JPH06256256A - Production of highly pure 2,6-naphthalene dicarboxylic acid - Google Patents

Abstract

PURPOSE:To provide a method for producing highly pure 2,6-naphthalene dicarboxylic acid applicable as a raw material for functional polymers from dimethyl 2,6-naphthalene dicarboxylate produced by a general method as a raw material. CONSTITUTION:This is a method for producing highly pure 2,6-naphthalene dicarboxylic acid by decomposing dimethyl 2,6-naphthalene dicarboxylate ester in the presence of an acid catalyst in an organic solvent is characterized by adding a lower aliphatic carboxylic acid to the reaction system and distilling out the by-produced methyl lover aliphatic carboxylate ester.

Description

Detailed Description of the Invention

[0001]

This invention relates to a high performance polyester,
The present invention relates to a method for producing high-purity 2,6-naphthalenedicarboxylic acid useful as a raw material for high-performance polymers such as liquid crystal polyester and polyamide.

[0002]

2. Description of the Related Art 2,6-naphthalenedicarboxylic acid (hereinafter referred to as 2,
6-NDCA), a method of oxidizing 2,6-dialkylnaphthalene with a heavy metal and a bromide, or a Co or Mn catalyst (JP-B-48-43893, JP-A-48-34153, and JP-A-48-34153). Kaisho
60-89445), 2-alkyl-6-acylnaphthalene as C
Oxidation with a Br catalyst, Co, Mn, Br catalyst, or a catalyst in which Fe or Cu is added thereto (JP-A-62-61946, JP-A-62-61946)
-67048, JP-A-62-42946, JP-A-1-180851, etc.) are known. 2,6-obtained by these oxidation reactions
NDCA contains intermediates such as aldehydes, impurities such as oxidative polymers, and impurities derived from raw materials.

The following method is known as a method for producing high-purity 2,6-NDCA by purifying 2,6-NDCA obtained by the above method. (1) In JP-B-45-13096, 2,6-NDCA is dissolved in an alkaline aqueous solution, the dialkali salt precipitated by concentration is dissolved in water, carbon dioxide gas is blown to precipitate a monoalkali salt,
A method of dissolving the separated monoalkali salt in water and heating to disproportionate to precipitate 2,6-NDCA, (2) in Japanese Examined Patent Publication No. 57-36901, an aqueous alkaline solution of 2,6-NDCA is used. 220 ° C
In the presence of a catalyst such as palladium, platinum or ruthenium at the following temperature, catalytic hydrogenation is performed, carbon dioxide gas is blown to precipitate a monoalkali salt, and the separated monoalkali salt is dissolved in water and heated to disproportionate. A method of precipitating 2,6-NDCA,
(3) In JP-A-48-54051, 2,6-NDCA is dissolved in an alkaline aqueous solution, heated to 100 to 250 ° C., decolorized and concentrated with activated carbon to precipitate a dialkali salt, and the dialkaline is further deposited. A method is disclosed in which a salt is made into an aqueous solution again, and an acid is added to cause precipitation.

Further, (4) Japanese Patent Laid-Open No. 62-212342 discloses 2,6-ND.
CA is added to an aqueous solution containing an alkali and a neutral salt of the same cation as the alkali and stirred to precipitate as a dialkali salt, and the separated dialkali salt is added in an amount of 1 to 3 wt.
% Sodium chloride aqueous solution, treated with activated carbon and acid precipitation with carbon dioxide or sulfur dioxide,
(5) In JP-A-62-230747, 2,6-NDCA is dissolved in an organic solvent such as N, N-dimethylacetamide, N, N-dimethylformamide, dimethylsulfoxide at 80 to 189 ° C and treated with activated carbon. , -15 to 40 ° C. and recrystallization.

Further, in Japanese Patent Application Laid-Open No. 64-294909, (6) 2,6-NDC
A to 100-200 in methanol solvent in the presence of sulfuric acid catalyst
Dimethyl 2,6-naphthalenedicarboxylate (hereinafter referred to as 2,6-NDCM), which was esterified at a temperature of ℃, distilled, recrystallized, and purified to 99% or more by a solid adsorbent, etc. A method is disclosed in which a group-valent polycarboxylic acid is used for hydrolysis at 200 to 230 ° C. in an inert gas-substituted Zr autoclave. Also, as a well-known method (7)
There is a method in which the 2,6-NDCM obtained by the above method is saponified in an alkali to form a dialkali salt, and an acid is added to cause precipitation.

