JPH06293698A - Production of 2,6-naphthalenedicarboxylic acid - Google Patents

Abstract

PURPOSE:To obtain 2,6-naphthalenedicarboxylic acid in high yield in a shortened time by suppressing the formation of by-products such as trimellitic acid. CONSTITUTION:6-Methyl-2-naphthoic acid is used as a raw material and is oxidized with molecular oxygen in the presence of a catalyst containing a heavy metal compound and bromine to give the objective 2,6- naphthalenedicarboxylic acid.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing 2,6-naphthalenedicarboxylic acid (hereinafter abbreviated as NDCA) by oxidizing 6-methyl-2-naphthoic acid with molecular oxygen. Since NDCA provides a film or a fiber product excellent in heat resistance, mechanical strength, and dimensional stability, the demand for NDCA as a raw material for polyethylene naphthalate, polyamide, etc. is increasing.

[0002]

2. Description of the Related Art As a method for producing NDCA by oxidizing 6-methyl-2-naphthoic acid with molecular oxygen, an example of carrying out an oxidation reaction using cobalt as a catalyst and propionic acid as a solvent (US Pat. No. 3,055) , 839 specification),
When NDCA is produced by oxidizing 2,6-dimethylnaphthalene, 6-methyl-2 partially produced in the first reaction
-Method of reacting by changing the reaction temperature in the presence of a catalyst composed of a heavy metal compound and a bromine compound in an acetic acid solvent, using an oxidation intermediate mixture of 2,6-dimethylnaphthalene containing naphthoic acid without separation and purification (Japanese Patent Publication Sho 59-1
3495). However, in the method described in the above-mentioned US Pat. No. 3,055,839, a reaction time of 23 hours and a yield of 48% are the best results, and since the reaction time is too long and the yield is low, It is hard to say that it is an industrially applicable manufacturing method. In addition, Japanese Examined Japanese Patent Publication Sho 59-13
In the method described in Japanese Patent No. 495, the 6-methyl-2-naphthoic acid thus produced is directly subjected to the second stage reaction without separation and purification. However, in such a method, the amount of trimellitic acid produced is increased. You can't hold back. Japanese Patent Publication 59-134
The purpose of the method in Japanese Patent No. 95 is to carry out two-stage oxidation for the purpose of suppressing oxidative decomposition of acetic acid used as a solvent, rather than suppressing by-products.

[0003]

Conventionally, the oxidation reaction of dialkylnaphthalene such as 2,6-dimethylnaphthalene has been well known as a method for producing NDCA. In the oxidation reaction of dialkylnaphthalene, a naphthalene ring is particularly preferable. It has been pointed out that a major problem is the by-product of trimellitic acid due to the cleavage of. This trimellitic acid forms a poorly soluble salt with the heavy metal of the catalyst in the oxidation reaction solution and precipitates together with NDCA, which has the drawbacks that the purification process becomes complicated and the catalytic activity decreases. Therefore, there has been a strong demand for a method for producing NDCA in which these trimellitic acids are not produced as much as possible. The present invention solves the above problems in the prior art, and provides a method for producing NDCA in a short time in a short time with almost no by-produced trimellitic acid.

[0004]

The inventors of the present invention can suppress by-products in the conventional oxidation reaction of dialkylnaphthalene by using 6-methyl-2-naphthoic acid as a raw material in a relatively high purity. The surprisingly difficult trimellitic acid produced NDCA with almost no by-products.
The present invention has been accomplished by finding a method of manufacturing That is, the present invention, by using 6-methyl-2-naphthoic acid substantially free of dialkylnaphthalene as a raw material, in the presence of a catalyst containing a heavy metal compound and bromine, by oxidizing with molecular oxygen to produce NDCA, It is possible to obtain NDCA in a good yield with a low catalyst amount, with almost no by-product of trimellitic acid which complicates the purification process and lowers the catalytic activity.

The present invention will be further described below. (Raw material) The 6-methyl-2-naphthoic acid used in the present invention is produced by any method as long as it does not substantially contain dialkylnaphthalene, specifically, a dialkylnaphthalene content of 1% by weight or less. But it doesn't matter. However, as seen in the two-stage oxidation reaction of 2,6-dimethylnaphthalene, when it is produced as an oxidation reaction intermediate, many by-products, raw materials, NDCA and the like are mixed and the dialkylnaphthalene content is 1% by weight or less. High purity 6-
It is difficult to obtain methyl-2-naphthoic acid, and therefore the effect of suppressing trimellitic acid, which is the object of the present invention, cannot be expected so much. Although it may contain other impurities, particularly impurities not involved in the reaction, the purity of 6-methyl-2-naphthoic acid is 90%.
It is preferable that the amount is 6% by weight or more, and particularly 95% by weight or more. As a method for producing 6-methyl-2-naphthoic acid,
It is preferable to use an organic synthetic means in which p-xylene and maleic anhydride are used as starting materials.

