Method for producing fluorenone

Abstract

A method for producing fluorenone comprises, in sequence: an oxidation step of oxidizing fluorene in the presence of an aliphatic carboxylic acid having 2 to 3 carbon atoms, a metal catalyst, a bromine compound, and oxygen; a solvent removal step of removing the aliphatic carboxylic acid; a heating step of heating at 120 to 350° C.; and a distillation step.

Description

Technical Field

[0001] The present invention relates to a method for producing fluorenone. Background Art

[0002] Fluorenone is used as a raw material or intermediate for pharmaceuticals, resins, etc. Specifically, it is a very useful compound as a raw material for electrophotographic photoreceptors, a raw material for pigments, and a raw material for optical resins.

[0003] Fluorenone is produced by oxidizing fluorene. Among these methods, a production method utilizing liquid phase oxidation using an oxygen-containing gas such as air has been developed.

[0004] For example, Patent Document 1 discloses a method for producing fluorenones in order to obtain fluorenones in high yield, characterized in that fluorenes are oxidized with molecular oxygen in an organic solvent in the presence of a phase transfer catalyst and a solid alkali metal hydroxide.

[0005] Furthermore, Patent Document 2 discloses a method of reacting a dimethyl sulfoxide solution of fluorene with oxygen molecules in the presence of a small amount of alkali metal hydroxide in order to obtain fluorenone in high yield.

[0006] Patent Document 3 discloses a method for obtaining diallyl ketone by reacting an aromatic compound with oxygen molecules using a low saturated aliphatic monocarboxylic acid as a solvent and a heavy metal as an oxidation catalyst in order to obtain diallyl ketone simply, economically, and in high yield. As an example, a method for obtaining fluorenone is disclosed.

[0007] Prior art literature

[0008] Patent Literature

[0009] Patent Document 1: Japanese Patent Application Laid-Open No. 2007-182399

[0010] Patent Document 2: U.S. Patent No. 3,875,237

[0011] Patent Document 3: U.S. Patent No. 3,038,940 Summary of the Invention

[0012] According to Patent Document 3, fluorenone is synthesized using the so-called Amoco method, resulting in a yield of 76%. To remove impurities such as byproducts, the fluorenone is further purified by recrystallization from benzene and hexane, according to Patent Document 3. However, obtaining high-purity fluorenone is difficult. Furthermore, this method is difficult to apply to industrial production. Specifically, it is difficult to produce high-purity fluorenone in large quantities and continuously.

[0013] Therefore, an object of the present invention is to provide a method for producing fluorenone that can effectively remove by-products and the like generated by the oxidation reaction and can industrially obtain high-purity fluorenone.

[0014] The present inventors have conducted intensive studies and have found that the above-mentioned problems can be solved by oxidizing fluorene in the presence of a specific solvent, a metal catalyst, and a bromine compound, removing the solvent, and heating and distilling at a specific temperature.

[0015] The present invention relates to the following [1] to [7].

[0016] [1] A method for producing fluorenone, comprising, in sequence: an oxidation step of oxidizing fluorene in the presence of an aliphatic carboxylic acid having 2 to 3 carbon atoms, a metal catalyst, a bromine compound, and oxygen; a solvent removal step of removing the aliphatic carboxylic acid; a heating step of heating at 120 to 350°C; and a distillation step.

[0017] [2] The method for producing fluorenone according to [1] above, wherein the heating time in the heating step is 5 minutes or longer.

[0018] [3] The method for producing fluorenone according to [1] or [2] above, wherein the mixture supplied to the heating step contains fluorenone and bromide ions, and the content of the bromide ions in the heating step is 0.01 to 5 parts by mass relative to 100 parts by mass of fluorenone.

[0019] [4] The method for producing fluorenone according to any one of [1] to [3] above, wherein the distillation step comprises, in sequence, a step of removing high-boiling-point components and a step of removing low-boiling-point components.

[0020] [5] The method for producing fluorenone according to any one of [1] to [4] above, wherein the metal catalyst is at least one selected from the group consisting of a cobalt catalyst, a manganese catalyst, a zirconium catalyst, a cerium catalyst, and a nickel catalyst.

[0021] [6] The method for producing fluorenone according to any one of [1] to [5] above, wherein the aliphatic carboxylic acid is acetic acid.

[0022] [7] The method for producing fluorenone according to any one of [1] to [6] above, wherein oxygen is supplied by introducing air in the oxidation step.

