JP4467343B2 - Method for producing 2,6-naphthalenedicarboxylic acid - Google Patents

Description

  The present invention includes a step of acidifying after di-lower alkyl ester of 2,6-naphthalenedicarboxylic acid is hydrolyzed in the presence of a basic compound to obtain a solution of 2,6-naphthalenedicarboxylic acid dicarboxylate. The production method of 2,6-naphthalenedicarboxylic acid.

  2,6-naphthalenedicarboxylic acid (hereinafter referred to as 2,6-NDA) is an important compound as a monomer for various polymers such as polyethylene naphthalate, liquid crystalline polyester, and polyamide. Further, 2,6-naphthalenedicarboxylic acid di-lower alkyl ester (hereinafter referred to as 2,6-NDC) is important as a monomer for various polymers, like 2,6-NDA. Of 2,6-NDC, 2,6-naphthalenedicarboxylic acid dimethyl ester is the most important and widely used because of its physical properties such as melting point and ease of use as a monomer.

  Conventionally, 2,6-NDA is produced by using naphthalene substituted at the 2,6-position with an alkyl group and / or an acyl group and a heavy metal such as cobalt or manganese as a catalyst, and then converting the alkyl group and / or acyl group into a molecule. A production method that oxidizes with gaseous oxygen is known. However, the crude 2,6-NDA obtained by this method contains impurities such as aldehyde-type intermediates and oxidation polymers, so it cannot be used directly as a polymer monomer. there were. For this reason, various purification methods have been studied for the crude 2,6-NDA obtained by the above method.

  As a method for purifying crude 2,6-NDA, for example, 2,6-NDA was obtained by esterification of crude 2,6-NDA with a lower alcohol such as methanol and then by distillation, recrystallization and the like. Later, a method for decomposing an ester group to obtain 2,6-NDA with high purity is generally known.

  As a method of producing high purity 2,6-NDA by decomposing the ester group of 2,6-NDC, a method of decomposing the ester group with an acid catalyst, or decomposing the ester group with water under specific conditions A method and a method of decomposing an ester group with a basic catalyst have been proposed.

  As a method for decomposing an ester group with an acid catalyst, a method is known in which the ester group of 2,6-NDC is decomposed in the presence of an acid catalyst and an aliphatic carboxylic acid to obtain 2,6-NDA of high purity. (See Patent Document 1). However, this method has a problem that a long time is required for the reaction, and aliphatic carboxylic acid esters are generated as a by-product in the ester group decomposition step.

  A method for decomposing ester groups under certain conditions with water includes a sufficient amount of water to solubilize at least about 10% of the 2,6-NDA produced at the reaction temperature under liquid phase conditions. There is known a method of hydrolyzing the ester group of 2,6-NDC at a reaction temperature of at least 450 degrees Fahrenheit (232 degrees Celsius) in the presence of (see Patent Document 2). However, this method requires a very high temperature of 450 degrees Fahrenheit, or requires a reaction at a high pressure by reacting at a temperature much higher than the boiling point of water. It is accompanied by.

As a method for decomposing an ester group with a basic catalyst, hydrolysis of the ester group with a basic catalyst in water or a mixed solvent of water and a water-miscible organic solvent is performed, and then 2,6-NDA is obtained by acid precipitation. A method of collecting is known (see Patent Document 3). However, in this method, the solubility of 2,6-NDC in water or a mixed solvent of water and a water-miscible organic solvent is so small that 2,6-NDC is not completely hydrolyzed or completely dissolved. There is a problem that it takes a long time to hydrolyze.
JP-A-6-256256 JP-T 6-505512 JP-A-3-240750

  It is an object of the present invention to provide a method for producing high-purity 2,6-NDA in a short time with a simple process that does not require special conditions and does not require severe conditions such as high temperature and high pressure. To do.

