Method for preparing 2-bromofluorene through oxidative bromination

Abstract

The invention relates to a method for preparing 2-bromofluorene through oxidative bromination. Silver bromide is prepared from silver nitrate and bromine salt and is loaded on activated carbon to prepare a silver bromide catalyst, and 2-bromofluorene is prepared from fluorene and hydrogen bromide as raw materials through hydrogen peroxide oxidation and bromination by using the catalyst. The preparation method of the catalyst is simple, the catalyst is used for catalyzing high-selectivity bromination of fluorene to prepare 2-bromofluorene, the catalytic effect is good, the catalyst is easy to recycle and reuse, and the catalyst has a very good industrial application prospect.

Description

Technical Field

[0001] The invention relates to a halogenation reaction of aromatic compounds using a silver catalyst, and in particular to a method for preparing 2-bromofluorene by oxidative bromination. Background Art

[0002] Fluorene is one of the important components of coal tar, with large output, wide application and low price. Its derivatives are usually used as raw materials and are widely used in the fields of medicine, pesticides, dyes, plastics and functional polymer materials. 2-Bromofluorene is one of the fluorene derivatives. It can be used as an additive of photoconductive materials and can also be used as a synthetic raw material for luminescent materials. Therefore, the study of its synthesis method is of great significance. At present, the preparation method of 2-bromofluorene reported at home and abroad mainly uses fluorene as raw material, and reacts with bromine or N-bromosuccinimide (NBS) in organic solvents such as chloroform to obtain 2-bromofluorene. Among them, Thursyon et al. used fluorene and bromine as raw materials, and used iodine as catalyst in solvent benzene to prepare 2-bromofluorene with a yield of 35%. There are also reports that 2-bromofluorene is prepared by catalysis of benzoyl peroxide in N-methylpyrrolidone (NMP) solvent with fluorene and N-bromosuccinimide (NBS) as raw materials, and the yield is 71%. However, using N-bromosuccinimide (NBS) as a bromine source is too expensive and is not conducive to large-scale industrial production.

[0003] Li Qiang, Wang Guangxing and others used fluorene and hydrogen bromide as raw materials to produce 2-bromofluorene through hydrogen peroxide oxidation and bromination. The effects of solvent type, material ratio, reaction temperature and time on the yield were investigated. The experimental results show that in carbon tetrachloride solvent, the material ratio n (fluorene) : n (hydrogen bromide) : n (hydrogen peroxide) = 1: 1.5: 2, the reaction temperature is 0-5°C, the reaction time is 4h, and the product yield is 81.9%. However, the use of carbon tetrachloride is extremely toxic, and using it as a solvent can easily cause damage to the human body, which is not conducive to use.

[0004] Yue Gang, Wang Zhiqiang and others used 2-aminofluorene and hydrobromic acid as raw materials to react and prepare 2-bromofluorene. Hydrobromic acid and 2-aminofluorene were placed in a reactor, stirred, heated, and refluxed for 2-3 hours, then cooled to 40-60°C, added cuprous compounds, stirred evenly, and then added dropwise nitrite compounds. After the addition was complete, the mixture was kept warm for 1-2 hours. Toluene was added to dissolve the product, and the organic layer was filtered, desalted, separated, washed, and concentrated to obtain 2-bromofluorene. The steps are too complicated. Guo Yaning, Wang Hui and others mixed fluorene with hydrobromic acid, triphenylphosphine dibromide, and a catalyst (benzoyl peroxide), heated and refluxed for 1-1.5 hours, then cooled to 25-35°C, added dibromohydantoin, stirred evenly, and kept warm for 3-5 hours. After the reaction solution was allowed to stand, the aqueous phase and the organic phase were separated. After the organic phase was washed with water, it was dried, filtered, concentrated, and recrystallized in turn to obtain 2-bromofluorene. The operation is too complicated. Summary of the invention

[0005] The purpose of the present invention is to improve the deficiencies of the prior art and provide a method for preparing 2-bromofluorene by oxidative bromination. First, a green, environmentally friendly and highly active silver catalyst is provided, and then a method for preparing 2-bromofluorene by oxidative bromination using the catalyst is provided.

