JP5318596B2 - Method for producing 2,6-naphthalenedicarboxylic acid - Google Patents

Description

  The present invention relates to a dialkali metal salt of 2,6-naphthalenedicarboxylic acid obtained by reacting a di-lower alkyl ester of 2,6-naphthalenedicarboxylic acid with a basic alkali metal compound in the presence of an aqueous medium. The present invention relates to a method for producing 2,6-naphthalenedicarboxylic acid, which comprises a step of acidifying a solution.

  2,6-naphthalenedicarboxylic acid (hereinafter, 2,6-naphthalenedicarboxylic acid is sometimes referred to as 2,6-NDA) is important as a monomer for various polymers such as polyethylene naphthalate, liquid crystalline polyester, and polyamide. A compound. Further, di-lower alkyl esters such as dimethyl ester of 2,6-naphthalenedicarboxylic acid (hereinafter, di-lower alkyl esters of 2,6-naphthalenedicarboxylic acid may be referred to as 2,6-NDC) From the viewpoint of physical properties and ease of use as a monomer, it is widely used as a monomer for various polymers in the same manner as 2,6-NDA.

  Conventionally, as a method for producing 2,6-NDA, an alkyl group and / or an acyl group is obtained by using naphthalene substituted at the 2,6-position with an alkyl group and / or an acyl group and using a heavy metal such as cobalt or manganese as a catalyst. A production method is known in which is oxidized with molecular oxygen. However, the crude 2,6-NDA obtained by this method cannot be used directly as a monomer for a polymer because it contains impurities such as aldehyde-type intermediates and oxidized polymers.

  For this reason, various purification methods have been studied for the crude 2,6-NDA obtained by the above method.

  For example, by esterifying crude 2,6-NDA with a lower alcohol such as methanol to 2,6-NDC, and then purifying 2,6-NDC by distillation, recrystallization, etc., followed by decomposition of the ester group, Methods for obtaining high purity 2,6-NDA are generally known.

  As a method for producing high purity 2,6-NDA by decomposing the ester group of 2,6-NDC, the ester group is decomposed with a basic alkali metal compound by using water and / or an organic solvent as a solvent. , 6-NDA salt solution is obtained, and then 2,6-NDA is recovered by acid precipitation (see Patent Documents 1 to 4).

  However, these methods have a problem that a large amount of alkali metal is contained in the obtained 2,6-NDA, and a problem that the process is complicated such that a liquid separation process is required in production.

JP-A-3-240750 JP 2005-272423 A JP 2005-272424 A JP 2005-272425 A

  The object of the present invention is that it does not require violent conditions such as high temperature and high pressure, and in a simple process without using a special apparatus, high-purity 2,6-NDA with a low alkali metal content can be obtained in a short time. It is to provide a method of manufacturing.

  The present inventors reacted 2,6-NDC with a basic alkali metal compound in the presence of an aqueous medium to obtain a solution of 2,6-NDA dialkali metalate, As a result of intensive studies on a method for producing 2,6-NDA comprising a step of analyzing, after diluting the 2,6-NDA dialkalimetalate solution obtained by the reaction to a predetermined concentration, By subjecting it to acid precipitation, it was found that high-purity 2,6-NDA with a low alkali metal content can be easily prepared, and the present invention has been completed.

〔Ｉ〕
［式中、Ｒは分岐を有してもよい炭素原子数１〜６のアルキル基を表す］。 That is, this invention provides the manufacturing method of 2, 6- naphthalene dicarboxylic acid including the process of the following (1)-(3):
(1) A di-lower alkyl ester of 2,6-naphthalenedicarboxylic acid represented by the formula [I] and a basic alkali metal compound are used in an amount of 4-7 with respect to the di-lower alkyl ester of 2,6-naphthalenedicarboxylic acid. Reacting in the presence of double weight of aqueous medium to obtain a dialkali metal salt solution of 2,6-naphthalenedicarboxylic acid;
(2) 2,6-naphthalenedicarboxylic acid obtained in step (1) so that the aqueous medium has a weight of 7.1 to 20 times the charged amount of di-lower alkyl ester of 2,6-naphthalenedicarboxylic acid. Diluting a solution of a dialkali metal salt of an acid with an aqueous medium; and
(3) A step of acidifying out a solution of a dialkali metal salt of 2,6-naphthalenedicarboxylic acid diluted in step (2), and separating and recovering the precipitated 2,6-naphthalenedicarboxylic acid;

[I]
[Wherein R represents an alkyl group having 1 to 6 carbon atoms which may have a branch].

