JPH0529022B2 - - Google Patents

Description

[Detailed description of the invention]

(a) Industrial Application Field The present invention relates to a method for producing 2,6-naphthalene dicarboxylic acid by oxidizing 2,6-diisopropylnaphthalene or its oxidized derivative with molecular oxygen. More specifically, the present invention relates to a method for obtaining the desired 2,6-naphthalene dicarboxylic acid in an extremely high yield by carrying out the oxidation in an acetic acid-containing solvent in the presence of a catalyst containing heavy metals and bromine. (b) Prior art 2,6-naphthalene dicarboxylic acid (hereinafter sometimes abbreviated as "NDA") or its derivatives such as esters and acid chlorides are valuable as dibasic acid components of various polyesters, polyamides, etc. Certain compounds, particularly polyethylene naphthalate formed from NDA and ethylene glycol, have better heat resistance and mechanical properties than polyethylene terephthalate, and are useful as polymers for producing films and textile products. . Conventionally, methods for producing NDA include an oxidation reaction of 2,6-dimethylnaphthalene, such as a method in which 2,6-dimethylnaphthalene is catalytically oxidized with molecular oxygen in an acetic acid solvent in the presence of a catalyst consisting of cobalt, manganese, and bromine. It has been known. In this method, the oxidation itself of 2,6-dimethylnaphthalene to NDA is relatively easy, and the desired NDA can be obtained with relatively high purity and high yield. However, the manufacturing method for 2,6-dimethylnaphthalene, which is a raw material in this method, is complicated, and it is difficult to obtain it in large quantities at low cost. That is,
Methylation of naphthalene, isomerization of dimethylnaphthalene, disproportionation of monomethylnaphthalene, and other trans-alkylation methods are known as methods for synthesizing 2,6-dimethylnaphthalene. , 6-dimethylnaphthalene, especially 2,7-dimethylnaphthalene, isomers other than 2,7-dimethylnaphthalene cannot be avoided. This was extremely difficult because the boiling points and solubility characteristics are extremely similar. On the other hand, diisopropylnaphthalene can be easily synthesized from naphthalene and propylene, and can be easily synthesized from mixed diisopropylnaphthalene by separation of the 2,6-isomer, alkylation, disproportionation, isomerization, trans alkyl naphthalene, etc. It is also relatively easy to convert. However, according to the research of the present inventors, 2.
The oxidation reaction of 6-diisopropylnaphthalene (hereinafter sometimes abbreviated as "DIPN") is
When oxidized according to the above-mentioned known method, the yield of NDA is extremely low at less than 50% under reaction conditions suitable for oxidizing p-xylene and 2,6-dimethylnaphthalene, and a large amount of by-products are produced. The purity of NDA obtained from DIPN is also low, and therefore it is completely impossible to obtain NDA from DIPN industrially by the above-mentioned known method. There was no industrial consideration at all. Although the reason why the oxidation of DIPN did not give satisfactory results is not clear, the present inventors have found from many experiments that the oxidation of DIPN is different from the oxidation of other alkyl-substituted aromatic hydrocarbons. In the oxidation of DIPN, which has an isopropyl group and a naphthalene nucleus that have high activity and low oxidation stability, radicals and hydroperoxides are generated very easily and quickly due to hydrogen abstraction from the isopropyl group at the initial stage of the reaction, while the isopropyl group of the catalyst bromine is The addition to the furopyl radical, the accompanying decrease in catalyst activity, the resulting promotion of naphthalene nuclear cleavage, and the formation of stable catalyst complexes (such as ortho-benzenecarboxylic acid complexes) inactivation proceed rapidly in sequence. It is speculated that this is because the desired oxidation does not proceed sufficiently and side reactions are actually promoted. First, the present inventors suppressed the side reactions by using a much larger amount of cobalt and/or manganese than previously known amounts for the oxidized object in the oxidation of DIPN or its oxidized derivative. ,
He proposed a method for obtaining NDA in high yield (Patent Applications 1975-58, 58-197559, and 59-1979).
