Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic acids and salts thereof
Reexamination Certificate
2001-06-26
2003-05-13
Rotman, Alan L. (Department: 1625)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic acids and salts thereof
C562S400000, C562S405000, C562S465000, C562S466000, C562S487000, C562S480000
Reexamination Certificate
active
06562998
ABSTRACT:
TECHNICAL FIELD
The present invention provides a granular product of 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, the compound is synthesized by reacting &bgr;-naphthol with sodium hydride to give sodium &bgr;-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 &bgr;-naphtholate and carbon dioxide. Said reactions however, has some problems such as more than 50 hours of long reaction time, high amount of wasted &bgr;-naphthol because of thermal heterogeneity at the high reaction temperature and difficulties in controlling the reaction due to the phase conversion, and a stable yield can be hardly obtained. In order to solve those problems, a number of methods including a method using a reaction medium 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 &bgr;-naphtholate and &bgr;-naphthol, with carbon dioxide (Japanese Patent Publication (KOKOKU) No. 53296/11981) and said process has been industrially used. This process can be carried out successively and can provide 2-hydroxynaphthalene-3-carboxylic acid with very low amount of impurities and with highly stable quality. According to said method, 2-hydroxynaphthalene-3-carboxylic acid with high quality, such as those having 220-221° C. of melting point and 99.5% of purity and containing only 0.03% of sodium &bgr;-naphtholate, can be obtained. In the process, 2-hydroxynaphthalene-3-carboxylic acid is isolated from the mother liquid by means of acid precipitation, filtration, centrifugation and the like, washed with water, dried and then, is used as an intermediate for pigments or dyes.
Crystalline product of 2-hydroxynaphthalene-3-carboxylic acid usually comprises very fine particles and, therefore, is highly dusty. In addition to the dust, 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 vessel 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. They 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 mounted a vacuum at a position other than the supply port and a filter to trap the fine particles. However, they are not enough.
The reason why 2-hydroxynaphthalene-3-carboxylic acid dusts significantly is believed that said compound consists of very fine crystalline particles, and that said compound is hardly dissolved in water and, therefore, hardly uptakes moisture; and therefore, each crystalline particles do not agglomerate or bind together through water of adhesion. As a consequence, the fine crystalline particles move individually upon an external impact.
Further, when fine particles of 2-hydroxynaphthalene-3-carboxylic acid are added to a medium, the particles tend to agglomerate to lower the solubility of the same which deteriorate the operability.
In order to suppress the dust of the material having the above-described characteristics, Japanese patent Application Laid Open No. 196841/1983 discloses granular product prepared by a wet extrusion granulating process comprising steps of kneading 2-hydroxynaphthalene-3-carboxylic acid particles having a certain particle properties and containing 13-30% of water, granulating the same by means of extrusion granulator and drying. Thus obtained granules are made of small particles which are attracted each other with relatively low bonding force, and tends to be degraded during transporting or forwarding the granules to give original small particles which is highly dusty.
Further, said process requires complicated steps such as adding a certain amount of water to the dry particles and controlling moisture content of acid precipitated 2-hydroxynaphthalene-3-carboxylic acid particles by means of centrifugation or the like, and therefore, is not suitable for large scale production.
In the field of pharmaceutical preparation, it is proposed that good granular product may be obtained by adding binder component such as dextrin, starch and carboxymethyl cellulose to the base component as well as water or alcohol, kneading and granulating the same. However, if a binder component is added during preparation of 2-hydroxynaphthalene-3-carboxylic acid, high purity product cannot be obtained and the azo pigment or molded polymer prepared with the product might have imposed color tone or deteriorated properties.
Accordingly, the object of the present invention is to solve the above-mentioned problems and to provide granular product of 2-hydroxynaphthalene-3-carboxylic acid with well-suppressed dusting tendency.
DISCLOSURE OF INVENTION
The present invention provides granular product of 2-hydroxynaphthalene-3-carboxylic acid having an average particle size of equal to or more than 150 &mgr;m and a hardness of 70-3000 g. The granular product of the present invention exhibits well suppressed dusting tendency and therefore, is easy to handle and the affects little to environment and human beings. In addition, the granular product of 2-hydroxynaphthalene-3-carboxylic acid is strong enough to resist against fairly strong impact such that it is not degraded to the original fine particles by certain impact. Therefore degradation of the product during transportation or the like is well suppressed. Further, despite the large average particle size of over 150 &mgr;m, the granular product of the present invention exhibits excellent dissolution property, which is even superior to that of conventional powdery product having a small particle size (40-70&mgr;m) and therefore is useful as an intermediate for preparing dyes and pigments.
The granular product of the present invention may be prepared by a method comprising the steps of, dry compressing powdery 2-hydroxynaphthalene-3-carboxylic acid to give a compressed material, pulverizing and classifying the same. Accordingly, the method for preparing the granular product is also in the scope of the present invention.
DEFINITIONS
Average Particle Size
An average particle size represents the value measured as follows:
A sample product is weighted and then is sequentially screened with sieves having aperture of 1180 &mgr;m, 500 &mgr;m, 297 &mgr;m, 180 &mgr;m, 106 &mgr;m and 74 &mgr;m in this order. Firstly, the weighted sample product is screened with the sieve having aperture of 1180 &mgr;m at 230 rpm for 10 minutes. The amount of the residues on the sieve was weighted and the weight ratio (wt %) to the starting amount is calculated. The sample passed through the 1180 &mgr;m sieve was then screened with the sieve having aperture of 500 &mgr;m in the same manner as above. These steps repeated successively and at the last, the amount of the product passed through the 74 &mgr;m sieve is weighed. The average particle size is the value calculated as follows:
average particle size (&mgr;m)=(1180×
residue on the 1180 &mgr;m
sieve (wt %)/100)+(500×
residue on the 500 &mgr;m sieve
(wt %)/100)+(297×
residue on the 297 &mgr;m sieve
(wt %)/100)+(106×
residue on the 106 &mgr;m
sieve (wt %)/100)+(74×
residue on the 74 &mgr;m
sieve (wt %)/100)&plu
Izumichi Nobutaka
Kitayama Masaya
Kittaka Masaharu
Nara Syungo
Ueno Ryuzo
Kabushiki Kaisha Ueno Seiyako Oyo Kenkyujo
Reyes Hector M
Rotman Alan L.
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