CRYSTAL OF 2-HYDROXYNAPHTHALENE-3-CARBOXYLIC ACID AND PROCESS FOR THE PREPARATION THEREOF

Abstract: The present invention provides crystalline 2-hydroxynaphthalene-3-carboxylic acid (BON) characterized in that the average particle size is equal to or more than 157µm and the proportion of the particles of which particle size is less than 74µm is equal to or less than 14%. The crystalline composition of the present invention can be prepared by a process comprising the step of recrystallizing BON, especially at a high temperature, or by carrying out the acid precipitation step in the method for preparing BON at a high temperature.

Description: TECHNICAL FIELD The present invention provides a crystalline 2-hydroxynaphthalene-3-carboxylic acid having significantly suppressed dusting tendency, and a process for preparing the same. BACKGROUND ART 2-hydroxynaphthalene-3-carboxylic acid is important as an intermediate for pigments or dyes. Generally, it is prepared by reacting β-naphthol with sodium hydride to give sodium β-naphtholate, reacting the resulting compound with carbon dioxide under pressure to give sodium 2-hydroxynaphthalene-3-carboxylate and then, isolating the desired compound by means of acid precipitation i.e. by adding a mineral acid to the salt. For a long time, the Kolbe-Schmitt reaction, a solid-gas phase reaction, had been employed for the reaction between sodium β-naphtholate and carbon dioxide. Said reaction, however, had some problems, such as more than 50 hours of reaction time were required, a large amount of β-naphthol was wasted because of thermal heterogeneity at the high reaction temperature, control of the reaction was difficult due to the phase conversion and a stable yield was hardly obtained. In order to solve those problems, a number of methods including a method using reaction media had been proposed. One of the present inventors had invented a process comprising the step of reacting a liquid mixture consisting of light oil or kerosene, sodium β-naphtholate and β-naphthol, with carbon dioxide (Japanese Patent Publication (KOKOKU) No. 53296/1981) and said process has been industrially used at present. This process can be carried out successively and can provide 2-hydroxynaphthalene-3-carboxylic acid with a very low amount of impurities and with highly stable quality. According to said method, 2-hydroxynaphthalene-3-carboxylic acid with high quality, such as a melting point of 220-221°C a purity of 99.5% and containing only 0.03% of sodium β-naphtholate, can be obtained. In the process, 2-hydroxynaphthol-3-carboxylic acid is isolated from the mother liquid by means of acid precipitation, filtration, centrifugation and the like, washed with water, dried and is then used as an intermediate for pigments or dyes. A crystalline composition of 2-hydroxynaphthalene-3-carboxylic acid usually comprises very fine particles and, therefore, is very dusty. In addition to the dusting tendency, due to the severe mucosal irritativeness of 2-hydroxynaphthalene-3-carboxylic acid, handling of the compound is highly obstructed. For example, when 2-hydroxynaphthalene-3-carboxylic acid is added into a reaction tank as an intermediate for a pigment or dye, fine particles of 2-hydroxynaphthalene-3-carboxylic acid fly in the air as powdery dust. The fine particles of 2-hydroxynaphthalene-3-carboxylic acid flown in the air are hardly precipitated, disperse widely, pollute the environment, and stimulate the skin and mucosa of the operators to make them uncomfortable. In order to diminish the problems concerning workability and safety in the feeding step, operators wear dust-proof glasses and masks and the reactor is provided with a vacuum at a position other than the supply port to deaerate the fine particles and a filter to trap the same. However, they are not enough. The reason why 2-hydroxynaphthalene-3-carboxylic acid dusts significantly is believed to be due to said compound consisting of very fine crystalline particles, and to said compound being hardly dissolved in water and, therefore, hardly uptaking moisture; and therefore the crystalline particles do not agglomerate or bind together through the free water. As a consequence, the fine crystalline particles move individually upon an external impact. In order to suppress the dusting tendency of the material having