JPH08311030A - Purification of pyridine carboxylic acids - Google Patents

Abstract

PURPOSE: To purify the subject compound into the purified product remarkably reduced in the content of bromine impurities, improved in the color tone, and suitable as a additive for feeds or as a raw material for medicines, etc., by subjecting a crude pyridine carboxylic acid to a catalytic hydrogenation treatment using a specific catalyst at a specific temperature. CONSTITUTION: A method for purifying a pyridine carboxylic acid comprises subjecting (A) the crude pyridine carboxylic acid obtained by oxidizing an alkylpyridine in a liquid phase to a catalytic hydrogenation treatment in the presence of (B) a VIII group metal catalyst (e.g. palladium-active carbon catalyst) in (C) a solvent such as water or acetic acid at a temperature of 100-250 deg.C. The component C is used in an amount of 2-20wt. times, especially 3-10wt. times, that of the component A, and the reaction pressure is atmospheric pressure to 80kg/cm<2> G, especially 5-20kg/cm<2> G.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for purifying pyridinecarboxylic acids which are useful as raw materials for feed additives and pharmaceuticals.

[0002]

2. Description of the Related Art As an industrial production method of pyridinecarboxylic acids, a method of directly oxidizing alkylpyridines is known, and catalytic vapor-phase oxidation is carried out using a catalyst, and nitric acid is oxidized in a liquid phase as an oxidant. Those which undergo liquid-phase air oxidation using heavy metals and halogen elements as catalysts (Japanese Patent Publication No. 34-9868)
No.) etc.

Among these industrial processes for producing pyridinecarboxylic acids, liquid-phase air oxidation has the advantages of high yield and low oxidation cost, but the problem that impurities containing bromine are mixed in the obtained pyridinecarboxylic acid. There is. The crude pyridinecarboxylic acid obtained by liquid-phase air oxidation usually contains several tens to several
Contains 100 ppm nonionic bromine. It is necessary to remove such bromine impurities in pyridinecarboxylic acids used for feeds, pharmaceuticals and the like. However, little is known about the purification of pyridinecarboxylic acids. For example, Japanese Patent Publication No. 37-16737 discloses a purification method by sublimation, but in the case of pyridinecarboxylic acids in which a very small amount of impurities poses a problem, the Has low purification efficiency and is not practical.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for industrially advantageously purifying crude pyridinecarboxylic acids obtained by liquid-phase oxidation of alkylpyridines to reduce bromine impurities. Is.

[0005]

Means for Solving the Problems As a result of diligent investigations by the present inventors on a method for purifying a crude pyridinecarboxylic acid having the above-mentioned problems, the crude pyridinecarboxylic acid containing bromine was converted into a molecule in the presence of a Group VIII metal catalyst. The present inventors have found that the influence of bromine impurities can be significantly reduced to a negligible amount by the treatment with hydrogen gas in the form of hydrogen gas, and at the same time, the hue of the product is improved, and the present invention has been completed. That is, according to the present invention, crude pyridinecarboxylic acids obtained by liquid-phase oxidation of alkylpyridines are treated in the presence of a Group VIII metal catalyst at 100 to 25
A method for purifying pyridinecarboxylic acid, which comprises performing a catalytic hydrogenation treatment at a temperature of 0 ° C.

The crude pyridinecarboxylic acids used as a raw material in the present invention are those obtained by liquid-phase oxidation of alkylpyridines. The alkylpyridines are aromatic heterocyclic compounds containing nitrogen such as pyridine or quinoline. Ring compounds such as methyl group, ethyl group, n-propyl group, i-propyl group, n-butyl group, i-butyl group, n-pentyl group, i-pentyl group, n-hexyl group, i-hexyl group, n -Heptyl group,
Number of carbon atoms such as i-heptyl group, n-octyl group, i-octyl group, n-nonyl group, i-nonyl group, n-decyl group, i-decyl group 1
Is a compound having at least one alkyl side chain of 10 or more. In particular, as the raw material in the present invention, nicotinic acid and isonicotinic acid obtained by liquid-phase oxidation of 3-methylpyridine and 4-methylpyridine are preferably used.

