JPS6293254A - Production of 2,6-naphthalenedicarboxylic acid - Google Patents

Abstract

PURPOSE:To suppress the formation of nuclear brominated substance caused by Br components and obtain the titled compound in good yield, by oxidizing a 2,6-diisopropylnaphthalene with molecular O2 in the presence of a specific catalyst in a solvent consisting of an aliphatic monocarboxylic acid. CONSTITUTION:2,6-Diisopropylnaphthalene or an oxidation intermediate thereof expressed by formula I (R1 is formula II, III or IV; R2 is R1, -COOH or -COH) is reacted with molecular O2 in the presence of a catalyst containing a heavy metal, e.g. Co such as cobalt acetate and/or Mn such as manganese acetate, and Br at 1X10<-4>-<1X10<-2> atomic ratio of Br to the above-mentioned heavy metal, e.g. ammonium bromide, as constituent components in a solvent consisting of a <=3C aliphatic monocarboxylic acid, e.g. acetic acid, at 140-210 deg.C under >=0.1kg/cm<2> (absolute) partial pressure of O2 to afford the aimed compound. USE:A raw material for polyethylene naphthalate, polyamide, etc., useful as a raw material for producing films, textile products, etc.

Description

Detailed Description of the Invention The present invention provides polyethylene naphthalate and other polyesters useful as raw materials for producing films and textile products.
This invention relates to an advantageous process for the production of 2,6-naphthalene dicarboxylic acid for use in the production of polyamides.

Conventionally, 2,6-naphthalene dicarboxylic acid has been produced by oxidizing 2,6-dimethylnaphthalene, for example, by oxidizing 2,6-dimethylnaphthalene with cobalt, manganese and bromine in an acetic acid solvent. A method of oxidation with molecular oxygen in the presence of a catalyst consisting of components is known, in which the oxidation reaction described above is carried out in a comparatively balanced manner.

Since it is easy, 2,6-naphthalene dicarboxylic acid can be obtained with relatively high purity and high yield.

However, the 2,6 used as starting material in this method
- Dimethylnaphthalene is difficult to obtain in large quantities and at low cost because the method for producing it is complicated. That is, as methods for synthesizing 2,6-dimethylnaphthalene, methylation of naphthalene, isomerization of dimethylnaphthalene, disproportionation of monomethylnaphthalene, trans-alkylation, etc. are known, but any of these methods However, the formation of isomers other than 2,6-dimethylnaphthalene, especially 2,7-dimethylnaphthalene, cannot be avoided, and the 2,7-isomer has a lower melting point, boiling point, and solubility. Since it is similar to 2,6-dimethylnaphthalene in this respect, it is extremely difficult to isolate 2,6-dimethylnaphthalene from the reaction mixture obtained by each of the above synthesis methods.

On the other hand, compared to the above-mentioned 2,6-dimethylnaphthalene, diisopropylnaphthalene can be easily synthesized by reacting naphthalene and propylene, and its alkylation, disproportionation, isomerization, and trans-alkylation are also compared. It has the advantage of being easy to implement. In addition, 2.
6. Separation of the unit is also easy. Incidentally, for example, since the melting point of 2,7-unit coexisting in the above-mentioned mixed diisopropylnaphthalene is significantly different from that of 2.6-unit, it can be easily separated by utilizing this melting point difference.

However, according to the research of the present inventors, although 2,6-diisopropylnaphthalene is easily available as mentioned above, when oxidizing it, p-xylene and 2,6-diisopropylnaphthalene are easily available.
- If the known reaction conditions used to oxidize dimethylnaphthalene are used, large amounts of by-products will be produced;
- Even if diisopropylnaphthalene is not used as a starting material and oxidized to produce 2,6-naphthalene dicarboxylic acid, the yield and purity are low, and therefore 2,6-naphthalene dicarboxylic acid is produced industrially. This is not a practical method.

Regarding the above-mentioned method by oxidation of 2,6-diisopropylnaphthalene, conventionally, for example, 2,6-diisopropylnaphthalene is oxidized in an aliphatic monocarboxylic acid solvent in the presence of a catalyst consisting of components of heavy metals such as cobalt and manganese and bromine. Below, when oxidizing with molecular oxygen, 12
．． A method has been proposed in which a mixed isopropylnaphthalene containing 6% l of diisopropylnaphthalene is used as the starting material, and a catalyst containing cobalt, manganese, and bromine in the following quantitative ratio is used (Tokuko Sho). No. 48-27318).