[0006]

As described above, 2,6-NDCA produced by a usual method contains impurities, and when a polymer is produced by using this, a sufficiently high yield is obtained. It is inevitable that a polymer having a molecular weight cannot be obtained, mechanical properties and heat resistance are deteriorated, and quality is deteriorated due to coloring. In order to obtain a high-quality polymer, it is required that the purity is at least 99% or higher, and the high-purity 2,6-NDCA with little coloring is required.

Therefore, various refining methods as described above have been proposed, but none of them are satisfied.
That is, by precipitating a monoalkali salt and disproportionating the separated monoalkali salt, in the method of (1) and (2), in the step of precipitating a monoalkali salt by adjusting pH, a monoalkali salt and a dialkali salt are added. Since the acid has a delicate equilibrium relationship, it is difficult to control the crystal composition and the amount of precipitation. Further, since the monoalkali salt is water-soluble, the monoalkali salt is eluted when washing the mother liquor attached to the crystals after separation by filtration,
The recovery rate of 6-NDCA decreases. It also has a step of precipitating 2,6-NDCA from the dialkaline salt aqueous solution by acid precipitation (3)
In methods (4) and (4), fine crystals of about 1 μ are deposited during this acid precipitation, which makes filtration and washing extremely difficult.

Recrystallization using an organic solvent (5)
In this method, expensive organic solvents such as N, N-dimethylacetamide, N, N-dimethylformamide, and dimethylsulfoxide must be used in large amounts, and these organic solvents are odorous and toxic. It is difficult to handle and difficult to carry out industrially. In addition, in the method of (7), which has a step of saponifying the purified 2,6-NDCM and precipitating 2,6-NDCA by acid precipitation, in the same manner as (3) and (4) above, during the acid precipitation, Fine crystals of about 1μ are deposited on the surface, which makes filtration and washing very difficult. Further, in the method (6) of hydrolyzing with an aromatic polycarboxylic acid as a catalyst, the reaction is carried out using an acid catalyst under high temperature and high pressure. In the device, pressure resistance becomes a problem, and the material of the reaction device is limited.

The present inventors have conducted extensive studies on a method of obtaining high purity 2,6-NDCA by ester-decomposing 2,6-NDCM under normal pressure using an acid catalyst in an organic solvent. By allowing a lower aliphatic carboxylic acid to exist in the system and distilling the resulting lower aliphatic carboxylic acid out of the system, 2,6-NDCA can be obtained in a high yield, and a small amount of water is added. I found that the reaction speed increased by this,
The present invention has been completed based on this finding. That is, the present invention, 2,6-naphthalenedicarboxylic acid dimethyl ester having a purity of 99% or more in the presence of an acid catalyst in an organic solvent,
When the ester is decomposed, one or more lower aliphatic carboxylic acid having 1 to 5 carbon atoms is present in the reaction system in an amount corresponding to at least twice the molar amount of 2,6-naphthalenedicarboxylic acid dimethyl ester, and the temperature is kept at 100 ° C or higher. It is a method for producing high-purity 2,6-naphthalenedicarboxylic acid, which comprises heating at 250 ° C. and distilling the produced lower aliphatic carboxylic acid methyl ester out of the system.

The raw material 2,6-NDCM to which the method of the present invention is applied is
By the method as described above, 2,6-dialkylnaphthalene or 2-
It is obtained by esterifying 2,6-NDCA obtained by oxidizing alkyl-6-acylnaphthalene. The lower aliphatic carboxylic acid used in the present invention is a compound having 1 to 5 carbon atoms, and specifically, formic acid, acetic acid, propionic acid, butyric acid, isobutyric acid, valeric acid,
Isovaleric acid, particularly preferably acetic acid. Aliphatic carboxylic acids having 6 or more carbon atoms have problems in handling,
It is also expensive and not economical. The amount of the lower aliphatic carboxylic acid used in the present invention is 2 to 50 with respect to the raw material 2,6-NDCM.
It is a double mole, preferably 25 to 40 moles. If it is less than 2 times by mole, unreacted methyl ester groups remain, and if it exceeds 50 times by mole, the reaction rate does not change and it is not economical. The solvent used in the present invention is benzene, toluene, xylene, chlorobenzene, bromobenzene, dichlorobenzene, dibromobenzene, dimethylsulfoxide, an aliphatic carboxylic acid, or an anhydride thereof, and the lower aliphatic carboxylic acid as a reaction agent is used as it is. You may use it as a solvent. The amount of solvent is such that the total amount of the lower aliphatic carboxylic acid as a reaction agent and the solvent is 5 to 20 times by weight, preferably 7 to 6 times the raw material 2,6-NDCM.
~ 12 times the weight. If it is less than 5 times by weight, the reaction rate is lowered due to deterioration of the slurry property of the reaction system, and if it is more than 20 times by weight, the reaction rate does not change, so that it is not economical.