  In the present specification and claims, the term “lower” means 1 to 6 carbon atoms.

  According to the method of the present invention, high-purity 2,6-NDA with a low alkali metal content can be produced in a short time.

  The 2,6-NDC represented by the formula [I] used in the present invention may be obtained by any conventionally known method. For example, by oxidizing naphthalene substituted at the 2,6-position with an alkyl group and / or acyl group with a heavy metal such as cobalt or manganese as a catalyst, the alkyl group and / or acyl group is oxidized with molecular oxygen. The obtained crude 2,6-NDA can be obtained by reacting with a lower alcohol in the presence of an acid catalyst such as sulfuric acid or p-toluenesulfonic acid.

  Preferable specific examples of 2,6-NDC represented by the formula [I] used in the present invention include 2,6-naphthalenedicarboxylic acid dimethyl ester, 2,6-naphthalenedicarboxylic acid diethyl ester, 2,6- Naphthalenedicarboxylic acid di-n-propyl ester, 2,6-naphthalenedicarboxylic acid di-iso-propyl ester, 2,6-naphthalenedicarboxylic acid di-n-butyl ester, 2,6-naphthalenedicarboxylic acid di-iso-butyl ester Examples thereof include one or more compounds selected from the group consisting of esters, 2,6-naphthalenedicarboxylic acid di-n-pentyl ester, and 2,6-naphthalenedicarboxylic acid di-n-hexyl ester.

  Among these specific examples of 2,6-NDC, 2,6-naphthalenedicarboxylic acid dimethyl ester is particularly preferable from the viewpoint of availability.

  In the present invention, an aqueous medium is used as a solvent for reacting 2,6-NDC with a basic alkali metal compound. The aqueous medium refers to water alone or an aqueous solution of a water-soluble organic solvent up to a concentration of 20% by weight.

  The water-soluble organic solvent that can be used in the present invention is not particularly limited as long as it dissolves in water up to 20% by weight at 25 ° C. For example, methanol, ethanol, isopropanol, 2-methoxyethanol, 2-ethoxy Alcohol solvents such as ethanol and ethylene glycol, ketone solvents such as acetone, N, N-dimethylacetamide, N, N-dimethylformamide, dimethyl sulfoxide, hexamethylphosphoramide, N-methyl-2-pyrrolidone and the like Examples include protic polar solvents. These water-soluble organic solvents may be used in combination of two or more.

  Hereafter, process (1)-(3) in this invention is demonstrated in order.

  First, in step (1), 2,6-NDC represented by the formula [I] and the basic alkali metal compound are 4 to 7 times by weight, preferably 5 to 7 times by weight with respect to 2,6-NDC. In the presence of an aqueous medium. When the amount of the aqueous medium used for 2,6-NDC is less than 4 times the weight, stirring becomes difficult, and when it is more than 7 times the weight, the reaction takes a long time and the productivity tends to decrease. is there.

  In the present invention, the basic alkali metal compound used in step (1) is, for example, selected from the group consisting of sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, sodium bicarbonate, and potassium bicarbonate. 1 type or more is mentioned.

  Among these basic alkali metal compounds, it is preferable to use sodium hydroxide or potassium hydroxide because of its reactivity, availability, and low cost. The basic alkali metal compound may be solid when it is used in the reaction system, or may be in the form of a solution dissolved in an aqueous medium.

  The amount of the basic alkali metal compound used is 1 to 2. ester of 2,6-NDC represented by the formula [I]. It is preferably 0 to 5.0 equivalents, and more preferably 1.0 to 2.0 equivalents.