The oxygen-containing gas used in the liquid phase oxidation of alkylpyridines in the present invention is pure oxygen,
Alternatively, a mixed gas of oxygen and another inert gas such as air can be used.

The Group VIII metals used in the catalyst of the catalytic hydrotreatment in the present invention include cobalt, nickel,
Examples thereof include ruthenium, rhodium, palladium, osmium, iridium and platinum, and a hydrogenation catalyst selected from these metal oxides can be used, and palladium is particularly preferable. These catalyst metals or metal oxides can be used as they are, but usually those supported on a support are used, and examples of the support include activated carbon, silica, alumina, silica-alumina, and the like. Is preferred.

As the solvent in the catalytic hydrogenation treatment of the present invention, water, acetic acid, or a mixed solution of acetic acid and water is used.
The amount of the solvent based on the crude pyridinecarboxylic acid is 2 to 20 parts by weight, preferably 3 to 10 parts by weight. The reaction temperature of the catalytic hydrotreatment depends on the catalytic activity, but it is generally 100 to 250 ° C, preferably 120 to 180 ° C. The pressure may be any pressure that can maintain the solvent in the liquid phase, but generally atmospheric pressure to 80 kg / cm
² G, preferably 5 to 20 kg / cm ² G. If the reaction temperature is too low, the reduction of bromine impurities will not be sufficient, and if the reaction temperature is too high, the reaction system will be at a high pressure, increasing the cost of the apparatus and increasing the operational problems. The catalytic hydrogenation treatment can be performed either batchwise or continuously.

Purification of aromatic carboxylic acids by catalytic hydrogenation, for example reduction of impurities 4-carboxybenzaldehyde (4-CBA) and improvement of hue in terephthalic acid, is generally known, but pyridinecarboxylic acid is known. It is not known to use catalytic hydrotreating to purify acids. Purification of terephthalic acid mainly reduces the impurity 4-CBA, but in the case of pyridinecarboxylic acids, it reduces organic bromine compounds. Further, pyridinecarboxylic acids include a basic pyridine ring in the molecule, and particularly in a reaction involving coordination with a transition metal such as a hydrogenation reaction with a Group VIII metal, terephthalic acid having a nonpolar benzene ring. It is difficult to predict that the same behavior as the above will be exhibited.

[0011]

EXAMPLES Next, the present invention will be specifically described based on examples. However, the present invention is not limited to these examples. An example of producing nicotinic acid, which is one of pyridinecarboxylic acids, is shown as a reference example. Since bromine ions derived from the mother liquor are attached to the crystals of this reference example, the crude nicotinic acid after oxidation was recrystallized in 5% hydrous acetic acid and then analyzed. Bromine in nicotinic acid was measured by fluorescent X-ray analysis. The dissolution b value is a Hunter scale b value measured by a color difference meter using 1 part by weight of nicotinic acid dissolved in 10 parts by weight of a 1N sodium hydroxide aqueous solution and using transmitted light in a 10 mm cell, and indicates the hue of nicotinic acid. Is.

Reference Example 1 50 parts by weight of 3-methylpyridine and cobalt acetate were placed in an autoclave equipped with a stirrer, a gas introduction pipe, and a reflux device for the generated steam.
Charge 0.76 parts by weight, manganese acetate 0.54 parts by weight, tetrapropylammonium bromide 2 parts by weight and 5% water-containing acetic acid 150 parts by weight, and at a temperature of 210 ° C and a pressure of 25 kg / cm ² G, 60 Nl (normal liter) / Air was supplied at a rate of hr while stirring was continued. About until oxygen absorption is exhausted
After reacting for 2.3 hours and cooling the reaction-terminated liquid to 0 ° C., 43.4 parts by weight of crude nicotinic acid was obtained by filtering the precipitated nicotinic acid crystals, washing with acetic acid, and drying. The crude nicotinic acid was recrystallized from 4 times by weight of 5% hydrous acetic acid and analyzed. As a result, the bromine concentration was 470 ppm, and the dissolved b value was 5.10.
Met.