261765). These methods are extremely useful industrially because they yield higher yields and higher purity NDA than any conventionally known method, but on the other hand, they use large amounts of expensive and environmentally harmful catalyst metals. The drawback is that a great deal of consideration is required for handling, recovery, circulation, pollution prevention, etc. during these reactions. (c) Structure of the invention For this reason, the inventors have further developed an industrially advantageous structure.
As a result of continuing research on oxidation methods for DIPN or its oxidized derivatives, it was discovered that an extremely excellent effect can be obtained by allowing an alkali metal to exist in the presence of bromine used as a catalyst, and the present invention was achieved. That is, the present invention provides 2,6-diisopropylnaphthalene or an oxidized derivative thereof in a solvent containing at least 50% by weight of acetic acid, and (i) a heavy metal consisting of gobalt and/or manganese and (ii) a catalyst consisting of bromine. A method for producing 2,6-naphthalenedicarboxylic acid by oxidizing 2,6-naphthalene with molecular oxygen in the presence of 2,6-naphthalene, characterized in that the oxidation is carried out at a predetermined concentration in the presence of a specific alkali metal compound. This is a method for producing dicarboxylic acid. Conventionally, alkyl-substituted aromatic hydrocarbons, especially p-xylene, are oxidized with molecular oxygen in an aliphatic monocarboxylic acid using a catalyst consisting of heavy metals such as cobalt and manganese and bromine. The method of performing this in the coexistence of alkali metals such as sodium and potassium, alkaline earth metals such as _calcium , and _ammonium is known. Hydroxides such as HBr,
Used in combination with CoBr ₂ and MnBr ₂ . However, as far as is known so far, the effect of adding such alkali metals to the reaction system is extremely small with respect to the essence of the reaction, for example,
In Example 10 of Publication No. 25936 and Comparative Examples 6 to 8, when p-xylene was oxidized using cobalt acetate, manganese acetate, and hydrobromic acid as catalysts, sodium bromide and odorant were used instead of hydrobromic acid. It has been shown that the yield of terephthalic acid obtained when potassium chloride or ammonium bromide is used is slightly lower (97 mol% for the former and 96-94 mol% for the latter). . In addition, Japanese Patent Publication No. 59-8252 similarly states that in the oxidation of p-xylene, a specific amount (7/
Although a method of adding alkali metal atoms (9 or less) is shown, there is no mention of an increase or decrease in the yield of terephthalic acid due to this, but only a change in the properties of the product is shown. Japanese Patent Publication No. 56-3337 shows examples in which ammonium is added when dimethylnaphthalene is oxidized (Examples 1 to 3) and examples in which ammonium is not added (Example 6), but the yield of naphthalene dicarboxylic acid produced is is mostly 94-96 mol%. In this way, there are many examples in conventionally known literature, patent specifications, etc. of the addition of alkali metals, etc. to such oxidation reactions, but there is no mention of a particularly significant effect on the yield resulting from this. However, there are some descriptions (for example, JP-A-51-127037 and JP-B-49-25936) that state that it is unfavorable for the properties of the product. , it is difficult to think that the addition of an alkali metal is essentially essential for this oxidation reaction. In fact, in the experiments conducted by the present inventors, in the conventionally known oxidation reactions of p-xylene, dimethylnaphthalene, etc., the effect of adding alkali metals, ammonium, etc. was not observed to improve the yield by at most 5%, and the yield was almost the same or even better. In many cases, it showed a decrease. On the contrary, in the oxidation of DIPN or its oxidized derivative according to the present invention, as shown by the results of many examples described later, the effect of adding an alkali metal in the reaction is remarkable, and therefore the present invention It can be seen that the addition of alkali metal is essentially an essential element. In the present invention, the starting material is 2,6-diisopropylnaphthalene (DIPN) or its oxidized derivative, and although it is preferable that they have high purity, they are not necessarily pure, and the influence on the oxidation reaction or the purity of the NDA produced, Other components may be included within the range permitted for coloring. The oxidized derivative of DIPN is produced by oxidation of DIPN, and is oxidized in the reaction system to ultimately give the desired NDA. Therefore, the starting material of the present invention is specifically represented by the following general formula (). [However, R ₁ in the formula is