the above-described characteristics, Japanese patent Application Laid Open No. 196841/1983 discloses a method for granulating 2-hydroxynaphthalene-3-carboxylic acid particles. Although the thus obtained granulated 2-hydroxynaphthalene-3-carboxylic acid particles exhibited suppressed dusting tendency, said process is highly complicated. More particularly, the process comprises the steps of adding a determined amount of water to 2-hydroxy-naphthalene-3-carboxylic acid and controlling the water content of acid precipitated 2-hydroxynaphthalene-3-carboxylic acid by centrifugation. Therefore the process was not suitable for mass production. Further, Japanese Patent Application Laid Open NO. 212533/1986 discloses a process for preparing granules comprising the step of granulating 2-hydroxynaphthalene-3-carboxylic acid together with an aqueous mixture containing a hydrophilic organic solvent having lower boiling point such as a lower alcohol. In this process, the step of adding the organic solvent is required and therefore the whole process becomes longer. Accordingly, the object of the present invention is to solve the above-mentioned problems and to provide crystalline 2-hydroxynaphthalene-3-carboxylic acid with well-suppressed dusting tendency. DISCLOSURE OF INVENTION The present invention provides a crystalline composition of 2-hydroxynaphthalene-3-carboxylic acid with a extremely suppressed dusting tendency, the product being characterised in that the average particle size is equal to or more than 157 µm, that the proportion of the particles of which particle size are equal to or less than 74µm is equal to or less than 14%, and that the lightness is 38-69 and whiteness is 4.6-18.0 In the present specification and claims, each "%" represents weight % except for indicated particularly. In the present specification and claims, the average particle size means the value determined as below: The sample material is weighed and is then sequentially screened with sieves having apertures of 710µm, 297µm, 170µm, 106µm, 74µm and 45µm in this order. The residue on the respective sieves and the amount passed through the 45µm sieve are weighed. The average particle size is calculated as follows: average particle size (µm)=(710 × residue on the 710µm sieve (wt%)/100) + (297 × residue on the 297µm sieve (wt%)/100) +(170 × residue on the 170µm sieve (wt%)/100) +(106 × residue on the 106µm sieve (wt%)/100) +(74 × residue on the 74µm sieve (wt%)/100) +(45×residue on the 45µm sieve (wt%)/100) +(25 × passed the 45µm sieve (wt%)/100). The crystalline particles of 2-hydoroxynaphthalene-3-carboxylic acid having the characteristics recited in the present invention are more than 2-4.5 times as large as the conventional crystalline 2-hydoroxynaphthalene-3-carboxylic acid particles. The crystalline composition of the present invention exhibits significantly suppressed dusting tendency, and may therefore be easily handled with significantly reduced risk to the environment and human beings. Further, said crystalline particles of the present invention can easily be pulverized into fine particles and exhibit the dissolution rate comparable to the conventional small size (50-90µm) crystalline particles. That is, the crystalline composition of the present invention may preferably be used as intermediate of pigments or dyes. The large-size crystalline 2-hydroxynaphthalene-3-carboxylic acid of the present invention possesses chromaticity of, 38-69 of lightness and 4.6-18.0 of whiteness. "Chromaticity" used herein means a property of a color stimulus determined by chromaticity coordinates or by combination of dominant wavelength or complementary wavelength and purity (JIS Z 8120). "Lightness" means an attribute of a color in respect of relative contrast of the surface of an object, which is classified on the basis of white surface that is illuminated by the same condition (JIS Z 8105). In the present specification and claims, "lightness" represents L value of the "Lab" color representation system, which is well known in the art. The Lab values are calculated by the following formula from tristimulus values (X,Y,Z) measured according to JIS Z 8722: L = 10(Y) 1/2 a = 17.5(1.02X-Y)/(Y) 1/2 b = 7.0(Y-0.847Z)/(Y) 1/2 "Whiteness" is a number of one-dimensional value representing the degree of white of the surface