A green process for the preparation of 4,4'-difluorobenzophenone

Abstract

The application discloses a green preparation method of 4,4'-difluorobenzophenone. The method uses 4,4'-difluorobenzene as raw material, potassium bromide as catalyst, acetic acid as solvent, and oxygen as oxidant, and 4,4'-difluorobenzophenone is generated in high selectivity through one-step oxidation under mild conditions. The application surprisingly finds that in the presence of potassium bromide, a new non-metallic catalytic oxidation system of potassium bromide / acetic acid / oxygen is used to realize high-efficiency and high-selectivity conversion of the C-H bond at the benzyl position. Compared with the traditional method, the application does not need to use a transition metal catalyst, does not need to use carbon tetrachloride and other materials damaging the ozone layer, and does not need to involve a dangerous intermediate such as a diazonium salt, the process route is short, the atomic economy is high, the product yield is high, the product purity is high, the catalyst is cheap and easy to obtain, and the application has excellent industrial application prospect and green chemistry characteristics.

Description

Technical Field

[0001] This invention belongs to the field of preparation of pharmaceutical and chemical organic compounds, specifically relating to a green preparation method of the fluorinated organic compound 4,4'-difluorobenzophenone. Background Technology

[0002] 4,4'-Difluorobenzophenone (DFBP) is an important fluorinated organic compound with wide applications in various high-tech fields. In the pharmaceutical field, it serves as a key intermediate in the synthesis of many drugs, such as flubendioxanone for treating hypoxic-ischemic brain diseases and doxycycline for treating Alzheimer's disease. It is also used in the research and development of novel antiviral, antitumor, and antibiotic drugs. Another important application is as a key monomer in the synthesis of novel aromatic thermoplastic engineering plastics such as polyetheretherketone (PEEK). PEEK possesses excellent heat resistance, wear resistance, corrosion resistance, self-lubricating properties, and good biocompatibility, and is widely used in high-precision fields such as aerospace, automotive manufacturing, electronics, precision instruments, and medical devices. DFBP can be used as an imaging agent and charge control agent in optical and electrical recording materials for information storage technology. It can also be used as a polymerization initiator or copolymer monomer to improve the heat resistance, wear resistance, and chemical stability of materials. With the continuous expansion of downstream application areas, especially the sustained growth in demand in areas such as lightweighting of new energy vehicles, semiconductor manufacturing, and orthopedic implant materials, the market demand for DFBP has been increasing year by year, and the research and development of its synthesis technology has received widespread attention.

[0003] The main methods for synthesizing 4,4'-difluorobenzophenone reported in the literature are as follows:

[0004] (1) The Friedel-Crafts alkylation hydrolysis method uses fluorobenzene and carbon tetrachloride as raw materials to generate 4,4'-difluorodiphenyl dichloromethane under Lewis acid catalysis such as anhydrous aluminum trichloride, and then hydrolyzes it to obtain the target product.

[0005]

[0006] This method uses readily available raw materials, has a short synthesis route, and low production costs. However, it has several drawbacks: carbon tetrachloride damages the ozone layer and is a substance restricted by the Montreal Protocol; aluminum trichloride is used in large quantities, generating significant amounts of aluminum-containing wastewater and creating considerable environmental pressure; and the product contains isomers such as 2,4'-difluorobenzophenone, which affects product purity.

[0007] (2) Friedel-Crafts acylation method uses fluorobenzene and p-fluorobenzoyl chloride (or p-fluorobenzoic acid, phosgene, etc.) as raw materials to react under Lewis acid catalysis to generate 4,4'-difluorobenzophenone.

[0008]

[0009] This method boasts high synthesis yields and stable product quality, making it one of the main routes for industrial production in China. However, it has drawbacks: raw materials such as p-fluorobenzoyl chloride are expensive and in short supply, making production costs difficult to control effectively; the large amount of aluminum trichloride catalyst used generates substantial amounts of aluminum-containing wastewater, resulting in high environmental treatment costs; and when using phosgene as a raw material, the highly toxic nature of phosgene makes production control difficult and poses safety hazards.

