Crystalline 9,9-bis(4-hydroxyphenyl)-2,3-benzofluorene

Abstract

The objective of the present invention is to provide a crystal of 9,9-bis(4-hydroxyphenyl)-2,3-benzofluorene that has a specific melting point, is not an inclusion compound, or has a residual organic solvent content of 1% by weight or less. As a means for solving this problem, the inventors have discovered that by crystallizing 9,9-bis(4-hydroxyphenyl)-2,3-benzofluorene, which has the chemical structure represented by the following formula (1), using a specific solvent, a crystal can be obtained that does not form an inclusion compound and has a residual organic solvent content of 1% by weight or less. [Formula 1]

Description

[Technical Field]

[0001] The present invention relates to a crystalline form of 9,9-bis(4-hydroxyphenyl)-2,3-benzofluorene, which is characterized by having a melting point of 182 to 187°C as determined by differential scanning calorimetry, is not an inclusion compound, or has a residual organic solvent content of 1% by weight or less, and a method for producing the crystalline form. [Background technology]

[0002] Conventionally, compounds having a fluorene skeleton such as 9,9-bis(4-hydroxyphenyl)fluorene have been used in applications such as thermoplastic synthetic resin raw materials such as polycarbonate resins, thermosetting resin raw materials such as epoxy resins, antioxidant raw materials, thermal recording medium raw materials, and photosensitive resist raw materials due to their excellent heat resistance and optical properties. [ka] Resins produced from 9,9-bis(4-hydroxyphenyl)-2,3-benzofluorene having a chemical structure represented by the following formula have attracted attention for their excellent optical properties (for example, Patent Document 1, etc.). A known method for producing 9,9-bis(4-hydroxyphenyl)-2,3-benzofluorene represented by the above formula (1) involves condensing 2,3-benzo-9-fluorenone and phenol in a dimethyl carbonate solvent in the presence of 3-mercaptopropionic acid and methanesulfonic acid, and then separating and drying the precipitated crystals (Patent Document 1). The crystals obtained by this method are clathrate crystals in which dimethyl carbonate is clathrated in 9,9-bis(4-hydroxyphenyl)-2,3-benzofluorene. In addition, a method is known in which acetone is added to a reaction mixture containing 9,9-bis(4-hydroxyphenyl)-2,3-benzofluorene, the precipitated crystals are separated, and then recrystallized with acetone (Patent Document 2). However, the obtained crystals are clathrate crystals of 9,9-bis(4-hydroxyphenyl)-2,3-benzofluorene and acetone. In conventional clathrate crystals of 9,9-bis(4-hydroxyphenyl)-2,3-benzofluorene, the temperature at which the guest compound, the solvent, is released is above the melting point of the crystals. Therefore, even if the temperature is raised to remove the enclosed solvent, the crystals melt. Therefore, no method for obtaining solvent-free crystals was known. Compounds having a fluorene skeleton, such as 9,9-bis(4-hydroxyphenyl)fluorene, are known to form inclusion compounds with reaction solvents and solvents used in purification. However, removing the enclosed solvent requires a long time at high temperatures, making it difficult to apply them on an industrial scale. In addition, it is also known that compounds having a fluorene skeleton with an enclosed solvent have problems when used industrially as raw materials for producing epoxy resins, polyesters, etc., or for other purposes (Patent Document 3). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-036249 [Patent Document 2] International Publication No. 2015 / 147115 [Patent Document 3] Japanese Patent Application Publication No. 10-245352 Summary of the Invention [Problem to be solved by the invention]

[0004] The present invention has been made in light of the above-mentioned circumstances, and an object of the present invention is to provide a crystal of 9,9-bis(4-hydroxyphenyl)-2,3-benzofluorene that has a specific melting point, is not an inclusion compound, or has a residual organic solvent content of 1% by weight or less, and a method for producing the crystal. [Means for solving the problem]

[0005] As a result of extensive research to solve the above-mentioned problems, the present inventors have found that, by crystallization using a specific solvent, it is possible to obtain crystals of 9,9-bis(4-hydroxyphenyl)-2,3-benzofluorene that have a specific melting point and are not an inclusion compound or have a residual organic solvent content of 1% by weight or less, and have completed the present invention.