Example 1 20 parts by weight of crude nicotinic acid (bromine concentration: 470 ppm, dissolution b value: 5.10) obtained in Reference Example 1 in an autoclave equipped with a stirrer, a gas introduction tube, and a generated vapor refluxing device, 1% by weight 1 part by weight of a catalyst prepared by supporting palladium on activated carbon and 200 parts by weight of water were charged, hydrogen was charged at a pressure of 6 kg / cm ² G, and stirring was continued at a temperature of 130 ° C. for 2 hours. The reaction completion liquid was filtered at high temperature to remove the catalyst palladium-supporting activated carbon, and the obtained filtrate was cooled to room temperature and the precipitated nicotinic acid crystals were filtered, washed with water and dried to obtain 9.4 parts by weight of purified nicotinic acid. Was obtained. This nicotinic acid contained 5 ppm of bromine and had a dissolved b value of 1.19.

Reference Example 2 25 parts by weight of 3-methylpyridine and cobalt acetate were placed in an autoclave equipped with a stirrer, a gas inlet tube, and a reflux device for the generated steam.
0.38 parts by weight, 0.27 parts by weight of manganese acetate, 1 part by weight of tetrapropylammonium bromide and 150 parts by weight of acetic acid containing 5% water were charged, and air was supplied at a rate of 60 Nl / hr at a temperature of 210 ° C and a pressure of 25 kg / cm ² G. It was fed while stirring was continued. The reaction was carried out for about 1.6 hours until oxygen absorption stopped, and the reaction completed liquid was cooled to 0 ° C., and the precipitated nicotinic acid crystals were filtered, washed with acetic acid and dried to obtain 21.7 parts by weight of crude nicotinic acid. This crude nicotinic acid was recrystallized in 4 times by weight 5% hydrous acetic acid and analyzed.
The value was 608 ppm and the dissolved b value was 5.44.

Example 2 Crude nicotinic acid obtained in Reference Example 2 (bromine concentration 608 ppm, dissolved b
(Value 5.44) 20 parts by weight, 0.5 parts by weight of a catalyst obtained by supporting 1% by weight of palladium on activated carbon was purified under the same conditions as in Example 1 using 100 parts by weight of water as a solvent. As a result, 11.2 parts by weight of purified nicotinic acid was obtained. When this nicotinic acid was analyzed, the dissolved b value was 2.03 at a bromine concentration of 31 ppm.

Example 3 Purification was carried out in the same manner as in Example 2 except that the solvent was 100 parts by weight of acetic acid containing 20% by weight of water. As a result, 9.7 parts by weight of purified nicotinic acid was obtained. This nicotinic acid contained 14 ppm of bromine and had a dissolved b value of 1.55.

[0017]

As is clear from the examples, catalytic hydriding treatment of crude pyridinecarboxylic acids obtained by liquid phase air oxidation of alkylpyridines by the method of the present invention markedly reduces the content of bromine impurities. At the same time, the hue of the product is improved. The method of the present invention can be easily carried out industrially, and the industrial significance of the present invention is great.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location // C07B 61/00 300 C07B 61/00 300

Claims (2)

[Claims] 1. A pyridine characterized in that a crude pyridinecarboxylic acid obtained by liquid-phase oxidation of an alkylpyridine is subjected to catalytic hydrogenation treatment at a temperature of 100 to 250 ° C. in the presence of a Group VIII metal catalyst. Method for purifying carboxylic acid. 2. The method for purifying pyridinecarboxylic acid according to claim 1, wherein the catalytic hydrogenation treatment is carried out using a solvent of water and / or acetic acid.