【formula】

【formula】

[Formula] A group selected from the group consisting of R ₂ is the group represented by R ₁ above and

[Formula] A group selected from the group consisting of -COOH and -CHO, which may be the same as or different from R ₁ . ] As a starting material, R ₁ in the above formula ()
and R ₂ are the same or different,

[Formula] and

Preferably, one selected from the following formula: In the present invention, as the oxidation catalyst, the following () to () are used as described above. () Heavy metal consisting of cobalt and/or manganese (component A) () Bromine (component B) and () Alkali metal (component C) Both components A and B are in a form that can be dissolved in the oxidation reaction system of the present invention. It may be any metal, element, or compound, if any. Examples of cobalt and manganese forming component A include inorganic salts such as oxides, hydroxides, carbonates, halides, especially bromides, as well as acetic acid and other aliphatic monocarboxylic acids or aromatic carboxylic acids, especially
Examples include organic acid salts such as NDA, but preferred among these are bromides and fatty acid salts, especially acetates. Further, the bromine forming component B may be any organic compound or inorganic compound as long as it dissolves in the oxidation reaction system and generates Br ions.
Specifically, for example, molecular bromine (Br ₂ ), hydrogen bromide, inorganic bromine compounds such as hydrobromide, methyl bromide, ethyl bromide, bromoform, ethylene bromide, other alkyl bromides, or bromoacetic acid. , organic bromine compounds such as brominated fatty acids such as polybromoacetic acid, but preferred among these are molecular bromine, hydrogen bromide, sodium bromide, potassium bromide,
Lithium bromide, cobalt bromide, manganese bromide, etc. These oxidation catalysts are generally thought to participate in the reaction as ions of their single salts or complex salts, with the B component forming coordination, bonding, or ion pairs with the A component, and therefore, such oxidation catalysts participate in the reaction during the reaction. Single metals or insoluble metal compounds in a state where it is difficult to form ions, or organic bromine compounds that are difficult to decompose and release bromide ions at the reaction temperature, such as nuclear brominated aromatic compounds, may be used as catalysts. The effect is small and it is not a good idea. No matter what compound form the bromine is added to the oxidation reaction system in the reaction of the present invention, a part of it is directly or secondarily added to the isopropyl side of the oxidized product DIPN or its oxidized derivative. It is easy to add to the chain to form these side chain organobromine compounds. Under the oxidation reaction conditions of the present invention, these are more or less decomposed to desorb and regenerate bromide ions. Therefore, such side chain bromine compounds of oxidizable substances are also effective as a source of the catalyst B component in the method of the present invention. The alkali metal forming component C, which is an important component of the present invention, is preferably carbonate, acetate, and bromide in addition to hydroxide; other salts bring other unnecessary ions into the reaction system. So this is not good. In particular, strong inorganic acid salts (other than bromides) such as sulfates, nitrates, and chlorides should be avoided. Preferred alkali metals are sodium, potassium, and lithium. Even if an alkaline earth metal such as ammonium, calcium, or barium is used as the C component in place of sodium, potassium, or lithium, the effect may be small or practically ineffective. The present inventors have filed the said patent application No. 58-197558, 58-
As described in the specifications of No. 197559 and No. 59-261765, in this oxidation reaction, from the viewpoint of reaction yield, the higher the ratio of component A to the raw material and the concentration of component A to the solvent, the better. is practically difficult to define. However, industrially, excessive use of catalyst leads to a decrease in productivity, and the use of the specific amount of alkali metal shown in the present invention allows for high reaction yields even with the use of a much smaller amount of catalyst than described in the above-mentioned patent. Therefore, the practical amount of component A used is in the range of 0.2 to 6.0% by weight, preferably 0.5 to 4.0% by weight of cobalt and/or manganese metal content based on the aliphatic monocarboxylic acid solvent used. It is. As component A, cobalt, manganese, or a mixture of both can be used. When using a mixture of cobalt and manganese, the preferred mixing ratio depends on, for example, reaction temperature, time, amount of catalyst used, amount of solvent used, etc. Range is affected. But usually
The Co:Mn atomic ratio is preferably in the range of 1:99 to 99:1, particularly 10:90 to 95:5. According to the observations of the present inventors, the optimum concentration of bromine used in the reaction depends not only on the concentration of component A used but also on other reaction conditions such as reaction temperature, raw material concentration, and amount of solvent. Therefore, it is difficult to uniquely regulate the bromine concentration in the method of the present invention, but in general, the atomic ratio to the A component used is 0.1 to 5.0, preferably 0.2 to 2.5.