  The present inventors include a step of hydrolyzing 2,6-NDC in the presence of a basic compound to obtain a 2,6-NDA carboxylate solution and then acidifying it. As a result of intensive investigations on the production method of 1,6-NDA, first, in the presence of a small amount of water, first hydrolysis with a basic compound is performed in an organic solvent freely mixed with water, and 2,6-NDC is hydrolyzed. After being almost converted to a 2,6-NDA monoester or 2,6-NDA carboxylate by decomposition, a large amount of water is added to perform a second hydrolysis, which is obtained by the second hydrolysis. It was found that high purity 2,6-NDA can be obtained quickly by acidifying the obtained reaction solution, and the present invention has been completed.

That is, the present invention comprises a step of hydrolyzing 2,6-NDC in the presence of a basic compound to obtain a 2,6-NDA dicarboxylate solution, and then acidifying it. -The manufacturing method of 2,6-NDA characterized by including the process of the following (1)-(3) in the manufacturing method of NDA.
(1) A basic compound in an organic solvent that is freely miscible with 5 to 20 times the weight of 2,6-NDC in the presence of 2 to 10 moles of water with respect to 1 mole of 2,6-NDC And a first hydrolysis step in which 2,6-NDC is reacted until 80% or more of 2,6-NDC is converted.
(2) A second hydrolysis step in which 5 to 20 times weight of water is added to the first hydrolysis reaction solution with respect to 2,6-NDC charged in step (1) and further reacted.
(3) A step of acidifying the second hydrolysis reaction solution to obtain 2,6-naphthalenedicarboxylic acid.
In the present specification and claims, the term “lower” means one having 1 to 6 carbon atoms.

The 2,6-NDC used in the present invention may be obtained by any conventionally known method. For example, naphthalene substituted at the 2,6 position with an alkyl group and / or an acyl group is obtained by oxidizing a alkyl group and / or an acyl group with molecular oxygen using a heavy metal such as cobalt or manganese as a catalyst. The obtained crude 2,6-NDA can be obtained by reacting with a lower alcohol or the like in the presence of an acid catalyst such as sulfuric acid or p-toluenesulfonic acid.
The lower alkyl in 2,6-NDC may be any straight-chain or branched saturated hydrocarbon group having 1 to 6 carbon atoms, but methyl is preferred from the standpoint of availability. .

The method of the present invention is characterized in that the first hydrolysis of 2,6-NDC is carried out in an organic solvent freely mixed with water in the presence of a small amount of water necessary for hydrolysis.
The amount of water present in the system during the first hydrolysis is 2 to 10 mol, preferably 4 to 6 mol, relative to 2,6-NDC.

  Examples of organic solvents that are freely mixed with water used in the present invention include alcohol solvents such as methanol, ethanol, isopropanol, 2-methoxyethanol, 2-ethoxyethanol, ethylene glycol, glycerin and polyethylene glycol 200, and acetone. Examples include ketone solvents, aprotic polar solvents such as N, N-dimethylacetamide, N, N-dimethylformamide, dimethyl sulfoxide, hexamethylphosphoramide, and N-methyl-2-pyrrolidone. The organic solvent that is freely miscible with water may be used alone or in combination of two or more selected from the above group.

  Among the above-mentioned solvents, alcohol solvents are preferable because they are easily purified by distillation, are stable under basic hydrolysis conditions, and have little deterioration in quality.

  In the first hydrolysis step of the present invention, the amount of the organic solvent that is freely miscible with water is 5 to 20 times the weight, preferably 7 to 10 times the weight of 2,6-NDC. If the weight of the organic solvent that is freely mixed with water is less than 5 times the weight of 2,6-NDC, the slurry concentration of the reaction solution is high, so that the stirring situation is deteriorated and the reaction rate is lowered. If it is more than 20 times the weight, the amount of 2,6-NDA dissolved in the mother liquor after acid precipitation increases, which causes a problem in terms of yield.

  In the present invention, the basic compound used for hydrolysis is preferably an alkali metal compound. Examples of the alkali metal compound include alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, alkali metal carbonates such as sodium carbonate and potassium carbonate, alkali metal hydrogen carbonates such as sodium hydrogen carbonate and potassium hydrogen carbonate, Examples include alkali metal lower alkoxides such as sodium methoxide and potassium methoxide.