X+Y+Z≧2.0 Y≧0.15/ X 0.2≦ Z ≦lO However, when the above proposed method is applied to the oxidation of a starting material consisting essentially only of 2,6-diisopropylnaphthalene, 2,6-diisopropylnaphthalene is replaced by a large amount of monoisopropylnaphthalene as in the method. Probably because it was not diluted with water, many side reactions occurred, resulting in a yield of about 50%.
Therefore, it cannot be said to be an industrially advantageous method.

Further, as a method for oxidizing 2,6-diisopropylnaphthalene or its oxidized intermediate, a method characterized in that cobalt and/or manganese as the catalyst component is present in an amount of 0.2 mole or more per mole of each of the above starting materials. has also been proposed (Japanese Patent Laid-Open No. 60-89445). In addition,
In this method, it is difficult to unambiguously control the amount of bromine, which is another component of the catalyst, but it can be present in an atomic ratio of 0.01 to 2 with respect to the total amount of cobalt and/or manganese. It is disclosed that a part of the bromine compound used at that time is converted into a nuclear bromide that is difficult to decompose.

By the way, in the above method, the side chains of diisopropylnaphthalene as a starting material and its oxidized intermediate nuclear bromide are oxidized to carboxylic acids in the same way as diisopropylnaphthalene, but these carboxylic acids are converted into naphthalene dicarboxylic acids. Because the naphthalene dicarboxylic acid has physical properties similar to those of the above, it is extremely difficult to separate naphthalene dicarboxylic acid from the reaction mixture.

Regarding this car-loaded product, for example,
The publication discloses that in purifying 2,6-naphthalene dicarboxylic acid, removal of bromine derivatives is most necessary, and 2.6
- It is stated that if naphthalene dicarboxylic acid contains a bromine derivative, the softening point of the resin obtained using it as a raw material will decrease, resulting in a fatal defect.

In addition, the same publication states in its Examples that crude 2,6-naphthalene dicarboxylic acid contains 1000 to 2000 ppm+ bromine, but even after various purification methods, 10
This indicates that ~40 ppm of bromine remains without being removed.

That is, from the above, in the oxidation reaction of 2,6-diitubropylnaphthalene and its oxidized intermediate, 2.
．． It can be seen how difficult it is to remove the by-products of 6-naphthalene dicarboxylic acid.

1) tries to do Vntr. The old invention was made in view of the above-mentioned situation, and in producing 2,6-naphthalene dicarboxylic acid by oxidizing 2,6-diitubropylnaphthalene or its oxidized intermediate, It is an object of the present invention to provide a method for controlling the production of a 1 m long carton which adversely affects its physical properties and makes its purification difficult.

In the process of investigating the suppression of the formation of the above-mentioned carloads, the present inventors conducted an oxidation reaction on 2,6-diitupropylnaphthalene in the presence of a catalyst containing cobalt and/or manganese and bromine as components. As a result of a detailed study of the oxidation behavior of the two isopropyl groups of 2,6-diitubrobylnaphthalene in the case of It was found that the oxidation conditions for the formation of bulk products are different in the oxidation of isopropyl groups.

That is, bromine is not necessary or only needs to be present in a very small amount for the oxidation of the first isopropyl group,
At this time, if a large amount of bromine exists, the amount of loaded products will increase significantly, and the production of by-products such as heavy products that suppress the above oxidation will also increase, but on the other hand, the oxidation of the second isopropyl group It was found that if the amount of by-products produced during the previous step of oxidizing the isopropyl group III is small, oxidation can be effectively carried out outside the window if a trace amount of bromine is present. In addition, in the oxidation of the second isopropyl group, if a large amount of bromine is present, the formation of by-products in the form of piles and piles will increase.

Based on the above findings, the present inventors conducted an oxidation reaction of 2,6-diitupropylnaphthalene in the presence of a catalyst containing cobalt and/or manganese and an extremely small amount of bromine. We succeeded in obtaining 2,6-naphthalene dicarboxylic acid with very little by-product (derivative compound).

