high, which realizes the efficient utilization of polystyrene waste and expands the resource recycling method of polystyrene. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a flow chart for the preparation of 2-fluoro-4-nitrobenzoic acid of the present application.

[0030] Figure 2 It is the hydrogen spectrum of 2-fluoro-4-nitrobenzoic acid of the present application. DETAILED DESCRIPTION

[0031] The present application is further described in detail below with reference to the embodiments.

[0032] Unless otherwise specified, the raw materials used in the examples and comparative examples of the present application are all commercially available.

[0033] Example 1

[0034] A method for preparing 2-fluoro-4-nitrobenzoic acid, such as Figure 1 As shown, the following steps are included:

[0035] S1, 10g of polystyrene waste particles, 70mL of dichloromethane, 10.2mL of concentrated sulfuric acid, and 13.5g of concentrated nitric acid are mixed, heated to 70°C, refluxed for 2h, and alternately washed and dried with dichloromethane and hot water to obtain 4-nitrostyrene; the mass concentration of the concentrated sulfuric acid is 90g / mL; the mass concentration of the concentrated nitric acid is 65g / mL. The yield of 4-nitrostyrene is 96.3%.

[0036] S2, 5 g of 4-nitropolystyrene, 0.08 g of zinc nitrate, and 10 mL of concentrated nitric acid were mixed, the temperature was raised to 75°C, 20 mL of a saturated aqueous solution of sodium chlorate was added dropwise, ultrasonic reaction was performed for 40 min, the mixture was poured into ice water, filtered, washed with deionized water, then dissolved with alkali, and then diluted hydrochloric acid was added to precipitate, filtered, and dried to obtain 4-nitrobenzoic acid; the mass fraction of the concentrated nitric acid was 95%. The yield of 4-nitrobenzoic acid was 88.2%.

[0037] S3, 1 mol of 4-nitrobenzoic acid, 0.08 mol of iridium acetate, 0.16 mol of ligand, 2 mol of N-fluorobisbenzenesulfonamide, 2 mol of sodium nitrite, 1 mol of potassium fluoride, and 50 mL of carbon tetrachloride were mixed, stirred at 120°C for 20 h, adjusted to pH 2 with 1 mol / L hydrochloric acid solution, extracted with ethyl acetate, dried the upper extract with anhydrous sodium sulfate, filtered, and then evaporated to remove the solvent, and purified by column chromatography (ethyl acetate, petroleum ether, acetic acid volume ratio of 8:40:0.8) to obtain 2-fluoro-4-nitrobenzoic acid. The yield of 2-fluoro-4-nitrobenzoic acid is 66.8%.

[0038] The ligand structure is:

[0039] .

[0040] The ligand is prepared by the following method: 4-hydroxy-5-nitronicotinic acid, toluene, 4-amino-2-trifluoromethylbenzonitrile, and N,N-diisopropylethylamine are mixed in a dosage ratio of 1.1 mol:50 mL:1.0 mol:0.5 mL, heated under reflux at 100° C. for 10 hours, cooled to room temperature, added with ethyl acetate and water, extracted, separated, dried over anhydrous sodium sulfate, filtered, and then evaporated to remove the solvent, and purified by column chromatography (the volume ratio of petroleum ether to ethyl acetate is 1.5:1) to obtain the ligand.

[0041] Example 2

[0042] A method for preparing 2-fluoro-4-nitrobenzoic acid comprises the following steps:

[0043] S1, 11g of polystyrene waste particles, 75mL of dichloromethane, 10.8mL of concentrated sulfuric acid, and 14.2g of concentrated nitric acid are mixed, heated to 75°C, refluxed for 2.5h, and washed and dried alternately with dichloromethane and hot water to obtain 4-nitrostyrene; the mass concentration of the concentrated sulfuric acid is 96g / mL; the mass concentration of the concentrated nitric acid is 67g / mL. The yield of 4-nitrostyrene is 97.4%.

[0044] S2, 6 g of 4-nitropolystyrene, 0.09 g of zinc nitrate, and 12 mL of concentrated nitric acid were mixed, the temperature was raised to 80°C, 25 mL of a saturated aqueous solution of sodium chlorate was added dropwise, ultrasonic reaction was performed for 50 min, the mixture was poured into ice water, filtered, washed with deionized water, then dissolved with alkali, and then diluted hydrochloric acid was added to precipitate, filtered and dried to obtain 4-nitrobenzoic acid; the mass fraction of the concentrated nitric acid was 96%. The yield of 4-nitrobenzoic acid was 89.8%.