[0010] (3) The diazotization oxidation method uses 4,4'-diaminodiphenylmethane as raw material and reacts it with sodium nitrite in hydrofluoric acid or fluoroboric acid medium. After thermal decomposition, 4,4'-difluorodiphenylmethane is obtained, and then 4,4'-difluorodibenzophenone is obtained by nitric acid oxidation.

[0011]

[0012] This method has simple reaction steps and a high product yield, making it one of the main methods for industrial production abroad. However, it has drawbacks: diazonium salts are explosive, posing significant safety hazards during production; the reaction takes place in a strongly acidic medium, leading to severe equipment corrosion; it generates large amounts of nitrogen-containing wastewater and harmful gases, making waste treatment difficult and environmentally unfriendly; and the raw material price is relatively high.

[0013] (4) Halogen substitution method: 4,4'-dichlorobenzophenone is prepared by reacting 4,4'-difluorobenzophenone with fluorinating agents such as potassium fluoride in a polar aprotic solvent.

[0014]

[0015] This method is relatively simple. However, it has the following drawbacks: limited raw material sources; high reaction temperature and long reaction time, resulting in high energy consumption; unsatisfactory fluorination conversion rate; and difficulty in product purification.

[0016] (5) This method uses diphenylmethane as raw material, and chlorine gas is used to perform two-step chlorination to obtain 4,4'-dichlorophenyldichloromethane, which is then dechlorinated, hydrolyzed, and fluorinated to obtain the product 4,4'-difluorobenzophenone.

[0017]

[0018] This method yields a high rate of change. However, the reaction process is complex and difficult to industrialize.

[0019] (6) Using p-bromofluorobenzene as a raw material, Grignard reagent is first prepared by reacting it with metallic magnesium, then 4,4'-difluorodiphenylmethanol is prepared by reacting it with p-fluorobenzaldehyde, and finally 4,4'-difluorodibenzophenone is obtained by oxidation reaction.

[0020]

[0021] The raw materials used in this method, p-bromofluorobenzene and p-fluorobenzaldehyde, are expensive and have limited sources. The Grignard reaction and subsequent oxidation steps pose high safety risks in industrial production. Therefore, the industrial application value of this synthetic route is low.

[0022] In recent years, heterogeneous catalytic oxidation technology has become a research hotspot, and many studies have been dedicated to developing various composite structure catalysts (such as core-shell structure, metal-doped oxides, porous organic polymer-supported metals, etc.) for the oxidation reaction of CH bonds. However, the existing technology still has the following shortcomings: (1) The catalyst preparation process is complicated, involving multi-step synthesis, high-temperature calcination or the use of organic templates, resulting in a long preparation cycle and poor recycling efficiency, which is not conducive to industrial scale-up; (2) The reaction system often requires the addition of various co-catalysts (such as TEMPO, NHPI, etc.) or co-oxidants (such as TBHP), which increases the complexity and cost of the process; (3) Some processes still use organic peroxides such as tert-butyl hydroperoxide as oxidants, which are less safe and have lower atom economy than molecular oxygen.

[0023] In summary, existing methods for preparing 4,4'-difluorobenzophenone generally suffer from problems such as the use of toxic and hazardous raw materials, metal catalyst pollution, complex processes, numerous byproducts, and high safety risks. Therefore, developing a simplified, metal catalyst-free, oxygen-based, and environmentally friendly method for preparing 4,4'-difluorobenzophenone has significant industrial application value and academic importance. Summary of the Invention

[0024] To address the limitations of existing technologies, this invention discloses a green preparation method for 4,4'-difluorobenzophenone. The preparation process is simple, safe to operate, highly selective, produces high-purity products, and generates minimal waste, thus possessing high industrial application value.

