JPH06719B2 - Method for producing high-purity 2,6-diacetoxynaphthalene - Google Patents

Description

TECHNICAL FIELD The present invention relates to a highly pure compound suitable for use as a monomer in the production of aromatic polyesters capable of forming liquid crystals.
The present invention relates to a method for producing 2,6-diacetoxynaphthalene.

2. Description of the Related Art In recent years, various polymers having performance as engineering plastics have been developed, and as plastics in this field, there are aromatic polyesters, particularly aromatic polyesters having a liquid crystal forming ability.

Examples of the raw material of the aromatic polyester polymer include terephthalic acid, hydroquinone, parahydroxybenzoic acid, and the like. Recently, in order to improve the physical and / or chemical properties of the polymer, only the above-mentioned benzene derivative is used. In addition, naphthalene derivatives have come to be demanded as a raw material.

Examples of such naphthalene derivatives include 2,6-naphthalenediol and 2,6-diacetoxynaphthalene, and liquid crystal polymers derived from these chemical substances have excellent physical properties, and comonomers thereof. Since terephthalic acid used as the above is available at a low price, it is attracting attention as a monomer used for producing the above-mentioned aromatic polyesters having a liquid crystal forming ability.

However, since 2,6-naphthalenediol and 2,6-diacetoxynaphthalene have not been industrially produced at present, there is a problem that they cannot be obtained at low cost.

2,6-diacetoxynaphthalene can be obtained by acetylating 2,6-naphthalenediol, but the conventional method for producing 2,6-naphthalenediol is naphthalene or β.
The classical method of sulfonation of naphthols followed by alkali melting is known, and this method is introduced in the Beilstein complete book.

However, in this method, as shown in, for example, Japanese Patent Publication No. 56-77254, 2,6-
Since it is inevitable to produce isomers other than the body, 2,
The 6-form can only be obtained in low yields. Furthermore, even in the above alkali melting stage, for example, APKuriakose
et al., Journal Indian Chemical Society (J. Indian Chem. Soc.) 43 , 437 (1966), the sodium salt of 2-naphthol-6-sulfonic acid was alkali-melted. Since the yield of 2,6-naphthalene diol is about 50%, the total yield of 2,6-naphthalene diol obtained by the above method consisting of sulfonation of naphthalene or β-naphthol and then melting with alkali is extremely low. Becomes Therefore, it is difficult to separate the 2,6-body by this method, and in addition, the wastewater treatment peculiar to the alkali melting step is required, which causes a problem of increasing the manufacturing cost, which is industrially practical. Can be said to be scarce.

Since a method for producing hydroquinone from paraisopropylbenzene by applying the principle of phenol production by the cumene method (Japanese Patent Publication No. 51-33100) has been known, this method can be used for 2,6-naphthalene. As applied to the production of diol, 2,6-diisopropylnaphthalene as a starting material is oxidized to obtain 2,6-diisopropylnaphthalene dihydroperoxide, and the hydroperoxide is acid-decomposed to give 2,6-naphthalenediol. Although a method of converting to dihydroperoxide is also possible, in this case, the yield is lower than that of dihydroperoxide obtained by oxidation of paradiisopropylbenzene in the above-mentioned production method of hydroquinone, and
Since it is difficult to separate the produced dihydroperoxide, it cannot be said that the above method is industrially suitable.

On the other hand, the conventional formula A method for converting aromatic carbinols represented by the formula (wherein Ar represents an aromatic ring) into phenols represented by the general formula Ar-OH by oxidizing with hydrogen peroxide in the presence of a strong acid in a solvent. Are also known (for example, JP-A-52-5718, JP-B-3
5-7558, British Patent No. 910735, Tsunoda, Kato (Nikkei)
80 (7), 689 (1959), MSKHARASCH et al., Journal
Of Organic Chemistry (J.Org.Chem.) 15 , 7
48, 775, (1950)].

However, the reaction examples described in the above-mentioned respective documents include 2-hydroxy-2-propylbenzene, p-di (2-hydroxy-2-propyl) benzene, p-2-hydroxy-2-propyl-αα ′.
-A method for converting dimethylbenzyl hydroperoxide or the like into phenol or hydroquinone, and a method for converting carbinols having a naphthalene skeleton into naphthols is not found in the description of the above-mentioned prior art. Incidentally, even if the 2,6-naphthalenedicarbinol is oxidized in the solvent used in the method described in these documents, 2,6-naphthalenedicarbinol is not dissolved in the solvent, or 2, Despite the disappearance of 6-naphthalenedicarbinol from the reaction system, almost no 2,6-naphthalenediol is produced, or the solvent itself reacts, or the reaction rate is low, etc. It is virtually impossible to industrially obtain 1,6-naphthalenediol. And this means that the naphthalene derivative 2,6-
It is considered that naphthalene diol is derived from the fact that the benzene derivative carbinols disclosed in the above-mentioned prior arts are essentially different in physical and / or chemical properties.

Also, 2,6-naphthalenediol can be reacted with terephthalic acid or the like to form a polymer, but for that purpose, it is necessary to purify it to high purity.

For the purification method of 2,6-naphthalenediol, for example, Be
Although the recrystallization method with water, alcohol, acetic acid, etc. is suggested in the complete book of ilstein, the decolorization effect is insufficient, the purity does not become high, or the recovery rate is low. None of the material-based recrystallization methods is industrially satisfactory.

