JPH0571574B2 - - 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 isomers from mixed dimethylnaphthalene is difficult due to the melting point, boiling point, This was extremely difficult because the solubility characteristics were 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 2,6 monomers and other alkylation, disproportionation, isomerization, and trans-alkylation. It's 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 formed, and unlike in the case of oxidation of other alkyl-substituted aromatic hydrocarbons such as p-xylene or dimethylnaphthalene, it is possible to combine the isopropyl group, which has high activity and low oxidation stability, with the naphthalene nucleus. In the oxidation of DIPN, radicals and hydroperoxides are generated very easily and quickly due to hydrogen abstraction from the isopropyl group in the initial stage of the reaction. However, the stability of these radicals and hydroperoxides in the atmosphere is low, and their decomposition inhibits oxidation. Phenol (naphthol) with high properties and condensation properties
It is speculated that this is because the production of chemical compounds and the production of cleavage by-products due to their decomposition proceed rapidly, and as a result, the desired oxidation does not proceed sufficiently, and instead side reactions are promoted. . Previously, the present inventors suppressed the side reactions by using a much larger amount of cobalt and/or manganese than previously known for the oxidized object in the oxidation of DIPN or its oxidized derivative. proposed a method for obtaining NDA in high yield (see JP-A-60-89445, JP-A-60-89446 and JP-A-61-140540). 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 superior effect could be obtained by making an alkali metal present in the presence of bromine, which is 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 present 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. For this reason, the inventor has developed a method that is more industrially advantageous.
As a result of continued research on oxidation methods for DIPN or its oxidized derivatives, we also discovered that NDA could not be obtained in high yield without using such large amounts of cobalt and/or manganese in this oxidation. One of the reasons for this is that the acidity of acetic acid itself, which is used as a reaction solvent, is involved in the progress of the reaction. We discovered that it is possible to easily obtain NDA in high yield without using DIPN, and based on this knowledge, we have already published a patent application No. 60-257800 on a method to obtain NDA by oxidizing DIPN in propionic acid. proposed as a number. In this method, by simply replacing acetic acid, which has conventionally been widely used as the optimal solvent for the oxidation of alkyl-substituted aromatic hydrocarbons, with propionic acid, a higher yield can be achieved with the same amount of catalyst than in the case of acetic acid. For better yield, a smaller amount of catalyst is required.
It had the advantage of being able to obtain DIPN and NDA. However, in order to carry out this method industrially, propionic acid is considerably more expensive than acetic acid, so there are economical difficulties in its use. (c) Structure of the invention For this reason, the inventors have
As a result of continuing research to develop a more industrially advantageous oxidation method for DIPN or its oxidized derivatives when using propionic acid solvents, while retaining the advantages of No. 257800, we solved only its economic disadvantages. However, when the propionic acid used as a solvent in this oxidation is mixed with acetic acid, the superiority of propionic acid over acetic acid is proportional to the mixing ratio of the two, as would normally be expected in such a case. The present invention has been achieved by discovering that the expression is not expressed as a compound, but is significantly accentuated by replacing a relatively small amount of propionic acid with acetic acid. 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.
In a method of oxidizing with molecular oxygen in the presence of a catalyst containing at least one compound selected from the group consisting of propionate and bromide, the oxidation is carried out in a weight ratio to acetic acid.
2,6-diisopropylnaphthalene or an oxidized derivative thereof, characterized in that the reaction is carried out in a solvent containing a mixture of acetic acid and propionic acid in a ratio of from 90:10 to 50:50 at least 50% by weight of both in total. This is a method for producing 2,6-naphthalene dicarboxylic acid from Therefore, the present invention is a modification mainly based on the improvement of the earlier invention patent application No. 1983-257800 by the present inventor, and its effects are achieved when used in combination with the invention. 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. Methods for carrying out the process 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 accelerated or that there is any practical gain, and there are no examples in which a medium other than acetic acid is used as a medium for such an oxidation reaction, especially propionic acid used in the present invention. I can't find it. In particular, the effect of using acetic acid and propionic acid together while maintaining them within a specific ratio range as in the method of the present invention is a fact that was completely unknown in the oxidation method of alkyl-substituted aromatic hydrocarbons. . Furthermore, the method of the present invention is disclosed in the earlier patent application No. 60-157800.
Similar to the method in the above issue, it exhibits excellent effects in the presence of alkali metals, and this is also a completely unknown fact. In the oxidation of DIPN or its oxidized derivative of the present invention, as shown by the results of many examples described later, the effect of the combination of alkali metal and acetic acid and propionic acid in the reaction is remarkable, and this is due to the fact that p-xylene This effect is thought to be unique to the oxidation reaction of DIPN, unlike conventionally known oxidation reactions such as dimethylnaphthalene and dimethylnaphthalene. The first effect of the method of the present invention is that propionic acid, which is more expensive than acetic acid, is not used in large quantities as a solvent, but instead a small amount of propionic acid is used as a substitute for a part of cheap acetic acid. Gansho 60-
It is possible to maintain and exhibit the excellent reaction promoting effect when only propionic acid is used as the solvent in No. 257800. In other words, the patent application No. 60-257800
According to the method of the above issue, DIPN and its oxidized derivatives are oxidized with molecular oxygen in the presence of a catalyst consisting of cobalt manganese and bromine to obtain NDA, in which a specific amount of alkali metal is added to the catalyst, and the reaction is further carried out. When propionic acid is used instead of the conventionally known acetic acid as a solvent, the NDA yield at the same catalyst concentration is significantly improved compared to when the solvent consists of acetic acid, and it should be used to obtain the same NDA yield. Catalyst concentration can be significantly reduced. Therefore, compared to conventional oxidation methods such as p-xylene and dimethylnaphthalene, DIPN requires the use of a large amount of catalyst to obtain the desired product in high yield.