[0025] The technical solution adopted in this invention is as follows:

[0026] Using potassium bromide as a catalyst, 4,4'-difluorodiphenylmethane undergoes an oxidation reaction in a solvent under an oxygen atmosphere to yield the 4,4'-difluorobenzophenone, as shown in the following reaction formula:

[0027] The operating steps are as follows: Add a certain amount of 4,4'-difluorodiphenylmethane and catalyst to the high-pressure reactor, add an appropriate amount of solvent, add a magnetic stir bar, and introduce oxygen at a certain pressure through oxygen replacement. Stir the reaction for a certain time under a certain temperature and pressure, take samples for inspection, and calculate the conversion rate, selectivity, product output and yield using HPLC.

[0028] The solvent used is one of acetonitrile, toluene, acetic acid, and ethyl acetate. Acetic acid is preferred.

[0029] Based on the mass or volume of 4,4'-difluorodiphenylmethane, the catalyst dosage is 2 wt% to 20 wt%, and the solvent dosage is 1 to 20 v / v. Preferably, based on the mass ratio of 4,4'-difluorodiphenylmethane, the catalyst dosage is 5 wt% to 10 wt%, and the solvent dosage is 1.0 to 1.5 v / v.

[0030] The reaction temperature is 80–160℃, the oxygen pressure is 0.1 MPa–3.0 MPa, and the reaction time is 0.1 h–6 h. Preferably, the reaction temperature is 110–150℃, the oxygen pressure is 0.5 MPa–2.0 MPa, and the reaction time is 0.5 h–5 h.

[0031] After the reaction is complete, the catalyst is separated by filtration or centrifugation of the reaction solution. The filtrate is then concentrated, recrystallized, or purified by column chromatography to obtain a high-purity 4,4'-difluorobenzophenone product.

[0032] This invention discloses a green preparation method for 4,4'-difluorobenzophenone. The method uses 4,4'-difluorodiphenylmethane as a raw material, potassium bromide as a catalyst, acetic acid as a solvent, and oxygen as an oxidant, achieving highly selective one-step oxidation to 4,4'-difluorobenzophenone under mild conditions. This invention surprisingly discovers that, in the presence of potassium bromide, a novel non-metallic catalytic oxidation system of potassium bromide / acetic acid / oxygen is used to achieve highly efficient and selective conversion of the benzylic CH bond. Compared with traditional methods, this invention eliminates the need for transition metal catalysts, ozone-depleting raw materials such as carbon tetrachloride, and hazardous intermediates such as diazonium salts. The process route is short, atom-economical, and yields high-purity products. The catalyst is inexpensive and readily available, demonstrating excellent industrial application prospects and green chemistry characteristics. Specifically, during the research process, the present invention surprisingly discovered that when potassium bromide is used as a catalyst, 4,4'-difluorodiphenylmethane can be rapidly converted into 4,4'-difluorodibenzophenone through oxygen oxidation, and the purity of crude 4,4'-difluorodibenzophenone exceeds 95%, with high selectivity and few byproducts. High-purity 4,4'-difluorodibenzophenone can be obtained by simple purification operations such as distillation and recrystallization.

[0033] Compared with the prior art, the beneficial effects of this invention are reflected in:

[0034] (1) A new catalytic synthesis method for synthesizing 4,4'-difluorobenzophenone was developed using 4,4'-difluorodiphenylmethane as raw material and potassium bromide catalysis in the presence of oxygen in a one-step reaction. It has the advantages of cheap and readily available catalyst, green and safe oxidant, simple operation, high synthesis yield, high product purity and no metal residue.

[0035] (2) This study first discovered and systematically verified that potassium bromide can efficiently catalyze the selective oxidation of the benzylic CH bond of diarylmethane in the acetic acid / oxygen system. The synergistic mechanism of bromide ions, acetic acid and oxygen was confirmed by the control experiment, providing a new non-metallic catalytic pathway for the green synthesis of diaryl ketone compounds.

[0036] (3) Compared with the traditional Friedel-Crafts acylation process, this study does not require the use of Lewis acid catalysts such as anhydrous aluminum trichloride, thus avoiding the generation of a large amount of aluminum-containing wastewater; compared with the halogen replacement process, the reaction time is shortened from tens of hours to several hours, and the yield is significantly improved.

