JPH0564938B2 - - 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, it relates to a method for obtaining the desired 2,6-naphthalene dicarboxylic acid in an extremely high yield by carrying out the oxidation in a propionic acid-containing solvent in the presence of a catalyst containing heavy metals, bromine, and alkali metals. (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, NDA has been produced by an oxidation reaction of 2,6-dimethylnaphthalene, for example, 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. Are 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. The production of isomers other than 6-dimethylnaphthalene, especially 2,7-dimethylnaphthalene, cannot be avoided, and the isolation of 2,6-isomer from mixed dimethylnaphthalene has a melting point of 2,7-isomer and
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, and trans-alkylation. is also relatively easy. 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 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 yield satisfactory results is not clear, the present inventors have found from numerous experiments that the production yield of the target product NDA is low in this oxidation reaction. If it is low, the relative yield of trimellitic acid (hereinafter sometimes abbreviated as "TMA"), a byproduct of naphthalene cleavage, is high, and in particularly severe cases, it may be a tar-like or resin-like product of unknown structure, or a polycondensation product. It was discovered that a large amount of the product is produced, and unlike in the case of oxidation of other alkyl-substituted aromatic hydrocarbons such as p-xylene or dimethylnaphthalene, the isopropyl group, which has high activity and low oxidation stability, and the naphthalene nucleus are combined. In the oxidation of DIPN, radicals and hydroperoxides are generated very easily and quickly due to hydrogen abstraction from isopropyl groups at the initial stage of the reaction. However, these radicals and hydroperoxides have low stability in the atmosphere, and their decomposition causes oxidation interference. Phenol (naphthol) with high condensation properties
It is speculated that this is because the production of chemical compounds and the production of nuclear cleavage by-products due to their decomposition proceed rapidly in sequence, which prevents the desired oxidation from proceeding sufficiently and instead accelerates side reactions. . First, the present inventors investigated the above-mentioned side reactions by using a much larger amount of cobalt and/or manganese in the oxidation of DIPN or its oxidized derivatives than previously known amounts for the oxidized material. We have previously proposed a method for suppressing NDA and obtaining NDA in high yield (see Japanese Patent Application Laid-open Nos. 60-89445 and 60-89446, and Japanese Patent Application No. 59-261765). 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. Therefore, the present inventors have further developed an industrially advantageous method.
As a result of continuing research on oxidation methods for DIPN or its oxidized derivatives, we proposed that an extremely excellent effect could be obtained by allowing an alkali metal to exist in the bromine used as a catalyst in an acetic acid solvent. 60-86563). This method has the advantage that by simply making a specific amount of alkali metal exist relative to the catalytic bromine, the same effect can be obtained even with a much smaller amount of the catalytic metal compared to previous proposals. It was hot. However, under suitable conditions in this method,
In order to obtain the desired NDA with a high yield of 80% or more,
1% by weight or more, preferably about 2% by weight or more based on the solvent acetic acid, or based on 100 moles of the oxidation raw material DIPN or its oxidized derivative
More than 10 gram atoms, preferably more than 20 gram atoms, of catalyst metal were required. (c) Structure of the invention For this reason, the inventor has developed a more industrially advantageous method.
As a result of continuing research on oxidation methods for DIPN or its oxidized derivatives, we unexpectedly discovered that NDA could not be obtained in high yield without using such a large amount of cobalt and/or manganese in this oxidation. One of the reasons for this was that the acidity of acetic acid itself, used as a reaction solvent, was involved in the progress of the reaction. Furthermore, to avoid this, when using propionic acid instead of acetic acid as a solvent,
Easy and high yield without using large amounts of catalyst
We discovered that it is possible to obtain an NDA and arrived at the present invention. That is, the present invention provides 2,6-diisopropylnaphthalene or its oxidized derivative with (i) a heavy metal consisting of cobalt and/or manganese, (ii) bromine, and (iii) an alkali metal hydroxide, carbonate, or acetate.
