Method for producing fluorenone

Abstract

A method for producing fluorenone comprises the following in the indicated sequence: an oxidation step for oxidizing fluorene in the presence of a C2-3 aliphatic carboxylic acid, metal catalyst, bromine compound, and oxygen; a solvent removal step for removing the aliphatic carboxylic acid; a heating step for heating at 120-350°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 chemicals, resins, etc. Specifically, it is a very useful compound as a raw material for electrophotographic photoreceptors, a raw material for dyes, and a raw material for optical resins.

[0003] As a method for producing fluorenone, a method of oxidizing fluorene is carried out. Among them, a production method by liquid-phase oxidation using an oxygen-containing gas such as air has been developed. For example, Patent Document 1 discloses a method for producing fluorenones, which comprises oxidizing fluorenes with molecular oxygen in an organic solvent in the presence of a phase transfer catalyst and a solid alkali metal hydroxide for the purpose of obtaining fluorenones in a high yield. Further, 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 an alkali metal hydroxide for the purpose of obtaining fluorenone in a high yield. Patent Document 3 discloses a method for obtaining diallyl ketone simply, economically and in a high yield, in which a lower saturated aliphatic monocarboxylic acid is used as a solvent and a heavy metal is used as an oxidation catalyst, and an aromatic compound is reacted with oxygen molecules to obtain diallyl ketone, and as an example thereof, a method for obtaining fluorenone is disclosed.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

[0005] According to Patent Document 3, fluoronone is synthesized by the so-called Amoco method, and the product is obtained in a yield of 76%. Here, in order to remove impurities such as by-products, according to Patent Document 3, it is further recrystallized from benzene and hexane to purify fluoronone, but it has been difficult to obtain high-purity fluoronone. Furthermore, it has been difficult to use this method for industrial production. That is, it has been difficult to produce high-purity fluoronone in large quantities and continuously. Therefore, an object of the present invention is to provide a production method capable of efficiently removing by-products and the like generated by an oxidation reaction and obtaining industrially high-purity fluoronone. [Means for Solving the Problems]

[0006] As a result of intensive studies by the present inventors, it has been found that the above problems can be solved by oxidizing fluorene in the presence of a specific solvent, a metal catalyst, and a bromine compound, removing the solvent, heating at a specific temperature, and distilling. The present invention relates to the following [1] to [7]. [1] A method for producing fluoronone, comprising 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 in this order. [2] The method for producing fluoronone according to [1], wherein the heating time in the heating step is 5 minutes or more. [3] The method for producing fluoronone according to [1] or [2], wherein the mixture subjected to the heating step contains fluoronone and bromide ions, and the content of the bromide ions in the heating step is 0.01 to 5 parts by mass with respect to 100 parts by mass of fluoronone. [4] The method for producing fluoronone according to any one of [1] to [3], wherein the distillation step has a step of removing high-boiling components and a step of removing low-boiling components in this order. [5] The manufacturing method of 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. [6] The manufacturing method of fluorenone according to any one of [1] to [5] above, wherein the aliphatic carboxylic acid is acetic acid. [7] The manufacturing method of fluorenone according to any one of [1] to [6] above, wherein in the oxidation step, oxygen is supplied by introducing air. [Advantages of the Invention]

[0007] According to the manufacturing method of the present invention, by-products and the like generated by the oxidation reaction can be efficiently removed, and high-purity fluorenone can be obtained industrially. [Embodiments for Carrying Out the Invention]

[0008] The manufacturing method of fluorenone of the present invention includes 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 in this order. The manufacturing method of the present invention will be described in detail below.

[0009] [Oxidation Step] In the manufacturing method of fluorenone of the present invention, first, fluorene is oxidized. By this oxidation step, fluorene can be oxidized to obtain fluorenone as the main product. The oxidation step in the manufacturing method of fluorenone of the present invention oxidizes fluorene 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 having fluorenone as the main product.

[0010] [Aliphatic Carboxylic Acid Having 2 to 3 Carbon Atoms] The aliphatic carboxylic acid used in this process is an aliphatic carboxylic acid having 2 to 3 carbon atoms, and more preferably an aliphatic carboxylic acid having 2 carbon atoms. Specifically, the aliphatic carboxylic acid is preferably at least one selected from the group consisting of acetic acid and propionic acid, and more preferably acetic acid. When using acetic acid, a mixed solution may be prepared in advance by mixing acetic acid and water described below and used, or only acetic acid may be used. Using the above aliphatic carboxylic acid can increase the activity of the catalyst, so it is preferable.