(Reaction type) The reaction can be carried out by a method similar to the conventional liquid phase oxidation. There is no particular limitation on the method of supplying 6-methyl-2-naphthoic acid to the reactor. For example, a method of collectively charging the raw material, the solvent and the catalyst into the reactor (batch type), a method of continuously supplying the raw material to the reactor already charged with the solvent and the catalyst (semi-continuous type), and the like may be used. However, since the starting material 6-methyl-2-naphthoic acid has a very high melting point of about 230 ° C., when continuously supplying the starting material, it is preferable to dissolve the starting material in acetic acid or the like before supplying it. . From the industrial point of view, the semi-continuous type is preferable because the yield per catalyst is improved. Naturally, the conditions such as the amount of catalyst used and the reaction time greatly differ depending on these reaction modes.

(Catalyst) The catalyst used in the present invention contains a heavy metal compound and bromine. Examples of the heavy metal compound used as a catalyst in the method of the present invention include heavy metal compounds generally known as oxidation catalysts such as cobalt, manganese, cerium, iron, nickel, chromium, vanadium, copper, lead and palladium. These may be used alone or in combination, but it is most preferable to use cobalt and manganese together. These heavy metal compounds are preferably those that dissolve in a solvent under the reaction conditions, for example, formic acid, acetic acid, propionic acid, oxalic acid, aliphatic carboxylic acid salts such as maleic acid,
Alicyclic carboxylic acid salts such as naphthenic acid, benzoic acid, terephthalic acid, aromatic carboxylic acid salts such as naphthoic acid and naphthalenedicarboxylic acid, and acetylacetonate complexes,
Inorganic salts such as hydroxides, oxides, carbonates and halides can be mentioned. Among these, acetate, acetylacetonate complex and bromide are particularly preferable.

When the cobalt compound and the manganese compound are used together in the reaction, the ratio of the cobalt compound and the manganese compound used is a metal molar ratio of cobalt: manganese of 99: 1 to 1:99. It is preferably used, and more preferably in the range of 95: 5 to 5:95. The amount of the heavy metal compound used is in the range of 0.0001 to 10 moles, preferably 0.001 to 5 moles, as the total number of moles of metal atoms with respect to the raw material 6-methyl-2-naphthoic acid.

The bromine compound contained in the catalyst component includes, for example, inorganic bromine compounds such as molecular bromine, hydrogen bromide, alkali metal bromide, alkyl earth metal bromide and methyl bromide, ethyl bromide, bromoform, bromide. An organic bromine compound such as ethylene can be exemplified. Among these, alkali metal bromides, such as potassium bromide, are particularly preferable. The amount of the bromine compound used as the bromine atom is in the range of 0.1 to 10 times by mole, preferably 0.2 to 5 times by mole, with respect to the total number of moles of the metal atoms of the heavy metal compound contained in the solvent.

6-methyl-2 used as a raw material in the present invention
-The most characteristic feature of the oxidation of naphthoic acid is that when a divalent metal such as cobalt (II) acetate and manganese (II) acetate that is commonly used in the oxidation reaction of alkylnaphthalenes is used, methylnaphthalenes are There is an induction period that is not seen in the oxidation of. Therefore, in the reaction of only these divalent metals, sometimes the reaction does not proceed well and decarboxylation of the raw material may occur. Therefore, as a catalyst used in this reaction, in order to allow the reaction to proceed more smoothly,
It is preferable to use a trivalent metal. As a specific method, manganese (III) acetylacetonate, which is easily available as a commercial product, is used, or manganese acetate is used as described in Experimental Chemistry Course (4th Edition) Organic Synthesis V, Oxidation Reaction. (III) is separately synthesized and used,
When a divalent metal such as cobalt (II) acetate is used, as a pretreatment of the catalyst, the solvent and the catalyst are charged into a reactor, and oxygen is introduced under heating to increase the trivalent concentration. Then, a method of supplying a raw material and reacting may be used. The increase in the trivalent cobalt concentration can be easily confirmed by the color change from blue purple to blue.