2,6 characterized in that the oxidation is carried out with molecular oxygen in a solvent containing at least 50% by weight of propionic acid in the presence of a catalyst containing at least one selected from the group consisting of propionate and bromide. - A method for producing naphthalene dicarboxylic acid. Conventionally, alkyl-substituted aromatic hydrocarbons, especially p-xylene, are oxidized with molecular oxygen in a resinous monocarboxylic acid using a catalyst consisting of heavy metals such as cobalt and manganese and bromine. Methods for performing this in a medium other than acetic acid are known, and it was believed that benzoic acid, propionic acid, water, etc. can be used for that purpose. However, as far as is known so far, it is only known that such media other than acetic acid can be used in place of acetic acid, and this substitution substantially improves the reaction compared to when acetic acid is used. There is no description that the oxidation reaction is promoted or that there is any practical gain, and there are no examples in which a medium other than acetic acid, especially the propionic acid used in the present invention, is used industrially as a catalyst for such an oxidation reaction. I can't find it. In particular, the effect of the combined use of aryl metal and propionic acid as in the method of the present invention is a fact that has not been previously known in the oxidation method of alkyl-substituted aromatic hydrocarbons. In the oxidation of DIPN or its oxidized derivatives of the present invention, as shown by the results of many examples described later, the effect of the combined use of an alkali metal and propionic acid in the reaction is remarkable;
-Unlike conventionally known oxidation reactions such as xylene and dimethylnaphthalene, this effect is thought to be unique only to the oxidation reaction of DIPN. The first effect of the method of the present invention is an improvement in the yield of NDA. That is, in the method of obtaining NDA by oxidizing DIPN and its oxidized derivatives with molecular oxygen in the presence of a catalyst consisting of cobalt, manganese and bromine, a specific amount of alkali metal is added to the catalyst, and a conventionally known reaction solvent is added. When propionic acid is used instead of acetic acid, the NDA at the same catalyst concentration is lower than when the solvent consists of acetic acid.
Yields are significantly improved and the catalyst concentration that must be used to obtain equivalent NDA yields can be significantly reduced. Therefore, compared to conventional oxidation methods such as p-xylene and dimethylnaphthalene, the desired product could not be obtained in high yield unless a large amount of catalyst was used.
It can be said that the disadvantages of DIPN oxidation have been overcome by the method of the present invention. Furthermore, according to the method of the present invention, when propionic acid is used as the reaction solvent instead of the known acetic acid, an unexpected advantage has been found that as a side effect, the degree of coloration of the produced NDA is significantly reduced. It was done. In other words, when oxidizing DIPN, which has lower oxidative stability than p-xylene or dimethylnaphthalene, it has been almost inevitable that the main product, NDA, will be colored yellowish brown, but the propionic acid of the present invention NDA, which is the main product during oxidation in a solvent, is
It is easily obtained as highly pure, slightly yellowish white crystals, and there is almost no catalyst contamination in these crystals, so it has become clear that the post-treatment and purification operations are easy, which was a totally unexpected advantage. Summer. 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 shown 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 a group represented by the above R ₁ 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. () A heavy metal consisting of cobalt and/or manganese (component A), () bromine (component B), and () at least one selected from the group consisting of hydroxides, carbonates, acetates, propionates, and bromides of alkali metals. Type 1 (Component C) Component A and component B may be any metal, element, or compound as long as they are in a form that can be dissolved in the oxidation reaction system of the present invention. Cobalt and manganese forming component A include, for example, inorganic salts such as oxides, hydroxides, carbonates, halides, especially bromides, as well as organic acid salts such as acetic acid, propionic acid, or aromatic carboxylic acids, especially NDA. Preferred among these are bromide and fatty acid salts, especially acetate and propionate. 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, inorganic bromine compounds such as molecular bromine (Br ₂ ), hydrogen bromide, and hydrobromide, or methyl bromide, ethyl bromide, bromoform, ethylene bromide, and other alkyl bromides or bromo Examples include organic bromine compounds such as brominated fatty acids such as acetic acid and polybromoacetic acid, but preferred among these are molecular bromine, hydrogen bromide, sodium bromide, potassium bromide, lithium bromide, or cobalt bromide. Manganese bromide, etc. These oxidation catalysts are generally thought to participate in the reaction as ions in their single salts or complex salts, with component B forming coordination, bonding, or ion pairs with component A, and therefore, such ions 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. There is no effect at all, or even if there is, it is so small that it is not a good idea. In the reaction of the present invention, bromine added to the oxidation reaction system, no matter what compound form it is given, is partially absorbed directly or secondarily into 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 a side chain bromine compound of the oxidizable substance is also effective in the reaction of the present invention as a source of the catalyst B component in the method of the present invention. As the alkali metal forming the C component used in the method of the present invention, hydroxides, carbonates, acetates, propionates, and bromides are preferable, and in particular sulfates, nitrates, chlorides, etc. (other than bromides) are preferable.
