JPH0335307B2 - - 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 intermediate 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 a solvent containing an aliphatic monocarboxylic acid 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 is
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 other isomers other than 6-dimethylnaphthalene, especially 2,7-dimethylnaphthalene, cannot be avoided, and isolation of the 2,6-isomer from mixed dimethylnaphthalene is difficult since the 2,7-isomer and the melting point, This was extremely difficult because the boiling point and solubility characteristics were very 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-mentioned known method, the yield of NDA is extremely low under reaction conditions suitable for oxidizing p-xylene and 2,6-dimethylnaphthalene.
NDA obtained due to the formation of large amounts of by-products
The purity of DIPN was also low, and therefore it was completely impossible to industrially obtain NDA from DIPN by the above-mentioned known method. In the above-mentioned method of oxidizing in an aliphatic monocarboxylic acid solvent using a catalyst consisting of heavy metals such as cobalt and manganese and bromine, various alkyl-substituted aromatic hydrocarbons, especially alkyl-substituted naphthalenes such as dimethylnaphthalene, are oxidized. When the desired product is not obtained in low yield or its purity is low when oxidizing the same, the following two methods have conventionally been adopted as remedies. One way is to divide this oxidation reaction into multiple steps,
This is a so-called multi-step heating reaction method in which the reaction temperature is raised stepwise or continuously from an initial reaction at a low temperature to complete the reaction. For example, in Japanese Patent Application Laid-open No. 52-17453, there are 2,6
-An example is described in which dimethylnaphthalene is oxidized in two steps at temperatures of 100°C and 190°C to obtain NDA in a yield of 91% (74% in a single step of oxidation at 190°C). However, DIPN
Even when applied to the oxidation of
It is only about 50% and cannot be called industrial (see Comparative Example 2 described later). Another improvement measure is the so-called low-concentration raw material oxidation method, in which the oxidation reaction is carried out while keeping the concentration of the raw material to the solvent in the reaction system low. For example, Japanese Patent Publication No. 56-3337, Japanese Patent Application Publication No. 1983-
Publication No. 142544 and Japanese Patent Application Laid-open No. 1979-7945, etc., describe that NDA or the corresponding naphthoic acid can be obtained in relatively high yields by using a low concentration oxidation method of raw materials in the oxidation of dimethylnaphthalenes and acenaphthenes, respectively. has been done. However, such low concentration raw material oxidation method is
Even when applied to the case of the oxidation reaction, the yield of produced NDA is still far from being industrially satisfactory (see Comparative Examples 3, 4, 5, and 6 described later). In this way, the production of NDA by oxidation of DIPN is
In the oxidation of alkyl aromatic hydrocarbons, even if the known conditions of the oxidation reaction using heavy metals and bromine, which is said to be the most powerful oxidation method, are used, the application of conventional knowledge to the method is still insufficient. Therefore, until now, DIPN using this method
The production of NDA from 100% has never been considered industrially. Although it is not clear why the oxidation of DIPN did not yield satisfactory results,
The present inventors have found through many experiments that unlike the oxidation of other alkyl-substituted aromatic hydrocarbons, the production of oxidized intermediates is abnormally rapid in the early stage of the reaction, and that the oxidation reaction mixture The catalyst inside temporarily loses its activity,
It is surmised that this is because the desired oxidation does not proceed sufficiently, and rather side reactions are promoted. As a result of our research aimed at suppressing the decrease in the yield of NDA due to the side reaction in the oxidation of DIPN, the present inventors found that DIPN
When oxidizing 2,6-naphthalene dicarboxylic acid (NDA) by oxidizing or its oxidized intermediate, the use of much higher amounts of heavy metal per solvent present in the oxidation reaction mixture than previously known; Unexpectedly, we have found that the yield of NDA is dramatically increased and have arrived at the present invention. That is, the present invention uses DIPN or its oxidized intermediate as an aliphatic monocarboxylic acid having 3 or less carbon atoms.