Incidentally, as mentioned above, conventionally, catalysts have been used for the oxidation of 2,6-diitupropylnaphthalene, P-xylene, and dimethylnaphthalene.

In other words, the atomic ratio of bromine to cobalt and manganese is 0.
．． Because the catalyst contained in the concentration range of 01 to 10 was used, side reactions increased, for example, 2,6-
Even if measures were taken, such as supplying a small amount of diisopropylnaphthalene to improve dispersion within the system or reducing the concentration within the system, the formation of carloads could not be suppressed.

In other words, in view of the conventional state of the art, it is unexpected that the formation of the above-mentioned carloads can be effectively suppressed by reducing the concentration of bromine in the catalyst to an extremely small amount.

The present invention will be explained in detail below.

A feature of the present invention is that 2,6-diitupropylnaphthalene or its oxidized intermediate is oxidized with molecular oxygen in a solvent consisting of an aliphatic monocarboxylic acid having 3 or less carbon atoms.
- A method for producing naphthalene dicarboxylic acid, in which the oxidation is performed using a heavy metal such as cobalt and/or manganese and bromine as constituent components, and the bromine atom is 1×10-◆ to 1×10-” per mole of heavy metal atom. The method is carried out in the presence of a catalyst containing less than or equal to

The term "oxidized intermediate of 2,6-diisopropylnaphthalene" as used herein means a compound represented by the following formula (1).

Cl1i CI! 3 represents -ε-CH1, R2 is each of the above groups and -COO
1) or -Cl (represents O, R1 and R2 may be the same or different) ■ For determining the fortune of 7.

As mentioned above, the present invention uses as an oxidation catalyst an oxidation catalyst containing an extremely small amount of bromine atoms in the range of 1 x 10-'' to less than 1 x 10-2 per mole of heavy metal atoms consisting of cobalt and/or manganese. These catalyst components are exemplified by the following.

Components of the heavy metals cobalt and manganese include inorganic salts such as oxides, hydroxides, carbonates, and halides, as well as organic acid salts such as formic acid, acetic acid, propionic acid, naphthenic acid, and aromatic carboxylic acids. Preferred among these are fatty acid salts, especially acetates.

The bromine component may be any organic compound or inorganic compound as long as it dissolves in the oxidation reaction system and produces bromide ions, such as molecular bromine, hydrogen bromide, hydrobromide salts, etc. Examples include inorganic bromine compounds, alkyl bromides such as methyl bromide and ethyl bromide, and brominated fatty acids such as bromoacetic acid.

Among these, preferred are hydrogen bromide, sodium bromide, potassium bromide, ammonium bromide, cobalt bromide, manganese bromide, and the like.

In the present invention, the upper bromine compound as a catalyst component is used in an atomic ratio of 1× to the heavy metal component consisting of cobalt and manganese.
In the range of 10 → to less than 1×10 −2 , preferably 5×1
It is added in a range of 0-' to 8XIO-'.

If the above atomic ratio of the bromine compound is lower than 1 x 10→, the oxidation reaction to 2,6-naphthalene dicarboxylic acid is too slow to be considered industrial, while on the other hand, if it is higher than 1 x 10-2, side reactions may occur. This is not suitable as it increases the amount of nuclear bromide produced.

Incidentally, as mentioned above, an oxidation catalyst with an extremely small amount of bromine component can be used for the oxidation reaction of aromatic hydrocarbons whose side chains are methyl groups, such as P-xylene and 2,6-dimethylnaphthalene. In some cases, the catalytic effect is so low that it is not practical. On the other hand, in 2,6-diisopropylnaphthalene and its oxidized intermediates, the tertiary hydrogen in the isopropyl group in the side chain of these substances is more active than the hydrogen in the methyl group, so the above-mentioned bromine component is extremely Even in the presence of a trace amount of catalyst, the catalytic effect remains unchanged.
While the oxidation reaction is carried out, it becomes possible to suppress the production of nuclear bromide caused by the bromine component, as described above.

That is, 2,6-naphthalene dicarboxylic acid can be advantageously produced without side reactions by an oxidation reaction using an oxidation catalyst containing an extremely small amount of bromine component.
This can be said to be unique to the use of 6-diisopropylnaphthalene and its oxidized intermediates as starting materials.