Strong inorganic acid salts should be avoided. Preferred alkali metals are sodium, potassium, and lithium. Even if an alkaline earth metal such as aluminum, calcium, or barium is used as the C component in place of sodium, potassium, or lithium, the effect may be small or practically ineffective. However, no particular harm is observed when these are used in combination with the alkali metals. The A component, B component, and C component used in the method of the present invention promote the reaction as cobalt, manganese, bromine, and alkali metal ions that constitute them, and the components that form compounds when these ions are used. Although ions have a secondary effect of maintaining the solubility and dispersibility of the compound, they do not essentially have a promoting effect on the reaction of the present invention. Therefore, the A component, B component, and C component to be used should contain cobalt, manganese,
It is preferable to use salts of bromine and alkali metal ions with each other or with the solvent used for the reaction; other salts (such as carbonates, hydroxides, or free acids) are preferably used. (With the exception of salts that produce only harmless compounds such as carbon dioxide and water, which are reaction by-products of the present invention, and which do not accumulate in the system), they bring other unnecessary ions into the reaction system, so they are especially easily volatile or non-volatile. Other than those that accumulate,
It is better to avoid its use. The present inventors disclosed the above-mentioned Japanese Unexamined Patent Publication Nos. 60-89445 and 60-89445.
As stated in Publication No. 89446 and Japanese Patent Application No. 59-261765, in this oxidation reaction, as far as the reaction yield is concerned, the ratio of component A to the raw material and the concentration of component A to the solvent are both high. The higher the value, the better, and the upper limit is practically difficult to specify. However, industrially, excessive use of catalyst leads to a decrease in productivity, and the use of the specific amounts of alkali metal and propionic acid solvent shown in the present invention results in a much smaller amount of catalyst than described in the above patent. Since a high reaction yield can be achieved by using the component
or 0.2-5.0% by weight of manganese metal content,
Preferably 0.4 to 4.0% by weight, more preferably 0.5 to 4.0% by weight
It is in the range of 3.0% by weight. In addition, the ratio of component A to the raw material used is 1 to 30 g atoms, preferably 2 to 15 g atoms of the heavy metal consisting of cobalt and/or manganese, per 100 moles of the raw material 2,6-diisopropylnaphthalene or its oxidized derivative. More preferably 3 to 10 gram atoms are sufficient. As component A in the method of the present invention, either cobalt or manganese or a mixture of both is used. When these are used alone, manganese is preferable because it exhibits better activity than cobalt, but especially when cobalt and manganese are used in combination, when either one is used alone, It is the most excellent catalyst for the present invention because it exhibits extremely high activity. When using a mixture of cobalt and manganese, the mixing ratio is determined by, for example, the reaction temperature, time, amount of catalyst used,
The preferred range depends on the amount of solvent used. However, the atomic ratio of Co:Mn is preferably in the range of 1:99 to 99:1, particularly 10:90 to 95:5. In the method of the present invention, the concentration of DIPN and its oxidized derivatives during the reaction is desirably 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. According to the research of the present inventor, the optimal concentration of bromine used as component B in the reaction depends not only on the concentrations of components A and C used, but also on other reaction conditions such as reaction temperature, raw material concentration, and amount of solvent. . Therefore, it is difficult to unambiguously regulate the bromine concentration in the method of the present invention, but unlike component A, the higher the concentration of bromine in component B, the better it is; above a certain concentration, the NDA yield is almost negligible. Not only does it no longer increase in proportion to the concentration of component B, but also the yield of NDA tends to decrease if the concentration of component B is too high, depending on the ratio of component B and component C described later. . From a practical standpoint, it is not preferable to use an unnecessarily large amount of component B, so the concentration of component B should be within a range that does not exceed 2.0 mol per 1000 g of the solvent used, and in an atomic ratio to component A used.