In a method for producing 2,6-naphthalene dicarboxylic acid by oxidation with molecular oxygen in a solvent containing 50% by weight, the oxidation is carried out using a heavy metal consisting of (i) cobalt and/or manganese and (ii) a catalyst consisting of bromine. 2,6-diisopropylnaphthalene in the presence of 2,6-diisopropylnaphthalene and in the presence of at least 1% by weight of the heavy metal based on the solvent. In the present invention, the starting material is 2,6-diisopropylnaphthalene (DIPN) or its oxidized intermediate, and although it is preferable that they have high purity, they do not necessarily have to be pure, and may affect the oxidation reaction or the NDA produced. Other components may be included within acceptable ranges for purity and coloring. DIPN oxidation intermediate is produced by oxidation of DIPN,
Moreover, it ultimately gives the desired NDA by being oxidized in the reaction system. Therefore, the starting materials of the present invention are specifically shown in the following general formula (). [However, R ₁ in the formula is

【formula】

【formula】

[Formula] and

A group selected from the group consisting of [Formula], R ₂ is a group represented by R ₁ above and -
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, (i) a heavy metal (A
component) and (ii) bromine (component B) are used. Component A and component B may be any metal, element, or compound as long as they can be dissolved in the oxidation reaction system of the present invention. Examples of cobalt and manganese forming component A include inorganic salts such as oxides, hydroxides, carbonates, halides, especially bromides, as well as formic acid, acetic acid, propionic acid, naphthenic acid, or aromatic carboxylic acids, especially NDA. Among these, preferred are bromides and fatty acid salts, especially acetates. In addition, as the bromine that forms the B component, if it dissolves in the oxidation reaction system and generates Br ions,
It may be either an organic compound or an inorganic compound. Specifically, for example, inorganic bromine compounds such as molecular bromine (Br ₂ ), hydrogen bromide, 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, ammonium bromide and These include ethyl bromide, bromoacetic acid, cobalt bromide, manganese bromide, etc. These oxidation catalysts are generally considered to participate in the reaction as ions of their single salts or complex salts, and therefore, they are considered to be simple metals or insoluble metal compounds in a state where it is difficult to form such ions during the reaction, or decompose at the reaction temperature. Organic bromine compounds that are difficult to remove bromide ions from, such as nuclear brominated aromatic compounds, are not advisable because their effectiveness is small even if they are used as catalysts. As component A in the oxidation catalyst of the present invention, either cobalt, manganese, or a mixture of both is used, and manganese is preferred because it exhibits better activity than cobalt. In particular, when cobalt and manganese are used in combination, they exhibit extremely high activity compared to when either of them is used alone, and is therefore the most excellent catalyst for the present invention. When a mixture of cobalt and manganese is used as component A of the catalyst, the preferred range of the mixing ratio depends on, for example, reaction temperature, time, amount of catalyst used, amount of solvent used, etc. However, the atomic ratio of Co:Mn is usually 1:99 to 99:1,
Particularly preferred is a range of 10:90 to 95:5. The solvent used in the method of the present invention may be a lower aliphatic carboxylic acid having at least 50% of carbon atoms, and other solvents are not particularly limited. Examples of lower aliphatic carboxylic acids include formic acid, acetic acid,
Examples include propionic acid, oxalic acid, bromoacetic acid, etc., but acetic acid is most suitable. These are used by mixing with water or other medium as appropriate. When water is included, its proportion is desirably 30% by weight or less, particularly 20% by weight or less. Solvents are used essentially to dissolve at least a portion of the feedstock and catalyst and to facilitate their contact with molecular oxygen, but they also serve to dissipate heat, remove heat, and improve fluidity of the product. The purpose of this invention is to promote and promote the crystal growth of the product and to facilitate the industrial implementation of the method of the present invention. Therefore, the amount 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, the total weight of the raw materials and target NDA in the system 2~
20 times, preferably 3 to 15 times, particularly preferably 3 to 15 times
Using about 10 times is convenient for implementation. 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. As mentioned above, the method of the present invention is characterized in that the oxidation is carried out in the presence of an extremely high concentration of heavy metals in the solvent in the oxidation reaction mixture,
By doing so, the desired NDA can be obtained in a much higher yield than conventional methods. That is, the heavy metal of component A is present in the solvent in an amount of at least 1% by weight, preferably 1.2 to 25% by weight, and more preferably 2 to 20% by weight. If the proportion of the heavy metal in component A is less than 1% by weight based on the solvent, it becomes difficult to obtain NDA in a high yield. In carrying out the method of the present invention, heavy metals are used at high concentrations in the solvent as described above, and
It is even more advantageous to use a large amount of heavy metals for DIPN, which is the oxidized product, or its oxidized intermediate.