[0023] According to the production method of the present invention, by-products and the like generated by the oxidation reaction can be effectively removed, and high-purity fluorenone can be obtained industrially. DETAILED DESCRIPTION

[0024] The method for producing fluorenone of the present invention sequentially comprises: an oxidation step of oxidizing fluorene in the presence of an aliphatic carboxylic acid having 2 to 3 carbon atoms, a metal catalyst, a bromine compound, and oxygen; a solvent removal step of removing the aliphatic carboxylic acid; a heating step of heating at 120 to 350° C.; and a distillation step.

[0025] Hereinafter, the production method of the present invention will be described in detail.

[0026] [Oxidation process]

[0027] In the method for producing fluorenone of the present invention, fluorene is first oxidized. This oxidation step can oxidize fluorene to obtain fluorenone as a main product.

[0028] In the oxidation step of the method for producing fluorenone of the present invention, fluorene is oxidized in the presence of an aliphatic carboxylic acid having 2 to 3 carbon atoms, a metal catalyst, a bromine compound, and oxygen to obtain an oxidation reaction mixture containing fluorenone as a main product.

[0029] <Aliphatic carboxylic acid having 2 to 3 carbon atoms>

[0030] The aliphatic carboxylic acid used in this step is an aliphatic carboxylic acid having 2 to 3 carbon atoms, and more preferably an aliphatic carboxylic acid having 2 carbon atoms.

[0031] Specific aliphatic carboxylic acids are preferably at least one selected from acetic acid and propionic acid, more preferably acetic acid. When acetic acid is used, a mixed solution prepared by mixing water and acetic acid as described below may be prepared in advance, or only acetic acid may be used.

[0032] The use of the above-mentioned aliphatic carboxylic acids is preferred because the activity of the catalyst can be enhanced.

[0033] The amount of the aliphatic carboxylic acid used in the oxidation step is preferably 10 to 1000 parts by mass, more preferably 50 to 400 parts by mass, further preferably 70 to 200 parts by mass, and even more preferably 80 to 100 parts by mass, based on 100 parts by mass of fluorene.

[0034] When the amount of the aliphatic carboxylic acid is greater than or equal to the lower limit, the viscosity can be adjusted appropriately, the handling becomes easier, and the reaction heat can be controlled to prevent a rise in the reactor temperature. Furthermore, when the amount of the aliphatic carboxylic acid is less than or equal to the upper limit, the production efficiency is excellent and the economics are also excellent.

[0035] The above-mentioned aliphatic carboxylic acids may be used alone or in combination of two or more.

[0036] <Metal Catalyst>

[0037] The metal catalyst used in this step is preferably at least one selected from a transition metal catalyst and a rare earth metal catalyst, and more preferably a transition metal catalyst.

[0038] As a specific transition metal catalyst, at least one selected from a cobalt catalyst, a manganese catalyst, a zirconium catalyst, a cerium catalyst, and a nickel catalyst is preferred, and at least one selected from a cobalt catalyst and a manganese catalyst is more preferred. It is further preferred to use a cobalt catalyst and a manganese catalyst simultaneously.

[0039] As described above, the metal catalyst used in this step is preferably at least one selected from a cobalt catalyst, a manganese catalyst, a zirconium catalyst, a cerium catalyst, and a nickel catalyst, more preferably at least one selected from a cobalt catalyst and a manganese catalyst. It is further preferred to use a cobalt catalyst and a manganese catalyst simultaneously.

[0040] The metal catalyst can be used in the form of a salt, a single metal, an oxide, a hydroxide, or the like. However, the metal catalyst used in this step is preferably a salt, more preferably an aliphatic carboxylate, even more preferably a lower aliphatic carboxylate, and even more preferably an acetate. Among these, at least one selected from cobalt acetate and manganese acetate is even more preferred.

[0041] The use of the above-mentioned metal catalyst is preferred because fluorenone can be obtained in high yield.

[0042] The amount of the metal catalyst used in the oxidation step is preferably 0.02 to 10 parts by mass, more preferably 0.05 to 5 parts by mass, further preferably 0.1 to 3 parts by mass, and even more preferably 0.1 to 1 part by mass, based on 100 parts by mass of fluorene, in terms of metal element.

[0043] When the catalyst concentration is above the lower limit, the reaction rate increases and the yield also increases. When the catalyst concentration is below the upper limit, the catalyst cost is low and there is no adverse effect on the reaction.