0.1-20, preferably 0.3-10.0, more preferably
Approximately 0.5 to 3.0 is preferable. Generally, the lower the concentration of component A, the higher this ratio is. The optimum concentration of the C component used in the method of the present invention depends on other reaction conditions and cannot necessarily be determined unambiguously, but it is necessary to have at least 0.8 g atoms per 1 g atom of bromine present in the reaction system, 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;
Not only does the NDA yield not increase in proportion to the concentration of the C component, but depending on the ratio of the B component to the C component, if the concentration of the C component is too high, the NDA yield may actually decrease. . 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 is lower than the amount per gram of bromine atom. It is preferable not to exceed 6.0g atoms. That is, the amount of component C used is 0.8 to 6.0 g atoms, more preferably 1.1 to 4.0 g atoms, and even more preferably 1.5 to 3.0 g atoms per 1 g of bromine atoms present in the reaction system. According to the research conducted by the present inventors, the best ratio of C component/B component is approximately 2/1 (g atomic ratio). 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 component C is within the above range, the concentration of component C should be determined relative to the propionic 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 contain at least 50% propionic 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. Water is produced as a by-product in the reaction of the present invention, and therefore it is practically difficult to completely avoid the presence of water in the reaction solvent during the reaction. However, in the oxidation of DIPN, p-xylene and dimethylnaphthalene The presence of water tends to have a more negative effect on the reaction than in other cases. 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. Promote crystal growth of products, 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 and 8Kg/cm ^2- abs or less is sufficient, and when used in a mixed state with an inert gas, the reaction proceeds quickly at a total pressure of 30Kg/cm ^2- G or less with high yield. You can get an NDA. 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 the solvent cannot be ignored. Generally, the preferred reaction temperature is 120-240℃,
More preferably 160-230℃, particularly preferably 180℃
A range of ~220°C is advantageous. 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 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 is either internal heat removal such as accompanying heat due to evaporation of the reaction medium or release of blown gas, or external cooling using a refrigerant such as water or steam, or both. This is easily possible using the known method. When the raw materials in the reaction system disappear and the reaction approaches the 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 is carried out either directly in the oxidation reaction vessel following the main oxidation reaction, or by transferring the main oxidation reaction to a separate 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. The method of the present invention can be carried out either batchwise or continuously; however, batch reactions require a low concentration of raw materials relative to the catalyst as described above, and are not necessarily practical. 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, NDA, which could conventionally be obtained only in low yield from DIPN or its oxidized intermediate, can now be easily obtained in high yield and high purity, and can be obtained industrially by any conventional method. It has become possible to supply NDA at a lower price and with higher quality. 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 Gas discharge pipe with reflux cooler, gas blowing pipe,
150 parts propionic acid cobalt acetate tetrahydrate (Co(OAc) _{2.4H 2} O) in a titanium-lined pressurized reaction vessel with a continuous feed pump and a stirrer.
3.11 parts manganese acetate tetrahydrate (Mn(OAc) _{2.4H 2} O)
3.06 parts potassium bromide (KBr) 11.90 parts potassium acetate (KOAc) 9.81 parts were charged and ^2,6 -diisopropylnaphthalene ( DIPN) 53.08 parts continuously
The oxidation reaction was carried out by feeding over 4 hours and passing excess compressed air. After completing the DIPN delivery, 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. This was washed with hot acetic acid and hot water and then dried.
49.13 parts of a yellowish white microcrystalline product with an NDA purity of 99.88% was obtained. This corresponds to a yield of 90.80 mol% based on the raw material DIPN used. Comparative Example 1 The same reaction as in Example 1 was carried out in the same reaction apparatus as in Example 1 except that 150 parts of acetic acid was used instead of propionic acid. As a result, the product obtained is
It was 42.53 parts of a tan solid with an NDA purity of 98.41%.
This is the yield based on the raw material DIPN used.
This corresponds to 77.44 mol%. Example 2 A catalyst heavy metal salt was converted to cobalt acetate tetrahydrate (Co(OAc) ₂ ·4H ₂ O) in the same reactor as in Example 1.
1.56 parts manganese acetate tetrahydrate (Mn(OAc) _{2.4H 2} O)
The same reaction as in Example 1 was carried out except that the amount was changed to 1.53 parts. The resulting product has an NDA purity of 99.00%
of 43.57 parts of pale ocher solid, corresponding to a yield of 79.82 mol% based on DIPN. Example 3 A catalyst heavy metal salt was converted to cobalt acetate tetrahydrate (Co(OAc) ₂ 4H ₂ O) in the same reactor as in Example 1.
12.45 parts manganese acetate tetrahydrate (Mn(OAc) _{2.4H 2} O)
The same reaction as in Example 1 was carried out except that the amount was changed to 12.25 parts. As a result, the product obtained was almost pure NDA.
50.20 parts of yellowish white microcrystals consisting of raw material
This corresponds to a ratio of 92.88 mol% to DIPN.

Claims (1)

[Scope of Claims] 1. 2,6-diisopropylnaphthalene or its oxidized derivative, (i) a heavy metal consisting of cobalt and/or manganese, (ii) bromine, and (iii) an alkali metal hydroxide, carbonate, acetate,
2, characterized in that the oxidation is carried out with molecular oxygen in a solvent containing at least 50% by weight of propionic acid in the presence of a catalyst containing at least one selected from the group consisting of propionate and bromide; Method for producing 6-naphthalene dicarboxylic acid.