[0037] (4) This study uses oxygen as the only oxidant and water as the only byproduct, which has high atom economy. Potassium bromide catalyst is a bulk chemical product that does not require complicated preparation. It is widely available and inexpensive. After the reaction, the catalyst can be separated by simple filtration and centrifugation. The product is easy to purify and has no metal residue. It is suitable for continuous industrial production and has good economic and industrial value. Attached Figure Description

[0038] Figure 1 This is the liquid phase spectrum of 4,4'-difluorobenzophenone prepared in Example 1 of the present invention. Detailed Implementation

[0039] The present invention will be further described in detail below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0040] Example 1

[0041] A magnetic stir bar, 2.0 mL (2.3 g, 11.26 mmol) of 4,4'-difluorodiphenylmethane, 0.23 g of potassium bromide catalyst, and 10 mL of acetic acid were added to a 25 mL high-pressure reactor. The reactor was purged with oxygen at 1.0 MPa three times, followed by purging with oxygen at 1.0 MPa again. The reaction was stirred at 150 °C for 5 h. After the reaction, the catalyst was separated by centrifugation, and analysis was performed by liquid chromatography. The calculated conversion rate of 4,4'-difluorodiphenylmethane was 99.2%, the selectivity of 4,4'-difluorodibenzophenone was 99.8%, the yield was 95.2%, and the purity was 99.8%.

[0042] Example 2

[0043] A magnetic stir bar, 2.0 mL (2.3 g, 11.26 mmol) of 4,4'-difluorodiphenylmethane, 0.23 g of potassium bromide catalyst, and 10 mL of acetic acid were added to a 25 mL high-pressure reactor. The reactor was purged with oxygen at 1.0 MPa three times, followed by purging with oxygen at 1.0 MPa again. The reaction was carried out at 140 °C with stirring for 5 h. After the reaction was completed, the catalyst was separated by centrifugation, and the analysis was performed by liquid chromatography. The calculated conversion rate of 4,4'-difluorodiphenylmethane was 97.8%, the selectivity of 4,4'-difluorodibenzophenone was 99.2%, the yield was 93.5%, and the purity was 99.5%.

[0044] Example 3

[0045] A magnetic stir bar, 2.0 mL (2.3 g, 11.26 mmol) of 4,4'-difluorodiphenylmethane, 0.23 g of potassium bromide catalyst, and 10 mL of acetic acid were added to a 25 mL high-pressure reactor. The reactor was purged with oxygen at 1.0 MPa three times, followed by purging with oxygen at 1.0 MPa again. The reaction was carried out at 130 °C with stirring for 5 h. After the reaction was completed, the catalyst was separated by centrifugation, and the analysis was performed by liquid chromatography. The calculated conversion rate of 4,4'-difluorodiphenylmethane was 97.63%, the selectivity of 4,4'-difluorodibenzophenone was 99.56%, the yield was 92.8%, and the purity was 99.2%.

[0046] Example 4

[0047] A magnetic stir bar, 2.0 mL (2.3 g, 11.26 mmol) of 4,4'-difluorodiphenylmethane, 0.23 g of potassium bromide catalyst, and 10 mL of acetic acid were added to a 25 mL high-pressure reactor. The reactor was purged with oxygen at 1.0 MPa three times, followed by purging with oxygen at 1.0 MPa again. The reaction was carried out at 110 °C with stirring for 5 h. After the reaction was completed, the catalyst was separated by centrifugation, and the analysis was performed by liquid chromatography. The calculated conversion rate of 4,4'-difluorodiphenylmethane was 91.34%, the selectivity of 4,4'-difluorodibenzophenone was 99.47%, the yield was 87.5%, and the purity was 98.4%.