[0006] Aryl silver complexes are well known, indicating that Ag or Ag+ can activate the aromatic ring through the aryl-silver intermediate. At the same time, hydrogen bromide is oxidized to bromine by hydrogen peroxide, and the aromatic ring is activated by the Ag catalyst to form an aryl silver intermediate, which then reacts with bromine to obtain the brominated product.

[0007] The technical scheme of the present invention is: a method for preparing 2-bromofluorene by oxidative bromination, and the specific steps are: A. preparation of activated carbon-supported silver bromide catalyst: dissolving soluble silver salt in water to prepare a solution, adding activated carbon thereto, stirring evenly, then adding bromine salt, stirring for reaction; after the reaction is completed, drying the water to obtain the activated carbon-supported silver bromide catalyst; B. preparation of 2-bromofluorene: adding fluorene, solvent, bromine source, oxidant, and the catalyst prepared in step A into a reaction container, heating at a certain temperature for reaction for a period of time, phase separation, distillation, purification, and obtaining the product 2-bromofluorene.

[0008] Preferably, the molar amount of the bromide salt added in step A is 1.5-2 times the molar amount of the soluble silver salt; the mass of the silver bromide in the prepared catalyst accounts for 5% to 16% of the total mass of the catalyst.

[0009] Preferably, the bromine salt described in step A is sodium bromide or potassium bromide; and the soluble silver salt is silver nitrate or silver acetate.

[0010] Preferably, the reaction time in step A is 2-3 hours, the reaction temperature is room temperature; the drying temperature is 100-120° C., and the drying time is 10-12 hours.

[0011] Preferably, the added mass of the catalyst described in step B is 1% to 6% of the mass of fluorene; the added molar amount of the bromine source is 1.1-1.5 times the molar amount of fluorene; and the added molar amount of the oxidant is 1.2 to 3 times the molar amount of fluorene.

[0012] Preferably, the bromine source in step B is hydrobromic acid; the oxidant is hydrogen peroxide; and the solvent is acetonitrile.

[0013] Preferably, the reaction temperature in step B is 40-70° C. and the reaction time is 1-4 h.

[0014] The principle of the present invention is as follows:

[0015]

[0016] Beneficial effects:

[0017] The silver catalyst provided by the present invention has a simple preparation method, uses activated carbon with extremely fine particles as a carrier, has a high specific surface area, has an activation effect on aromatic rings, and is used in the preparation of 2-bromofluorene, has high reaction activity, and has heterogeneity and reusability, which is very important for green and sustainable chemistry and is very suitable for industrial production. DETAILED DESCRIPTION

[0018] Embodiment 1: Silver bromide catalyst is prepared using silver nitrate as raw material, and bromofluorene is prepared by oxidizing bromide fluorene. 10g of silver nitrate is dissolved in 1000ml of water, and after it is completely dissolved, 90g of activated carbon is added and stirred evenly to obtain a mixed solution A. 8.2g of sodium bromide (the molar ratio of sodium bromide to silver nitrate is 1.5:1) is added to the mixed solution A, and the stirring reaction is continued for two hours to obtain a mixed solution B, and the mixed solution B is dried in an oven at 100°C for 12h to obtain a silver bromide catalyst A (the mass fraction of silver bromide in the catalyst is 10.9%). 170 g (1 mol) of fluorene, 224 g (1.1 mol) of hydrobromic acid (40%), 120 g (1.2 mol) of hydrogen peroxide, and 10 g of the catalyst prepared in Implementation Example 1 were added to a reaction container, and 300 ml of acetonitrile was added as a solvent. The mixture was stirred at 50 degrees for 4 hours. After the reaction was completed, it was extracted with dichloromethane, the organic phases were combined, and the solvent was evaporated under reduced pressure to obtain 200 g of 2-bromofluorene with a yield of 82%.