[0006] The present invention is as follows. 1. A crystalline form of 9,9-bis(4-hydroxyphenyl)-2,3-benzofluorene, characterized by a melting point of 182 to 187°C as determined by differential scanning calorimetry. 2. The crystalline form according to 1, which is not an inclusion complex. 3. The crystalline form according to 1. or 2., characterized in that the content of residual organic solvent is 1% by weight or less. 4. A method for producing the crystalline form according to any one of 1. to 3., comprising a step of crystallization using a mixed solvent of methanol and water. 5. The production method according to 4, further comprising a step of drying the crystals obtained by crystallization at a temperature of 45°C or higher and lower than the melting point. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a crystalline form of 9,9-bis(4-hydroxyphenyl)-2,3-benzofluorene that has a specific melting point, is not an inclusion compound, or has a residual organic solvent content of 1% by weight or less, and a method for producing the crystalline form. When 9,9-bis(4-hydroxyphenyl)-2,3-benzofluorene includes a compound such as an organic solvent, the inclusion compound inhibits the reaction when reacting the compound with, for example, (meth)acrylic acid, resulting in a problem of the reaction not proceeding. Furthermore, when the inclusion compound is melted and used as a resin raw material, vapors derived from the included organic solvent or other compounds generated during melting must be removed from the reaction apparatus. Furthermore, the remaining organic solvent or other compounds can degrade the quality of the target resin. Furthermore, depending on the flash point or fire point of the included organic solvent or other compounds, there are also concerns about fire safety during transportation and storage of the inclusion compound. As mentioned above, no crystalline form of 9,9-bis(4-hydroxyphenyl)-2,3-benzofluorene has been known that has a specific melting point, does not include compounds such as organic solvents, or has a residual organic solvent content of 1 wt % or less. Moreover, the only known methods for removing organic solvents from conventional inclusion crystals are those that involve melting the crystals for removal, which are difficult to implement industrially or are very costly. In other words, the provision of a novel crystalline form of 9,9-bis(4-hydroxyphenyl)-2,3-benzofluorene that has a specific melting point and does not include compounds such as organic solvents, or in which the content of residual organic solvents is 1% by weight or less, and a method for producing the same, is extremely useful for industrial use as a resin raw material, etc. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a diagram showing a differential scanning calorimetry (DSC) curve of the crystalline body (crystalline body of the present invention) obtained in a synthesis example. [Figure 2] FIG. 1 is a diagram showing a differential scanning calorimetry (DSC) curve of the crystalline body obtained in Example 1 (crystalline body of the present invention). [Figure 3] FIG. 2 is a diagram showing a differential scanning calorimetry (DSC) curve of the crystalline material obtained in Comparative Example 1. [Figure 4] FIG. 2 is a diagram showing a differential scanning calorimetry (DSC) curve of the crystalline material obtained in Comparative Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0009] The present invention will be described in detail below. The 9,9-bis(4-hydroxyphenyl)-2,3-benzofluorene of the present invention is a compound represented by the following formula (1). [ka]

[0010] <Synthesis method> The method for synthesizing the 9,9-bis(4-hydroxyphenyl)-2,3-benzofluorene of the present invention is not particularly limited, and any known method for producing a compound having a fluorene skeleton, such as 9,9-bis(4-hydroxyphenyl)fluorene, can be applied. For example, as shown in the following reaction formula, the compound can be obtained by using phenol and 2,3-benzo-9-fluorenone as raw materials and reacting them in the presence of an acid catalyst. [ka]