  The temperature at which the 2,6-NDC represented by the formula [I] is reacted with the basic alkali metal compound in the step (1) in the present invention is not particularly limited as long as the reaction proceeds well, but is 40 to 200 ° C. Is preferable, 60 to 150 ° C is more preferable, and 80 to 120 ° C is particularly preferable. When the reaction temperature exceeds the boiling point of the solvent, the reaction may be carried out using a pressure device.

  The reaction between 2,6-NDC and the basic alkali metal compound is not particularly problematic if carried out in air or in an inert gas atmosphere, but may be carried out in an inert gas atmosphere such as nitrogen or helium. preferable.

  The reaction time between 2,6-NDC and the basic alkali metal compound is typically 1 to 50 hours, preferably 2 to 20 hours, more preferably, depending on the type and amount of the solvent used and the reaction temperature. It takes 3-10 hours.

  The analysis means for confirming the completion of the reaction between 2,6-NDC and the basic alkali metal compound is not particularly limited. For example, it can be confirmed by analyzing the reaction solution by high performance liquid chromatography.

  The reaction of 2,6-NDC with a basic alkali metal compound is carried out at 95 mol% or more of the charged 2,6-NDC, more preferably 98 mol% or more, particularly preferably 99 mol% or more of 2,6-NDA. It may be carried out until it is converted to a dialkali metal salt.

  The aqueous medium solution of 2,6-NDA dialkali metal salt obtained by reacting 2,6-NDC and a basic alkali metal compound as described above removes insoluble foreign substances as desired. After performing a filtration treatment for the purpose and an adsorbent treatment with activated carbon for removing coloring substances, metals and the like, the solution is diluted to a predetermined concentration in step (2).

Next, step (2) will be described.
In the step (2), the 2,6-NDA dialkali metal salt solution obtained in the step (1) is added to the 2,6-NDC weight of the aqueous medium charged in the step (1). It is diluted to a weight of 7.1 to 20 times, preferably 7.1 to 15 times, more preferably 8 to 10 times. If the amount of the aqueous medium after dilution is less than 7.1 times the weight, the alkali metal content of the obtained 2,6-NDA will increase, and if it exceeds 20 times the weight, the effect of reducing the alkali metal will reach its peak.

  In addition, there exists a tendency for the alkali metal content of 2,6-NDA obtained to become low, so that the dilution rate in a process (2) is high, but there exists a problem that cost will become high when a dilution rate is too high.

  The method for diluting the aqueous medium solution of 2,6-NDA dialkali metal salt is not particularly limited, and a predetermined amount is contained in the reactor having the aqueous medium solution of 2,6-NDA dialkali metal salt used in step (1). The aqueous medium solution of 2,6-NDA may be transferred to a container separately provided with a predetermined amount of aqueous medium and diluted.

  The aqueous medium added for dilution in step (2) is not particularly limited as long as it is water alone or an aqueous solution of a water-soluble organic solvent having a concentration of up to 20% by weight, as in step (1). Although the same composition as the reaction medium used in step 1 may be used, it is preferable to use water.

  The temperature at which the solution of 2,6-NDA dialkali metal salt and a predetermined amount of the aqueous medium are mixed is not particularly limited, but it is preferably 60 to 100 ° C.

  The mixing of the 2,6-NDA dialkali metal salt solution with a predetermined amount of the aqueous medium has no particular problem whether it is performed in air or in an inert gas atmosphere. It is preferable to carry out in an active gas atmosphere.

  The above-described 2,6-NDA dialkali metal salt solution is filtered to remove insoluble foreign matter, and the adsorbent is treated with activated carbon to remove coloring substances, metals, and the like. You may carry out after the dilution of (2).

Next, step (3) will be described.
In step (3), the solution of the dialkali metal salt of 2,6-NDA diluted in step (2) is acidified. The acid used for acid precipitation 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. Also, organic acids such as acetic acid and propionic acid can be used.