of an object (JIS Z 8105). In the present specification and claims, "whiteness" represents the value calculated from the above described tristimulus values by the following formula: Whiteness = Z/1.1823. The crystalline 2-hydroxynaphthalene-3-carboxylic acid of the present invention can be prepared by recrystallizing 2-hydroxynaphthalene-3-carboxylic acid at a temperature of 120-180°C. The starting material of crystalline 2-hydroxynaphthalene-3-carboxylic acid may be prepared by any conventional process. For example, said starting material may be prepared by acid precipitating at 80-100°C 2-hydroxynaphthalene-3-carboxylic acid alkaline metal salt which is obtained by the Kolbe-Schmitt method described in Japanese Patent Publication (KOKOKU) No. 53296/1981. The recrystallizing step is carried out immediately after acid precipitation of 2-hydroxynaphthalene-3-carboxylic acid. The aqueous 2-hydroxynaphthalene-3-carboxylic acid solution obtained by the acid precipitating step may be added with water, a water-soluble solvent or a water insoluble solvent, stirred and heated to a temperature of 120-180°C under pressure. The temperature and pressure may be kept for 5 to 30 minutes and then, the mixture may be cooled to 50-90°C. After that, the solvent may be removed by centrifugation and the precipitate may be washed with water and dried to provide the desired crystalline composition. Water, a water-soluble solvent or a water-insoluble solvent may be added to the solution independently or in combination. Examples of water-soluble solvents include methanol, ethanol, 1-propanol and is opropylalcohol. Examples of water-insoluble solvents include acetophenone, cyclohexane and ethylhexylalcohol. When the recrystallization process is carried out by adding a solvent to the aqueous solution of 2-hydroxynaphthalene-3-carboxylic acid or sodium salt thereof, said solution may contain 7-20%, preferably 8-16%, more preferably 9-13% of said acid or salt. The amount of the solvent to be added may be 2-50%, preferably, 4-40%, and more preferably 10-30% of the total amount of the aqueous solution. The recrystallizing step may preferably be carried out at a temperature of 120-160°C and at a pressure of 0.1-20kg/cm 2 (G), preferably 0.2-14kg/cm 2 (G), more preferably 0.5-8kg/cm 2 (G). Thereafter, in the cooling step, the temperature may be reduced at the rate of 4°C/min-0.1°C/min., preferably 2°C/min.-0.2°C/min. In another embodiment, the crystalline 2-hydroxynaphthalene-3-carboxylic acid of the present invention may be prepared by operating the acid precipitation process at a temperature of 120-180°C in the process for preparing 2-hydrocynaphthalene-carboxylic acid comprising the step of acid precipitating an alkaline metal salt of 2-hydroxynaphthalene-3-carboxylic acid. This embodiment can be practised based on the conventional step by only raising the temperature of the acid precipitation step. Therefore, the conventional system can be easily adopted to practise the embodiment. According to the conventional Kolbe-Schmitt method, the solution before being subjected to the acid precipitating step generally contains 7-20% of the alkaline metal salt of 2-hydroxynaphthalene-3-carboxylic acid. In this embodiment, the aqueous solution of 2-hydroxynaphthalene-3-carboxylic acid alkaline metal salt containing said amount of the salt may be stirred and heated to a temperature of 120-180°C under pressure, and then the pH of the solution may be adjusted to 1-4 with sulfuric acid. After the pH is adjusted, the mixture may be cooled to 50-90°C, the solvent may be removed by centrifugation, and the residue may be washed with water and dried to provide the desired crystalline composition. In this embodiment, the acid precipitating step may preferably be carried out at a temperature of 120-160°C. When the temperature is lower than 120°C, the particle size of the obtained crystalline 2-hydroxynaohthalene-3-carboxylic acid will be reduced and therefore the effect to suppress dusting cannot be achieved. On the other hand, when the temperature of the acid precipitating step is higher than 180°C, 2-hydroxynaphthalene-3-carboxylic acid may be decomposed and the yield may be reduced. The pressure during the acid precipitating step may be 0.1-10kg/cm 2 (G), preferably, 0.2-5kg/cm 2 (G), more preferably, 0.5-3kg/cm 2 (G). The cooling step may be carried out as the same manner as in the above-described high temperature recrystallization embodiment. In order to obtain the large size crystalline 2-hydroxynaphthalene-3-carboxylic acid of the present invention, acids used in the acid precipitating step are not limited, but preferably are mineral acids or sulfuric acid. Examples of mineral acids include binary acids (hydro acids) such as hydrochloric acid and hydrofluoric acid and oxo acids such as nitric acid, phosphoric acid and perchloric acid. The pH of the acid precipitating step may preferably be adjusted between 1 and 4. The average particle size of the crystalline 2-hydroxynaphthalene-3-carboxylic acid of the present invention is equal to or higher than 157µm, and is preferably 167-367µm. When the average particle size is less than 157µm, the effect to suppress dusting cannot be achieved. The crystalline composition may contain particles of which particle sizes are equal to or less than 74µm up to 14%, preferably, up to 6% of the total amount of the composition. When the proportion of the particles of which particle sizes are equal to or less than 74µm is more than 14%, the crystalline composition starts to exhibit high dusting tendency due to those small size particles. Further, the proportion of most high frequent particle size of the crystalline composition of the present invention may preferably be between 170-297µm. The proportion of the particles of which particle sizes are higher than 297µm may be 14-89%, preferably 28-80%. Examples of the present invention will be illustrated below. EXAMPLE 1 800g of an aqueous solution containing 100g of sodium 2-hydroxynaphthalene-3-carboxylate prepared by means of the Kolbe-Schmitt method was fed to a 1L autoclave and heated to 160°C. Aqueous sulfuric acid (72%) was added dropwise to the solution over 50 minutes to adjust the pH of the mixture to 3.5. Then, the mixture was cooled to 80°C at the rate of 0.4°C/min. At the same temperature, the mixture was filtered to give 80.6 g of crystalline 2-hydroxynaphthalene-3-carboxylic acid. EXAMPLES 2, 3 AND COMPARATIVE EXAMPLES 1, 2 Crystalline compositions of 2-hydroxynaphthalene-3-carboxylic acid were prepared according to the procedure of EXAMPLE 1 except that the temperature at the acid precipitating steps varied from 100°C to 140°C. EXAMPLE 4 105.6 g of 2-hydroxynaphthalene-3-carboxylic acid synthesized by the Kolbe-Schmitt method and isolated by acid precipitation at 100°C, 100g of sodium sulfate and 794.4g of water were fed to a 1L autoclave and heated to 165°C to give an aqueous solution of 2-hydroxynaphthalene-3-carboxylic acid. This solution was cooled to 80°C at a rate of 0.4°C/min. At the same temperature, the mixture was filtered to give 103.8 g of crystalline 2-hydroxynaphthalene-3-carboxylic acid. EXAMPLE 5 21.1g of 2-hydroxy naphthalene-3-carboxylic acid synthesized by the Kolbe-Schmitt method and isolated by acid precipitation at 100°C, 19.9g of sodium sulfate and 959.0g of water were fed to a 1L autoclave and heated to 140°C to give an aqueous solution of 2-hydroxynaphthalene-3-carboxylic acid. This solution was cooled to 80°C at the rate of 0.4°C/min. At the same temperature, the mixture was filtered to give 18.4 g of crystalline 2-hydroxynaphthalene-3-carboxylic acid. EXAMPLE 6 878.8 g of an aqueous solution containing 103.6 g of sodium 2-hydroxynaphthalene-3-carboxylate prepared by the Kolbe-Schmitt method was fed to a 1L autoclave and heated to 100°C. Aqueous sulfuric acid (72%) was added dropwise to the solution over 50 minutes to adjust the pH to 3.5 and then 111.6 g of methanol was added thereto. The mixture was heated to 140°C to dissolve the 2-hydroxynaphthalene-3-carboxylic acid and then cooled to 80°C at the rate of 0.4°C/min. The mixture was filtered at the same temperature to give 88.3 g of crystalline 2-hydroxynaphthalene-3-carboxylic acid. EXAMPLE 7 878.8g of aqueous solution containing 103.6 g of sodium 2-hydroxynaphthalene-3-carboxylate prepared by the Kolbe-Schmitt method was fed to a 1L autoclave and heated to 100°C. Aqueous sulfuric acid (72%) was added dropwise to the solution over 50 minutes to adjust the pH to 3.5, then 71.5g of acetophenone was added. The mixture was heated to 140°C to dissolve the 2-hydroxynaphthalene-3-carboxylic acid and was then