Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic acids and salts thereof
Reexamination Certificate
2002-12-18
2004-01-06
Rotman, Alan L. (Department: 1625)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic acids and salts thereof
Reexamination Certificate
active
06673962
ABSTRACT:
TECHNICAL FIELD
The present invention provides a granular product of parahydroxybenzoic acid or a parahydroxybenzoic acid ester having significantly suppressed dusting and caking tendency, and a process for preparing the same.
BACKGROUND ART
Parahydroxybenzoic acid can be employed as a monomer component for a wide variety of polymer products. Recently, it draws the attention of the art as a monomer component for preparing liquid crystalline polymers, which exhibit high strength and high elastic modulus. In addition, many of its alkyl esters have been employed as fungicide for cosmetic products or industrial purposes. Generally, parahydroxybenzoic acid is prepared by a method comprising the steps of reacting phenol with potassium hydroxide to give potassium phenoxide, reacting the obtained potassium phenoxide with carbon dioxide under pressure to give potassium parahydroxybenzoate 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 of potassium phenoxide and carbon dioxide. Said reaction, however, has some problems such as long reaction time due to the solid-gas phase reaction, high amount waste of starting materials in side reaction because of thermal heterogeneity, difficulties in controlling the reaction which makes it difficult to attain a stable yield. In order to solve those problems, a number of methods had been proposed.
One of the instant inventors had proposed a process, which can produce the compound in a short time with high yield in a continuous manner. Said process comprises the step of reacting potassium phenoxide and carbon dioxide in the presence of an appropriate solvent at a temperature equal to or more than 180° C. in a dispersion, provided that phenol in an amount required to react with dipotassium parahydroxybenzoate to give potassium phenoxide is added to the reaction before the initiation of the carboxylation step (Japanese Patent Publication (KOKOKU) No. 9529/1970).
Thus obtained parahydroxybenzoic acid is then isolated from the solution by means of, such as, aciding out, filtration or centrifugation, and washed to give the compound to be used as a monomer component of polymers such as liquid crystalline polymers.
Parahydroxybenzoic acid esters may be prepared by a conventional process to obtain carboxylate esters; for example, by means of dehydration reaction between parahydroxybenzoic acid and an alcohol under the presence of acid catalyst such as sulfuric acid.
Crystalline product of parahydroxybenzoic acid or its ester usually comprises very fine particles and, therefore, is highly dusty causing operation problems. For example, when parahydroxybenzoic acid or its ester is added into a reaction vessel as a monomer component of a polymer or as a fungicide, fine particles of the compound fly in the air as powdery dust. The dust of parahydroxybenzoic acid or its ester flown in the air is hardly precipitated, and the widely dispersed dust causes problems in handling the same.
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.
Upon storage, the fine particles of parahydroxybenzoic acid or its ester tend to form cake and the caking tendency also causes problems in handling the same. Since the specific surface area increase as the diameter of the fine particles decrease and parahydroxybenzoic acid or its ester is soluble to water, the fine particles apt to bridge each other due to moisture in the air to form cakes and the caking tendency may be augmented by the capillary phenomenon.
Further, the fine particles of parahydroxybenzoic acid or its ester are easily to be charged and therefore, adhere to the surfaces of containers or plastic bags because of the electrostatic action.
In order to suppress dust of the material with the above-described characteristics, granular product prepared by a wet extrusion granulating process comprising steps of adding water to the particles of parahydroxybenzoic acid or its ester, kneading and granulating the same by means of extrusion granulator and drying could be proposed. Although thus obtained granules exhibit somewhat suppressed dusting and electrostatic properties, the particles agglomerate more easily due to the added water and therefore, the problem of caking still remains. In addition, thus obtained granules are made of small particles which are attracted each other with relatively low bonding force, and tends to be degraded during transportation to give the original dusty small particles.
On the other hand, in the field of pharmaceutical preparation, it has been proposed that good granular product may be obtained by a method comprising the steps of adding binder component such as dextrin, starch and carboxymethyl cellulose as well as water or alcohol to the base component, kneading and granulating the same. However, adding a binder component during preparation of parahydroxybenzoic acid will deteriorate the purity of the product and polymer products or molded articles made from such a product might have imposed color tone or deteriorated properties.
DISCLOSURE OF THE INVENTION
Accordingly, the object of the present invention is to solve the above-mentioned problems and to provide granular product of parahydroxybenzoic acid or its ester with well-suppressed dusting and caking tendency.
The present invention provides a granular product of parahydroxybenzoic acid or its ester having an average particle size of equal to or more than 150 &mgr;m and a hardness of 10-3000 g.
The granular product of the present invention exhibits well suppressed dusting tendency and therefore, is easy to handle and affects little to environment and human beings. In addition the product exhibit suppressed caking tendency which also causes improved workability of the product. In addition, the granular product of parahydroxybenzoic acid or its ester is strong enough to resist against fairly strong impact such that it is not easily degraded to the original fine particles and therefore degradation of the product during transportation or the like is well suppressed.
The granular product of the present invention may be prepared by a method comprising the steps of, dry compressing powdery parahydroxybenzoic acid or its ester 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 2800 &mgr;m, 1700 &mgr;m, 1180 &mgr;m, 840 &mgr;m, 500 &mgr;m and 250 &mgr;m in this order. Firstly, the weighted sample product is screened with the sieve having aperture of 2800 &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 2800 &mgr;m sieve was then screened with the sieve having aperture of 1700 &mgr;m in the same manner as above. These steps repeated successively and at the last, the amount of the product passed through the 250 &mgr;m sieve is weighed. The average particle size is the value calculated as follows: average particle size (&mgr;m)=(2800×residue on the 2800 &mgr;m sieve (wt %)/100)+(1700×residue on the 1700 &mgr;m sieve (wt %)/100)+(1180×residue on the 1180 &mgr;m sieve (wt %)/100)+(840×residue on the 840 &mgr;m sieve (wt %)/100)+(500×residue on the 500 &mgr;m sieve (wt %)/100)+(250×residue on the 250 &mgr;m sieve (wt %)/100)+(120×passed the 250 &mgr;m sieve (wt %)/100).
Hardness
Hardness is measured by the simplified granular hardness mete
Izumichi Nobutaka
Kitayama Masaya
Kittaka Masaharu
Ueno Ryuzo
Kabushiki Kaisha Ueno Seiyaku Oyo Kenkyujo
Reys Hector M.
Rotman Alan L.
Sughrue & Mion, PLLC
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