[0044] The metal catalyst may be used alone or in combination of two or more.

[0045] <Bromine compounds>

[0046] Preferred bromine compounds used in this step include hydrogen bromide, bromide salts, and organic bromine compounds, more preferably at least one selected from hydrogen bromide and bromide salts, and even more preferably hydrogen bromide.

[0047] Hydrogen bromide is preferably used in the form of an aqueous solution.

[0048] Specific examples of the bromide salt include sodium bromide, potassium bromide, and ammonium bromide.

[0049] The amount of the bromine compound used in the oxidation step is preferably 0.01 to 5 parts by mass, more preferably 0.05 to 3 parts by mass, further preferably 0.05 to 1 part by mass, and even more preferably 0.05 to 0.5 parts by mass, based on 100 parts by mass of fluorene, in terms of bromine.

[0050] When the amount of the bromine compound is above the lower limit of the range, the reaction rate and yield are increased. When the amount of the bromine compound is below the upper limit of the range, corrosion is less likely to occur, and the use of high-quality equipment is not required.

[0051] The bromine compound may be used alone or in combination of two or more.

[0052] Water

[0053] In this step, water can be used, and it is preferred to use water in order to easily dissolve the bromine compound.

[0054] The amount of water used in the oxidation step is preferably 1 to 200 parts by mass, more preferably 1 to 100 parts by mass, further preferably 2 to 50 parts by mass, and even more preferably 3 to 10 parts by mass, relative to 100 parts by mass of fluorene.

[0055] When the water concentration is within the above range, it is possible to prevent the catalyst activity from being reduced and to dissolve the bromine compound, thereby increasing the yield of fluorenone.

[0056] Oxygen

[0057] The oxygen used in this step may be oxygen gas or a mixed gas with an inert gas, etc. However, in this step, it is preferred to supply oxygen by introducing air from the viewpoint of safety and economic efficiency.

[0058] The oxygen used in this step is preferably introduced so that the oxygen concentration in the exhaust gas (waste gas) discharged from the reactor during the raw material supply becomes 0.1 to 8 volume %, more preferably 1 to 5 volume %.

[0059] By maintaining the amount of oxygen introduced within the above range, the reaction can be carried out safely and efficiently below the explosion range of the solvent, which is preferable.

[0060] <Oxidation process conditions, etc.>

[0061] The temperature during the oxidation reaction in this step is preferably 120 to 280°C, more preferably 160 to 260°C, and even more preferably 190 to 240°C.

[0062] When the temperature during the oxidation reaction is at least the lower limit of the range, the reaction rate increases, and when the temperature during the oxidation reaction is at most the upper limit of the range, the formation of by-products is suppressed, and the yield increases.

[0063] The pressure during the oxidation reaction in this step may be any pressure that can maintain the reaction liquid in a liquid phase, and is preferably 0.1 to 4 MPa.

[0064] When oxygen is supplied by introducing air, the reaction time of the oxidation reaction in this step is preferably 0.1 to 10 hours, more preferably 0.5 to 5 hours, and even more preferably 1 to 3 hours.

[0065] In this step, from the viewpoint of safety, it is preferred to introduce an inert gas such as nitrogen into the reaction vessel containing the raw materials before introducing oxygen.

[0066] [Solvent Removal Step]

[0067] The method for producing fluorenone of the present invention includes a solvent removal step of removing the aliphatic carboxylic acid having 2 to 3 carbon atoms after the oxidation step.

[0068] In the solvent removal step in the method for producing fluorenone of the present invention, the aliphatic carboxylic acid having 2 to 3 carbon atoms is removed from the oxidation reaction mixture obtained in the oxidation step to obtain a mixture containing fluorenone as a main component.

[0069] When water is used in the oxidation reaction step, the water may also be removed in this step.

[0070] In this step, in order to improve production efficiency, the solvent may be distilled off by heating under reduced pressure, or may be distilled off by heating under atmospheric pressure.

[0071] The pressure during the solvent removal in this step is preferably 80 kPa or less, more preferably 1 to 60 kPa, and even more preferably 2 to 50 kPa.

[0072] The temperature during the solvent removal in this step is preferably 80 to 200°C, more preferably 90 to 180°C, and even more preferably 100 to 150°C.