[0045] S3, 1 mol of 4-nitrobenzoic acid, 0.09 mol of iridium acetate, 0.18 mol of ligand, 2.2 mol of N-fluorobisbenzenesulfonamide, 2.2 mol of calcium nitrite, 1.1 mol of potassium fluoride, and 55 mL of n-pentane were mixed, stirred at 125°C for 22 h, adjusted to pH 2 with 1.5 mol / L hydrochloric acid solution, extracted with ethyl acetate, dried the upper extract with anhydrous sodium sulfate, filtered, and then evaporated to remove the solvent, and purified by column chromatography (ethyl acetate, petroleum ether, acetic acid volume ratio of 8:40:0.8) to obtain 2-fluoro-4-nitrobenzoic acid. The yield of 2-fluoro-4-nitrobenzoic acid was 69.3%.

[0046] The ligand structure is:

[0047] .

[0048] The ligand is prepared by the following method: 4-hydroxy-5-nitronicotinic acid, toluene, 4-amino-2-trifluoromethylbenzonitrile, and N,N-diisopropylethylamine are mixed in a dosage ratio of 1.1 mol:50 mL:1.0 mol:0.5 mL, heated under reflux at 105° C. for 11 hours, cooled to room temperature, added with ethyl acetate and water, extracted, separated, dried over anhydrous sodium sulfate, filtered, and then evaporated to remove the solvent, and purified by column chromatography (the volume ratio of petroleum ether to ethyl acetate is 1.5:1) to obtain the ligand.

[0049] Example 3

[0050] A method for preparing 2-fluoro-4-nitrobenzoic acid comprises the following steps:

[0051] S1, 12g of polystyrene waste particles, 80mL of dichloromethane, 11.3mL of concentrated sulfuric acid, and 14.8g of concentrated nitric acid are mixed, heated to 80°C, refluxed for 3h, and alternately washed and dried with dichloromethane and hot water to obtain 4-nitrostyrene; the mass concentration of the concentrated sulfuric acid is 98g / mL; the mass concentration of the concentrated nitric acid is 68g / mL. The yield of 4-nitrostyrene is 98.2%.

[0052] S2, 7g of 4-nitropolystyrene, 0.1g of zinc nitrate, and 15mL of concentrated nitric acid were mixed, the temperature was raised to 85°C, 30mL of a saturated aqueous solution of sodium chlorate was added dropwise, ultrasonic reaction was performed for 60min, the mixture was poured into ice water, filtered, washed with deionized water, then dissolved with alkali, and then diluted hydrochloric acid was added to precipitate, filtered and dried to obtain 4-nitrobenzoic acid; the mass fraction of the concentrated nitric acid was 98%. The yield of 4-nitrobenzoic acid was 91.3%.

[0053] S3, 1 mol of 4-nitrobenzoic acid, 0.1 mol of iridium acetate, 0.2 mol of ligand, 2.5 mol of N-fluorobisbenzenesulfonamide, 2.5 mol of cerium nitrite, 1.2 mol of potassium fluoride, and 60 mL of n-heptane were mixed, stirred at 130°C for 24 h, adjusted to pH 1 with 2 mol / L hydrochloric acid solution, extracted with ethyl acetate, dried the upper extract with anhydrous sodium sulfate, filtered and evaporated to remove the solvent, and purified by column chromatography (ethyl acetate, petroleum ether, acetic acid volume ratio of 8:40:0.8) to obtain 2-fluoro-4-nitrobenzoic acid. The yield of 2-fluoro-4-nitrobenzoic acid was 72.5%. Using deuterated methanol as solvent, the hydrogen spectrum of 2-fluoro-4-nitrobenzoic acid was measured as follows: Figure 2 shown.

[0054] The ligand structure is:

[0055] .

[0056] The ligand is prepared by the following method: 4-hydroxy-5-nitronicotinic acid, toluene, 4-amino-2-trifluoromethylbenzonitrile, and N,N-diisopropylethylamine are mixed in a ratio of 1.2 mol:80 mL:1.0 mol:0.6 mL, heated under reflux at 110° C. for 12 h, cooled to room temperature, added with ethyl acetate and water, extracted, separated, dried over anhydrous sodium sulfate, filtered, and then evaporated to remove the solvent, and purified by column chromatography (the volume ratio of petroleum ether to ethyl acetate is 1.5:1) to obtain the ligand ( 1 HNMR (400MHz, DMSO-d6, δ): 13.4 (s, 1H), 12.18 (s, 1H), 9.32 (d, J=5.8, 1H), 9 .21 (d, J=3.2Hz, 1H), 8.21 (s, 1H), 7.83 (d, J=7.1, 1H), 7.63 (d, J=4.5, 1H)).

[0057] Comparative Example 1

[0058] The same as Example 3, except that no ligand is added.

[0059] The yield of 2-fluoro-4-nitrobenzoic acid was 6.8%.

[0060] Comparative Example 2

[0061] The same as Example 3, except that the ligand of the present application is replaced with an equimolar amount of 3-N,N-diisopropylethylamine sulfonic acid.

[0062] The yield of 2-fluoro-4-nitrobenzoic acid obtained was 36.9%.