cooled to 80°C at the rate of 0.4°C/min. The mixture was filtered at the same temperature to give 87.2 g of crystalline 2-hydroxynaphthalene-3-carboxylic acid. EVALUATION crystalline compositions of 2-hydroxynaphthalene-3-carboxylic acid obtained in the respective examples and comparative examples were examined. Their particle size, ML value, chromaticity properties including lightness and whiteness, particle characteristics and dusting tendency were determined/evaluated according to the following methods: PARTICLE SIZE Particle size was determined with sieves of 20Mon (710µm aperture), 48Mon (297µm aperture), 83Mon (170µm, aperture), 140Mon (106µm aperture), 200Mon (74µm aperture) and 330Mon (45µm aperture), and a shaker (MEIDENSHA Type E4-SNR), by measuring the ratios of the residues on the respective sieves. In detail, firstly, the whole crystalline composition was screened with the 710µm sieve for 10 minutes at 230rpm by means of the shaker and the weight % of the residue on the sieve based on the starting weight of the composition was determined. Then, the whole composition passed through the sieve was then screened with the 297µm sieve in the same manner. The composition was screened successively by the sieves listed above and lastly, was screened with 45µm sieve and the amount of the composition passed the sieve was also determined. Average particle sizes, proportion of the particles higher than 297µm and those less than 74µm are shown in table 1; particle size distribution is shown in table 2; ML value and chromaticity are shown in table 3 and the particle characteristics are shown in table 4. The average particle size means the value determined by the following formula: average particle size (µm)=(710 × residue on the 710µm sieve (wt%)/100) + (297 × residue on the 297µm sieve (wt%)/100) + (170 × residue on the 170µm sieve (wt%)/100) + (106µm × residue on the 106µm sieve (wt%)/100) +(74 × residue on the 74µm sieve (wt%)/100) + (45 × residue on the 45µm sieve(wt%)/100) + (25 × passed 45µm sieve (wt%)/100). ML VALUE ML value is obtained by multiplying the absorbance at 530nm per 1g of the compound by 200. In detail, 6g of the sample was weighed and dissolved into methyl alcohol to give the total volume of 200ml, filtered with No.5A filter paper (12.5cm) and then the absorbance of the solution was measured using methyl alcohol as a control. The ML value was determined according to the following formula: ML value = absorbance/amount of the sample (g) × 200. Results are shown in Table 3. CHROMATICITY Chromaticity characteristics, that is L, a, and b values and whiteness were determined by measuring the tristimulus values with a ZE2000 color meter (NIHON DENSHOKU KOGYO KABUSHIKI KAISHA) and calculating according to the above definitions. Results are shown in table 3. PARTICLE CHARACTERISTICS Powdertester (Type PT-N, HOSOKAWA MICRON CO., Ltd) was used. The following values were determined according to the instruction attached to the device. AERATED BULK DENSITY The sample on the sieve was shaken to allow falling into a standard container through the shout, then the standard container was weighed to determine the aerated bulk density. PACKED BULK DENSITY The sample was filled into a standard container, the container was tapped from the given height for the given times and then the bulk density of the sample packed by tapping was determined. COMPRESSION RATE The compression rate is the value obtained according to the following formula: (packed bulk density - aerated bulk density)/packed bulk density × 100 SPATULA ANGLE The angle of the powder composition deposited on the spatula was measured. Results are summarized in Table 4. DISSOLUTION TIME Each of the 2-hydroxynaphthalene-3-carboxylic acid samples were weighed 10 g and added to 104g of 5% aqueous sodium hydroxide and stirred. The time required to completely dissolve the each of the samples was visually determined. The results are shown in Table 4. EVALUATION OF DUST DISPERSION 50g of each crystalline compositions was slid down along a slope of 60° for a distance of 50 cm. When the composition reached to the bottom, the height and distance to which the dust flew were measured. The results are shown in Table 5. acid precipitation temp. (°C) average particle size (µm) ≧297µm (%) ≦74µm (%) Ex. 1 160 367.4 88.16 0.69 Ex. 2 