[0073] In this step, an apparatus generally used for heating distillation is used, and specific examples include a single distillation apparatus, a precision distillation apparatus, a molecular distillation apparatus, a thin film distillation apparatus, etc. In addition to these distillation apparatuses, a dryer or the like may be used to remove the solvent.

[0074] This step is a step in which the amount of the residual aliphatic carboxylic acid having 2 to 3 carbon atoms in the mixture obtained after this step is preferably reduced to 5% by mass or less. It is more preferably reduced to 3% by mass or less, and even more preferably reduced to 1% by mass or less. This step can also completely remove the aliphatic carboxylic acid having 2 to 3 carbon atoms. Removing the solvent in this step increases the reaction rate of byproducts in the subsequent heating step, thereby effectively removing impurities and obtaining high-purity fluorenone, which is preferred.

[0075] [Heating process]

[0076] The method for producing fluorenone of the present invention includes a heating step of heating at 120 to 350° C. after the solvent removal step.

[0077] In the heating step of the method for producing fluorenone of the present invention, the mixture containing fluorenone as a main component obtained in the solvent removal step is heated at 120 to 350° C. to obtain a heat-treated mixture.

[0078] This step can be carried out by any method. Heating can be performed in the vessel used in the solvent removal step, in a separate vessel prepared for the heating step, or in a distillation apparatus used in the subsequent distillation step. In any method, the mixture can be heated at 120-350°C. If necessary, the mixture containing fluorenone as the main component can be refluxed under reduced pressure.

[0079] In the present invention, by providing a heating step, impurities such as by-products produced by the oxidation reaction can be effectively removed, and high-purity fluorenone can be obtained industrially. The reason for this is not yet clear, but is considered as follows.

[0080] This is believed to be because byproducts such as fluorenone undergo chemical reactions during the heating step, transforming them into compounds with boiling points significantly different from the target fluorenone, allowing them to be effectively removed in the subsequent distillation step. In particular, the aliphatic carboxylic acid fluorenyl ester, a major byproduct, has a boiling point close to that of the target fluorenone, making it difficult to remove by simple distillation. However, by adding a heating step after the oxidation reaction, the carboxylic acid fluorenyl ester decomposes and polymerizes, increasing its molecular weight. This allows for efficient removal in the subsequent distillation step, allowing high-purity fluorenone to be obtained through distillation, an industrial process.

[0081] The heating temperature in this step is 120 to 350°C, preferably 180 to 280°C, more preferably 220 to 280°C, further preferably 220 to less than 260°C, and even more preferably 240 to less than 260°C.

[0082] In this step, the mixture supplied to the heating step contains bromide ions. The inclusion of bromide ions is believed to promote the decomposition and polymerization of the fluorenyl carboxylate. If the bromine compound used in the oxidation step also remains in this step, the addition of bromide ions is unnecessary. However, if the bromine compound is removed or discharged during the oxidation and solvent removal steps, reducing its content, it is preferable to add bromide ions. By adding bromide ions, the appropriate content can be adjusted.

[0083] The mixture supplied to this step is the mixture containing fluorenone as a main component obtained in the solvent removal step. Specifically, the mixture supplied to this heating step contains fluorenone and bromide ions. The content of bromide ions in this heating step is preferably 0.01 to 5 parts by mass, more preferably 0.05 to 3 parts by mass, even more preferably 0.05 to 1 part by mass, even more preferably 0.05 to 0.5 parts by mass, and even more preferably 0.1 to 0.4 parts by mass per 100 parts by mass of fluorenone.

[0084] In this step, the bromine compound supplying bromide ions is preferably the same bromine compound used in the oxidation step. Specifically, preferred examples include hydrogen bromide, bromide salts, and organic bromine compounds. More preferred is at least one selected from hydrogen bromide and bromide salts, and even more preferred is hydrogen bromide.

[0085] Specific examples of the bromide salt include sodium bromide, potassium bromide, and ammonium bromide.

[0086] In this step, a metal catalyst is preferably used. It is convenient and preferable to use the metal catalyst as it is used in the oxidation step in the previous step.

[0087] The metal catalyst preferably used in this step is preferably the same as that used in the oxidation step. Specifically, it is preferably at least one selected from a cobalt catalyst, a manganese catalyst, a zirconium catalyst, a cerium catalyst, and a nickel catalyst, and more preferably at least one selected from a cobalt catalyst and a manganese catalyst. It is further preferred to use both a cobalt catalyst and a manganese catalyst.