[0048] Example 5

[0049] A magnetic stir bar, 2.0 mL (2.3 g, 11.26 mmol) of 4,4'-difluorodiphenylmethane, 0.23 g of potassium bromide catalyst, and 10 mL of acetic acid were added to a 25 mL high-pressure reactor. The reactor was purged with oxygen at 1.0 MPa three times, followed by purging with oxygen at 1.0 MPa again. The reaction was carried out at 150 °C with stirring for 2 h. After the reaction was completed, the catalyst was separated by centrifugation, and the analysis was performed by liquid chromatography. The calculated conversion rate of 4,4'-difluorodiphenylmethane was 98.45%, the selectivity of 4,4'-difluorodibenzophenone was 99.76%, the yield was 94.6%, and the purity was 99.4%.

[0050] Example 6

[0051] A magnetic stir bar, 2.0 mL (2.3 g, 11.26 mmol) of 4,4'-difluorodiphenylmethane, 0.23 g of potassium bromide catalyst, and 10 mL of acetic acid were added to a 25 mL high-pressure reactor. The reactor was purged with oxygen at 1.0 MPa three times, followed by purging with oxygen at 1.0 MPa again. The reaction was carried out at 140 °C with stirring for 2 h. After the reaction was completed, the catalyst was separated by centrifugation, and the analysis was performed by liquid chromatography. The calculated conversion rate of 4,4'-difluorodiphenylmethane was 97.02%, the selectivity of 4,4'-difluorodibenzophenone was 99.31%, the yield was 94.8%, and the purity was 99.2%.

[0052] Example 7

[0053] A magnetic stir bar, 2.0 mL (2.3 g, 11.26 mmol) of 4,4'-difluorodiphenylmethane, 0.115 g of potassium bromide catalyst, and 10 mL of acetic acid were added to a 25 mL high-pressure reactor. The reactor was purged with oxygen at 1.0 MPa three times, followed by purging with oxygen at 1.0 MPa again. The reaction was stirred at 140 °C for 2 h. After the reaction was complete, the catalyst was separated by centrifugation, and analysis by liquid chromatography revealed a 97.72% conversion rate of 4,4'-difluorodiphenylmethane, a 97.58% selectivity for 4,4'-difluorodibenzophenone, a yield of 93.5%, and a purity of 97.4%.

[0054] Example 8

[0055] A magnetic stir bar, 2.0 mL (2.3 g, 11.26 mmol) of 4,4'-difluorodiphenylmethane, 0.23 g of potassium bromide catalyst, and 10 mL of acetic acid were added to a 25 mL high-pressure reactor. The reactor was purged with oxygen at 1.0 MPa three times, followed by purging with oxygen at 0.5 MPa, and stirred at 140 °C for 2 h. After the reaction, the catalyst was separated by centrifugation, and analysis was performed by liquid chromatography. The calculated conversion rate of 4,4'-difluorodiphenylmethane was 98.84%, the selectivity of 4,4'-difluorodibenzophenone was 99.25%, the yield was 94.7%, and the purity was 98.4%.

[0056] Example 9

[0057] A magnetic stir bar, 2.0 mL (2.3 g, 11.26 mmol) of 4,4'-difluorodiphenylmethane, 0.0625 g of potassium bromide catalyst, and 10 mL of acetic acid were added to a 25 mL high-pressure reactor. The reactor was purged with oxygen at 1.0 MPa three times, followed by purging with oxygen at 0.5 MPa. The reaction was stirred at 140 °C for 0.5 h. After the reaction was complete, the catalyst was separated by centrifugation, and analysis by liquid chromatography revealed a conversion rate of 86.06% for 4,4'-difluorodiphenylmethane, a selectivity of 95.87% for 4,4'-difluorodibenzophenone, a yield of 83.5%, and a purity of 94.4%.

[0058] Example 10

[0059] A magnetic stir bar, 2.0 mL (2.3 g, 11.26 mmol) of 4,4'-difluorodiphenylmethane, 0.23 g of potassium bromide catalyst, and 4 mL of acetic acid were added to a 25 mL high-pressure reactor. The reactor was purged with oxygen at 1.0 MPa three times, followed by purging with oxygen at 0.5 MPa, and stirred at 140 °C for 2 h. After the reaction, the catalyst was separated by centrifugation, and analysis by liquid chromatography revealed a 96.2% conversion rate of 4,4'-difluorodiphenylmethane, a 95.87% selectivity for 4,4'-difluorodibenzophenone, a yield of 91.2%, and a purity of 91.6%.