degree is preferred. Generally, the lower the concentration of component A, the better this ratio is higher. In the method of the present invention, it is desirable that the concentration of DIPN and its oxidized derivatives during the reaction be kept not too high in order to prevent the rapid reaction described above. During the reaction, the concentration of DIPN and its oxidized derivatives in the reaction system preferably does not exceed a molar ratio of 2.0 to the component A in the catalyst present in the system, preferably 1.0 or less, especially 0.5 or less. Pair A of DIPN and its oxidized derivative in the reaction system
If the molar ratio of the components is high, no matter how well the catalyst concentration is maintained, it will be difficult to suppress the occurrence of side reactions due to the rapid progress of the reaction, and the desired product will not be produced.
A tendency for the yield of NDA to decrease is observed. However, in general, for continuous or at least semi-continuous reactions, the reaction temperature and oxygen concentration (oxygen partial pressure)
As long as the above conditions are maintained within a suitable range, the raw materials disappear quickly through the reaction, and it is relatively easy to maintain the raw material concentration during the reaction below the above-mentioned regulation value. The optimal concentration of the C component used in the method of the present invention depends on other reaction conditions and cannot necessarily be determined uniquely, but at least 0.8 g atoms per 1 g atom of bromine present in the reaction system is required, Below that, the yield of NDA is extremely low and is not practical. However, the higher the concentration of C component relative to bromine atoms, the better; if it is too high,
The yield of NDA may even decrease depending on the ratio of component B to component C. Also, from a practical standpoint, using an unnecessarily large amount of C component not only has no effect, but is often harmful, and from this point of view, the amount of C component used should be reduced per gram of bromine atom. It is preferable not to exceed 15.0g atoms. That is, the amount of component C used is 0.8 to 15.0 g atoms, more preferably 1.1 to 8.0 g atoms, and even more preferably 1.5 to 4.0 g atoms per 1 g of bromine atoms present in the reaction system.
It is an atom. When using C component in the reaction of the present invention, the most important factor is the ratio of B component to C component, and according to the inventor's experiments, C component/B component = 2/1 (g atomic ratio) is the best in terms of NDA yield. However, this ratio tends to be larger as the concentration of component B (bromine) is lower, and therefore, the optimum amount of component C to be used is most practically within the above range. In addition, even if the concentration of the C component is within the above range, the concentration of the C component should be adjusted to the acetic acid solvent used.
It is desirable that it does not exceed 4.0mol/1000g. The solvent used in the method of the present invention may be at least 50% acetic acid, and other solvents are not particularly limited. If necessary, it is used by appropriately mixing with water or other medium. If water is included, the proportion is 30
It is preferably less than 20% by weight, especially less than 20% by weight. Solvents are essentially used to dissolve at least a portion of the raw materials and catalyst and to help bring them into contact with molecular oxygen, but they also serve to dissipate and remove heat, improve the fluidity of the product, etc. Promotion of product crystal growth, etc.
The purpose is to facilitate the industrial implementation of the method of the present invention. Therefore, the amount to be used should be determined according to these purposes, and the amount of solvent used in the method of the present invention is essentially not regulated, but in practice it should be 1 to 1% of the total weight of the raw materials and target NDA in the system. It is convenient to use the amount up to 10 times, preferably 2 to 5 times. If the amount of solvent used is too small, the purpose of the present invention will not be fully achieved and the smooth progress of the reaction will be hindered.On the other hand, if the amount of solvent used is too large than the above amount, the reaction itself will be hindered. However, this is not a good idea as it will not accelerate the process and will only increase the loss due to oxidative combustion of the solvent. In the method of the present invention, in addition to pure oxygen, a mixed gas diluted with other inert gases is used as molecular oxygen, but air is the most easily available molecular oxygen-containing gas in practice, and It can be used as it is or after being concentrated or diluted with oxygen or other inert gas as necessary. Although the oxidation reaction in the method of the present invention is possible under normal pressure, it proceeds more rapidly under increased pressure. In general, the reaction proceeds more quickly as the oxygen partial pressure in the system is higher, but from a practical standpoint, the oxygen partial pressure should be 0.1 Kg/cm ² -abs or higher, preferably 0.2 Kg/cm ²
-abs or more 8Kg/cm ² -abs or less is sufficient,
When this is used in a mixed state with an inert gas, the reaction proceeds rapidly at a total pressure of 30 Kg/cm ² -G or less, and NDA can be obtained in high yield. Therefore, there is little industrial advantage in increasing the oxygen partial pressure to 8 Kg/cm ² -abs or higher. Although the reaction proceeds at 60°C, the reaction rate is slow and not necessarily economical. Also, the reaction temperature
When the temperature exceeds 240℃, the production ratio of by-products increases.