The biggest drawback in oxidation reactions is overcome by the method of the invention. On the other hand, the present invention takes the method of the prior invention one step further and uses a mixed solvent of acetic acid and propionic acid within a specific mixing ratio range instead of propionic acid as the solvent used in the method of the prior invention. This makes it possible to obtain a reaction promotion effect equal to or greater than when used alone. Furthermore, as a second effect of the method of the present invention, the product developed when propionic acid is used as a solvent, as previously shown in Japanese Patent Application No. 60-257800.
The coloring reduction effect of NDA is due to the effect of acetic acid and
It can be mentioned that even when a propionic acid mixed solvent is used, it is maintained as it is. That is, when oxidizing DIPN, which has lower oxidative stability than p-xylene or dimethylnaphthalene, in an acetic acid solvent, the yellowish brown coloration of the main product NDA, which has been an almost unavoidable fate, is due to propionic acid in the method of the present invention. By adding an appropriate amount of NDA, the coloration is significantly reduced, and NDA with high purity and slightly yellowish white crystals can be easily obtained, and since there is almost no contamination of the catalyst etc. in the crystals, post-processing and purification operations are unnecessary. The advantage of ease of use has also become clear. 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 , may contain other components within an acceptable range for coloring. Oxidized derivatives of DIPN are produced by oxidation of DIPN,
Moreover, it ultimately gives the desired NDA by being oxidized in the reaction system. 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】

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

[Formula] A group selected from the group consisting of -COOH and -CHO, and R ₁
may be the same or different. ] 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. 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, cobalt bromide, manganese bromide, etc. It is. 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. Metal units 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 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 component C 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 bromine) 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 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. 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 are constituent cobalt, manganese, bromine, and alkali metal ions that promote the reaction, and when these ions are used, they form compounds. Although the 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, as far as possible, the A, B, and C components to be used should be salts of the constituent cobalt, manganese, bromine, and alkali metal ions, or salts of these and the solvent used for the reaction. Preferably, other salts (e.g. carbonates,
(With the exception of salts such as hydroxides or free acids that produce only harmless compounds such as carbon dioxide gas and water, which are reaction by-products of the present invention, and which do not accumulate in the system) Since other ions are brought in, it is best to avoid using them unless they are particularly volatile or non-accumulative. The present inventors disclosed the above-mentioned Japanese Unexamined Patent Publication Nos. 60-89445 and 60-89445.
As described in No. 89446 and JP-A-61-140540, 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. In fact, it is difficult to define the upper limit. However, industrially, excessive use of a catalyst will lead to a decrease in productivity, and the use of a specific amount of alkali metal as shown in the present invention and acetic acid/propionic acid mixed solvent within a specific mixing ratio will result in a decrease in productivity as described in the above patent. Since a high reaction yield can be achieved with a much smaller amount of catalyst than the above, the practical amount of component A used is 0.2 to 5.0% by weight of the cobalt and/or manganese metal content, preferably 0.2 to 5.0% by weight of the solvent used. It ranges from 0.4 to 4.0% by weight, more preferably from 0.5 to 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 20 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 15 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, 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, it is preferable that the concentration of DIPN and its oxidized derivatives in the reaction system does not exceed a molar ratio of 2.0, particularly 1.0 or less, relative to the A component in the catalyst present in the system.
In particular, 0.5 or less is appropriate. 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 may be 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. not only does not increase in proportion to the concentration of component B, but also component B and C described later.
Regardless of the ratio of component B to component B, if the degree of dryness of component B is too high, the yield of NDA may actually decrease. From a practical standpoint, it is undesirable 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 0.5
~5.0 is preferable. Generally, the lower the concentration of component A, the higher this ratio is. 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 the bromine concentration present in the reaction system is
0.8g atoms per 1g atom 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; above a certain level, almost no NDA
The yield not only does not increase in proportion to the concentration of the C component, but also depends on the ratio of the B component to the C component.