You can get an NDA. In this case, the raw material
It is desirable to use at least 0.2 mol of the heavy metal of component A to oxidize 1 mol of DIPN or its oxidized intermediate. According to the observations of the present inventors, as far as the reaction yield is concerned, the higher the ratio of component A to the raw material, the better, and it is practically difficult to define the upper limit. However, from an industrial perspective, an excessive ratio leads to a decrease in productivity, so in practical terms the stoichiometric ratio of component A per mole of starting material is 0.20 to 10.0, preferably 0.3 to 10.0 in mole.
A range of 5.0, more preferably 0.5 to 3.0 is appropriate. On the other hand, during the reaction, a small portion of bromine, which is the B component of the oxidation catalyst, becomes a volatile compound and escapes, or becomes a nuclear bromide that is difficult to decompose under the reaction conditions and is lost. The part is reacting,
It remains in the reaction system and repeatedly exerts its catalytic effect without becoming deactivated. Therefore, unlike component A, bromine does not need to be used in a stoichiometric amount relative to the starting material, nor does it essentially need to be used in proportion to the amount of component A in the reaction system. Even the ratio is effective enough. According to the research conducted by the present inventors, the optimal concentration of bromine used in the reaction is determined not only by the concentration of component A used;
It also depends 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 generally the A
Atomic ratio to the component: 0.01 to 2, preferably 0.05 to 2
Approximately 0.5 is preferable. In the method of the present invention, it is desirable to keep the concentration of DIPN during the reaction not too high in order to prevent the rapid reaction progress. During the reaction, the concentration of DIPN in the reaction system preferably does not exceed a molar ratio of 0.2 to the component A in the catalyst present in the system, particularly preferably 0.1 or less, especially 0.05 or less. When the molar ratio of DIPN to component A in the reaction system is high,
No matter how well the stoichiometric ratio of the catalyst A component to DIPN is maintained, it becomes difficult to suppress the occurrence of side reactions due to the rapid progress of the reaction, and the yield of the desired product NDA tends to decrease. Is recognized. However, in general, in the case of a continuous reaction or at least a semi-batch reaction, as long as the reaction temperature and oxygen concentration (oxygen partial pressure) are kept within the appropriate range, the disappearance of the raw materials through the reaction is rapid, and the raw material concentration during the reaction is It is relatively easy to maintain the above regulation value or less. In the method of the present invention, in addition to pure oxygen, a mixed gas obtained by diluting this with other inert gases is used as molecular oxygen, but air is the most easily available molecular fusion-containing gas in practice. It can be used as 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 can be carried out at normal pressure, it proceeds more rapidly under increased pressure. Generally, the higher the oxygen partial pressure in the system, the faster the reaction will proceed, 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 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 at a total pressure of 30 Kg/cm ² G or less, resulting in a high NDA can be obtained based on the 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. Furthermore, when the reaction temperature exceeds 220°C, the proportion of by-products generated 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 80~
A range of 220°C, more preferably 140-210°C, particularly preferably 160-200°C is advantageous. In carrying out the oxidation reaction of the method of the present invention,
NDA can be obtained by charging the catalyst, solvent, and raw materials into a reaction vessel simultaneously or separately (after heating if necessary) and blowing molecular oxygen-containing gas into the reactor while maintaining the predetermined pressure and temperature. Allow sufficient time for the reaction to occur. 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 it is necessary to remove the heat to maintain the predetermined reaction temperature. It is necessary to maintain it. At this time, heat removal can be carried out internally by evaporating the reaction medium such as acetic acid or water or entraining 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 in combination. 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 reaction intermediates in the reaction system that have not been completely converted to NDA. It may be approved. In such cases, if necessary, completing the reaction by further contacting it with molecular oxygen (so-called post-oxidation) will improve the yield of NDA and at the same time eliminate unnecessary by-products from its 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 reaction pressure and temperature of the post-oxidation need not be the same as those of the main reaction, and may be higher or lower. As mentioned above, in the oxidation reaction of the present invention, the A component of the oxidation catalyst temporarily deactivates and loses its activity, so in practice, a stoichiometrically large amount of the A component (Co,
Mn) must be used. After the completion of the reaction, the separation and recovery of NDA from the reaction product mixture and the purification of NDA are carried out after the reaction mother liquor from which NDA has been removed is processed, recycled, reused, etc.