The yield of NDA decreases. Furthermore, at high temperatures, combustion loss of solvents such as acetic acid cannot be ignored. Generally the preferred reaction temperature is 120
A range of from 180 to 220°C is advantageous, more preferably from 160 to 230°C, particularly preferably from 180 to 220°C. In carrying out the oxidation reaction of the method of the present invention, the catalyst, solvent, and raw materials are charged into a reaction vessel simultaneously or separately (after heating if necessary), and a molecular oxygen-containing gas is blown into the reaction vessel. The reaction is carried out for a sufficient time until NDA is obtained while maintaining the predetermined pressure and temperature. As the reaction progresses, molecular oxygen is absorbed and a large amount of reaction heat is generated, so external heating is usually not necessary during the oxidation reaction, but rather heat is removed to maintain the predetermined reaction temperature. It is necessary to maintain At this time, heat removal can be carried out internally by evaporating the reaction medium such as acetic acid or water or accompanied by heat by releasing blown gas, or by cooling from the outside using a refrigerant such as water or steam, or both. This can be easily achieved by a known method such as using them in combination. When the raw materials in the reaction system disappear and the reaction approaches its end, the absorption of molecular oxygen appears to almost stop, but at this point there are still reaction intermediates in the reaction system that have not been completely converted to NDA. In some cases, the existence of In such cases, if necessary, the reaction can be completed by so-called post-oxidation, in which the product is further brought into contact with molecular oxygen, to improve the yield of NDA and at the same time eliminate unnecessary by-products and their intermediates. It is also possible to improve the purity of NDA produced by oxidative decomposition. Such post-oxidation can be carried out in the oxidation reaction vessel following the main oxidation reaction, or by transferring the main oxidation reaction to another vessel and contacting it with molecular oxygen for a required period of time. At this time, the post-oxidation reaction pressure,
The temperature does not need to be the same as for the main reaction, and may be higher or lower. After the completion of the reaction, separation and recovery of NDA from the reaction product mixture, purification of NDA, and post-treatment, circulation, and reuse of the reaction mother liquor from which NDA has been removed are performed using conventional methods known in the production of other NDA and terephthalic acid. You can do it accordingly. Although the method of the present invention can be carried out either batchwise or continuously, the batch reaction is not necessarily practical due to the low concentration of raw materials relative to the catalyst. As much as possible, the oxidation reaction is preferably carried out either continuously or by a so-called semi-continuous method in which the reaction is carried out by adding raw materials to the catalyst solution in small batches or continuously. As described above, by carrying out the method of the present invention, DIPN or its oxidized intermediate, which could only be obtained with low shrinkage, can be reduced.
NDA can now be easily obtained in high yield and purity, making it possible to industrially supply NDA at a lower cost and with higher quality than by any conventional method. The method of the present invention will be described in detail below with reference to Examples and Comparative Examples. In addition, in the following examples, all parts refer to parts by weight. Example 1 150 parts of glacial acetic acid and cobalt acetate tetrahydrate (Co(OAc) _2.4H ) were placed in a titanium-lined pressurized reaction vessel equipped with a reflux condenser, gas blowing pipe/discharge pipe, raw material continuous feed pump, and stirrer. ₂ O6.23 parts Manganese acetate tetrahydrate (Mn(OAc) ₂・4H ₂ O
6.13 parts potassium bromide (KBr) 2.98 parts potassium acetate (KOAc) ^7.36 parts were charged, and 2,6-diisopropyl. Naphthalene (DIPN)
The oxidation reaction was carried out by continuously feeding 53.08 parts over 4 hours and passing excess compressed air. After completing the feeding of DIPN, continue to heat at 200℃ and 30℃.
After completing the reaction by maintaining the air flow at Kg/cm ² -G for 1 hour, the reaction product was taken out and mainly produced as 2,6-naphthalene dicarboxylic acid (NDA).
The resulting solid precipitate was separated. After washing, drying and analyzing this, the yield of NDA was 45.55 parts, and the yield of this relative to DIPN was
It was 85.08 mol%. Examples 2 to 4 In a reactor similar to Example 1, 150 parts of glacial acetic acid, 6.23 parts of cobalt acetate/tetrahydrate, 6.13 parts of manganese acetate/tetrahydrate, 11.90 parts of potassium bromide, and 0.98 parts of potassium acetate in Example 2 were added. In Example 3, 9.81 parts and in Example 4, 29.44 parts were charged, and 53.08 parts of 2,6-diisopropyl naphthalene was continuously added thereto under vigorous stirring at a temperature of 200°C and a pressure of 30 kg/cm ² -G. The oxidation reaction was carried out by feeding the mixture over a period of 4 hours and passing an excess of compressed air. After completing the feeding of DIPN, continue to heat at 200℃ and 30℃.
After completing the reaction by continuing air circulation for 1 hour while maintaining the temperature at Kg/cm ² -G, the subsequent operations were carried out in the same manner as in Example 1, and the resulting 2,6-naphthalene dicarboxylic acid was recovered. The percentages are shown in Table 1 below.