The acid catalyst used in the present invention is a mineral acid or an organic sulfonic acid, preferably sulfuric acid, hydrochloric acid, nitric acid, p-toluenesulfonic acid, and more preferably sulfuric acid. The catalyst concentration is 1 to 40% by weight, preferably 8 to 25% by weight, based on the whole system. If the catalyst concentration is less than 1% by weight, the reaction rate decreases, and if the catalyst concentration exceeds 40% by weight, the product may be colored, which is not preferable. The amount of water used in the present invention is 0 to 2 times, preferably 0.2 to 1.5 times the mol of 2,6-NDCM. If the amount exceeds 2 times the molar amount, the solubility of 2,6-NDCM in the solvent becomes small and the reaction rate decreases.

The reaction temperature in the method of the present invention varies depending on the type of solvent, but is 80 to 250 ° C., preferably
100-190 ℃. At temperatures lower than 80 ° C, the reaction rate is low, and at temperatures above 250 ° C, the corrosiveness of the catalyst is high, so special reaction equipment must be used. The reaction pressure in the method of the present invention is defined by the reaction temperature, but is preferably atmospheric pressure to 3 kg / cm ² , more preferably atmospheric pressure. The reaction time can be appropriately selected, but is usually 3 to 24.
Hours, preferably 6 to 12 hours. If the reaction time is less than 3 hours, the reaction will not proceed completely, and if the reaction time is more than 24 hours, the reaction rate will be improved only slightly, which is not economical.

Since the reaction proceeds by distilling the produced aliphatic carboxylic acid methyl ester out of the system, it is necessary to efficiently remove the aliphatic carboxylic acid methyl ester in the reaction system. For that purpose, it is preferable that a reactor is provided with a dephlegmator to separate the aliphatic carboxylic acid methyl ester from the solvent and the aliphatic carboxylic acid, and to guide only the aliphatic carboxylic acid methyl ester to the outside of the reaction system. .
At that time, circulating an inert gas such as nitrogen, argon, or helium in the reaction system is effective for improving the reaction rate in the latter half of the reaction.

After the completion of the reaction, the reaction solution is gradually cooled to room temperature to precipitate 2,6-NDCA. Precipitated 2,6-ND
CA can be separated by a known solid-liquid separation method such as pressure filtration, vacuum filtration, or centrifugation. The separated 2,6-NDCA is washed with an appropriate washing solvent until the unreacted aliphatic carboxylic acid, catalyst and solvent are removed, and then dried to obtain highly pure 2,6-NDCA. can get.
As the cleaning solvent, water, methanol, ethanol, acetone, methyl ethyl ketone and the like are preferable. When using an aliphatic carboxylic acid and acetic acid as the reaction solvent, water can be used as the washing solvent, which is one of the preferred embodiments. After separation, the reaction liquid containing the solvent and the catalyst has the same composition as the initial charge by supplementing the solvent and the catalyst lost by adhering to the aliphatic carboxylic acid and 2,6-NDCA consumed in the reaction. A reaction solution is obtained and can be used as the next reaction solution. After that, the reaction solution recovered by the same operation can be repeatedly used. The solution may become colored after repeated use, but the resulting 2,6-ND
It does not affect the CA tone.

[0015]

Industrial Applicability The method of the present invention does not require the use of a large amount of alkali which causes the mixing of inorganic ions, the use of an expensive solvent, the use of a special reaction apparatus, and the use of a relatively inexpensive solvent or catalyst. In addition, high-purity 2,6-NDCA can be recovered in high yield under mild conditions of atmospheric pressure to 3 kg / cm ² . Also 2,
After separating 6-NDCA, the recovered reaction solution can be used repeatedly by supplementing the amount of lower aliphatic carboxylic acid and catalyst lost by the reaction or adhesion to the product, which is extremely industrially advantageous. That's the method.