In addition, the amount of cobalt component and manganese component, which are heavy metal components of the catalyst used in the present invention, is 10% of the solvent used in the reaction system.
The amount is in the range of 0.03 to 0.15 mol, preferably 0.04 to 0.12 mol per 0 g.

Note that the cobalt component and the manganese component can be used alone or in a mixture, but the mixture exhibits higher activity. In the case of a mixture, the mixing ratio may be arbitrary, but it is preferable that the atomic ratio of cobalt to manganese is 5=95 to 70:30.

The solvent may be any lower aliphatic carboxylic acid having 3 or less carbon atoms, and examples include formic acid, acetic acid, propionic acid, and oxalic acid, with acetic acid being most preferred.

In the present invention, 2,6-diisopropylnaphthalene as a starting material and its oxidized intermediate are
It is preferable to supply it to the reaction system at a concentration of 20 parts by weight or less per part by weight; if the concentration is higher than the above, it is not preferable because it inhibits the /8 decomposition of oxygen used for oxidation in the system.

The molecular oxygen used in the above oxidation can be pure oxygen or a mixed gas obtained by diluting it with an inert gas, but in practice it is preferable to use air, which is an oxygen-containing gas.

The oxidation reaction in the present invention progresses more rapidly as the oxygen partial pressure in the system is higher, but in practice, it is 0.1 kg/cd (absolute) or more, preferably 0.2 kg/ca+ (absolute) to 8
An oxygen partial pressure of the order of kg/cA (absolute) is sufficient. For example, when molecular oxygen is used in a mixed state with an inert gas, the reaction proceeds rapidly at a total pressure of 30 kg/cdG or less.

Also, the temperature of one reactor is 140 to 210°C, preferably 160°C.
~200° C., and lower temperatures slow down the reaction, while higher temperatures (higher temperatures increase the combustion loss of the solvent in the system, which is not a good idea).

EXAMPLES The present invention and its effects will be specifically explained by showing Examples and Comparative Examples below. In addition, parts in each example indicate weight unless otherwise specified.

Example 1 2070 parts of glacial acetic acid, 132 parts of cobalt acetate/tetrahydrate, and 3 parts of manganese acetate/tetrahydrate were added to a titanium pressurized reactor having a reflux condenser, a gas blowing pipe, a discharge pipe, and an ffl stirring tank.
752 parts of a solution containing 1 part of ammonium bromide and 1 part of ammonium bromide were introduced per hour at a temperature of 180°C and a pressure of 10 kg/hour.
While maintaining the temperature at cdG and stirring vigorously, compressed air was passed through the reactor at an oxygen introduction rate of 171 parts per hour.

At this time, the atomic ratio of the bromine component to the heavy metal components of cobalt and manganese in the system is Br/ (Co+Mn)
= 5X10-'.

Next, 2,6-diitubrobylnaphthalene (DIPN) was fed into the system at a rate of 60 parts per hour to carry out a reaction.

After completion of the reaction, mainly 2.6-
The solid precipitate consisting of naphthalene dicarboxylic acid (NDCA) was filtered off, washed with hot acetic acid, and separated into crude NDCA and the filtrate.

The yield of the obtained NDCA relative to the raw material D [PN was 85.
At 3%, the bromine content of crude NDCA was 1) 05 pp.

This crude NDCA was purified according to the procedure described in Example 1 of Japanese Patent Publication No. 56-3858.

First, 410 parts of crude NDC was dissolved in 80 parts of a 5χ-a01) aqueous solution, a small amount of alkali insoluble matter was filtered off, and the filtrate was lowered to pH=7 using 6N hydrochloric acid to precipitate the monosodium salt of NDCA.

Subsequently, 10 parts of the monosodium salt to NDC was added to 200 parts of water.
In addition, the pH was lowered to 2 with 6N hydrochloric acid at about 90°C, and acid precipitation was performed to obtain purified NDC^. Bromine in purified NDCi was below ippm.

Example 2 In a pressurized reactor similar to Example 1, 2070 parts of glacial acetic acid, 132 parts of cobalt acetate tetrahydrate, and 3 parts of manganese acetate tetrahydrate were added.
A solution consisting of 91 parts of ammonium bromide and 0.1 part of ammonium bromide was introduced at 1000 parts per hour.

