A process for the preparation of 9-fluorenone

Abstract

The application discloses a preparation method of 9-fluorenone, and relates to the technical field of organic compound synthesis, characterized by the following steps: taking benzophenone as a reaction raw material, and through the synergistic effect of a palladium catalyst and a silver assistant catalyst, 9-fluorenone is prepared by reaction in an acid medium with oxygen or air as an oxidant; the method uses benzophenone as the raw material, which is low in price and widely available, and through the synergistic catalysis of the palladium catalyst and the silver assistant catalyst, air or oxygen is selected as a green oxidant, and high-purity 9-fluorenone is synthesized through one-step oxidation reaction under high pressure or normal pressure, the reaction condition is mild, the operation is simple, and the method is suitable for large-scale industrial production.

Description

Technical Field

[0001] This invention relates to the field of organic compound synthesis technology, and specifically provides an efficient chemical synthesis method for preparing 9-fluorenone by using benzophenone as a reactant in a one-step catalytic oxidation reaction. Background Technology

[0002] 9-Fluorenone is an important fine organic chemical intermediate with wide applications in pharmaceuticals, pesticides, dyes, optoelectronics, and functional polymer materials. Its former chemical names were bis(benzophenone) or dibenzopentane ketone, and its chemical formula is C2. 13 H8O, a yellow crystalline solid, has a melting point of 84℃ and a boiling point of 341.5℃. Thanks to its unique chemical structure and properties, 9-fluorenone has become an indispensable reaction intermediate in the fine chemical industry, playing a vital role in pharmaceuticals, pesticides, dyes, polymer materials, and optical materials. For example, it is a key intermediate in the synthesis of the anticonvulsant drug 2-hydroxyaminoacetylfluorenone, anticancer drugs, and sympathetic nerve inhibitors. It is also an intermediate used in the preparation of insecticides, plant growth regulators, and aromatic diamine dyes. Furthermore, bisphenol fluorene compounds synthesized from 9-fluorenone are important monomers and modifiers for the preparation of novel engineering plastics. Their resins possess excellent optical properties, high heat resistance, high transparency, and high refractive index, and are widely used in optoelectronic materials such as smartphone lenses, digital camera lenses, liquid crystal display films, and dashcam probes, showing promising market prospects. With the continuous expansion of 9-fluorenone's applications and the ongoing in-depth research, the demand for 9-fluorenone in domestic and international markets will continue to grow year by year.

[0003] Currently, the main method for preparing 9-fluorenone is through the oxidation of fluorene, which is obtained from large quantities of coal tar. Coal tar is a complex mixture containing hundreds of compounds with different chemical structures, of which fluorene content is low, only 1-2%. Therefore, separating fluorene from complex coal tar mixtures requires high-precision separation technologies, such as distillation, extraction, and recrystallization, which are complex and costly. Furthermore, the waste and emissions generated during coal tar refining cause serious environmental pollution because these wastes contain large amounts of heavy metals, polycyclic aromatic hydrocarbons, and other harmful substances, posing a serious threat to water, soil, and atmospheric environments. On the other hand, traditional fluorene oxidation methods typically use heavy metal oxidants such as chromium trioxide (CrO3) and potassium permanganate (KMnO4). These oxidants are not only expensive but also prone to producing peroxidation products, reducing product selectivity and increasing the difficulty of product separation. Although 9-fluorenone can also be prepared by air oxidation of fluorene, the selectivity of the corresponding oxidation reaction is not ideal, and a large amount of black tar byproducts that are difficult to remove are generated, further increasing the difficulty of product separation.

[0004] Given that obtaining fluorene from coal tar (or 9-fluorenone prepared from fluorene) is insufficient to meet the growing market demand, developing efficient and environmentally friendly chemical synthesis methods for 9-fluorenone has significant academic research value and industrialization implications. Currently, existing research has explored reaction routes for synthesizing 9-fluorenone using non-fluorene raw materials, mainly including synthetic strategies using biphenyl derivatives and benzophenone or their derivatives as reactants. For example, 9-fluorenone can be prepared from 2-carboxybiphenyl derivatives via Friedel-Crafts reaction (Tetrahedron Lett., 2015, 56(4), 612-618; J.Org.Chem., 1979, 44(21), 3724-3725; Chemical Research and Application, 2024, 36(3), 663-667). However, the preparation cost of 2-carboxybiphenyl is high, and it is usually prepared by hydrolysis of 9-fluorenone under alkaline conditions (CN1775726A), making this chemical synthesis route difficult to industrialize. Similarly, benzoylaniline can also be used as a raw material to prepare 9-fluorenone via the Comberg-Bachmann reaction (Synthetic Chemistry, 2015, 23(5), 428-430; Green Chem., 2017, 19, 5390-5395), but this chemical synthesis route also lacks cost advantages! To date, there is no industrially viable chemical synthesis method for preparing 9-fluorenone using a non-fluorene-based chemical synthesis method. Therefore, developing an efficient, environmentally friendly, and low-cost chemical synthesis method for 9-fluorenone is of great significance and can break through the industrialization bottleneck of preparing 9-fluorenone from fluorene extracted from coal tar.