  The amount of these acids used is preferably 1.0 to 1.5 equivalents, more preferably 1.0 to 1.1, and more preferably 1.0 to 1 with respect to the amount of 2,6-NDA dialkali metal salt. .05 is particularly preferred.

  The temperature during acid precipitation is preferably 30 to 200 ° C, more preferably 80 to 120 ° C, and particularly preferably 90 to 110 ° C. The acid precipitation time varies depending on the scale of the reaction, but is preferably 50 to 70 minutes, more preferably 55 to 65 minutes.

  The acid precipitation is not particularly problematic if carried out in air or in an inert gas atmosphere, but is preferably carried out in an inert gas atmosphere such as nitrogen or helium.

  The 2,6-NDA slurry obtained by acid precipitation is separated and recovered from the slurry 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 obtained in this way is suitably used as a raw material for various chemical products. However, since it has a high purity and a small content of alkali metal, it can be used for liquid crystalline polyester, polyethylene naphthalate, polyamide, etc. It is particularly preferably used as various polymer monomers.

  2,6-NDA obtained by the method of the present invention has a low alkali metal content of less than 100 ppm, preferably less than 70 ppm.

  Hereinafter, the present invention will be described in detail by way of examples.

Example 1
146.6 g of 2,6-naphthalenedicarboxylic acid dimethyl ester, 769 g of water, 7.8 g of methanol, and 102.5 g of 48% NaOH water were charged into a 2 L flask equipped with a stirrer, a reflux condenser and a thermometer, and 98 ° C. The mixture was heated to rt and stirred to obtain a reflux state, and this state was maintained for 5.5 hours to obtain a sodium 2,6-naphthalenedicarboxylate aqueous solution.

  After cooling this aqueous solution to 50 ° C. and filtering off the slightly remaining raw material (insoluble matter), the mother liquor was transferred to the same 2 L flask, 440 g of water was added, and the sodium 2,6-naphthalenedicarboxylate concentration was 10.6. % Aqueous solution.

  The aqueous solution was heated while stirring at a rate of 250 rpm, and when 90 ° C. was reached, 107.1 g of 62% sulfuric acid was added dropwise with a tube pump. All of this was dropped (acid precipitation) to obtain a white slurry liquid of 2,6-naphthalenedicarboxylic acid. After cooling this slurry liquid to 50 degreeC, solid content of 2, 6- naphthalene dicarboxylic acid was obtained by solid-liquid separation.

  This solid content was dried with a blast dryer at 120 ° C. to obtain 129.1 g of a solid (yield 99.5%). As a result of HPLC analysis, 2,6-naphthalenedicarboxylic acid was 99.8%, and 2,6-naphthalenedicarboxylic acid dimethyl ester as a raw material was not detected. The amount of Na element contained in the obtained 2,6-naphthalenedicarboxylic acid was determined by atomic absorption analysis and found to be 56 ppm. The results are shown in Table 1.

Example 2
Example, except that 726 g of water, 7.3 g of methanol, the maintenance time at reflux was 7 hours, the amount of water added to the mother liquor after filtration was 704 g, and the sodium 2,6-naphthalenedicarboxylate concentration was 9.3%. In the same manner as in Example 1, 129.2 g of 2,6-naphthalenedicarboxylic acid was obtained (yield 99.6%). Table 1 shows the Na content. The raw material 2,6-naphthalenedicarboxylic acid dimethyl ester was not detected.

Example 3
Example except that 944 g of water, 9.5 g of methanol, the maintenance time in the reflux state was 6 hours, the amount of water added to the mother liquor after filtration was 484 g, and the sodium 2,6-naphthalenedicarboxylate concentration was 9.3%. In the same manner as in Example 1, 129.6 g of 2,6-naphthalenedicarboxylic acid was obtained (yield 99.9%). Table 1 shows the Na content. The raw material 2,6-naphthalenedicarboxylic acid dimethyl ester was not detected.