[0019] Embodiment 2: Silver bromide catalyst is prepared using silver nitrate as raw material, and bromofluorene is prepared by oxidizing bromide fluorene. Dissolve 5g of silver nitrate in 1000ml of water, wait until it is completely dissolved, add 90g of activated carbon, stir evenly, and obtain mixed solution A. Add 5.5g of sodium bromide (the molar ratio of sodium bromide to silver nitrate is 2:1) to mixed solution A, continue stirring and reacting for two hours, and obtain mixed solution B (the mass fraction of silver bromide in the catalyst is 5.75%), and dry mixed solution B in an oven at 120°C for 10h to obtain silver bromide catalyst B. 170 g (1 mol) of fluorene, 224 g (1.1 mol) of hydrobromic acid (40%), 120 g (1.2 mol) of hydrogen peroxide, and 10 g of the catalyst prepared in Implementation Example 2 were added to a reaction container, and 300 ml of acetonitrile was added as a solvent. The mixture was stirred at 50 degrees for 4 hours. After the reaction, it was extracted with dichloromethane, the organic phases were combined, and the solvent was evaporated under reduced pressure to obtain 186 g of 2-bromofluorene with a yield of 76%.

[0020] Embodiment 3: Silver bromide catalyst is prepared using silver nitrate as raw material, and bromofluorene is prepared by oxidizing bromide fluorene. 15g of silver nitrate is dissolved in 1000ml of water, and after it is completely dissolved, 90g of activated carbon is added and stirred evenly to obtain a mixed solution A. 12.3g of sodium bromide (the molar ratio of sodium bromide to silver nitrate is 1.5:1) is added to the mixed solution A, and the stirring reaction is continued for three hours to obtain a mixed solution B. The mixed solution B is dried in an oven at 100°C for 12h to obtain a silver bromide catalyst C (the mass fraction of silver bromide in the catalyst is 15.5%). 170 g (1 mol) of fluorene, 224 g (1.1 mol) of hydrobromic acid (40%), 120 g (1.2 mol) of hydrogen peroxide, and 10 g of the catalyst prepared in Implementation Example 3 were added to a reaction container, and 300 ml of acetonitrile was added as a solvent. The mixture was stirred at 50 degrees for 4 hours. After the reaction, it was extracted with dichloromethane, the organic phases were combined, and the solvent was evaporated under reduced pressure to obtain 184 g of 2-bromofluorene with a yield of 75%.

[0021] Embodiment 4: Silver bromide catalyst is prepared using silver acetate as raw material, and bromofluorene is prepared by oxidizing bromide fluorene. 10g of silver acetate is dissolved in 1000ml of water, and after it is completely dissolved, 90g of activated carbon is added and stirred evenly to obtain a mixed solution A. 8.2g of sodium bromide (the molar ratio of sodium bromide to silver acetate is 1.5:1) is added to the mixed solution A, and the stirring reaction is continued for two hours to obtain a mixed solution B. The mixed solution B is dried in an oven at 100°C for 12h to obtain a silver bromide catalyst D (the mass fraction of silver bromide in the catalyst is 11.1%). 170 g (1 mol) of fluorene, 224 g (1.1 mol) of hydrobromic acid (40%), 120 g (1.2 mol) of hydrogen peroxide, and 10 g of the catalyst prepared in Implementation Example 4 were added to a reaction container, and 300 ml of acetonitrile was added as a solvent. The mixture was stirred at 50 degrees for 4 hours. After the reaction was completed, it was extracted with dichloromethane, the organic phases were combined, and the solvent was evaporated under reduced pressure to obtain 199 g of 2-bromofluorene with a yield of 82%.