[0011] The reaction between phenol and 2,3-benzo-9-fluorenone shown in the above reaction scheme will be explained below. The molar ratio of phenol to 2,3-benzo-9-fluorenone is not particularly limited as long as it is equal to or greater than the theoretical value (2.0), but is usually in the range of 2 to 20 times the molar amount, and preferably 3 to 10 times the molar amount. The acid catalyst used is not particularly limited, and known acid catalysts can be used. Specific examples of acid catalysts include inorganic acids such as hydrochloric acid, hydrogen chloride gas, 60 to 98% sulfuric acid, and 85% phosphoric acid; organic acids such as p-toluenesulfonic acid, methanesulfonic acid, oxalic acid, formic acid, trichloroacetic acid, and trifluoroacetic acid; and solid acids such as heteropolyacids. Hydrogen chloride gas is preferred. The amount of such an acid catalyst used varies depending on the reaction conditions. For example, in the case of hydrogen chloride gas, the air in the reaction system is replaced with an inert gas such as nitrogen gas, and then hydrogen chloride gas is blown in to adjust the hydrogen chloride gas concentration in the gas phase in the reaction vessel to 75 to 100% by volume, thereby saturating the hydrogen chloride concentration in the reaction solution. In the case of 35% hydrochloric acid, the amount used is in the range of 5 to 70 parts by weight, preferably 10 to 40 parts by weight, and more preferably 20 to 30 parts by weight, per 100 parts by weight of phenol. In the reaction, a co-catalyst may be used together with the acid catalyst, if necessary. For example, when hydrogen chloride gas is used as the catalyst, the reaction rate can be accelerated by using a thiol as the co-catalyst. Examples of such thiols include alkyl mercaptans and mercaptocarboxylic acids, preferably alkyl mercaptans having 1 to 12 carbon atoms and mercaptocarboxylic acids having 1 to 12 carbon atoms, such as methyl mercaptan, ethyl mercaptan, n-octyl mercaptan, n-dodecyl mercaptan, and alkali metal salts thereof, such as sodium salts, thioacetic acid, and β-mercaptopropionic acid. These can be used alone or in combination of two or more. The amount of thiols used as the co-catalyst is usually in the range of 1 to 30 mol %, preferably 2 to 10 mol %, relative to the starting material 2,3-benzo-9-fluorenone.

[0012] A reaction solvent does not necessarily have to be used during the reaction, but may be used for reasons such as improving operability and reaction rate during industrial production. The reaction solvent is not particularly limited as long as it does not distill out of the reactor at the reaction temperature and is inert to the reaction, and examples include organic solvents such as aromatic hydrocarbons such as toluene and xylene, lower aliphatic alcohols such as methanol, ethanol, 1-propanol and 2-propanol, saturated aliphatic hydrocarbons such as hexane, heptane and cyclohexane, water, and mixtures thereof. Of these, aromatic hydrocarbons are preferably used. The reaction temperature varies depending on the type of phenol used as the raw material and the type of acid catalyst, but when hydrogen chloride gas is used as the acid catalyst, it is usually in the range of 10 to 60° C., preferably 25 to 50° C. The reaction is usually carried out under normal pressure, but depending on the boiling point of the organic solvent that may be used, the reaction may be carried out under increased or reduced pressure so that the reaction temperature falls within the above range. The reaction time varies depending on the reaction conditions such as the type of phenol as the raw material, the acid catalyst, and the reaction temperature, but is usually completed in about 1 to 30 hours. The end point of the reaction can be confirmed by liquid chromatography or gas chromatography. The end point of the reaction is preferably determined to be the point at which unreacted 2,3-benzo-9-fluorenone has disappeared and no increase in the amount of the target product is observed. In the reaction, the method of adding the reaction raw materials is not particularly limited, but can be carried out according to the known method of producing a compound having a fluorene skeleton such as 9,9-bis(4-hydroxyphenyl)fluorene. According to a preferred embodiment, for example, a method can be mentioned in which a predetermined amount of phenol, an acid catalyst, and optionally a co-catalyst and a reaction solvent are charged into a reaction vessel, and the mixture is heated to a predetermined reaction temperature while stirring under a nitrogen stream, and then 2,3-benzo-9-fluorenone is gradually added thereto.