Comparative Example 1
Example 1 except that 1147 g of water, 11.6 g of methanol, the maintenance time in the reflux state was 10 hours, the amount of water added to the mother liquor after filtration was 279 g, and the sodium 2,6-naphthalenedicarboxylate concentration was 9.3%. In the same manner as in Example 1, 129.0 g of 2,6-naphthalenedicarboxylic acid was obtained (yield 99.4%). Table 1 shows the Na content. The raw material 2,6-naphthalenedicarboxylic acid dimethyl ester was not detected.

Comparative Example 2
2,6-Naphthalenedicarboxylic acid 129 in the same manner as in Example 1 except that 944 g of water, 9.5 g of methanol, the maintenance time at reflux was 6 hours, and no water was added to the mother liquor after filtration. 0.5 g was obtained (yield 99.8%). Table 1 shows the Na content. The raw material 2,6-naphthalenedicarboxylic acid dimethyl ester was not detected.

1) 原料２，６−ナフタレンジカルボン酸ジメチルエステルに対する重量倍率

1) Weight ratio to raw material 2,6-naphthalenedicarboxylic acid dimethyl ester

  When diluted such that the aqueous medium ratio at the time of reaction was 4 to 7 times by weight and the aqueous medium ratio at the time of acid precipitation was 7.1 to 20 times by weight, the reaction time was short, 6-Naphthalenedicarboxylic acid had a low Na content.

  When the aqueous medium ratio at the time of reaction exceeds 7 times the weight, the reaction takes a long time. When the aqueous medium ratio at the time of acid precipitation is less than 7.1 times the weight, the obtained 2,6-naphthalene is obtained. The dicarboxylic acid had a high Na content.

Claims (5)

A process for producing 2,6-naphthalenedicarboxylic acid, comprising the following steps (1) to (3):
(1) A di-lower alkyl ester of 2,6-naphthalenedicarboxylic acid represented by the formula [I] and a basic alkali metal compound are used in an amount of 4-7 with respect to the di-lower alkyl ester of 2,6-naphthalenedicarboxylic acid. Reacting in the presence of double weight of aqueous medium to obtain a dialkali metal salt solution of 2,6-naphthalenedicarboxylic acid;
(2) 2,6-naphthalenedicarboxylic acid obtained in step (1) so that the aqueous medium has a weight of 7.1 to 20 times the charged amount of di-lower alkyl ester of 2,6-naphthalenedicarboxylic acid. Diluting a solution of a dialkali metal salt of an acid with an aqueous medium; and
(3) A step of acidifying out a solution of a dialkali metal salt of 2,6-naphthalenedicarboxylic acid diluted in step (2), and separating and recovering the precipitated 2,6-naphthalenedicarboxylic acid;

[I]
[Wherein R represents an alkyl group having 1 to 6 carbon atoms which may have a branch] ,
Here, the composition of the aqueous medium in the step (1) and the aqueous medium in the step (2) may be the same or different, and water alone or methanol, ethanol, isopropanol, 2-methoxyethanol, One selected from the group consisting of 2-ethoxyethanol, ethylene glycol, acetone, N, N-dimethylacetamide, N, N-dimethylformamide, dimethyl sulfoxide, hexamethylphosphoramide, and N-methyl-2-pyrrolidone An aqueous solution of the above water-soluble organic solvent up to a concentration of 20% by weight.   The method for producing 2,6-naphthalenedicarboxylic acid according to claim 1, wherein the di-lower alkyl ester of 2,6-naphthalenedicarboxylic acid represented by the formula [I] is 2,6-naphthalenedicarboxylic acid dimethyl ester.   The basic alkali metal compound is one or more compounds selected from the group consisting of sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, sodium bicarbonate and potassium bicarbonate. A method for producing 2,6-naphthalenedicarboxylic acid. The method for producing 2,6-naphthalenedicarboxylic acid according to any one of claims 1 to 3, wherein the aqueous medium in step (1) is an aqueous solution of methanol, and the aqueous medium in step (2) is water.   The method for producing 2,6-naphthalenedicarboxylic acid according to any one of claims 1 to 4, wherein the alkali metal content of 2,6-naphthalenedicarboxylic acid obtained after separation and recovery in step (3) is less than 100 ppm. .