[0011] 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, still more preferably 70 to 200 parts by mass, and even more preferably 80 to 100 parts by mass with respect to 100 parts by mass of fluorene. When the amount of the aliphatic carboxylic acid is equal to or more than the lower limit value, the viscosity can be made appropriate, handling becomes easy, the reaction heat can be controlled, and the rise in the reactor temperature can be prevented. Also, when the amount of the aliphatic carboxylic acid is equal to or less than the upper limit value, the production efficiency is excellent and it is also excellent economically. The aliphatic carboxylic acid may be one kind or two or more kinds may be used.

[0012] <Metal catalyst> The metal catalyst used in this process is preferably at least one selected from the group consisting of transition metal catalysts and rare earth metal catalysts, and more preferably a transition metal catalyst. Specifically, the transition metal catalyst is preferably at least one selected from the group consisting of cobalt catalysts, manganese catalysts, zirconium catalysts, cerium catalysts, and nickel catalysts, and more preferably at least one selected from the group consisting of cobalt catalysts and manganese catalysts. It is more preferable to use both a cobalt catalyst and a manganese catalyst. As described above, as the metal catalyst used in this step, it is preferably 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, and more preferably at least one selected from the group consisting of a cobalt catalyst and a manganese catalyst. It is even more preferable to use both a cobalt catalyst and a manganese catalyst. The metal catalyst can be used in the form of a salt, a simple metal, an oxide, a hydroxide, etc. However, the metal catalyst used in this step is preferably a salt, more preferably an aliphatic carboxylate, still more preferably a lower aliphatic carboxylate, and even more preferably an acetate. Among them, it is even more preferably at least one selected from the group consisting of cobalt acetate and manganese acetate. Since fluorenone can be obtained in a high yield by using the above metal catalyst, it is preferable.

[0013] 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, still more preferably 0.1 to 3 parts by mass, and even more preferably 0.1 to 1 part by mass in terms of the metal element, based on 100 parts by mass of fluorene. When the catalyst concentration is equal to or higher than the lower limit value, the reaction rate is improved and the yield is also improved. When the catalyst concentration is equal to or lower than the upper limit value, the catalyst cost is low and no adverse effect on the reaction occurs. The metal catalyst may be one kind or two or more kinds may be used.

[0014] <Bromine compound> The bromine compound used in this step preferably includes hydrogen bromide, bromide salts, and organic bromine compounds, more preferably at least one selected from the group consisting of hydrogen bromide and bromide salts, and still more preferably hydrogen bromide. Hydrogen bromide is preferably used as an aqueous solution. Specific examples of the bromide salts include sodium bromide, potassium bromide, ammonium bromide, etc.

[0015] 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, still more preferably 0.05 to 1 part by mass, and even more preferably 0.05 to 0.5 part by mass in terms of bromine relative to 100 parts by mass of fluorene. When the amount of the bromine compound is at least the lower limit of the range, the reaction rate is improved and the yield is also improved. When the amount of the bromine compound is at most the upper limit of the range, it is less likely to corrode and equipment using a high-grade material becomes unnecessary. The bromine compound may be one kind or two or more kinds may be used.

[0016] <Water> In this step, water may be used. Since the bromine compound is easily solubilized, it is preferable to use water. 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, still more 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. When the moisture concentration is within the above range, the yield of fluorenone can be improved because the bromine compound can be dissolved while preventing a decrease in catalytic activity.

[0017] <Oxygen> As the oxygen used in this step, oxygen gas may be used, or a mixed gas with an inert gas or the like may be used. Among them, in this step, it is preferable from the viewpoints of safety and economy that oxygen is supplied by introducing air.

[0018] The oxygen used in this step is preferably introduced so that the oxygen concentration in the exhaust gas (off-gas) discharged from the reactor during the raw material supply is 0.1 to 8% by volume, and preferably introduced so that it is 1 to 5% by volume. By maintaining the introduction amount of oxygen within the above range, the reaction can be carried out safely and efficiently below the explosion range of the solvent, which is preferable.