[0088] The metal catalyst can be used in the form of a salt, a single metal, an oxide, a hydroxide, or the like. However, the metal catalyst used in this step is preferably a salt, more preferably an aliphatic carboxylate, even more preferably a lower aliphatic carboxylate, and even more preferably an acetate. Among these, at least one selected from cobalt acetate and manganese acetate is even more preferred.

[0089] It is considered that the decomposition and polymerization of fluorenyl carboxylate can be promoted by using the above-mentioned metal catalyst.

[0090] The amount of the metal catalyst used in the heating step can be an amount determined by directly using the metal catalyst used in the oxidation step, and is preferably 0.02 to 10 parts by mass, more preferably 0.05 to 5 parts by mass, further preferably 0.1 to 3 parts by mass, and even more preferably 0.1 to 1 part by mass, relative to 100 parts by mass of fluorene, which is a raw material for the oxidation step, when converted into metal elements.

[0091] Generally, heating in the presence of a catalyst is not performed after the reaction is completed in order to prevent deterioration of the target product. However, in the production method of the present invention, heating in the presence of a metal catalyst and bromide ions is performed after the oxidation reaction is completed and the solvent is removed. This allows by-products to be effectively removed in the subsequent distillation step, and high-purity fluorenone can be obtained industrially.

[0092] The heating time of this heating step is preferably 5 minutes or more, more preferably 10 minutes or more, further preferably 20 minutes to 100 hours, further preferably 30 minutes to 20 hours, and further preferably 1 to 10 hours. It should be noted that the heating time is preferably adjusted appropriately according to the heating temperature and the bromide ion content. When the heating temperature is high or the bromide ion content is high, the effects of the present invention can be achieved even with a short heating time. Furthermore, when the heating temperature is high and the bromide ion content is high, the effects of the present invention can be achieved even with a shorter heating time.

[0093] By extending the heating time, the purity of the target fluorenone can be further improved. However, since the target fluorenone deteriorates due to prolonged heating, it is preferable to determine the end point of heating from the viewpoint of preventing deterioration of fluorenone and improving the yield of fluorenone.

[0094] As a specific example, when the bromide ion content is adjusted to 0.1 to 0.4 parts by mass relative to 100 parts by mass of fluorenone and the heating temperature is set to 150°C or higher and lower than 220°C, the heating time is preferably 15 minutes to 10 hours, more preferably 1 to 7 hours, and even more preferably 2 to 5 hours.

[0095] When the bromide ion content is adjusted to 0.1 to 0.4 parts by mass per 100 parts by mass of fluorenone and the heating temperature is set to 220°C or higher and lower than 260°C, the heating time is preferably 5 minutes to 3 hours, more preferably 15 minutes to 2 hours, and even more preferably 45 minutes to 1.5 hours.

[0096] When the bromide ion content is adjusted to 0.1 to 0.4 parts by mass per 100 parts by mass of fluorenone and the heating temperature is 260°C or higher and lower than 300°C, the heating time is preferably 5 minutes to 1 hour, more preferably 5 minutes to 45 minutes, and even more preferably 10 minutes to 30 minutes.

[0097] When the bromide ion content is adjusted to 0.1 to 0.4 parts by mass based on 100 parts by mass of fluorenone and the heating temperature is set to 300 to 320° C., the heating time is preferably 5 to 30 minutes, more preferably 5 to 15 minutes.

[0098] [Distillation process]

[0099] The method for producing fluorenone of the present invention includes a distillation step after the heating step.

[0100] The distillation step in the method for producing fluorenone of the present invention may be any method as long as it can separate and recover the target fluorenone, but the distillation step preferably includes a step for removing high-boiling-point components and a step for removing low-boiling-point components, and the distillation step more preferably includes a step for removing high-boiling-point components and a step for removing low-boiling-point components in sequence.

[0101] In the step of removing low-boiling components using a distillation column, if the residence time at the bottom of the column is long, fluorenone may be deteriorated or colored. Therefore, it is preferable to further include a step of removing the coloring component.

[0102] Hereinafter, two-stage distillation as a preferred embodiment will be described.

[0103] (High-boiling-point component removal step)

[0104] First, it is preferred to remove high-boiling components. High-boiling components are believed to contain various impurities and by-products. By removing high-boiling components at the beginning of the distillation process, it is believed that the increase in impurities caused by deterioration of the target product and decomposition of high-boiling components can be suppressed.