【table】

[Table] Comparative Example 1 Cobalt acetate 4 in the same reactor as Example 1
Cobalt bromide hexahydrate (CoBr ₂ 6H ₂ O) 8.17 parts Manganese bromide tetrahydrate (MnBr ₂ 4H ₂ O) 7.17 parts acetic acid instead of manganese acetate tetrahydrate and potassium bromide The same reaction as in Example 1 was carried out except that 0 parts of potassium was used. The results are shown in Table-1. Comparative Example 2 Manganese acetate 4 was produced in the same reaction apparatus as in Example 1.
The reaction was carried out in the same manner as in Example 1, except that 7.17 parts of manganese bromide/tetrahydrate was used instead of aqueous salt, and 5.95 parts of potassium bromide and 0 parts of potassium acetate were added (6.23 parts of cobalt acetate/tetrahydrate remained unchanged). I went. The results are shown in Table-1. Example 5 Same as Examples 2 to 4 except that 10.29 parts of sodium bromide (NaBr) and 8.20 parts of sodium acetate (NaOAc) were used in place of potassium bromide and potassium acetate in the same reaction apparatus as in Examples 2 to 4. The reaction was carried out. The yield of the obtained 2,6-naphthalene dicarboxylic acid was 44.68 parts, and the yield relative to DIPN was 82.61 mol%. Comparative Example 3 The same reaction as in Comparative Example 1 was carried out except that 8.8 parts of calcium acetate monohydrate (Ca(OAc) ₂ H ₂ O) was further added to the reaction system shown in Comparative Example 1. The resulting solid was dark brown and contained a large amount of tar-like products, with a dry weight of 33.62 parts, but analysis revealed that its NDA content was only 52.14% by weight (equivalent to 17.53 parts), and the NDA yield was 32.75 mol. Example 6 In the same reaction apparatus as in Examples 2 to 4, 10.49 parts of lithium bromide (LiBr.H ₂ O) and 6.60 parts of lithium acetate (LiOAc) were used instead of potassium bromide and potassium acetate. The same reactions as in Examples 2 to 4 were carried out except that the reaction was carried out in the same manner as in Examples 2 to 4. The yield of the obtained 2,6-naphthalene dicarboxylic acid was 40.63 parts, and the yield relative to DIPN was 75.18 mol%. Comparative Example 4 Example Same as Examples 2 to 4 except that 9.79 parts of ammonium bromide (NH ₄ Br) and 7.71 parts of ammonium acetate (NH ₄ OAc) were used instead of potassium bromide and potassium acetate in the same reaction apparatus as in Examples 2 to 4. The resulting 2,6-naphthalene dicarboxylic acid was a brown solid with a dry weight of 42.95 parts.
Analysis revealed that the purity was low and the NDA yield was only 54.22 mol%.

[Claims]

linear equation (wherein R is alkylene), in a two-phase aqueous-organic reaction medium, the following formula is used: (wherein M ⁺ is an alkali metal) is subjected to a dihaloalkane reaction of the following formula: X ¹ -RX ² (wherein R is alkylene and each of X ^{1 and} the aqueous-organic phase biphasic reaction medium containing water, the reactant salts described above, and the dihydrogen salts described above;

Claims (1)

5. The method for producing 2,6-naphthalene dicarboxylic acid according to claim 1, wherein the oxidation is carried out at a temperature in the range of 160 to 230°C. 6. The method for producing 2,6-naphthalene dicarboxylic acid according to claim 1, wherein the oxidation is carried out under an oxygen partial pressure of 0.1 to 8.0 Kg/ ^cm2 . 7 The solvent is added to the 2,6-
1 of the total weight of diisopropylnaphthalene, its oxidized intermediate and 2,6-naphthalene dicarboxylic acid
A method for producing 2,6-naphthalene dicarboxylic acid according to claim 1, wherein at least 1 part by weight is used per part by weight.