It can be carried out according to the conventional method known in the production of terephthalic acid and terephthalic acid. Although the method of the present invention can be carried out either batchwise or continuously, batch reactions are not necessarily practical because the concentration of raw materials relative to the catalyst is low. As much as possible, the oxidation reaction is preferably carried out either continuously or by the so-called semi-batch method, in which the reaction is carried out by adding the raw material 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 industrially it can be obtained from any conventional method. It has become possible to supply NDA at a lower cost and with higher quality than by other methods. 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 2,6-diisopropylnaphthalene (DIPN) in a titanium-lined autoclave with reflux condenser, gas inlet and outlet tubes, and agitator.
333 parts glacial acetic acid (AcOH) 15000 parts cobalt acetate tetrahydrate (Co(OAc) _{2.4H 2} O)
433 parts manganese acetate tetrahydrate (Mn(OAc) _{2.4H 2} O)
853 parts (Co + Mn/AcOH = 1.96% by weight) and 85 parts of ammonium bromide (NH ₄ Br) were simultaneously charged at a temperature of 160°C and a pressure of 30 kg/cm ² G, and while stirring vigorously, oxygen was introduced with compressed air. The reaction was carried out for 3 hours by flowing at a rate of 40 parts per minute. After the reaction, the analysis of the reactants revealed that the raw materials
DIPN almost disappeared and 271 parts of NDA with a purity of 96.1% was obtained. This corresponds to a yield of 76.7 mol% based on the raw material DIPN. Example 2 2,6-diisopropylnaphthalene (DIPN) was added to the same reactor as in Example 1.
333 parts Glacial acetic acid (AcOH) 15,000 parts Cobalt acetate/tetrahydrate 290 parts Manganese acetate/tetrahydrate 569 parts (Co+Mn/AcOH=1.31% by weight) and 87 parts of ammonium bromide were simultaneously charged and the same procedure as in Example 1 was carried out. I reacted with After the reaction, the reaction product was analyzed and the purity was 98.6.
%NDA255 parts were obtained. This corresponds to a yield of 74.2 mol%. Example 3 8420 parts of glacial acetic acid (AcOH) 137 parts of cobalt acetate tetrahydrate were added to a titanium-lined pressurized reactor equipped with a reflux condenser, a gas blowing pipe/discharge pipe, a continuous feed pump, and a stirrer. 269 parts of tetrahydrate (Co+Mn/AcOH=1.10% by weight) and lithium bromide monohydrate (LiBr・H ₂ O)
Charge 17 parts and maintain the temperature at 180℃ and the pressure at 30Kg/cm ² G.
Add 2,6-diisopropylnaphthalene (DIDN) to this while stirring vigorously.