[0105] The distillation temperature can be appropriately adjusted to about the boiling point of fluorenone (the boiling point at 1 atmosphere is 342°C) by adjusting the pressure during distillation. For example, when the distillation pressure is adjusted to 1.5 to 3.5 kPa, it is preferably 150 to 300°C, more preferably 160 to 250°C, further preferably 170 to 240°C, and even more preferably 180 to 220°C.

[0106] When a distillation column is used in the high-boiling-point component removal step, a mixture containing fluorenone and low-boiling-point components is recovered from the top of the column.

[0107] (Low-boiling-point component removal step)

[0108] Next, low-boiling point components are preferably removed.

[0109] The distillation temperature in this step can be appropriately adjusted to about the boiling point of fluorenone (the boiling point at 1 atmosphere is 342°C) according to the pressure during distillation. For example, when the distillation pressure is adjusted to 1.5 to 3.5 kPa, it is preferably 150 to 300°C, more preferably 160 to 250°C, further preferably 165 to 230°C, and further preferably 170 to 200°C.

[0110] When a distillation column is used in the low-boiling-point component removal step, high-purity fluorenone can be recovered from the bottom of the column.

[0111] Furthermore, if the residence time at the bottom of the column is long, fluorenone may be deteriorated or colored. Therefore, in order to remove the coloring components, it is preferable to further perform distillation (coloring component removal step) after the present distillation step and recover high-purity fluorenone from the top of the column.

[0112] Example

[0113] The present invention will be specifically described based on the following examples, but the present invention is not limited to these examples.

[0114] <Method for measuring the concentration (composition) of each component>

[0115] The composition of each component (fluorene, fluorenone, 9-fluorenyl acetate, and 9,9'-bifluorene) in the reaction product after the oxidation step, the solvent removal step, and the heating step was calculated by the internal standard method (internal standard: triphenylmethane) using gas chromatography.

[0116] The purity of fluorene and 9-fluorenones (fluorene, fluorenone, and 9-fluorenyl acetate (fluorenyl acetate)) after the distillation step is expressed as area percentage by gas chromatography.

[0117] The bromide ion concentration was determined by titration using silver nitrate.

[0118] It should be noted that as impurities contained in the final recovered product, the raw material fluorene and the main by-product 9-fluorenyl acetate were quantified, and the lower their amounts, the higher the purity of the obtained fluorenone, which is preferred. The results are shown in Table 1.

[0119] Gardner Color Number Measurement Method

[0120] The Gardner color number of the Examples and Comparative Examples was determined by melting the purified fluorenone at 140° C. and using a colorimeter.

[0121] Production of Fluorenone

[0122] Example 1

[0123] (1. Oxidation process)

[0124] Cobalt acetate tetrahydrate, manganese acetate tetrahydrate, 48% by mass aqueous hydrogen bromide solution, glacial acetic acid, and water were mixed so as to have a cobalt metal atomic concentration of 0.75% by mass, a manganese metal atomic concentration of 0.75% by mass, a bromide ion concentration of 0.075% by mass, an acetic acid concentration of 88.425% by mass, and a water concentration of 10% by mass to obtain a catalyst solution.

[0125] 150 g of the above-mentioned catalyst liquid was placed in a 500 mL titanium autoclave equipped with a gas exhaust pipe with a reflux cooler, a gas blowing pipe, a raw material continuous liquid feeding pump and a stirrer. Under a nitrogen atmosphere, the pressure and temperature were increased to 1.0 MPa and 200°C. 150 g of fluorene was supplied within 120 minutes. The throughput was 1.3 g / min. Air was introduced at the same time as the raw material supply began, and the amount of air introduced was adjusted so that the oxygen concentration in the exhaust gas was less than 4% by volume to carry out the oxidation reaction. After the supply of fluorene was completed, the absorption of oxygen was completed, and the introduction of air was completed when the oxygen concentration in the exhaust gas was 8% by volume. After the reaction, the oxidation reaction product was extracted. The recovery amount was 310 g (weight recovery rate 99.4%). As a result of analysis, the composition of the oxidation reaction product containing acetic acid as a solvent was 2.64 mass % of fluorene, 41.6 mass % of fluorenone, 2.78 mass % of 9-fluorenyl acetate, and 0.41 mass % of 9,9'-bifluorene.