[0019] <Conditions of the oxidation step, etc.> The temperature during the oxidation reaction in this process is preferably 120 to 280 °C, more preferably 160 to 260 °C, and even more preferably 190 to 240 °C. When the temperature during the oxidation reaction is at or above the lower limit of this range, the reaction rate is improved. When the temperature during the oxidation reaction is at or below the upper limit of this range, the formation of by-products is suppressed and the yield is improved. Moreover, the pressure during the oxidation reaction in this process may be within the pressure range that can keep the reaction solution in the liquid phase, and is preferably 0.1 to 4 MPa. When supplying oxygen by introducing air, the reaction time of the oxidation reaction in this process is preferably 0.1 to 10 hours, more preferably 0.5 to 5 hours, and even more preferably 1 to 3 hours. In this process, from the viewpoint of safety, it is preferable to introduce an inert gas such as nitrogen into the reaction vessel containing the raw materials before introducing oxygen.

[0020] [Solvent removal process] In the method for producing fluorenone of the present invention, a solvent removal process for removing the aliphatic carboxylic acid having 2 to 3 carbon atoms is included after the oxidation process. The solvent removal process in the method for producing fluorenone of the present invention removes the aliphatic carboxylic acid having 2 to 3 carbon atoms from the oxidation reaction mixture obtained in the oxidation process to obtain a mixture mainly containing fluorenone. In the oxidation reaction process, when water is used, water may also be removed together in this process.

[0021] In this process, in order to improve production efficiency, the solvent may be removed by heating and distilling under reduced pressure, or the solvent may be removed by heating and distilling at atmospheric pressure. The pressure during solvent removal in this process is preferably 80 kPa or less, more preferably 1 to 60 kPa, and even more preferably 2 to 50 kPa. The temperature during solvent removal in this process is preferably 80 to 200 °C, more preferably 90 to 180 °C, and even more preferably 100 to 150 °C. In this process, equipment used for general heating distillation is employed, specifically including simple distillation equipment, precision distillation equipment, molecular distillation equipment, thin-film evaporators, etc. In addition to these distillation apparatuses, a dryer or the like may be used to remove the solvent. This process is a process of making the amount of the aliphatic carboxylic acid having 2 to 3 carbon atoms remaining preferably 5% by mass or less, more preferably 3% by mass or less, and still more preferably 1% by mass or less in the mixture obtained after this process. In this process, the aliphatic carboxylic acid having 2 to 3 carbon atoms may be completely removed. By removing the solvent in this process, the reaction rate of by-products is improved in the subsequent heating process, impurities can be efficiently removed, and high-purity fluorenone can be obtained, which is preferable.

[0022] [Heating Process] In the method for producing fluorenone of the present invention, a heating process of heating at 120 to 350°C is included after the solvent removal process. The heating process in the method for producing fluorenone of the present invention heats a mixture containing fluorenone as a main component obtained in the solvent removal process at 120 to 350°C to obtain a heat-treated mixture.

[0023] This process may be carried out by any method. It may be heated in the container used in the solvent removal process, or a container used in the heating process may be prepared separately and heated in that container, or it may be heated in the distillation apparatus used in the distillation process which is the next process. In any method, it is sufficient that the mixture is heated at 120 to 350°C, and if necessary, the mixture containing fluorenone as a main component may be refluxed under reduced pressure.

[0024] In the present invention, by providing the heating process, it is not clear why impurities such as by-products generated by the oxidation reaction can be efficiently removed and high-purity fluorenone can be obtained industrially, but it is considered as follows. In the heating step, by-products and the like are changed by chemical reactions to form compounds with significantly different boiling points from the target product, fluorenone, and it is considered that these can be efficiently removed in the subsequent distillation step. In particular, the aliphatic carboxylic acid fluorenyl ester, which is the main by-product, has a boiling point close to that of the target product, fluorenone, and is difficult to remove by simple distillation. However, by providing a heating step after the oxidation reaction, the carboxylic acid fluorenyl ester decomposes and polymerizes, resulting in a higher molecular weight. For this reason, it can be efficiently removed in the subsequent distillation step, and high-purity fluorenone can be obtained by distillation, which is an industrial method.