[0060] Example 11

[0061] A magnetic stir bar, 40.0 mL (46 g, 225.2 mmol) of 4,4'-difluorodiphenylmethane, 4.6 g of potassium bromide catalyst, and 200 mL of acetic acid were added to a 1000 mL high-pressure reactor. The reactor was purged with oxygen at 1.0 MPa three times, followed by purging with oxygen at 0.5 MPa, and stirred at 140 °C for 2 h. After the reaction, the catalyst was separated by centrifugation, and analysis was performed by liquid chromatography. The calculated conversion rate of 4,4'-difluorodiphenylmethane was 99.2%, the selectivity of 4,4'-difluorodibenzophenone was 99.8%, the yield was 96.2%, and the purity was 99.6%.

[0062] Comparative Example 1

[0063] A magnetic stir bar, 0.23 g of 4,4'-difluorodiphenylmethane, 0.23 g of potassium chloride catalyst, and 10 mL of acetic acid were added to a 25 mL high-pressure reactor. The reactor was purged with oxygen at 1.0 MPa three times, followed by purging with oxygen at 0.5 MPa, and stirred at 140 °C for 2 h. After the reaction, the catalyst was separated by centrifugation and analyzed by liquid chromatography. The calculated conversion rate of 4,4'-difluorodiphenylmethane was 12.37%, and the selectivity of 4,4'-difluorodibenzophenone was 94.92%.

[0064] Comparative Example 2

[0065] A magnetic stir bar, 0.23 g of 4,4'-difluorodiphenylmethane, 0.23 g of N-hydroxyphthalimide catalyst, and 10 mL of acetic acid were added to a 25 mL high-pressure reactor. The reactor was purged with oxygen at 1.0 MPa three times, followed by purging with oxygen at 0.5 MPa, and stirred at 140 °C for 2 h. After the reaction, the catalyst was separated by centrifugation and analyzed by liquid chromatography. The calculated conversion rate of 4,4'-difluorodiphenylmethane was 89.41%, the selectivity of 4,4'-difluorodibenzophenone was 96.06%, the yield was 84.2%, and the purity was 95.1%.

[0066] Comparative Example 3

[0067] A magnetic stir bar, 0.23 g of 4,4'-difluorodiphenylmethane, 0.23 g of N-hydroxyphthalimide catalyst, and 10 mL of acetic acid were added to a 25 mL high-pressure reactor. The reactor was purged with oxygen at 1.0 MPa three times, followed by purging with oxygen at 1.0 MPa again. The reaction was carried out at 140 °C with stirring for 2 h. After the reaction, the catalyst was separated by centrifugation and analyzed by liquid chromatography. The calculated conversion rate of 4,4'-difluorodiphenylmethane was 90.66%, the selectivity of 4,4'-difluorodibenzophenone was 94.11%, the yield was 86.1%, and the purity was 93.6%.

[0068] Comparative Example 4

[0069] A magnetic stir bar, 0.23 g of 4,4'-difluorodiphenylmethane, 0.23 g of N-hydroxyphthalimide catalyst, and 10 mL of acetic acid were added to a 25 mL high-pressure reactor. The reactor was purged with oxygen at 1.0 MPa three times, followed by purging with oxygen at 1.0 MPa again. The reaction was carried out at 150 °C with stirring for 5 h. After the reaction was completed, the catalyst was separated by centrifugation and analyzed by liquid chromatography. The calculated conversion rate of 4,4'-difluorodiphenylmethane was 92.25%, the selectivity of 4,4'-difluorodibenzophenone was 94.70%, the yield was 87.8%, and the purity was 93.1%.