[0126] (2. Solvent Removal Process)

[0127] 310 g of the oxidation reaction product was transferred to a 500 mL glass flask and subjected to simple distillation at a heater temperature of 120°C and an internal pressure of 5 to 40 kPa over 1 hour to remove acetic acid and 153 g of water. The composition of the reaction product after solvent removal was 4.76 mass% fluorene, 79.8 mass% fluorenone, 5.36 mass% 9-fluorenyl acetate, and 0.74 mass% 9,9'-bifluorene.

[0128] (3. Heating process)

[0129] The reaction product after solvent removal was introduced into a distillation column with a plate count equivalent to 9, and refluxed at a pressure of 2 kPa and 245.0-250.0°C for 2 hours. The bromide ion concentration in the reaction product used in this step was 0.075 parts by mass per 100 parts by mass of fluorenone. The composition of the heated reaction product was 2.96% by mass of fluorene, 79.4% by mass of fluorenone, and 2.38% by mass of 9,9'-bifluorene. 9-fluorenyl acetate was absent.

[0130] (4. Distillation step (high boiling point component removal step))

[0131] After the heating step, extraction was initiated using the distillation column used in the heating step, with distillation conditions set at a pressure of 2 kPa, a top temperature of 188.0°C, and a bottom temperature of 196.0°C. 107 g of fluorenone, including the resulting low-boiling-point component, was extracted from the top of the distillation column. The composition was 5.6% fluorene and 94.4% fluorenone, resulting in a distillation recovery rate of 80.0% for fluorenone.

[0132] (5. Distillation step (low-boiling-point component removal step))

[0133] Using a distillation column with nine plates, batch distillation was performed to separate the fluorenone, which contained low-boiling components, from the top of the column into the low-boiling components and fluorenone. Distillation conditions were a pressure of 1.7 kPa, a top temperature of 185.0°C, and a bottom temperature of 190.0°C. Purified fluorenone was obtained from the bottom of the distillation column. The resulting purified fluorenone had a purity of 99.99%, a fluorenone distillation recovery of 76.2%, and a Gardner color number of 8.5. Furthermore, the purified fluorenone contained 0.01% of the raw material fluorene and no 9-fluorenyl acetate (detection limit: less than 0.001%).

[0134] Example 2

[0135] The same procedures as in Example 1 were followed until Step 3. Heating. After Step 3. Heating, Step 5. Distillation (low-boiling-point component removal) was performed. The resulting fluorenone, which contained high-boiling-point components and was obtained from the bottom of the distillation column, was subjected to Step 4. Distillation (high-boiling-point component removal). The purified fluorenone was obtained from the top of the distillation column. The resulting purified fluorenone had a purity of 99.29%, a total yield of 51.1%, and a Gardner color number of 8.2. Furthermore, the purified fluorenone contained 0.68% of the raw material fluorene and no 9-fluorenyl acetate (detection limit: 0.001% or less).

[0136] Example 3

[0137] The same procedures as in Example 1 were followed until step 5. Removal of Low-Boiling Components. After step 5. Distillation (low-boiling component removal), the fluorenone obtained from the bottom of the distillation column was subjected to a coloring component removal step (distillation at a pressure of 1.7 kPa and a temperature of 190°C). Purified fluorenone was obtained from the top of the distillation column. The resulting purified fluorenone had a purity of 99.99% and a Gardner color number of 8.2. Furthermore, the purified fluorenone contained 0.01% of the raw material fluorene and no 9-fluorenyl acetate (detection limit: 0.001% or less).

[0138] Comparative Example 1

[0139] The same procedures as in Example 1 were followed up to step 2. Solvent Removal to obtain a solvent-removed reaction product. The solvent-removed reaction product was introduced into a distillation column with nine plates. Step 3. Heating was omitted, and steps 4. Distillation (high-boiling-point component removal) and 5. Distillation (low-boiling-point component removal) were performed sequentially as in Example 1. Purified fluorenone was obtained from the bottom of the distillation column. The resulting purified fluorenone had a purity of 97.16%, a total yield of 46.7%, and a Gardner color number of 8.5. The purified fluorenone contained 0.01% of the raw material fluorene and 2.76% of 9-fluorenyl acetate.