Br/(Co+Mn) in the solution at this time = 5X
It was 10-' (atomic ratio).

Next, the above solution was heated at a temperature of 180°C and a pressure of 20kg/c.
Maintaining the temperature at JG and stirring vigorously, increase the oxygen supply rate.
The reaction was carried out by flowing compressed air at a rate of 1.80 parts per hour and DIPN at a rate of 80 parts per hour.

After the reaction was completed, crude NDC was filtered off in the same manner as in Example I. Raw material 1) The yield of NDCA based on 1PN is 73.
3%, and the bromine content in crude N1) CA is 40p
It was pm.

Comparative Example 1 In Example 1, a solution containing 14.9 parts of ammonium bromide in the reaction system (Br/(Co
+Mn) = 7.5X10-" (In particle ratio)], and the reaction was carried out under the same conditions as described in Example 1, except for JT. The yield of NDCA in the raw material DII"N was 64.9%, and the bromine content in the obtained crude NDCA was significantly increased to 3765 ppm.

This crude NDC was purified in the same manner as in Example 1, but the bromine content in NDCA was only reduced to 33 ppra.

Example 3 In a pressurized reactor similar to Example 1, 2410 parts of glacial acetic acid, 97 parts of cobalt acetate/tetrahydrate PA, and 1 part of manganese acetate/tetrahydrate were added.
A solution containing 93 parts of ammonium bromide and 0.12 parts of ammonium bromide was introduced at a rate of 870 parts per hour. At this time, Br/(Co+gate n) in the above solution = 1. lX10-'
(atomic ratio).

Next, the above solution was heated at a temperature of 170°C and a pressure of 30 kg/ct.
While stirring vigorously at G, the oxygen introduction rate was 17 per hour.
80 parts per hour of DIPN was introduced while passing 4 parts of compressed air.

The yield of the obtained NDCA was 72% with respect to the raw material DII'N.
．． At 3%, the bromine content in crude 1-DCA was 53 ppm.

Example 4 In a pressurized reactor similar to Example 1, 2070 parts of glacial acetic acid, 350 parts of cobalt acetate tetrahydrate, and 1 part of manganese acetate tetrahydrate were added.
A solution consisting of 70 parts of ammonium bromide and 1.5 parts of ammonium bromide was introduced at 1296 parts per hour. At this time, Br/ (Co+Mn) -7,4XIO-' (
atomic ratio).

Next, the above liquid /8 was heated at a temperature of 185°C and a pressure of 20 kg /
The reaction was carried out by introducing 104 parts per hour of 1llt'll while maintaining the aJG and vigorously working the mixture, while passing compressed air through the reactor at an oxygen introduction rate of 240 parts per hour.

The yield of the obtained NDCA was 8 for the raw materials 1)1)'N
It was 0.7%. In addition, the bromine content in crude NrlCA is 2
It was 12 ppm.

When this phase NDCA was purified in the same manner as in Example 1, the bromine content in NDCA was reduced to 2 ppm.

Comparative Examples 2 to 5 100 parts of glacial acetic acid and each catalyst shown in the table below were placed in a chikun autoclave equipped with a reflux condenser, a gas blowing pipe, a discharge pipe, and a stirrer, and 10 parts of DIPN and 10 parts of DIPN were added to this.
2,6-dimethylnaphthalene (DMN) was introduced to perform oxidation.

The oxidation reaction was carried out at a temperature of 180° C., a pressure of 10 kg/cJG, and air flowing at a rate of 8 parts per hour for 3 hours.

The results are shown in the table.

Proceedings 1) Author: December 5, 1985 Director General of the Patent Office U ¥X'fi Department 1, Indication of the case: 1985 Patent Application No. 232776 2, Title of the invention: Production of 2,6-naphthalene dicarboxylic acid Law 3, Relationship with the case of the person making the amendment Patent applicant name (1) 0) Kureha Chemical Industry Co., Ltd. 4, agent address 5, Shinbashi Kokusai Building, 2-7-7 Higashi-Shinbashi, Minato-ku, Tokyo, order for amendment The date of the petition 6, the number of inventions increased by the amendment 8, and the statement of contents of the amendment are amended as follows.