[0005] Benzophenone is an inexpensive and widely available organic chemical raw material, commonly used in the preparation of fragrance fixatives, ultraviolet light absorbers, and photocuring reaction initiators. As early as 1975, The method for synthesizing 9-fluorenone from benzophenone using palladium acetate as a catalyst was first reported by researchers, but this method required the consumption of 2 equivalents of palladium acetate and the yield was only 65% ​​(J. Org. Chem., 1975, 40, 1365-1367). Subsequently, researchers continuously improved the experimental method by introducing 2-3 equivalents of silver oxide as an oxidant and reducing the amount of palladium acetate catalyst to the catalytic equivalent (5-10 mol%), successfully increasing the yield to about 85% (Org. Lett., 2012, 14, 4850-4853; Chem. Comm., 2012, 48, 9379-9381; Catal. Sci. Technol., 2015, 5, 3363-3367). Although these improvements have provided new ideas for the development of methods for synthesizing 9-fluorenone, further optimization is still needed to reduce costs and improve reaction efficiency. Therefore, developing an efficient, environmentally friendly, and low-cost chemical synthesis method for 9-fluorenone has significant scientific importance and practical application value. Summary of the Invention

[0006] To address the problems of high cost, severe environmental pollution, and complex processes in existing chemical synthesis methods for 9-fluorenone, this invention provides an efficient, environmentally friendly, and economical chemical synthesis method for 9-fluorenone.

[0007] A method for preparing 9-fluorenone, characterized in that: benzophenone is used as a reactant, and in an acidic medium, 9-fluorenone is prepared by the synergistic effect of palladium catalyst and silver co-catalyst, with oxygen or air as the oxidant.

[0008] This invention uses inexpensive and widely available benzophenone as a raw material, and through the synergistic catalytic action of palladium catalyst and silver co-catalyst, employing air or oxygen as a green oxidant, to synthesize high-purity 9-fluorenone via a one-step oxidation reaction under high or normal pressure conditions. The relevant chemical reaction equations are as follows:

[0009]

[0010] Further settings are as follows:

[0011] The palladium catalyst is selected from any one or more of palladium acetate, palladium chloride, and palladium nitrate, preferably palladium acetate. The amount of palladium catalyst used is 0.05-15 mol.% of benzophenone, preferably 1-5 mol.%.

[0012] The silver co-catalyst is selected from any one or more of silver oxide, silver nitrate, silver chloride, silver carbonate, and silver oxalate, preferably silver oxide. The amount of silver co-catalyst used is 0.05-15 mol of benzophenone, preferably 1-5 mol.

[0013] The acidic medium is selected from any one or more of acetic acid, propionic acid, trifluoroacetic acid, methanesulfonic acid and trifluoromethanesulfonic acid, preferably trifluoroacetic acid.

[0014] The oxidant is air or oxygen, preferably oxygen, with an oxygen pressure of 0.5 to 1.0 atmospheres.

[0015] The reaction temperature is 50–200°C, preferably 100–160°C; the reaction time is 2–24 hours, preferably 6–12 hours.

[0016] Preferably, benzophenone, palladium catalyst, silver co-catalyst and acidic medium are added together to the reaction vessel and stirred thoroughly to dissolve the substances. Then, the reaction system is sealed and air or oxygen is introduced into it. The reaction vessel is heated to make the reaction continue for a certain time. After the reaction is completed, the material is cooled, then water is added, separated and recrystallized to obtain pure 9-fluorenone product.

[0017] The beneficial effects of this invention are as follows:

[0018] (1) Low raw material cost: Using inexpensive and readily available benzophenone as the starting material significantly reduces production costs.

[0019] (2) Green and environmentally friendly: Using air or oxygen as an oxidant avoids the environmental pollution problems caused by the use of toxic or expensive oxidants (such as chromium trioxide and potassium permanganate) in traditional methods.

[0020] (3) High efficiency and high selectivity: Through the synergistic effect of palladium catalyst and silver co-catalyst, the reaction has high selectivity, few by-products, and the products are easy to separate and purify.

[0021] (4) Simple process: The reaction conditions are mild and the operation is simple, making it suitable for large-scale industrial production.

[0022] (5) High yield: The optimized process can achieve high-yield synthesis, meeting the needs of industrial production. This invention not only solves the problems of high raw material costs, serious environmental pollution and complex processes in the prior art, but also provides an efficient, environmentally friendly and economical chemical synthesis route for the industrial production of 9-fluorenone, with broad market application prospects.