[0025] The temperature during heating in this step is 120 to 350 °C, preferably 180 to 280 °C, more preferably 220 to 280 °C, still more preferably 220 or more and less than 260 °C, and even more preferably 240 °C or more and less than 260 °C.

[0026] In this step, it is preferable that the mixture subjected to the heating step during heating contains bromide ions. It is considered that the decomposition and polymerization of the carboxylic acid fluorenyl ester can be promoted by containing bromide ions. If the bromine compound used in the oxidation step remains in this step, there is no need to add bromide ions. However, when the content decreases due to removal or discharge in the oxidation step and the solvent removal step, it is preferable to add them. By adding, the content can be adjusted to a suitable level. The mixture subjected to this step is a mixture mainly containing fluorenone obtained in the solvent removal step. That is, in this heating step, the mixture subjected to this heating step contains fluorenone and bromide ions, and the content of the bromide ions in this heating step is preferably 0.01 to 5 parts by mass, more preferably 0.05 to 3 parts by mass, still more preferably 0.05 to 1 part by mass, even more preferably 0.05 to 0.5 part by mass, and even more preferably 0.1 to 0.4 part by mass with respect to 100 parts by mass of fluorenone.

[0027] In this process, the bromine compound that provides bromide ions is preferably the same as that used in the oxidation step. Specifically, hydrogen bromide, bromide salts, and organic bromine compounds are preferably mentioned, more preferably at least one selected from the group consisting of hydrogen bromide and bromide salts, and even more preferably hydrogen bromide. Specific bromide salts include sodium bromide, potassium bromide, ammonium bromide, and the like.

[0028] In addition, in this process, it is preferable to use a metal catalyst. It is convenient and preferable to directly use the metal catalyst used in the previous oxidation step. The metal catalyst preferably used in this process is the same as that used in the oxidation step. Specifically, it is preferably 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. More preferably, it is at least one selected from the group consisting of a cobalt catalyst and a manganese catalyst. It is even more preferable to use both a cobalt catalyst and a manganese catalyst. The metal catalyst can be used in the form of salts, simple metals, oxides, hydroxides, etc. However, the metal catalyst used in this process is preferably a salt, more preferably an aliphatic carboxylate, even more preferably a lower aliphatic carboxylate, and even more preferably an acetate. Among them, even more preferably, it is at least one selected from the group consisting of cobalt acetate and manganese acetate. It is considered that the use of the above metal catalyst can promote the decomposition and polymerization of fluorenyl carboxylate.

[0029] The amount of the metal catalyst used in the heating step may be determined by directly using the amount used in the oxidation step. In terms of metal element conversion, it is preferably 0.02 to 10 parts by mass, more preferably 0.05 to 5 parts by mass, even more preferably 0.1 to 3 parts by mass, and even more preferably 0.1 to 1 part by mass with respect to 100 parts by mass of fluorene used as the raw material in the oxidation step. Generally, in order to prevent the deterioration of the target product, heating in the presence of a catalyst is not carried out after the reaction is completed. However, in the production method of the present invention, after the oxidation reaction is completed and after solvent removal, heating is carried out in the presence of a metal catalyst and bromide ions, so that by-products and the like can be efficiently removed in the subsequent distillation step, and industrially high-purity fluorenone can be obtained.

[0030] The heating time of this heating step is preferably 5 minutes or more, more preferably 10 minutes or more, still more preferably 20 minutes to 100 hours, even more preferably 30 minutes to 20 hours, and even more preferably 1 to 10 hours. It should be noted that the heating time is preferably adjusted as appropriate according to the heating temperature and the content of bromide ions. When the heating temperature is high or the content of bromide ions is large, the effects of the present invention can be achieved even with a short heating time. Furthermore, when the heating temperature is high and the content of bromide ions is large, the effects of the present invention can be achieved even with a shorter heating time. By increasing the heating time, the purity of the target fluorenone can be further increased. However, since the target fluorenone deteriorates due to long-term heating, it is preferable to determine the end point of heating from the viewpoint of preventing the deterioration of fluorenone and improving the yield of fluorenone. As a specific example, when the content of bromide ions is adjusted to 0.1 to 0.4 parts by mass based on 100 parts by mass of fluorenone and the heating temperature is 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 still more preferably 2 to 5 hours. When the content of bromide ions is adjusted to 0.1 to 0.4 parts by mass based on 100 parts by mass of fluorenone and the heating temperature is 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 still more preferably 45 minutes to 1.5 hours. When the content of bromide ions is adjusted to 0.1 to 0.4 parts by mass based on 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 still more preferably 10 minutes to 30 minutes. When the content of bromide ions is adjusted to 0.1 to 0.4 parts by mass with respect to 100 parts by mass of fluorenone and the heating temperature is 300 to 320 °C, the heating time is preferably 5 to 30 minutes, more preferably 5 minutes to 15 minutes.