[0022] Embodiment 5: Silver bromide catalyst is prepared using silver nitrate as raw material, and bromofluorene is prepared by oxidizing bromide fluorene. 10g of silver nitrate is dissolved in 1000ml of water, and after it is completely dissolved, 90g of activated carbon is added and stirred evenly to obtain a mixed solution A. 9.5g of potassium bromide (the molar ratio of potassium bromide to silver nitrate is 1.5:1) is added to the mixed solution A, and the stirring reaction is continued for two hours to obtain a mixed solution B. The mixed solution B is dried in an oven at 100°C for 12h to obtain a silver bromide catalyst E (the mass fraction of silver bromide in the catalyst is 10.9%). 170 g (1 mol) of fluorene, 224 g (1.1 mol) of hydrobromic acid (40%), 120 g (1.2 mol) of hydrogen peroxide, and 10 g of the catalyst prepared in Implementation Example 5 were added to a reaction container, and 300 ml of acetonitrile was added as a solvent. The mixture was stirred at 50 degrees for 4 hours. After the reaction, it was extracted with dichloromethane, the organic phases were combined, and the solvent was evaporated under reduced pressure to obtain 198 g of 2-bromofluorene with a yield of 79%.

[0023] Embodiment 6: Silver bromide catalyst is prepared using silver nitrate as raw material, and bromofluorene is prepared by oxidizing bromofluorene. 170g (1 mol) fluorene and 224g (1.1 mol) hydrobromic acid (40%), 120g (1.2 mol) hydrogen peroxide, and 10g of the catalyst prepared in Embodiment 1 are added to a reaction vessel, and 300ml acetonitrile is added as solvent. The mixture is stirred at 40 degrees for 4h. After the reaction is completed, it is extracted with dichloromethane, the organic phases are combined, and the solvent is evaporated under reduced pressure to obtain 191g of 2-bromofluorene, with a yield of 78%.

[0024] Embodiment 7: Silver bromide catalyst is prepared using silver nitrate as raw material, and bromofluorene is prepared by oxidizing bromofluorene. 170g (1 mol) fluorene and 224g (1.1 mol) hydrobromic acid (40%), 120g (1.2 mol) hydrogen peroxide, and 10g of the catalyst prepared in Embodiment 1 are added to a reaction vessel, and 300ml acetonitrile is added as solvent. The mixture is stirred at 60 degrees for 4h. After the reaction is completed, it is extracted with dichloromethane, the organic phases are combined, and the solvent is evaporated under reduced pressure to obtain 186g of 2-bromofluorene, with a yield of 76%.

[0025] Embodiment 8: Silver bromide catalyst is prepared using silver nitrate as raw material, and bromofluorene is prepared by oxidizing bromofluorene. 170g (1 mol) fluorene and 224g (1.1 mol) hydrobromic acid (40%), 120g (1.2 mol) hydrogen peroxide, and 10g of the catalyst prepared in Embodiment 1 are added to a reaction vessel, and 300ml acetonitrile is added as solvent. The mixture is stirred at 70 degrees for 4h. After the reaction is completed, it is extracted with dichloromethane, the organic phases are combined, and the solvent is evaporated under reduced pressure to obtain 176g of 2-bromofluorene, with a yield of 72%.

[0026] Embodiment 9: Silver bromide catalyst is prepared using silver nitrate as raw material, and bromofluorene is prepared by oxidizing bromofluorene. 170g (1 mol) fluorene and 224g (1.1 mol) hydrobromic acid (40%), 200g (2.0 mol) hydrogen peroxide, and 10g of the catalyst prepared in Embodiment 1 are added to a reaction vessel, and 300ml acetonitrile is added as solvent. The mixture is stirred at 50 degrees for 4h. After the reaction is completed, it is extracted with dichloromethane, the organic phases are combined, and the solvent is evaporated under reduced pressure to obtain 230g, with a yield of 94%.

[0027] Embodiment 10: Silver bromide catalyst is prepared using silver nitrate as raw material, and bromofluorene is prepared by oxidizing bromofluorene. 170g (1 mol) fluorene and 224g (1.1 mol) hydrobromic acid (40%), 300g (3.0 mol) hydrogen peroxide, and 10g of the catalyst prepared in Embodiment 1 are added to a reaction vessel, and 300ml acetonitrile is added as solvent. The mixture is stirred at 50 degrees for 4h. After the reaction is completed, it is extracted with dichloromethane, the organic phases are combined, and the solvent is evaporated under reduced pressure to obtain 235g, with a yield of 96%.