(1) The scope of claims is amended as shown in the attached sheet.

(2) In line 7 of page 1, the statement [bromine atoms per mole of all m-total atoms] is corrected to [the atomic ratio of bromine to heavy metals].

(3) In the 8th line of page 1, the phrase "contains less than" is amended to "contains less than".

(4) 1st) In the last line of the page, rclI3 rcH yo-
C-COII is corrected to -Kano001).

Cl13J CH3J (5) In the third line of page 12, it says "[may be different]" to "may be different, or one of them is -C1l (CH
3) It is 2. )” is corrected.

(6) On page 12, lines 6-7, the phrase “bromine atom per mole of heavy metal atom” should be replaced with “the atomic ratio of bromine to heavy metal.”
and correct it.

2. Claims fil 2,6-diisopropylnaphthalene or its oxidized intermediate is oxidized with molecular oxygen in a solvent consisting of an aliphatic monocarboxylic acid having 3 or less carbon atoms to produce 2,6-naphthalene dicarboxylic acid. In the manufacturing method, the oxidation is performed by combining (i) a heavy metal of cobalt and/or manganese;
1)) Contains bromine as a constituent and is resistant to heavy metals 74
A method for producing 2,6-naphthalene dicarboxylic acid, which is carried out in the presence of a catalyst with a prepressure of 1 x 10-'' to less than 1 x 10-2.

Procedural amendment dated January 8, 1985 2, Title of the invention Process for producing 2,6-naphthalene dicarboxylic acid 3, Relationship to the case of the person making the amendment Name of patent applicant (1) 0) Kureha Chemical Industry Co., Ltd. 4 , Agent address: 5 Shinbashi Kokusai Building, 412-7-7 Higashishin, Minato-ku, Tokyo Date of amendment order Voluntary action 6 Number of inventions increased by amendment 8 The detailed description of the amendment is amended as follows.

fil From the first line of page 17 to the last line of page 22, it says, ``Explain the effect in detail.
・・−・−−１−−−・−・−・・−・・−・・−・・
-The results are shown in the table. ” should be corrected as follows.

[The effect will be explained in detail.

Example 1 2070 g of glacial acetic acid, 132 g of cobalt acetate/tetrahydrate, and 391 g of manganese acetate/tetrahydrate were placed in a pressurized reactor manufactured by No. 51 Chikun, which had a reflux condenser, a gas blowing pipe, a discharge pipe, and a stirrer.
752 g of a solution containing 1 g of ammonium bromide and 1 g of ammonium bromide were introduced per hour at a temperature of 180°C and a pressure of 10 kg.
/cnlG, and while stirring vigorously, compressed air was passed through it at an oxygen feed rate of 171 g/hour.

At this time, the atomic ratio of the bromine component to the heavy metal components of cobalt and manganese in the system is 1) r / (Co+Mnl = 5 Xl0-'
Met.

Next, 2,6-diitupropylnaphthalene (DTI'N) was fed into the system at a rate of 60 g/hour to carry out a reaction.

After completion of the reaction, mainly 2.6-
Solidified I consisting of naphthalene dicarboxylic acid (NDCA)
The residue was filtered off and washed with hot acetic acid to separate crude NDCA and filtrate.

The yield of NDCA based on the raw material DIPN was 85
．． At 3%, the bromine content of crude NDCA was 105 ppi.

This crude ND(:A) was purified according to the procedure described in Example 1 of Japanese Patent Publication No. 56-3858.

First, phase NDCA Log was prepared using 5%-NaO1) aqueous solution 8
After dissolving a small amount of alkali insoluble matter by filtration, the filtrate was lowered to pH=7 using 6N hydrochloric acid to precipitate the monosodium salt of NDCA.

Next, add 10 g of monosodium salt of NDCA to 200 g of water.
In addition, the purified NDCA was acidified by lowering the pH to 2 with 6N hydrochloric acid at about 90° C. to obtain purified NDCA (q).The bromine content in the purified NDCA was 1 ppm or less.