[0140] Comparative Example 2

[0141] The same procedures as in Example 1 were followed until step 1. Oxidation to obtain an oxidation reaction product. The oxidation reaction product was then cooled to 30°C while stirring to precipitate crude fluorenone. Crystals were separated using a solid-liquid separator and washed with water, and the crude fluorenone crystals were then dried. A double amount of 70% aqueous acetic acid was added to the crude crystals, heated to 108°C to redissolve the crude crystals. The crude fluorenone solution was then cooled to 30°C to precipitate purified fluorenone. Crystals were separated using a solid-liquid separator and washed with water, and then dried. The purified fluorenone had a purity of 96.10%, a crystal yield of 41.4%, and a Gardner color number of 14.7. The purified fluorenone contained 0.20% of the raw material fluorene and 1.00% of 9-fluorenyl acetate.

[0142] [Table 1]

[0143] Table 1

[0144]

[0145] The results of the Examples and Comparative Examples show that the production method of the present invention can effectively remove by-products and the like generated by the oxidation reaction, and can obtain high-purity fluorenone by an industrially advantageous distillation method.

[0146] <Production of Fluorenone (Evaluation of By-product Removal Efficiency)>

[0147] The following test examples were used to evaluate the efficiency of removing by-products when the conditions of the heating step were changed.

[0148] Test Examples 1 to 9 and Comparative Test Example 1

[0149] The same procedures as in Example 1 were followed until step 2. Solvent Removal to obtain a reaction product after solvent removal. The reaction product after solvent removal was introduced into a distillation column with a plate number equivalent to 9 and refluxed at a pressure of 2 kPa, the temperature shown in Table 2, and the time shown in Table 2 (heating step). In Table 2, the residual amount of the by-product 9-fluorenyl acetate is expressed as a ratio relative to the reaction product after solvent removal. The lower the residual amount of 9-fluorenyl acetate, the better the by-product removal efficiency. The residual amount of 9-fluorenyl acetate is specifically calculated using the following formula.

[0150] Residual amount of 9-fluorenyl acetate (%) = (residual amount of 9-fluorenyl acetate in the reaction product after the heating step) / (residual amount of 9-fluorenyl acetate in the reaction product after the solvent is removed) × 100

[0151] Comparative Test Example 2

[0152] The same operation as in Example 1 was carried out up to step 1. Oxidation to obtain an oxidation reaction product.

[0153] The oxidation reaction product was introduced into a distillation column with 9 plates and refluxed at a pressure of 2 kPa for 2 hours (heating step). The heating temperature was approximately 110°C due to the reflux of acetic acid. In Table 2, the residual amount of the by-product 9-fluorenyl acetate is expressed as a ratio relative to the oxidation reaction product. The residual amount of 9-fluorenyl acetate was specifically calculated using the following formula.

[0154] Residual amount of 9-fluorenyl acetate (%) = (residual amount of 9-fluorenyl acetate in the reaction product after the heating step) / (residual amount of 9-fluorenyl acetate in the oxidation reaction product) × 100

[0155] [Table 2]

[0156] Table 2

[0157]

[0158] The results of the test examples and comparative test examples show that by-products generated by the oxidation reaction can be effectively removed by performing the solvent removal step and the heating step of the production method of the present invention.

Claims

1. A method for producing fluorenone, comprising: In the oxidation step, fluorene is oxidized in the presence of an aliphatic carboxylic acid having 2 to 3 carbon atoms, a metal catalyst, a bromine compound, and oxygen. The solvent removal step removes the aliphatic carboxylic acid. The heating process is carried out at 220-280°C. distillation process, and Coloring component removal process; The distillation step sequentially comprises a step of removing high-boiling-point components and a step of removing low-boiling-point components; The metal catalyst is at least one selected from the group consisting of a cobalt catalyst, a manganese catalyst, a zirconium catalyst, a cerium catalyst, and a nickel catalyst.

2. The method for producing fluorenone according to claim 1, wherein The heating time of the heating step is 5 minutes or more.

3. The method for producing fluorenone according to claim 1 or 2, wherein The mixture supplied to the heating step contains fluorenone and bromide ions, and the content of the bromide ions in the heating step is 0.01 to 5 parts by mass based on 100 parts by mass of fluorenone.

4. The method for producing fluorenone according to claim 1 or 2, wherein The aliphatic carboxylic acid is acetic acid.

5. The method for producing fluorenone according to claim 1 or 2, wherein In the oxidation step, oxygen is supplied by introducing air. The method for producing fluorenone according to claim 1 or 2, wherein in the heating step, heating is performed at 220°C or higher and lower than 260°C.

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