140 263.5 75.59 0.79 Ex. 3 120 156.7 14.09 2.52 Comp. Ex. 1 110 92.7 1.07 17.18 Comp. Ex. 2 100 71.5 1.39 45.78 Ex. 4 214.6 50.74 3.77 Ex. 5 265.5 75.07 0.45 Ex. 6 195.5 33.80 5.50 Ex. 7 172.1 28.88 6.83 particle distribution (%) 20 Mon (710µ) 48 Mon (297µ) 83 Mon (170µ) 140 Mon (106µ) 200 Mon (74µ) 330 Mon (45µ) passed 330 Mon Ex. 1 21.43 66.73 8.12 2.15 0.88 0.59 0.10 Ex. 2 0.20 75.39 20.31 2.83 0.49 0.59 0.20 Ex. 3 0.00 14.09 43.35 32.85 7.19 1.94 0.58 Comp. Ex. 1 0.10 0.97 7.38 44.95 29.42 14.27 2.91 Comp. Ex. 2 0.30 1.09 3.47 17.74 31.62 33.39 12.39 Ex. 4 0.74 50.00 21.91 14.71 8.87 2.71 1.0 Ex. 5 0.51 74.56 22.47 1.58 0.43 0.43 0.2 Ex. 6 0.20 33.60 45.00 13.20 2.50 3.10 2.4 Ex. 7 0.20 28.68 26.71 30.17 7.41 4.45 2.38 ML value chromaticity L lightness a redness b yellowness HW whiteness Ex. 1 - 40.41 4.12 16.32 6.91 Ex. 2 1.33 56.23 0.21 26.79 10.09 Ex. 3 1.23 66.14 3.87 31.66 13.83 Comp. Ex. 1 1.17 76.13 0.43 34.21 20.75 Comp. Ex. 2 1.03 80.82 -0.51 36.68 22.97 Ex. 4 1.80 38.15 6.61 18.26 4.61 Ex. 5 1.17 56.45 3.77 25.51 11.29 Ex. 6 1.37 54.49 7.38 28.25 7.70 Ex. 7 1.40 62.84 5.43 28.81 13.62 bulk density(g/cc) aerated/packed (%) compression rate (%) spatula angle (deg) dissolution time aerated packed Ex. 1 0.547 0.601 91.01 9.0 50.4 17′35″ Ex. 2 0.514 0.578 88.93 11.1 48.4 8′55″ Ex. 3 0.341 0.474 71.94 28.1 61.6 12′11″ Comp. Ex. 1 0.312 0.422 73.93 26.1 63.3 25′ Comp. Ex. 2 0.262 0.429 61.07 38.9 74.2 29′ Ex. 4 - - - - - 15′39″ Ex. 5 0.355 0.459 77.34 22.7 66.5 9′44″ Ex. 6 0.493 0.554 88.99 11.0 47.4 16′9″ Ex. 7 0.622 0.687 90.54 9.5 47.1 7′28″ distance(cm) height(cm) Ex. 1 5 10 Ex. 2 10 7 Ex. 3 30 15 Comp. Ex. 1 50 30 Comp. Ex. 2 > 100 25 Ex. 4 20 13 Ex. 5 15 10 Ex. 6 30 15 Ex. 7 35 15 Dust of the respective crystalline 2-hydroxynaphthalene-3-carboxylic acid of the examples dispersed 5-35cm in distance and 7-17 cm in height. It is revealed that the dusting tendency of the crystalline composition was significantly suppressed. On the other hand, dust of the crystalline 2- hydrpxynaphthalene-3-carboxylic acid of the comparative examples flew widely to more than 50cm in distance and more than 25 cm in height. INDUSTRIAL APPLICABILITY The compound of the present invention, 2-hydroxynaphthalene-3-carboxylic acid, is industrially useful as an intermediate for pigments or dyes. Since the crystalline 2-hydroxynaphthalene-3-carboxylic acid of the present invention shows significantly suppressed dusting tendency, the crystalline compound is easy to handle and affect significantly reduced influence to environment and human beings.

Claims: Crystalline 2-hydroxynaphthalene-3-carboxylic acid, characterized in that the average particle size is equal to or more than 157µm, that the proportion of the particles of which particle size are equal to or less than 74µm is equal to or less than 14%, and that the lightness is 38-69 and whiteness is 4.6-18-0. The crystalline 2-hydroxynaphthalene-3-carboxylic acid of claim 1, characterized in that the dissolution time determined by dissolving 10 g of the 2-hydroxynaphthalene-3-carboxylic acid in 104 g of 5% aqueous sodium hydroxide at an ambient temperature is less than 20 minutes. A method for preparing the crystalline 2-hydroxynaphthalene-3-carboxylic acid of claim 1, which comprises the step of recrystallizing 2-hydroxynaphthalene-3-carboxylic acid at a temperature of 120-180°C A method for preparing the crystalline 2-hydroxynaphthalene-3-carboxylic acid of claim 1 comprising the step of acid precipitating an alkaline metal salt of 2-hydroxynaphthalene-3-carboxylic acid, characterized in that further comprising the step of recrystallizing 2-hydroxynaphthalene-3-carboxylic acid at a temperature of 120-180°C immediately after the acid precipitating step. A method for preparing the crystalline 2-hydroxynaphthalene-3-carboxylic acid of claim 1 comprising the step of acid precipitating an alkaline metal salt of 2-hydroxynaphthalene-3-carboxylic acid, characterized in that the acid precipitation step is carried out at a temperature of 120-180°C.

Inventors: IZUMICHI NOBUTAKA, KATO HIROYUKI, KITAYAMA MASAYA, UENO RYUZO, IZUMICHI, NOBUTAKA, KATO, HIROYUKI, KITAYAMA, MASAYA, UENO, RYUZO
Applicants: UENO SEIYAKU OYO KENKYUJO KK, KABUSHIKI KAISHA UENO SEIYAKU OYO KENKYUJO
Application year: 2000
Main classification: C07C65
IPC codes: C07C65, C07C51