[0023] The technical solutions of the present invention will be further described clearly and completely below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the protection scope of the present invention. Detailed Implementation

[0024] Example 1

[0025] In a high-pressure reactor, 36 g of benzophenone, 0.5 g of palladium acetate, 0.48 g of Ag₂O, and 100 mL of trifluoroacetic acid were added. The oxygen pressure was 1.0 MPa, the reaction temperature was 160 °C, and the reaction time was 12 hours. After the reaction was complete, 500 mL of water was added, the mixture was filtered to separate the precipitate, and then recrystallized to obtain 9-fluorenone with a yield of 93% and a purity greater than 99%.

[0026] Example 2

[0027] The preparation method is the same as in Example 1, except that the type and amount of palladium catalyst are adjusted and its effect on the reaction yield is tested.

[0028] Table 1

[0029] Serial Number Palladium catalyst Dosage (g) Yield (%) Example 2-1 Pd / C (Palladium content: 5%) 10.7 88 Example 2-2 Pd / C (Palladium content: 5%) 4.28 82 Example 2-3 Palladium nitrate 0.5 90 Examples 2-4 Palladium acetate 0.1 75 Examples 2-5 Palladium acetate 1.0 94 .

[0030] Analysis: As can be seen from the experimental results in Table 1, the selection of different types of palladium catalysts has a significant impact on the reaction yield. When palladium acetate is selected as the catalyst and its dosage is 1 mol% of benzophenone, the optimal balance between cost and yield is achieved.

[0031] Example 3

[0032] The preparation method is the same as in Example 1, except that the type and amount of silver co-catalyst are adjusted and its effect on the reaction yield is tested.

[0033] Table 2

[0034]

[0035]

[0036] Analysis: As can be seen from the experimental results in Table 2, the addition of silver co-catalyst has a significant impact on the reaction. Silver catalyst can promote the oxidation of zero-valent palladium to divalent palladium. Specifically, when Ag2O is used as co-catalyst, the catalyst dosage is 1 mol% of benzophenone, which achieves the best results in terms of cost and yield.

[0037] Example 4

[0038] The preparation method is the same as in Example 1, except that the type and amount of acidic medium are adjusted and its effect on the reaction yield is tested.

[0039] Table 3

[0040] Serial Number acidic media Dosage (mL) Yield (%) Example 4-1 Trifluoroacetic acid 100 93 Example 4-2 Acetic acid 100 82 Example 4-3 propionic acid 100 70 Example 4-4 Methanesulfonic acid / acetic acid 20 / 80 91 Examples 4-5 Methanesulfonic acid / dichlorobenzene 50 / 50 86 .

[0041] Analysis: As can be seen from the experimental results in Table 3, different acidic media have a significant impact on the reaction. Among them, the reaction effect is best when trifluoroacetic acid is used as the acidic medium.

[0042] Example 5

[0043] The preparation method is the same as in Example 1, except that the reaction temperature and reaction time are adjusted, and the effect on the reaction yield is tested.

[0044] Table 4

[0045]

[0046]

[0047] Analysis: As can be seen from the experimental results in Table 4, the optimal reaction temperature is around 160℃ and the reaction time is 12h. Excessive reaction time leads to a decrease in reaction yield, which may be due to the destructive side reaction that occurs during the long reaction process of 9-fluorenone.

Claims

1. A process for the preparation of 9-fluorenone, characterized in that: The benzophenone is used as a reaction raw material, and 9-fluorenone is prepared by the synergistic effect of a palladium catalyst and a silver assistant catalyst in an acid medium, using oxygen or air as an oxidant; The acid medium is selected from any one or more of acetic acid, propionic acid, trifluoroacetic acid, methanesulfonic acid and trifluoromethanesulfonic acid; The palladium catalyst is selected from any one or more of palladium acetate, palladium chloride and palladium nitrate, and the amount of the palladium catalyst is 0.05-15 mol.% of benzophenone; The silver assistant catalyst is selected from any one or more of silver oxide, silver nitrate, silver chloride, silver carbonate and silver oxalate, and the amount of the silver assistant catalyst is 0.05-15 mol.% of benzophenone.

2. A process for the preparation of 9-fluorenone according to claim 1, characterized by: The palladium catalyst is palladium acetate, and the amount of the palladium catalyst is 1-5 mol.% of benzophenone.

3. The method for preparing 9-fluorenone according to claim 1, characterized in that: The silver assistant catalyst is silver oxide, and the amount of the silver assistant catalyst is 1-5 mol.% of benzophenone.

4. The method for preparing 9-fluorenone according to claim 1, characterized in that: The acid medium is trifluoroacetic acid.

5. The method for preparing 9-fluorenone according to claim 1, characterized in that: The oxidant is air or oxygen, and when the oxidant is oxygen, the oxygen pressure is 0.5-1.0 atm.

6. The method for preparing 9-fluorenone according to claim 1, characterized in that: The reaction temperature is 50-200℃, and the reaction time is 2-24 hours.

7. The method for preparing 9-fluorenone according to claim 6, characterized in that: The reaction temperature is 100-160℃, and the reaction time is 6-12 hours.

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