1247 parts were continuously fed at a rate of 20.8 parts per minute for 1 hour, and compressed air was passed through at a rate of 40 parts per minute as an oxygen supply rate. The reaction started at the same time as the feed was started, and absorption of oxygen was observed, but when the DIPN feed was stopped one hour later, almost no oxygen absorption was observed. Furthermore, for 2 hours, 180℃, 30Kg/cm ² G
After the reaction was completed by maintaining the temperature and continuing air circulation, the reaction product was taken out and analyzed. As a result, the raw material DIPN had almost disappeared and 936 parts of NDA with a purity of 97% was obtained. This is a yield of 71.5 based on the raw material DIPN.
Corresponds to mol%. Example 4 In a reactor similar to Example 3, 16,958 parts of glacial acetic acid (AcOH), 1,096 parts of cobalt acetate, tetrahydrate, 2,156 parts of manganese acetate, tetrahydrate (Co+Mn/AcOH=4.38% by weight) and ammonium bromide, 1 2,6-diisopropylnaphthalene (DIPN) was added to this while stirring vigorously while maintaining the temperature at 180°C and the pressure at 30Kg/ ^cm2G .
2550 parts were continuously fed at a rate of 42.5 parts per minute for 1 hour, and compressed air was passed at an oxygen supply rate of 80 parts per minute. 180℃ for another 2 hours after finishing the DIPN feed.
After the reaction was completed by maintaining air flow at 30 Kg/cm ² G, the reaction product was taken out and analyzed, and the yield of NDA was 85.6 mol%. Example 5 In a reactor similar to Example 3, 16902 parts of glacial acetic acid (AcOH) 3816 parts of cobalt acetate tetrahydrate 7510 parts of manganese acetate tetrahydrate (Co+Mn/AcOH=15.31% by weight) and sodium bromide (NaBr 473 parts of 2,6-diisopropylnaphthalene were charged into the reactor and 2,6-diisopropylnaphthalene was continuously fed at a rate of 21.0 parts per minute for 2 hours while maintaining the temperature at 180°C and the pressure at 20 kg/cm ² G with vigorous stirring. At the same time, compressed air was introduced at an oxygen feed rate of 65 parts per minute. After finishing the DIPN feed, keep at 180℃ for another 2 hours.
After the reaction was completed by maintaining air flow at 20 Kg/cm ² G, the reaction product was taken out and analyzed, and as a result, the yield of NDA reached 90.8 mol%. Example 6 Into the same reaction apparatus as in Example 3, 16971 parts of glacial acetic acid, 1089 parts of cobalt acetate tetrahydrate, 3215 parts of manganese acetate tetrahydrate (Co+Mn/AcOH=5.76% by weight) and 128 parts of ammonium bromide were charged. While maintaining the temperature at 200℃ and the pressure at 20Kg/ ^cm2・G and stirring vigorously, 2,6-diisopropylnaphthalene was continuously fed into this at a rate of 21.3 parts for 2 hours at a rate of 21.3 parts per minute. Compressed air was passed through at a rate of 80 parts per minute. After finishing the DIPN feed, keep at 200℃ for another 2 hours.
After completing the reaction by maintaining air circulation at 20Kg/cm ²・G, the reaction product is taken out and mainly
The resulting solid precipitate consisting of NDA was separated. The mother liquor, which mainly consisted of the catalyst liquid, was recycled to the next oxidation reaction, and the solid precipitate was washed, dried, and analyzed. As a result, the theoretical yield was 2248 parts of NDA and 86.55 mol % based on the raw material DIPN. Example 7 16,772 parts of glacial acetic acid, 3,235 parts of manganese acetate tetrahydrate (Mn/AcOH=4.56% by weight) and 136 parts of sodium bromide were charged into a reaction apparatus similar to that of Example 1, and the temperature was 180°C and the pressure was increased. Add 2,6-diisopropylnaphthalene (DIPN) to this while maintaining the temperature at 30Kg/cm ² G and stirring vigorously.