[0028] Embodiment 11: Silver bromide catalyst is prepared using silver nitrate as raw material, and bromofluorene is prepared by oxidizing bromofluorene. 170g (1 mol) fluorene and 224g (1.1 mol) hydrobromic acid (40%), 300g (3.0 mol) hydrogen peroxide, and 10g of the catalyst prepared in Embodiment 1 are added to a reaction vessel, and 300ml acetonitrile is added as solvent. The mixture is stirred at 50 degrees for 1 hour. After the reaction is completed, it is extracted with dichloromethane, the organic phases are combined, and the solvent is evaporated under reduced pressure to obtain 205g, with a yield of 84%.

[0029] Embodiment 12: Silver bromide catalyst is prepared using silver nitrate as raw material, and bromofluorene is prepared by oxidizing bromofluorene. 170g (1 mol) fluorene and 224g (1.1 mol) hydrobromic acid (40%), 300g (3.0 mol) hydrogen peroxide, and 1.7g of the catalyst prepared in Embodiment 1 are added to a reaction vessel, and 300ml acetonitrile is added as solvent. The mixture is stirred at 50 degrees for 4h. After the reaction is completed, it is extracted with dichloromethane, the organic phases are combined, and the solvent is evaporated under reduced pressure to obtain 220g, with a yield of 90%.

[0030] Embodiment 13: Silver bromide catalyst is prepared using silver nitrate as raw material, and bromofluorene is prepared by oxidizing bromofluorene. 170g (1 mol) fluorene and 305g (1.5 mol) hydrobromic acid (40%), 300g (3.0 mol) hydrogen peroxide, and 10g of the catalyst prepared in Embodiment 1 are added to a reaction vessel, and 300ml acetonitrile is added as solvent. The mixture is stirred at 50 degrees for 4h. After the reaction is completed, it is extracted with dichloromethane, the organic phases are combined, and the solvent is evaporated under reduced pressure to obtain 233g, with a yield of 95%.

[0031] Table 1:

[0032] The catalyst washed and dried after the reaction in Implementation Example 10 is reused. The process flow is consistent with the implementation case, and the catalyst recovery and use are as shown in the following table:

[0033] Recycling times Yield of 2-bromofluorene 1 94％ 2 93％ 3 91％ 4 91％

Claims

1. A method for preparing 2-bromofluorene by oxidative bromination, the specific steps of which are: A. Preparation of activated carbon-supported silver bromide catalyst: dissolving soluble silver salt in water to prepare a solution, adding activated carbon thereto, stirring evenly, then adding bromine salt, stirring for reaction; after the reaction is completed, drying the water to obtain the activated carbon-supported silver bromide catalyst; B. Preparation of 2-bromofluorene: adding fluorene, solvent, bromine source, oxidant, and the catalyst prepared in step A into a reaction container, heating the reaction at a certain temperature for a period of time, separating the phases, distilling, and purifying to obtain the product 2-bromofluorene.

2. A method according to claim 1, characterized in that: The molar amount of the added bromide salt in step A is 1.5-2 times the molar amount of the soluble silver salt; the mass of the silver bromide in the prepared catalyst accounts for 5%-16% of the total mass of the catalyst.

3. A method as claimed in claim 1, characterized in that: The bromine salt described in step A is sodium bromide or potassium bromide; the soluble silver salt is silver nitrate or silver acetate.

4. A method according to claim 1, characterized in that: The reaction time described in step A is 2-3 hours; the drying temperature is 100-120° C., and the drying time is 10-12 hours.

5. A method according to claim 1, characterized in that: The added mass of the catalyst described in step B is 1% to 6% of the mass of fluorene; the added molar amount of the bromine source is 1.1-1.5 times the molar amount of fluorene; and the added molar amount of the oxidant is 1.2 to 3 times the molar amount of fluorene.

6. A method according to claim 1, characterized in that: The bromine source described in step B is hydrobromic acid; the oxidant is hydrogen peroxide; and the solvent is acetonitrile.

7. The method according to claim 1, characterized in that: The reaction temperature in step B is 40-70° C. and the reaction time is 1-4 h.

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