[0031] [Distillation step] In the method for producing fluorenone of the present invention, a distillation step is included after the heating step. In the distillation step in the method for producing fluorenone of the present invention, any method may be used as long as the target fluorenone can be separated and recovered. However, the distillation step preferably has a step of removing high-boiling components and a step of removing low-boiling components, and more preferably has a step of removing high-boiling components and a step of removing low-boiling components in this order. In addition, 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 and colored. Therefore, it is preferable to further have a step of removing coloring components. The following describes a two-stage distillation, which is a preferred embodiment.

[0032] (Step for removing high-boiling components) First, it is preferable to remove high-boiling components. It is considered that high-boiling components contain various impurities, by-products, etc. By removing high-boiling components at the beginning of the distillation step, it is considered possible to suppress the deterioration of the target product and the increase in impurities due to the decomposition of high-boiling components. The distillation temperature may be appropriately adjusted to be about the boiling point of fluorenone depending on the pressure during distillation (the boiling point at 1 atm is 342 °C). 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, still more preferably 170 to 240 °C, and even more preferably 180 to 220 °C. When a distillation column is used in this step for removing high-boiling components, a mixture containing fluorenone and low-boiling components is recovered from the top of the column.

[0033] (Step for removing low-boiling components) Next, it is preferable to remove low-boiling components. The distillation temperature in this step may be appropriately adjusted to be about the boiling point of fluorenone depending on the pressure during distillation (the boiling point at 1 atm is 342 °C). For example, when the distillation pressure is adjusted to 1.5 - 3.5 kPa, it is preferably 150 - 300 °C, more preferably 160 - 250 °C, still more preferably 165 - 230 °C, and even more preferably 170 - 200 °C. When a distillation column is used in this low-boiling component removal step, high-purity fluorenone can be recovered from the bottom of the column. Also, when the residence time at the bottom of the column is long, fluorenone may deteriorate and color. Therefore, in order to remove the coloring components, distillation is further performed after this distillation step (coloring component removal step), and it is preferable to recover high-purity fluorenone from the top of the column.

Examples

[0034] The present invention will be specifically described based on the examples shown below, but the present invention is not limited by these examples.

[0035] <Measurement method of each component concentration (composition)> After the oxidation step, after the solvent removal step, and after the heating step, the composition of each component (fluorene, fluorenone, 9-fluorenyl acetate, and 9,9'-bisf luorenyl) in the reaction product was calculated by the internal standard method using gas chromatography (internal standard: triphenylmethane). Regarding the purity of fluorene and 9-fluorenones (fluorene, fluorenone, and 9-fluorenyl acetate (fluorenyl acetate)) after the distillation step, it is the area percentage by gas chromatography. The bromide ion concentration was determined by titration using silver nitrate. In addition, as impurities contained in the final recovered product, fluorene as a raw material and 9-fluorenyl acetate as a main by-product were quantified. The smaller these amounts are, the higher the purity of the obtained fluorenone, which is preferable. The results are shown in Table 1.

[0036] <Gardner Color Number Measurement Method> The Gardner color numbers of the examples and comparative examples were determined using a color difference meter after melting purified fluorenone at 140 °C.