Example 2 A solution consisting of 2070 g of glacial acetic acid, 132 g of cobalt acetate tetrahydrate, 391 g of manganese acetate tetrahydrate, and 0.1 g of ammonium bromide was added every hour to a pressurized reactor similar to Example 1. It was introduced at 1000g. Br/(Co+Mn) in the solution at this time = 5 Xl0-'
+ (atomic ratio).

Next, the above solution was heated at a temperature of 180°C and a pressure of 20kg/
cJG, compressed air at a rate of 180 g/hour while stirring vigorously, and 80 g/hour.
The reaction was carried out by flowing DIPN at a rate of .

After the reaction was completed, crude NDCA was filtered off in the same manner as in Example 1. The yield of NDCA based on the raw material DTPN was 73.3%, and the bromine content in the crude NDC was 40 ppm.

Comparative Example l In Example 1, ammonium bromide in the reaction system was
Contains 14.9g of skin (B)
r/(Go+Mn) = 7.5 Xl0-2 (atomic ratio)], the reaction was carried out under the same conditions as described in Example 1.
The yield of A was 64.9% (the bromine content in the given crude HDCA increased significantly to 3765 ppm).

This crude NDCA was purified in the same manner as in Example 1, but the bromine content in NDC^ was reduced only to 839p1)1.

Example 3 In a pressurized reactor similar to Example 1, 2410 g of glacial acetic acid, 97 g of cobalt acetate/tetrahydrate, and 19 g of manganese acetate/tetrahydrate were added.
A solution containing 3 g of ammonium bromide and 0.12 g of ammonium bromide was introduced at a rate of 870 g per hour. At this time, Br / (Co+Mn) in the above /8 solution = 1. IXl0-”
(atomic ratio).

Next, the above solution was heated at a temperature of 170°C and a pressure of 30kg/c.
While stirring vigorously with iG, the oxygen introduction rate was 1/hour.
DIPN is 80 per hour while flowing 74g of compressed air.
g was introduced.

The yield of the obtained NDCA was 72%, based on the raw material DIPN.
At 3%, the bromine content in l'1NDcA was 53 ppm.

Example 4 A solution consisting of 2070 g of glacial acetic acid, 350 g of cobalt acetate tetrahydrate, 170 g of manganese acetate tetrahydrate, and 1.5 g of ammonium bromide was added every hour to a pressurized reactor similar to Example 1. It was introduced at 1296 g. Br in the above solution at this time / ((:o+Mn) = 7.4
l0-' (atomic ratio).

Next, the above /8/& was heated at 185°C and 20kg under pressure.
/cnlG, and while vigorously stirring and flowing compressed air at an oxygen introduction rate of 240 g/hour, a reaction was carried out by introducing 140 g of []Il'N/hour.

The yield of the obtained NDCA was 80% based on the raw material DTPN.
It was 7%. In addition, the bromine content in crude NDCA is 212
It was ppm.

When this #1 NOcA was purified in the same manner as in the experiment (evening 1), the bromine content in NDCA was reduced to 2 ppm.

Comparative Examples 2 to 5 100 g of glacial acetic acid and each catalyst shown in the table below were placed in a 0.2i titanium autoclave equipped with a one-flow cooler, a gas blowing pipe, a discharge pipe, and a stirrer, and log of DIPN and log of 2, 6-dimethylnaphthalene (D-IN)
were introduced and oxidized.

The oxidation reaction is carried out at a temperature of 180°C and a pressure of 10kg/c+j.
The test was carried out by circulating air at a rate of 8 g/hour for 3 hours with an oxygen supply rate of 8 g/hour.

The results are shown in the table. (2) In the table on page 23, in the columns of Comparative Examples 2 to 5, the words ``part'' are corrected to ``1 g.''

Claims (1)

[Claims] (1) A method for producing 2,6-naphthalene dicarboxylic acid by oxidizing 2,6-diisopropylnaphthalene or its oxidized intermediate with molecular oxygen in a solvent consisting of an aliphatic monocarboxylic acid having 3 or less carbon atoms. , the above oxidation,
(i) heavy metals of cobalt and/or manganese; (ii)
) 2,6-naphthalene, characterized in that the reaction is carried out in the presence of a catalyst containing bromine as a constituent component and containing 1×10^-^4 to less than 1×10^-^2 bromine atoms per mole of heavy metal atoms. Method for producing dicarboxylic acid.