[0016]

EXAMPLES Next, the present invention will be described more specifically by way of examples. However, the present invention is not limited to these examples. Example 1 2,6-NDCM (24.4 g) and acetic acid (180 ml) were placed in a 500 ml four-necked flask equipped with a condenser (60 ° C. hot water) and a total condenser at the tip.
ml, 97% sulfuric acid 31 ml, and water 9 ml were charged, and the temperature was raised to 118 to 119 ° C., the boiling point of acetic acid, with stirring under a nitrogen stream of 0.3 l / min to start the reaction. The reaction was continued for 6 hours while distilling out methyl acetate produced by ester decomposition from the system. After completion of the reaction, the mixture was cooled to room temperature and the white solid deposited was filtered off. The white solid separated by filtration was washed with water until the filtrate became neutral, and then dried at 130 ° C. for 12 hours to obtain 2,6-NDCA. The results are shown in Table 1. The obtained white powder 2,6-NDCA had a L-value of 97.78, an a-value of -0.10, and a b-value of 1.00 as measured by a color difference meter.
Almost no impurities could be confirmed by analysis by liquid chromatography. The acid value of this powder is 517mgKOH /
g (theoretical acid value of 2,6-NDCA is 519 mgKOH / g), and the powder was confirmed to be pure 2,6-NDCA. The yield was 21.2 g, and the yield was 98%.

Example 2 Example 1 was repeated except that water was not present in the reaction system.
The reaction was carried out under the same conditions as above. The results are shown in Table 1. Example 3 After the completion of the reaction in Example 1, the filtrate was recovered, except that the reaction solution supplemented with the lost acetic acid, sulfuric acid, and water was used.
The reaction was carried out in the same manner as in Example 1. The results are shown in Table 1. Example 4 A reaction was performed in the same manner as in Example 1 except that 30 g of p-toluenesulfonic acid was used instead of sulfuric acid. The results are shown in Table 1.

Comparative Example 1 2,6-NDCM was hydrolyzed in a water solvent at 100 ° C. at 100 ° C. in a water solvent without adding a lower aliphatic carboxylic acid.
After a long time, the reaction did not proceed and 2,6-NDCA was not obtained. Comparative Example 2 The ester decomposition reaction of 2,6-NDCM was carried out for 6 hours using acetic acid as a solvent without adding an acid catalyst and water, but the reaction did not proceed.
6-NDCA was not obtained.

[0019]

[Table 1]

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁵ Identification code Internal reference number FI Technical display location B01J 31/02 103 31/04 C07C 51/09 69/76 A 9279-4H // C07B 61/00 300 (72) Inventor Ryoji Otaki 5-6-2 Higashi-Hachiman, Hiratsuka City, Kanagawa Sanryo Gas Chemical Co., Ltd. Plastics Center

Claims (5)

[Claims] 1. When the ester decomposition of 2,6-naphthalenedicarboxylic acid dimethyl ester having a purity of 99% or more is carried out in an organic solvent in the presence of an acid catalyst, the amount of the reaction product is adjusted to 2 times or more the molar amount of 2,6-naphthalenedicarboxylic acid dimethyl ester. A corresponding amount of one or more lower aliphatic carboxylic acid having 1 to 5 carbon atoms is allowed to exist in the reaction system and heated to 80 ° C to 250 ° C to distill the produced lower aliphatic carboxylic acid methyl ester out of the system. A method for producing high-purity 2,6-naphthalenedicarboxylic acid, which comprises erasing. 2. High purity 2, according to claim 1, wherein a mineral acid and / or an organic sulfonic acid is used as the acid catalyst.
Process for producing 6-naphthalenedicarboxylic acid. 3. The method for producing high-purity 2,6-naphthalenedicarboxylic acid according to claim 1, wherein acetic acid is used as the lower aliphatic carboxylic acid. 4. The high purity according to claim 1, wherein water is present in the reaction system in an amount not exceeding twice the mole of 2,6-naphthalenedicarboxylic acid dimethyl ester.
Process for producing 2,6-naphthalenedicarboxylic acid. 5. The high purity according to claim 1, wherein the solvent, the lower aliphatic carboxylic acid and the catalyst are repeatedly used.
Process for producing 2,6-naphthalenedicarboxylic acid.