[0037] <Production of Fluorenone> Example 1 (1. Oxidation Step) Cobalt acetate tetrahydrate, manganese acetate tetrahydrate, 48% by mass hydrogen bromide aqueous solution, glacial acetic acid, and water were mixed so that the cobalt metal atom concentration was 0.75% by mass, the manganese metal atom concentration was 0.75% by mass, the bromide ion concentration was 0.075% by mass, the acetic acid concentration was 88.425% by mass, and the water concentration was 10% by mass, to obtain a catalyst solution. 150 g of the catalyst solution was charged into a 500 mL titanium autoclave equipped with a gas discharge pipe with a reflux condenser, a gas injection pipe, a raw material continuous feeding pump, and a stirrer. The pressure was increased to 1.0 MPa and the temperature was raised to 200 °C under a nitrogen atmosphere. 150 g of fluorene was supplied over 120 minutes. The throughput was 1.3 g / min. Air was introduced simultaneously with the start of the raw material supply, and the amount of air introduced was adjusted so that the oxygen concentration in the off-gas was 4% by volume or less to carry out the oxidation reaction. After the supply of fluorene was completed, the introduction of air was terminated when the absorption of oxygen was completed and the oxygen concentration in the off-gas reached 8% by volume. After the reaction, the oxidation reaction product was withdrawn. 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% by mass of fluorene, 41.6% by mass of fluorenone, 2.78% by mass of 9-fluorenyl acetate, and 0.41% by mass of 9,9'-bisfluorenyl.

[0038] (2. Solvent Removal Step) 310 g of the oxidation reaction product was transferred to a 500 mL glass flask, and simple distillation was carried out over 1 hour at a heater temperature of 120 °C and an internal pressure of 5 - 40 kPa to distill off 153 g of acetic acid and water. The composition of the reaction product after solvent removal was 4.76% by mass of fluorene, 79.8% by mass of fluorenone, 5.36% by mass of 9-fluorenyl acetate, and 0.74% by mass of 9,9'-bisfluorenyl.

[0039] (3. Heating Process) The reaction product after solvent removal was introduced into a distillation column equivalent to 9 theoretical plates, and reflux was carried out at a pressure of 2 kPa and a temperature of 245.0 - 250.0 °C for 2 hours. The concentration of bromide ions contained in the reaction product used in this process was 0.075 parts by mass with respect to 100 parts by mass of fluorenone. The composition of the reaction product after heating was 2.96% by mass of fluorene, 79.4% by mass of fluorenone, and 2.38% by mass of 9,9'-bisfluorenyl, and 9-fluorenyl acetate was not contained.

[0040] (4. Distillation Process (High-Boiling Component Removal Process)) After the heating process, using the distillation column used in the heating process, the distillation conditions were set to a pressure of 2 kPa, a top temperature of 188.0 °C, and a bottom temperature of 196.0 °C, and extraction was started. 107 g of fluorenone containing low-boiling components obtained from the top of the distillation column was extracted, and the composition was 5.6% of fluorene and 94.4% of fluorenone, and the distillation recovery rate of fluorenone was 80.0%.

[0041] (5. Distillation Process (Low-Boiling Component Removal Process)) Batch distillation was carried out to separate low-boiling components and fluorenone using a distillation column equivalent to 9 theoretical plates for the fluorenone containing low-boiling components obtained from the top of the distillation column. The 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 purity of the obtained purified fluorenone was 99.99%, the distillation recovery rate of fluorenone was 76.2%, and the Gardner color number was 8.5. Also, the purified fluorenone contained 0.01% of fluorene as a raw material, and 9-fluorenyl acetate was not contained (detection limit: 0.001% or less).

[0042] Example 2 3. The same operations as in Example 1 were carried out up to the heating step. After the heating step, 5. a distillation step (low-boiling component removal step) was performed, and for the fluorenone containing high-boiling components obtained from the bottom of the resulting distillation column, 4. a distillation step (high-boiling component removal step) was performed to obtain purified fluorenone from the top of the distillation column. The purity of the obtained purified fluorenone was 99.29%, the total yield was 51.1%, and the Gardner color number was 8.2. Also, the purified fluorenone contained 0.68% of fluorene as a raw material and did not contain 9-fluorenyl acetate (detection limit: 0.001% or less).

[0043] Example 3 5. The same operations as in Example 1 were carried out up to the low-boiling component removal step. After the 5. distillation step (low-boiling component removal step), a coloring component removal step (distillation at a pressure of 1.7 kPa and a temperature of 190 °C) was performed on the fluorenone obtained from the bottom of the resulting distillation column to obtain purified fluorenone from the top of the distillation column. The purity of the obtained purified fluorenone was 99.99%, and the Gardner color number was 8.2. Also, the purified fluorenone contained 0.01% of fluorene as a raw material and did not contain 9-fluorenyl acetate (detection limit: 0.001% or less).