[0013] <Post-treatment of the reaction> After the completion of such a reaction, known post-treatment methods can be applied. For example, to the reaction-terminated liquid, an aqueous alkali solution such as aqueous sodium hydroxide or aqueous ammonia is added to neutralize the acid catalyst. The neutralized reaction mixture is allowed to stand, and if necessary, a solvent capable of separating from water is added to separate and remove the aqueous layer. If necessary, distilled water is added to the resulting oil layer, and the mixture is stirred and washed with water. This procedure of separating and removing the aqueous layer is repeated once or multiple times to remove the neutralized salt, and excess phenol is removed from the resulting oil layer by vacuum distillation. A solvent such as an aromatic hydrocarbon is added to the resulting residue to form a homogeneous solution, and the resulting crystals are cooled and separated to obtain crude crystals. These crude crystals or the residue can be subjected to the crystallization process of the present invention to produce 9,9-bis(4-hydroxyphenyl)-2,3-benzofluorene having a specific melting point, which is not an inclusion complex, or in which the content of residual organic solvent is 1% by weight or less.

[0014] <About the crystallization process> The production method of the present invention is characterized by including a step of crystallization using a mixed solvent of methanol and water. The methanol that can be used is not particularly limited, and any commercially available methanol, including special grade, first grade, and industrial grade, can be used. The water that can be used is not particularly limited, and tap water, distilled water, ion-exchanged water, natural water, etc., can be used as appropriate. The mixing ratio (weight ratio) of methanol to water is preferably 0.4 to 2.0:1.0. If the water content is lower than this mixing ratio (weight ratio) of methanol to water, the amount of remaining methanol in the target 9,9-bis(4-hydroxyphenyl)-2,3-benzofluorene increases. Furthermore, if the crude 9,9-bis(4-hydroxyphenyl)-2,3-benzofluorene crystals used for crystallization are an inclusion complex, a higher water content than the mixing ratio (weight ratio) of methanol to water is undesirable because it increases the amount of 9,9-bis(4-hydroxyphenyl)-2,3-benzofluorene that includes the solvent used in the reaction and post-reaction treatment, such as an aromatic hydrocarbon solvent such as toluene. In particular, the mixing ratio (weight ratio) of methanol to water is more preferably 1.0 to 1.8:1.0, and even more preferably 1.4 to 1.6:1.0. The amount of the mixed solvent of methanol and water used is preferably 250 to 1000 parts by weight, more preferably 300 to 700 parts by weight, even more preferably 400 to 600 parts by weight, and most preferably 450 to 550 parts by weight, relative to 100 parts by weight of 9,9-bis(4-hydroxyphenyl)-2,3-benzofluorene contained in the residue or crude crystals obtained by the post-treatment step of the reaction used in the crystallization step. If the amount of the mixed solvent of methanol and water used is too large, the yield of the obtained crystals will decrease, and if it is too small, the purity of the target product will decrease, which is undesirable. Furthermore, in the crystallization step of the present invention, the use of a solvent other than methanol and water is undesirable because it is impossible to obtain 9,9-bis(4-hydroxyphenyl)-2,3-benzofluorene that has a specific melting point and is not an inclusion compound or has a residual organic solvent content of 1% by weight or less.

[0015] The crystallization step of the present invention involves adding a mixed solvent of methanol and water in the above-mentioned ratio (by weight) to the residue or crude crystals after post-treatment of the reaction used, heating the mixture to below the boiling point of the mixed solvent under normal or increased pressure to dissolve the entire mixture into a homogeneous solution, and then cooling to obtain precipitated crystals. When cooling the mixture after heating to a homogeneous solution, it is preferable to cool it at a rate of 5 to 15°C / hour, preferably 8 to 12°C / hour, to 0 to 40°C, preferably 10 to 35°C, more preferably 20 to 30°C, and then separating the precipitated crystals by filtration or the like. Alternatively, methanol can be added to the residue or crude crystals after post-treatment of the reaction to be used to dissolve them all into a homogeneous solution, and water can be added dropwise with stirring to achieve the above-mentioned mixing ratio (weight ratio) of methanol and water to obtain precipitated crystals. In this case, it is preferable to maintain a temperature of 60°C or higher during crystal precipitation, and more preferably maintain this temperature for at least one hour after crystal precipitation before separating the precipitated crystals. Furthermore, when further cooling is required, it is preferable to cool at the above-mentioned rate.