If the concentration of the components is too high, the yield of NDA 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 should be reduced per gram of bromine atom. It is preferable not to exceed 6.0g atoms. That is, the amount of C component used is 0.8 to 15.0 g atoms per 1 g of bromine atoms present in the reaction system, more preferably
1.1 to 8.0 g atoms, more preferably 1.5 to 6.0 g atoms. According to the research conducted by the present inventors, the best C component/B component ratio 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. Further, it is desirable that the concentration of the C component does not exceed 4.0 mol/1000 g of the acetic acid/propionic acid mixed solvent used even if its ratio to bromine is within the above range. The solvent used in the method of the present invention may be at least 50%, preferably 70% or more, and even more preferably 80% or more of an acetic acid/propionic acid mixture, and the rest is not particularly limited. If necessary, it is used by appropriately mixing with water and other catalysts. If water is included, its 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. The mixing ratio of acetic acid and propionic acid in the acetic acid/propionic acid mixture used as a solvent does not change the effect on the reaction based on the arithmetic average of the two, but if the ratio of propionic acid to acetic acid is too small, the effect will not be expressed. This cannot be expected, and when the weight ratio of acetic acid to propionic acid is less than 90:10, almost no practical effect is observed. When the ratio of propionic acid to acetic acid increases beyond 90:10, the effect on the reaction, especially the NDA yield for the same amount of catalyst, increases in proportion to the ratio, and this effect becomes particularly noticeable at 75:25 or higher. However, the larger the ratio of propionic acid to acetic acid, the better; with a weight ratio of acetic acid to propionic acid of 50:50,
The NDA yield almost reached a maximum, and even if the ratio of propionic acid to acetic acid was further increased, no increase in effect was observed. Practically speaking, the smaller the ratio of the more effective propionic acid to the cheaper acetic acid, the better. From this point of view, the preferred ratio of acetic acid to propionic acid as a solvent used in the method of the present invention is a weight ratio of 75: 25 to 50:
It is 50. 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 method of the present invention allows the oxidation reaction to occur under normal pressure, it proceeds more rapidly under increased pressure. In general, the higher the oxygen partial pressure in the system, the faster the reaction will proceed; 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 higher.
cm ² -abs or more and 8 Kg/cm ² -abs or less is sufficient, and even when used in a mixed state with an inert gas, the reaction proceeds quickly and at a total pressure of 30 Kg/cm ² -G or less. NDA can be obtained based on the yield. Therefore,
There is little industrial advantage in setting 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 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. Therefore, during the oxidation reaction, external heating is not only unnecessary, but rather heating is performed gradually to maintain the predetermined reaction temperature. It is necessary to maintain In this case, heat removal can be carried out internally by evaporating the reaction medium or entraining heat by releasing blown gas, or by cooling from the outside using a refrigerant such as water or steam, or by using a combination of both. This is easily possible using known methods. 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 a so-called post-oxidation process in which the NDA 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 implementing the method of the present invention, NDA, which could conventionally be obtained only in low yield without using a high concentration catalyst from DIPN or its oxidized intermediate, can be easily obtained in high yield and high yield by using a low concentration catalyst. NDA can now be obtained with high 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. Examples 1 to 4, Comparative Examples 1 to 3 Gas discharge pipe with reflux condenser, gas blowing pipe,
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 and a total of 150 parts of the acetic acid/propionic acid mixture shown in Table 1 were charged at a temperature of 200℃ and a pressure of 30Kg/cm ² -G. 53.08 parts of 2,6-diisopropylnaphthalene (DIPN) was continuously added to this with vigorous stirring under the conditions of
The oxidation reaction was carried out by feeding over 4 hours and passing excess compressed air. After completing the feeding of DIPN, continue to heat at 200℃, 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 consisting of was separated. This was washed with hot acetic acid and hot water and dried, and the composition of the obtained solid product was determined using a gas chromatograph. In addition, the mother liquor from which the precipitate was separated and the washings are combined, most of the water and acetic acid/propionic acid are distilled off, and the remaining components are extracted with water and ether to remove organic substances (mainly reaction intermediates consisting of trimellitic acid (abbreviated as TMA in the table)). and by-products) and inorganic substances (catalysts), and the composition of the organic substances was determined using gas chromatography. The results are shown in Table-1.

[Table] *○ Weight%
Example 5 A reaction apparatus similar to Example 1 was charged with 3.11 parts of cobalt acetate tetrahydrate, 6.13 parts of manganese acetate tetrahydrate, 8.93 parts of potassium bromide, 7.35 parts of potassium acetate, and a mixture of 112.5 parts of acetic acid and 37.5 parts of propionic acid. The same reaction operation as in the example was carried out. The reaction result was a yield of NDA88.88 mol%,
TMA was 11.04%, and others were 1.20% by weight (all based on the starting materials).

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,
In a method of oxidizing with molecular oxygen in the presence of a catalyst containing at least one compound selected from the group consisting of propionate and bromide, the oxidation is carried out in a weight ratio of 90:10 to 50:1 to acetic acid. 2,6-diisopropylnaphthalene or an oxidized derivative thereof, characterized in that it is carried out in a solvent containing at least 50% by weight of acetic acid and propionic acid in total, including propionic acid which is 2,6-diisopropylnaphthalene or an oxidized derivative thereof. Method for producing naphthalene dicarboxylic acid. 2 The oxidation is carried out at a weight ratio of acetic acid to propionic acid of 75:
A method according to claim 1, which is carried out using a mixture of acetic acid and propionic acid in a ratio of 25 to 50:50.