[0044] Comparative Example 1 2. The same operations as in Example 1 were carried out up to the solvent removal step to obtain a reaction product after solvent removal. The reaction product after solvent removal was introduced into a distillation column equivalent to 9 stages, and without performing 3. the heating step, 4. a distillation step (high-boiling component removal step) and 5. a distillation step (low-boiling component removal step) were carried out in the same manner as in Example 1 in this order to obtain purified fluorenone from the bottom of the distillation column. The purity of the obtained purified fluorenone was 97.16%, the total yield was 46.7%, and the Gardner color number was 8.5. Also, the purified fluorenone contained 0.01% of fluorene as a raw material and 2.76% of 9-fluorenyl acetate.

[0045] Comparative Example 2 1. The same operations as in Example 1 were carried out up to the oxidation step to obtain an oxidation reaction product. Next, the oxidation reaction product after the oxidation reaction was cooled to 30 °C with stirring to precipitate crude fluorenone, and the crystals were separated with a solid-liquid separator and washed with water. Then, the crude fluorenone crystals were dried. To the obtained crude crystals, a two-fold amount of a 70% aqueous acetic acid solution was added, and the mixture was heated to 108 °C to redissolve the crude crystals. Then, the crude fluorenone solution was cooled to 30 °C to precipitate purified fluorenone, and the crystals were separated with a solid-liquid separator and washed with water. Then, the purified fluorenone was dried. The purity of the obtained purified fluorenone was 96.10%, the crystallization yield was 41.4%, and the Gardner color number was 14.7. Further, the purified fluorenone contained 0.20% of fluorene as a raw material and 1.00% of 9-fluorenyl acetate.

[0046]

Table 1

[0047] From the results of the examples and comparative examples, it can be seen that according to the production method of the present invention, by-products and the like generated by the oxidation reaction can be efficiently removed, and high-purity fluorenone can be obtained by a distillation method that is industrially advantageous.

[0048] <Production of Fluorenone (Evaluation of Removal Efficiency of By-Products)> The removal efficiency of by-products when the conditions of the heating step were changed was evaluated by the following test examples.

[0049] Test Examples 1 to 9 and Comparative Test Example 1 2. The same operations as in Example 1 were carried out up to the solvent removal step to obtain a reaction product after solvent removal. The reaction product after solvent removal was introduced into a distillation column equivalent to 9 stages, and reflux was carried out at a pressure of 2 kPa, the temperature shown in Table 2, and the time shown in Table 2 (heating step). Table 2 shows the remaining amount of 9-fluorenyl acetate, which is a by-product, as a ratio to the reaction product after solvent removal. The smaller the remaining amount of 9-fluorenyl acetate, the better the removal efficiency of the by-products. The remaining amount of 9-fluorenyl acetate is specifically determined by the following formula. 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 solvent removal) × 100

[0050] Comparative Test Example 2 1. The same operations as in Example 1 were carried out up to the oxidation step to obtain an oxidation reaction product. The oxidation reaction product was introduced into a distillation column equivalent to 9 stages, and reflux was carried out at a pressure of 2 kPa for 2 hours (heating step). The heating temperature was about 110°C due to the reflux of acetic acid. Table 2 shows the residual amount of 9-fluorenyl acetate as a by-product in terms of the ratio to the oxidation reaction product. The residual amount of 9-fluorenyl acetate is specifically determined by the following formula. 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

[0051]

Table 2

[0052] From the results of the test examples and comparative test examples, it can be seen that by performing the solvent removal step and the heating step of the production method of the present invention, by-products generated by the oxidation reaction can be efficiently removed.

Claims

1. 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 method for producing fluorenone, which includes the above steps in this order.

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

3. The mixture subjected 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 with respect to 100 parts by mass of fluorenone. The method for producing fluorenone according to claim 1 or 2.

4. The distillation step in the method for producing fluorenone according to any one of claims 1 to 3 has a step of removing high-boiling components and a step of removing low-boiling components in this order.

5. 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. The method for producing fluorenone according to any one of claims 1 to 4.

6. The aliphatic carboxylic acid is acetic acid. The method for producing fluorenone according to any one of claims 1 to 5.

7. In the oxidation step, oxygen is supplied by introducing air. The method for producing fluorenone according to any one of claims 1 to 6.

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