The basic compound such as an alkali metal compound may be used as a solid, or may be added as an aqueous solution or a solution of an organic solvent that is freely miscible with water.
The amount of the basic compound used is preferably 1.0 to 5.0 equivalents, particularly preferably 1.1 to 2.0 equivalents, relative to the ester group of 2,6-NDC.

In the present invention, the first hydrolysis is preferably performed at 40 to 100 ° C. More preferably, it is good to carry out at 60-100 degreeC. More preferably, although it depends on the solvent, the reaction should be carried out at reflux temperature at the boiling temperature in the system.
The first hydrolysis reaction time is preferably 1 to 5 hours.

The analysis means for confirming the conversion of 2,6-NDC indicating the end of the first hydrolysis is not particularly limited, but can be confirmed by a method such as high performance liquid chromatography.
Here, the conversion of 2,6-NDC means that 2,6-NDC is converted into a salt of a monoester of 2,6-NDA or a dicarboxylate of 2,6-NDA by a hydrolysis reaction. .

  The conversion rate of 2,6-NDC in the first hydrolysis reaction is preferably 80% or more, particularly preferably 90% or more, and more preferably 95% or more with respect to the charged amount. .

  The amount of hydrolysis in the second hydrolysis step of the present invention is 5 to 20 times, preferably 7 to 10 times the weight of 2,6-NDC charged in the first hydrolysis step. If the amount of water added is 5 times or less, 2,6-NDA monoester salt is likely to precipitate, resulting in a slow reaction rate. When the amount of water added is more than 20 times the weight, there is a problem that the volumetric efficiency is deteriorated.

The reaction temperature in the second hydrolysis may be the same as the conditions described in the first hydrolysis.
The second hydrolysis reaction time is preferably 0.5 to 2 hours.

To remove 2,6-NDA dicarboxylate solution obtained by the method of the present invention, if necessary, filtration for removing insoluble foreign substances, coloring substances, metals, etc. Adsorbent treatment using activated carbon or the like may be performed.
In addition, before acid precipitation, in order to prevent salt from being mixed into 2,6-NDA due to precipitation of salts caused by acid precipitation, an amount of water similar to that added in the second hydrolysis step is further added. You may add to a reaction liquid.

  The acid used in the acid precipitation step in the present invention is not particularly limited, but a mineral acid is preferably used. Examples of the mineral acid include binary acids such as hydrochloric acid and hydrofluoric acid, and oxo acids such as sulfuric acid, nitric acid, phosphoric acid, and perchloric acid.

  The 2,6-NDA slurry obtained by acid precipitation is separated by conventional methods such as centrifugation and filtration with a filter press. The separated 2,6-NDA is dried after being washed with cold water or hot water as necessary.

  The 2,6-NDA thus obtained is suitably used as a monomer for various polymers such as polyethylene naphthalate, liquid crystalline polyester, and polyamide.

Hereinafter, the present invention will be described in detail by way of examples.
Example 1
To a 2L glass four-necked Kolben equipped with a stirrer, thermometer, and Jimroth condenser, 2,6-naphthalenedicarboxylic acid dimethyl ester 40 g (0.164 mol), methanol 400 g, and 48% sodium hydroxide 28.6 g was charged. The water content at the start of the reaction was 5 times moles relative to 2,6-naphthalenedicarboxylic acid dimethyl ester.
The temperature was raised to 65 ° C. with stirring, and the reaction was performed for 1.5 hours as the first hydrolysis under reflux. At the time of 1.5 hours of reaction, the reaction solution was sampled, and 2,6-naphthalenedicarboxylic acid dimethyl ester was converted into 2,6-NDA monomethyl ester and 2,6-NDA salt by high performance liquid chromatography. 100% conversion was confirmed.
After adding 400 g of water to the reaction solution, the temperature was raised to 74 ° C., and the reaction was further performed for 30 minutes as the second hydrolysis. Thereafter, 400 g of water was added to the reaction solution, the temperature was raised to 80 ° C., 62 g of 30% sulfuric acid aqueous solution was dropped over 30 minutes and acidified to obtain a 2,6-NDA suspension.
The obtained 2,6-NDA suspension was subjected to suction filtration, washed with warm water, and dried. As a result, 35.4 g (0.164 mol, yield> 99%) and 2,6-NDA crystals were obtained. Obtained quantitatively.