[0070] Comparative Example 5

[0071] A magnetic stir bar, 0.23 g of 4,4'-difluorodiphenylmethane, 0.23 g of potassium bromide catalyst, and 10 mL of acetonitrile were added to a 25 mL high-pressure reactor. The reactor was purged with oxygen at 1.0 MPa three times, followed by purging with oxygen at 1.0 MPa, and stirred at 140 °C for 2 h. After the reaction, the catalyst was separated by centrifugation, and analysis was performed by liquid chromatography. The calculated conversion rate of 4,4'-difluorodiphenylmethane was 82.12%, the selectivity of 4,4'-difluorodibenzophenone was 99.62%, the yield was 78.2%, and the purity was 99.6%.

[0072] Comparative Example 6

[0073] A magnetic stir bar, 0.23 g of 4,4'-difluorodiphenylmethane, 0.23 g of potassium bromide catalyst, and 10 mL of acetic acid were added to a 50 mL flask. The mixture was stirred at 140 °C under open air for 2 h. After the reaction was complete, the catalyst was separated by centrifugation and analyzed by liquid chromatography. The results showed that the conversion rate of 4,4'-difluorodiphenylmethane was only 9.28%, and the selectivity of 4,4'-difluorodibenzophenone was 99.56%.

[0074] Comparative Example 7

[0075] A magnetic stir bar, 0.23 g of 4,4'-difluorodiphenylmethane, 0.23 g of potassium bromide catalyst, and 10 mL of acetic acid were added to a 50 mL flask. The flask was purged with nitrogen gas at 1.0 MPa three times, followed by purging with nitrogen gas at 0.5 MPa. The mixture was stirred at 140 °C under a nitrogen atmosphere for 2 h. After the reaction was completed, the catalyst was separated by centrifugation, and analysis by liquid chromatography showed that no 4,4'-difluorodiphenylmethane was detected.

[0076] The above comparative examples show that potassium bromide and oxygen must be present simultaneously as catalysts, and better conversion rate and selectivity can be obtained by using acetic acid as a solvent.

[0077] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing 4,4'-difluorobenzophenone, characterized in that, Using potassium bromide as a catalyst, 4,4'-difluorodiphenylmethane undergoes an oxidation reaction in a solvent under an oxygen atmosphere to yield 4,4'-difluorobenzophenone, as shown in the following reaction formula: 。 2. The preparation method according to claim 1, characterized in that, The selected solvent is one or more of glacial acetic acid, acetonitrile, toluene, acetic acid and ethyl acetate.

3. The preparation method according to claim 2, characterized in that, The solvent used is acetic acid.

4. The preparation method according to claim 1, characterized in that, Based on the mass ratio of 4,4'-difluorodiphenylmethane, the catalyst dosage is 2 wt% to 30 wt%; based on the volume ratio of 4,4'-difluorodiphenylmethane, the solvent dosage is 1 to 15 v / v.

5. The preparation method according to claim 4, characterized in that, Based on the mass ratio of 4,4'-difluorodiphenylmethane, the catalyst dosage is 5 wt% to 10 wt%; based on the volume ratio of 4,4'-difluorodiphenylmethane, the solvent dosage is 2.5 to 5 v / v.

6. The preparation method according to claim 1, characterized in that, The reaction temperature is 80℃~160℃, the oxygen pressure is 0.1 MPa~3.0 MPa, and the reaction time is 0.1 h~6 h.

7. The preparation method according to claim 1, characterized in that, The reaction temperature is 130℃~150℃, the oxygen pressure is 0.5 MPa~1.0 MPa, and the reaction time is 0.5 h~5 h.

8. The preparation method according to claim 1, characterized in that, The reaction is carried out in a high-pressure reactor, and the air inside the reactor is replaced with oxygen before the reaction.

9. The preparation method according to claim 1, characterized in that, The operating steps are as follows: add a certain amount of 4,4'-difluorodiphenylmethane and catalyst to the high-pressure reactor, add an appropriate amount of solvent, introduce oxygen at a certain pressure, and react for a certain time at a set temperature.

10. The preparation method according to claim 1, characterized in that, After the reaction is complete, insoluble matter is removed by filtration, and the reaction solution is concentrated, recrystallized or purified by column chromatography to obtain high-purity 4,4'-difluorobenzophenone product.

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