[0016] <About the drying process> By carrying out a drying step, the solvent (methanol or water) used in the crystallization step of the present invention can be removed. The drying step of the present invention can be carried out at a temperature of 45°C or higher and lower than the melting point of the crystals obtained in the crystallization step, but 70°C or higher is preferred, 90°C or higher is more preferred, and 120°C or higher is particularly preferred. Furthermore, since the color of the crystals may deteriorate due to heat depending on other conditions, a temperature of 150°C or lower is preferred, and 130°C or lower is more preferred. At temperatures lower than 45°C, the solvent (methanol or water) used in the crystallization step cannot be removed, or even if it can be removed, it takes an extremely long time, which is not preferred. The drying step may be carried out under normal pressure or reduced pressure, but when carried out industrially, it is preferable to carry out the drying step under reduced pressure, since this allows for more efficient removal of the solvent (methanol or water) used in the crystallization step. In addition, it is more preferable to carry out the drying step in an inert gas atmosphere such as nitrogen.

[0017] <Crystalline substance of the present invention> The crystalline form of 9,9-bis(4-hydroxyphenyl)-2,3-benzofluorene of the present invention is characterized by a melting point in the range of 182° C. or higher and 187° C. or lower as measured by differential scanning calorimetry. In particular, the lower limit of the melting point as measured by differential scanning calorimetry is preferably 183° C. or higher, and more preferably 184° C. or higher. The upper limit may be 186° C. or lower. Furthermore, the crystalline form of 9,9-bis(4-hydroxyphenyl)-2,3-benzofluorene of the present invention is not an inclusion complex, i.e., a crystalline form that does not include compounds such as organic solvents. As the crystalline form of the present invention that does not include compounds such as organic solvents, a crystalline form having a residual organic solvent content of 1 wt % or less is preferred, a crystalline form having a residual organic solvent content of 0.5 wt % or less is more preferred, a crystalline form having a residual organic solvent content of 0.3 wt % or less is even more preferred, and a crystalline form having a residual organic solvent content of 0.1 wt % or less is particularly preferred. [Example]

[0018] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. The analysis method is as follows. <Analysis method> 1.Powder X-ray diffraction (XRD) Approximately 100 mg of the crystals were filled into the sample filling section of a glass test plate, and the powder X-ray diffraction was measured using a powder X-ray diffractometer (Rigaku Corporation: SmartLab) under the following conditions. X-ray source:CuKα Scan axis: 2θ / θ Mode: Continuous Measurement range: 2θ=5°~70° Step: 0.01° Speed ​​measurement time: 2θ=2° / min IS:1 / 2 RS:20.00mm Output: 40kV-30mA 2. Differential Scanning Calorimetry (DSC) 5 mg of the crystals were weighed into an aluminum pan and measured using a differential scanning calorimeter (Shimadzu Corporation: DSC-60) under the following operating conditions, using aluminum oxide as a control. (Operating conditions) Heating rate: 10℃ / min Measurement temperature range: 30 to 260°C Measurement atmosphere: Open, nitrogen 50mL / min 3.Differential thermal / thermogravimetric analysis (DTG) 8 mg of the crystals was weighed into an aluminum pan and measured using a differential thermal / thermogravimetric analyzer (Shimadzu Corporation: DTG-60A) under the following operating conditions. (Operating conditions) Heating rate: 10℃ / min Measurement temperature range: 30 to 300°C Measurement atmosphere: Open, nitrogen 50mL / min 4. Hue (APHA) The crystals were dissolved in methanol to obtain a 10 wt % solution, and after the following measuring equipment was calibrated with methanol, the dissolution color of the 10 wt % solution was measured. Measuring equipment: Nippon Denshoku Industries Co., Ltd. TZ 6000