(Solvent) As a solvent, an aliphatic carboxylic acid such as acetic acid, propionic acid, butyric acid, or a mixture of these aliphatic carboxylic acids with an organic compound such as an aromatic compound such as benzene or an aliphatic compound such as hexane is mixed. However, it may be used as a mixed solvent. When a mixed solvent is used, the proportion of the aliphatic carboxylic acid in the mixed solvent is not particularly limited, but is preferably 25% or more, more preferably 50% or more. The amount of the solvent to be charged is not particularly limited, but with respect to the raw material 6-methyl-2-naphthoic acid,
Preferably 0.5 to 300 times by weight, more preferably 1
~ 150 times by weight.

(Molecular Oxygen) As the molecular oxygen, in addition to pure oxygen, pure oxygen diluted with an inert gas such as nitrogen, helium, or argon to an arbitrary concentration can be used, but generally air is used. Is enough.

(Reaction conditions) The reaction temperature is preferably 50.
To 300 ° C., more preferably 70 to 250 ° C., and if the reaction temperature is lower than this, the reaction rate is remarkably slowed, which is not preferable, and if the temperature is higher than this, loss due to combustion of the solvent or the raw materials increases. Again, this is not preferred. The reaction pressure is not particularly limited, but considering the reaction rate, the oxygen partial pressure in the gas phase is always 0.2 to 40 k.
A pressure that is g / cm ² GP (gauge pressure) is preferable.

The present invention will be described in more detail below with reference to examples and comparative examples. Example 1 6-Methyl-2-naphthoic acid (purity 100% by weight) 1.
05 g (5.66 mmol), cobalt (II) acetate tetrahydrate 28 mg (0.0113 mmol), manganese (II) acetate tetrahydrate 28 mg (0.113 mmol), potassium bromide 54 mg (0.453 mmol) and acetic acid Two
0 ml was charged into a 100 cc Hastelloy autoclave, and the air inside the autoclave was 100 kg / at room temperature.
Increase the pressure to cm ² . Then, the temperature rise was started. When the temperature was raised to 180 ° C, heat was suddenly generated and the temperature rose to about 195 ° C. Then adjust the temperature to 185 ℃ for 2 hours,
Heated and stirred. After completion of the reaction, the autoclave was cooled to room temperature, crude NDCA was filtered out from the reaction solution, washed with 5% by weight sulfuric acid water, and then quantified by liquid chromatography to obtain 0.87 g of NDCA (yield 71.5%). The by-product trimellitic acid was 0.04 g (yield 3.3%) in the acetic acid filtrate.
confirmed. The conversion rate of 6-methyl-2-naphthoic acid is 1
It was 00%.

Example 2 Instead of manganese (II) acetate tetrahydrate, manganese (II
I) 40 mg (0.113 mmo) of acetylacetonate
l) The same operation as in Example 1 was carried out except that it was used. In this case, there was no special heat generation up to the predetermined temperature (185 ° C). 0.86 g of NDCA obtained after the reaction (yield 70.
5%), trimellitic acid was not produced as a by-product. The conversion rate of 6-methyl-2-naphthoic acid was 96.5%.

Comparative Example 1 The same operation as in Example 1 was carried out except that 0.86 g (5.66 mmol) of 2,6-dimethylnaphthalene was used instead of 6-methyl-2-naphthoic acid. Even in this case, no special fever was observed. NDCA obtained after the reaction was 0.77 g (yield 63.6%) and trimellitic acid was 0.2.
4 g (yield 19.8%) was by-produced. The conversion of 2,6-dimethylnaphthalene was 100%.

[0017]

EFFECTS OF THE INVENTION Since the present invention is configured as described above, it is possible to suppress the production of by-products such as trimellitic acid even in a batch reaction, and to obtain NDCA in good yield in a short reaction time.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Tomoya Sakata 8-3-1 Chuo, Ami-cho, Inashiki-gun, Ibaraki Mitsubishi Petrochemical Co., Ltd. Tsukuba Research Institute

Claims (1)

[Claims] 1. A method of using 6-methyl-2-naphthoic acid substantially free of dialkylnaphthalene as a raw material, and oxidizing with molecular oxygen in the presence of a catalyst containing a heavy metal compound and bromine. Process for producing 6-naphthalenedicarboxylic acid.