(Examples 2 to 7)
2,6-NDA was prepared in the same manner as in Example 1 except that the solvent and reaction temperature were changed to the conditions shown in Table 1. In any case, when the first hydrolysis reaction was carried out for 1.5 hours, the reaction solution was sampled, and 2,6-naphthalenedicarboxylic acid dimethyl ester was converted to 2,6-NDA monomethyl ester by high performance liquid chromatography. And almost 100% conversion to 2,6-NDA salt.

(Comparative Example 1)
To a 2 L glass four-necked colben fitted with a stirrer, thermometer, and Jimroth condenser, 2,6-naphthalenedicarboxylic acid dimethyl ester 40 g (0.164 mol), 50 wt% aqueous methanol solution 800 g, and 48% sodium hydroxide (28.6 g) was charged.
The temperature was raised to 90 ° C. with stirring, and the reaction was carried out for 5 hours under reflux. At the time of 5 hours of reaction, the reaction solution was sampled and analyzed by high performance liquid chromatography.
As a result of the analysis, the ratio in the reaction solution was about 40% by weight of 2,6-naphthalenedicarboxylic acid dimethyl ester, about 40% by weight of 2,6-naphthalenedicarboxylic acid monomethyl ester, and about 20% by weight of 2,6-naphthalenedicarboxylic acid. In the reaction time of 5 hours, the hydrolysis reaction did not proceed completely.
Thus, when a one-stage hydrolysis reaction was performed in the presence of a large amount of water, 2,6-NDA could not be obtained efficiently.

Claims (4)

A step of hydrolyzing a di-lower alkyl ester of 2,6-naphthalenedicarboxylic acid in the presence of a basic compound to obtain a solution of a dicarboxylic acid salt of 2,6-naphthalenedicarboxylic acid, and then acidifying it. The method for producing 2,6-naphthalenedicarboxylic acid, comprising the following steps (1) to (3) :
(1) 2,6-naphthalene in the presence of 2 to 10 moles of water against the di-lower alkyl ester le of dicarboxylic acid, 5 to 20-fold weight relative to di-lower alkyl ester of 2,6-naphthalene dicarboxylic acid , Methanol, ethanol, isopropanol, 2-methoxyethanol, 2-ethoxyethanol, ethylene glycol, glycerin, polyethylene glycol 200, acetone, N, N-dimethylacetamide, N, N-dimethylformamide, dimethyl sulfoxide, hexamethyl phosphor In one or more organic solvents selected from the group consisting of amide and N-methyl-2-pyrrolidone , a basic compound and a di-lower alkyl ester of 2,6-naphthalenedicarboxylic acid are mixed with 2,6 80 di-lower alkyl esters of naphthalenedicarboxylic acid The first hydrolysis step of reacting until or converted;
(2) A second hydrolysis step in which 5 to 20 times weight of water is added to the first hydrolysis reaction solution with respect to the di-lower alkyl ester of 2,6-naphthalenedicarboxylic acid charged in step (1) and further reacted. ;and,
(3) A step of acidifying the second hydrolysis reaction solution to obtain 2,6-naphthalenedicarboxylic acid. Organic solvent, methanol, ethanol, isopropanol, 2-methoxyethanol, 2-ethoxyethanol, ethylene glycol, according to claim 1 at least one is selected from the group consisting of glycerol and polyethylene glycol 200 2,6 -Method for producing naphthalenedicarboxylic acid. The 2,6-naphthalenedicarboxylic acid according to claim 1 or 2 , wherein the basic compound is selected from the group consisting of alkali metal hydroxides, alkali metal carbonates, alkali metal bicarbonates, and lower alkoxides of alkali metals. Production method. The amount of a basic compound is 1.0-5.0 equivalent with respect to the ester group of the di-lower alkyl ester of 2, 6- naphthalene dicarboxylic acid, The 2,6 in any one of Claims 1-3 -Method for producing naphthalenedicarboxylic acid.