[0019] <Synthesis example> Synthesis of 9,9-bis(4-hydroxyphenyl)-2,3-benzofluorene A 1-liter four-neck flask equipped with a thermometer, stirrer, and condenser was purged with nitrogen, and 119 g (1.2 mol) of phenol was charged. Hydrogen chloride gas was then blown into the flask to purge the atmosphere with hydrogen chloride gas. 13 g of a 15% aqueous solution of methyl mercaptan sodium salt was added dropwise, followed by a mixture of 145 g (0.63 mol) of 2,3-benzo-9-fluorenone, 119 g (1.2 mol) of phenol, and 58 g of toluene over 1 hour. The mixture was stirred at 40°C for 3 hours. Liquid chromatography analysis confirmed the disappearance of the raw materials, marking the end of the reaction. Aqueous sodium hydroxide solution was added to the reaction mixture to neutralize the reaction solution. 60 g of toluene was added, and the mixture was allowed to stand. The aqueous layer was then removed. Distilled water was added to the resulting oil layer, and the mixture was stirred. After standing, the aqueous layer was removed. This procedure was repeated twice to remove the neutralized salt, and excess phenol was removed by vacuum distillation. 1009 g of toluene was added to the distillation residue to form a homogeneous solution, which was then cooled to precipitate crystals. Thereafter, the mixture was cooled to 25°C and the precipitated crystals were filtered off. The resulting crystals were dried at 90°C under a reduced pressure of 1.2 kPa for 2 hours and analyzed by headspace gas chromatography (HS-GC), which revealed a toluene content of 4% by weight. The crystals were further dried at 120°C under a reduced pressure of 1.2 kPa for 3 hours, but the toluene content remained unchanged. Furthermore, DTG analysis confirmed a weight loss of 2.0% at temperatures above the melting point. The differential scanning calorimetry (DSC) curve of the resulting crystals is shown in Figure 1. Appearance White crystal Hue 47(APHA) Purity: 98.7% (High-Performance Liquid Chromatography) Melting point: 144°C (differential scanning calorimetry)

[0020] Example 1 70 g of the white crystals obtained in the above "Synthesis Example" were dissolved in 210 g of methanol, and the solution was heated to a temperature above 60°C and below the boiling point (64.7°C). While maintaining the temperature at or above 60°C and below the boiling point, 135 g of distilled water was added dropwise over 30 minutes with stirring. Crystal precipitation was observed immediately after the dropwise addition. The temperature was maintained for 1 hour, then cooled to 25°C at a rate of 10°C per hour, and the precipitated crystals were filtered off. The resulting white crystals were gradually heated to 120°C under a reduced pressure of 1.2 kPa and dried at 120°C for 3 hours. HS-GC analysis confirmed that the residual methanol content was 0.5 wt% or less. The drying under reduced pressure was then terminated, yielding 64 g of the desired crystalline form of 9,9-bis(4-hydroxyphenyl)-2,3-benzofluorene, which was not an inclusion complex. The obtained crystals were analyzed by HS-GC analysis, and the remaining organic solvents were 460 ppm toluene and 290 ppm methanol, confirming that the obtained crystals were not clathrates. Furthermore, DTG analysis showed no weight loss at temperatures above the melting point. The differential scanning calorimetry (DSC) curve of the obtained crystals is shown in Figure 2. Appearance White crystal Hue 14(APHA) Purity: 99.1% (High-Performance Liquid Chromatography) Melting point: 185°C (differential scanning calorimetry)

[0021] The crystalline form of 9,9-bis(4-hydroxyphenyl)-2,3-benzofluorene obtained in "Example 1" above, which has a specific melting point of the present invention, is not an inclusion complex, and has a residual organic solvent content of 1 wt % or less, was subjected to powder X-ray diffraction (XRD), and the main peaks (those having a relative intensity of more than 5%) are listed in Table 1. [Table 1]