2454 parts were continuously fed at a rate of 40.9 parts per minute for 1 hour, and compressed air was passed at an oxygen supply rate of 80 parts per minute. Air circulation was continued for another 2 hours at 180° C. and 30 Kg/cm ² G after the DIPN feed was completed to complete the reaction. The 2,6-naphthalene dicarboxylic acid in the reaction product was 2005 parts solid with a purity of 94.1%. This corresponds to a yield of 75.5 mol% based on the raw material DIPN. Comparative Example 1 The same reaction as in Example 7 above was carried out with Mn/AcOH=
The same conditions were used except that the concentration was 0.57% by weight (Mn:Br=1:0.1). The yield of NDA was 51.0 mol%. Example 8 16,844 parts of glacial acetic acid, 3,287 parts of cobalt acetate tetrahydrate (Co/AcOH=4.62% by weight) and 136 parts of sodium bromide were charged into a reaction apparatus similar to that of Example 1, and the temperature was 160°C and the pressure was increased. Add 2,6-diisopropylnaphthalene (DIPN) to this while maintaining the temperature at 30Kg/cm ² G and stirring vigorously.
2491 parts were continuously fed at a rate of 41.5 parts per minute for 1 hour, and compressed air was passed at an oxygen supply rate of 80 parts per minute. Air circulation was continued for another 2 hours at 160° C. and 30 Kg/cm ² G after the DIPN feed was completed to complete the reaction. The 2,6-naphthalene dicarboxylic acid in the reaction product was 1783 parts solid with a purity of 92.2%. This corresponds to a yield of 64.8 mol% based on the raw material DIPN. Comparative Example 2 The same reaction as in Example 8 above was carried out with Co/AcOH=0.62.
The same conditions were used except that the weight percent (Co:Br=1:0.1) was used. The yield of NDA was 40.5 mol%. Comparative Example 3 2,6-diisopropylnaphthalene (DIPN) was added to the same reactor as in Example 1.
2670 parts glacial acetic acid 13350 parts cobalt acetate tetrahydrate 48 parts manganese acetate tetrahydrate 95 parts (Co+Mn/AcOH=0.24% by weight) and 5.7 parts ammonium bromide were charged at the same time at a temperature of 180℃ and a pressure of 30Kg/cm ² While maintaining the temperature at G and stirring vigorously, compressed air was passed through the reactor at a rate of 80 parts per minute to carry out the reaction for 3 hours. After the reaction, the analysis of the reactants revealed that the raw materials
180 parts of DIPN remained and 1106 parts of NDA with a purity of 85.6% was obtained. This corresponds to a yield of 37.3 mol%. Comparative Example 4 In the same reaction apparatus as in Example 3, 8422 parts of glacial acetic acid (AcOH), 68 parts of cobalt acetate tetrahydrate, 135 parts of manganese acetate tetrahydrate (Co+Mn/AcOH=0.55% by weight) and 1 lithium bromide were added. 2,6-diisopropylnaphthalene (DIPN) was added to the mixture while stirring vigorously while maintaining the temperature at 180℃ and the pressure at 30Kg/cm ² G.
1244 parts were continuously fed at a rate of 20.7 parts per minute for 1 hour, and compressed air was passed at an oxygen supply rate of 40 parts per minute. 180℃ for another 2 hours after finishing the DIPN feed.
After completing the reaction by maintaining air flow while maintaining 30Kg/cm ² G, the reaction product was taken out and analyzed. As a result, 49.5 parts of raw material DIPN remained and 2,6-naphthalene dicarboxylic acid was not recovered. The percentage was only 51.1 mol%.

Claims (1)

[Scope of Claims] 1. Oxidizing 2,6-diisopropylnaphthalene or its oxidized intermediate with molecular oxygen in a solvent containing at least 50% by weight of an aliphatic monocarboxylic acid having 3 or less carbon atoms, 2. In a method for producing 6-naphthalene dicarboxylic acid, the oxidation is carried out in the presence of a catalyst consisting of (i) a heavy metal consisting of cobalt and/or manganese and (ii) bromine, and the heavy metal in the oxidation reaction mixture is A method characterized in that it is carried out in the presence of at least 1% by weight.