[0063] Comparative Example 3

[0064] The same as Example 3, except that N-fluorobisbenzenesulfonamide is replaced by an equal molar amount of octane bis(tetrafluoroborate).

[0065] The yield of 2-fluoro-4-nitrobenzoic acid was 24.7%.

[0066] Comparative Example 4

[0067] The same as Example 3, except that N-fluorobisbenzenesulfonamide is replaced with an equimolar amount of 1-fluoro-N,N-diisopropylethylamine tetrafluoroborate.

[0068] The yield of 2-fluoro-4-nitrobenzoic acid obtained was 18.9%.

[0069] Comparative Example 5

[0070] The same as Example 3, except that iridium acetate is replaced by palladium acetate.

[0071] The yield of 2-fluoro-4-nitrobenzoic acid obtained was 38.5%.

[0072] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, a person skilled in the art may make non-creative modifications to the present embodiment as needed, and such modifications shall be protected by the patent law as long as they are within the scope of protection claimed in the present application.

Claims

1. A method for preparing 2-fluoro-4-nitrobenzoic acid, characterized in that: The following steps are involved: S1, mixing polystyrene waste particles, dichloromethane, concentrated sulfuric acid and concentrated nitric acid in proportion, heating to reflux, washing and drying to obtain 4-nitrostyrene; S2, mixing 4-nitrostyrene, zinc nitrate and concentrated nitric acid, heating to 75-85° C., adding a saturated aqueous solution of sodium chlorate dropwise, ultrasonically reacting for 40-60 minutes, pouring into ice water, filtering and washing, purifying to obtain 4-nitrobenzoic acid; S3, mixing 4-nitrobenzoic acid, iridium acetate, a ligand, N-fluorobisbenzenesulfonamide, nitrite, potassium fluoride and a solvent, stirring at 120-130° C. for 20-24 hours, adjusting the pH to 1-2 with an acid, extracting and purifying to obtain 2-fluoro-4-nitrobenzoic acid.

2. The method for preparing 2-fluoro-4-nitrobenzoic acid according to claim 1, characterized in that: The usage ratio of the polystyrene waste particles, dichloromethane, concentrated sulfuric acid and concentrated nitric acid in the S1 is: (10-12) g: (70-80) mL: (10.2-11.3) mL: (13.5-14.8) g; the mass concentration of the concentrated sulfuric acid is 90-98 g / mL; and the mass concentration of the concentrated nitric acid is 65-68 g / mL.

3. A method for preparing 2-fluoro-4-nitrobenzoic acid according to claim 2, characterized in that: In the S1, the heating temperature is 70-80°C, and the reflux time is 2-3h.

4. The method for preparing 2-fluoro-4-nitrobenzoic acid according to claim 1, characterized in that: The dosage ratio of 4-nitropolystyrene, zinc nitrate, concentrated nitric acid and saturated aqueous solution of sodium chlorate in S2 is: (5-7) g: (0.08-0.1) g: (10-15) mL: (20-30) mL; the mass fraction of the concentrated nitric acid is 95-98%.

5. The method for preparing 2-fluoro-4-nitrobenzoic acid according to claim 1, characterized in that: The dosage ratio of 4-nitrobenzoic acid, iridium acetate, ligand, N-fluorobisbenzenesulfonamide, nitrite, potassium fluoride and solvent in S3 is 1 mol: (0.08-0.1) mol: (0.16-0.2) mol: (2-2.5) mol: (2-2.5) mol: (1-1.2) mol: (50-60) mL.

6. The method for preparing 2-fluoro-4-nitrobenzoic acid according to claim 5, characterized in that: The ligand in S3 is prepared by the following method: 4-hydroxy-5-nitronicotinic acid, toluene, 4-amino-2-trifluoromethylbenzonitrile and N,N-diisopropylethylamine are mixed in proportion, heated under reflux at 100-110° C. for 10-12 h, extracted and dried, and purified to obtain the ligand.

7. The method for preparing 2-fluoro-4-nitrobenzoic acid according to claim 6, characterized in that: The dosage ratio of the 4-hydroxy-5-nitronicotinic acid, toluene, 4-amino-2-trifluoromethylbenzonitrile and N,N-diisopropylethylamine is (1.1-1.2) mol: (50-80) mL: 1.0 mol: (0.5-0.6) mL.

8. The method for preparing 2-fluoro-4-nitrobenzoic acid according to claim 1, characterized in that: The solvent in S3 is one or more of n-pentane, cyclohexane, n-heptane, chloroform, and carbon tetrachloride.

9. The method for preparing 2-fluoro-4-nitrobenzoic acid according to claim 1, characterized in that: The nitrite includes one or more of sodium nitrite, potassium nitrite, calcium nitrite and cerium nitrite.

10. The method for preparing 2-fluoro-4-nitrobenzoic acid according to claim 1, characterized in that: The acid in S3 is a 1-2 mol / L hydrochloric acid solution.

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