[0022] <Comparative Example 1> 9,9-bis(4-hydroxyphenyl)-2,3-benzofluorene was synthesized with reference to Example 20 of the above-mentioned "Patent Document 1." A 1-liter four-neck flask equipped with a thermometer, stirrer, and condenser was purged with nitrogen, and 10.5 g (0.046 mol) of 2,3-benzo-9-fluorenone, 21.5 g (0.228 mol) of phenol, and 6.6 g of toluene were added and heated to 40°C to dissolve. 0.17 g of 3-mercaptopropionic acid was added, followed by dropwise addition of 5.9 g of methanesulfonic acid over 30 minutes and stirring at 60°C for 1 hour. 69.9 g of toluene and 43.7 g of water were added to the reaction solution to wash the organic layer, and then 43.7 g of saturated saline was used three times for washing and separation. 8.1 g of dimethyl carbonate was then added, and the mixture was heated to 80°C and gradually cooled to 25°C to precipitate crystals, followed by stirring at 25°C for 1 hour. The precipitated crystals were filtered, and the resulting white crystals were gradually heated to 120°C under a reduced pressure of 1.2 kPa and dried under reduced pressure at 120°C for 1 hour. 1 The amount of the remaining organic solvent was measured by H-NMR analysis. Furthermore, drying was continued for 3 hours at 120°C under a reduced pressure of 1.2 kPa, but the amount of organic solvent contained in the crystals did not change. Appearance White crystal Purity: 97.4% (High-Performance Liquid Chromatography) Melting point: 170°C (differential scanning calorimetry) DTG analysis of the obtained crystals confirmed a weight loss of 4.2% at temperatures above the melting point. 1 H-NMR analysis confirmed that the crystals contained 1 mole of dimethyl carbonate per 5 moles of compound. This was found to be roughly the same as the "crystals containing 1 mole of dimethyl carbonate per 4.9 moles of compound" described in Example 20 of Patent Document 1. The differential scanning calorimetry (DSC) curve of the obtained crystals is shown in Figure 3.

[0023] <Comparative Example 2> 2 g of dried crystals from the synthesis example and 2 g of acetone were placed in a test tube containing a stirrer and dissolved at 50°C. While maintaining the internal temperature at 50°C, 7 g of water was gradually added dropwise. After stirring for a while, crystals precipitated. The mixture was then cooled to 25°C and filtered. The resulting crystals were heated to 100°C under a reduced pressure of 1.2 kPa and dried under reduced pressure for 3 hours to obtain 1.64 g of crystals. Further drying at 120°C under a reduced pressure of 1.2 kPa for 3 hours did not change the amount of organic solvent contained in the crystals. Measurement of the remaining organic solvent in the resulting crystals by HS-GC analysis revealed that they contained 4200 ppm toluene and 62100 ppm acetone. Furthermore, DTG analysis confirmed a 3.5% weight loss at temperatures above the melting point. Melting point: 139°C (differential scanning calorimetry) The differential scanning calorimetry (DSC) curve of the obtained crystals is shown in FIG.

[0024] <Comparative Example 3> 9,9-bis(4-hydroxyphenyl)-2,3-benzofluorene was synthesized with reference to Comparative Example 1 of the above-mentioned "Patent Document 1." A 1-liter four-neck flask equipped with a thermometer, stirrer, and condenser was purged with nitrogen. 10.5 g (0.046 mol) of 2,3-benzo-9-fluorenone, 21.5 g (0.228 mol) of phenol, and 6.6 g of toluene were added and heated to 40°C to dissolve the solution. 0.17 g of 3-mercaptopropionic acid was added, and 4.5 g of sulfuric acid was added dropwise over 30 minutes with stirring. The reaction was then carried out at 60°C for 1 hour. 69.9 g of toluene and 43.7 g of water were then added to the reaction solution, stirred, and allowed to stand. The aqueous layer was then separated and removed. This washing procedure, in which 43.7 g of saturated saline solution was added to the resulting organic layer, stirred, and allowed to stand, the aqueous layer was then separated and removed, was repeated three times. The organic layer was then gradually cooled to 5°C and stirred for an additional 5 hours, but no crystals precipitated. Stirring was continued at room temperature for an additional 15 hours, but no crystals precipitated.

Claims

1. A crystalline form of 9,9-bis(4-hydroxyphenyl)-2,3-benzofluorene, characterized by having a melting point of 184 to 186°C as determined by differential scanning calorimetry, not being an inclusion complex, and having a residual organic solvent content of 1% by weight or less.

2. 2. A method for producing the crystalline substance according to claim 1, comprising a step of crystallization using a mixed solvent of methanol and water.

3. The method according to claim 2, further comprising a step of drying the crystals obtained by crystallization at a temperature of 45°C or higher and lower than the melting point.

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