When acetic acid is used among the above substances, the decolorizing effect is relatively excellent, but the recovery rate is low at about 50%, and in addition, the filtrate is concentrated during recovery from the recrystallization filtrate. At this time, the 2,6-naphthalenediol dissolved in the liquid becomes tar-like, so that the above recovery is practically impossible. Furthermore, the purity by differential scanning calorimetry (DSC) does not reach 99%.

Problems to be Solved by the Invention The present inventors, in view of the above-mentioned state, as a result of examining an industrially advantageous production method of 2,6-diacetoxynaphthalene, industrially easily available 2, The inventors have found an advantageous method for producing and purifying 2,6-diacetoxynaphthalene using 2,6-naphthalenedicarbinol derived from 6-diisopropylnaphthalene as a raw material, and completed the present invention.

In the present invention, first, 2,6-naphthalenedicarbinol is oxidized under a specific condition to convert it into 2,6-naphthalene diol in a high yield, and then the obtained crude 2,6-naphthalene diol is converted. By acetylation and purification, 2,6-diacetoxynaphthalene can be obtained in high purity and high yield. Therefore, an object of the present invention is to provide a method capable of producing a high-purity 2,6-diacetoxynaphthalene of high purity suitable for producing an aromatic polyester having a liquid crystal forming ability from 2,6-naphthalenedicarbinol. To provide.

Incidentally, in the reaction for producing an aromatic polyester having a liquid crystal forming ability from 2,6-naphthalenediol, for example, as described in JP-B-54-50594, U.S. Pat.No. 4,375,530, etc., It is preferable to use it as 2,6-diacetoxynaphthalene rather than 2,6-naphthalenediol itself.

The present invention will be described in detail below.

Structure of the Invention The feature of the present invention is that α, α, α ′, α ′,-tetramethyl
-2,6-naphthalene dimethanol (hereinafter abbreviated as 2,6-naphthalene dicarbinol) was oxidized with hydrogen peroxide in acetonitrile or 1,4-dioxane in the presence of an inorganic acid to give 2,6- The purpose is to obtain naphthalene diol and then acetylate the 2,6-naphthalene diol to obtain 2,6-diacetoxynaphthalene.

The 2,6-naphthalenedicarbinol used as a starting material in the present invention can be obtained by applying a known reaction for producing dimethylphenylcarbinol from cumene to 2,6-diisopropylnaphthalene.

Means for Solving the Problems In the present invention, when 2,6-naphthalenecarbinol as a starting material is oxidized and converted into 2,6-naphthalenediol, acetonitrile or dioxane or a mixture of both is used as a reaction solvent. It is important to use a solvent, and as described above, it is difficult to industrially obtain 2,6-naphthalenediol by using another solvent. For example, ketones such as acetone and isobutyl methyl ketone, which are used as a solvent in the method disclosed in Japanese Patent Publication No. 52-5718, described above, are inert to the reaction for obtaining 2,6-naphthalenediol. Therefore, when these solvents are used, some 2,6-naphthalenediol is produced, but in addition, a large amount of by-products derived from ketones are produced. Further, when a lower alcohol such as methanol, ethanol or isopropanol is used as a solvent, the reaction rate is very small and the selectivity of the reaction is low, so that 2,6-naphthalenediol cannot be obtained in a high yield. . Furthermore, when a lower fatty acid such as acetic acid or propionic acid is used as a solvent, the starting material 2,6-naphthalenedicarbinol disappears, but the side reaction takes precedence and almost no 2,6-naphthalenediol is formed. In a hydrocarbon-based solvent, the solubility of 2,6-naphthalenedicarbinol and 2,6-naphthalenediol in it is very small.
Only a small amount of naphthalenediol is produced.

In the present invention, acetonitrile or 1,4-dioxane or a mixture of both as a solvent is used in an amount of 3 to 30 times (vol / wt) with respect to 2,6-naphthalenedicarbinol, and an inorganic acid and a peroxide are added thereto. The reaction is carried out by adding hydrogen oxide dropwise.

The inorganic acid used here is preferably sulfuric acid or perchloric acid,
Sulfuric acid is preferably used as concentrated sulfuric acid. When concentrated sulfuric acid is used, it may be diluted with hydrogen peroxide solution or the above solvent, and when using perchloric acid, the concentration is preferably 40% or more, and commercially available 70%, 60% %as well as
A 40% concentration of each product can be used. It is preferable to use these inorganic acids in an amount of 0.5 to 4 times (wt / wt) with respect to the above starting materials. If the amount used is too small, the reaction cannot be completed. It should be noted that it may cause coloration of the product.

In the present invention, hydrogen peroxide used together with the above-mentioned inorganic acid may be a commercially available 30% aqueous solution, and is used in an amount of 2 to 10 times the molar amount of the starting material. It should be noted that if the amount of hydrogen peroxide used is less than 2 moles relative to the starting material, the conversion of the starting material will be low, while if it is too large, the reaction product will be significantly colored.

In adding the inorganic acid and hydrogen peroxide to the starting material as described above, it is preferable to add a mixture of the two or to add the hydrogen peroxide and then the inorganic acid. It should be noted that when an inorganic acid is added, the reaction substrate disappears and impurities are produced.

The reaction temperature in the present invention can be selected in the range of room temperature to 80 ° C., but is preferably 30 to 60 ° C. in practice, and the reaction time also varies depending on the composition of the charged raw material and the reaction temperature,
The reaction is usually completed in 10 minutes to 3 hours. After completion of the reaction, for example, saturated saline is added to the obtained reaction mixture to separate the organic layer, and the organic layer is washed with saturated saline, and then the solvent is distilled off to give crude 2,6- Obtain naphthalene diol.

In the present invention, the crude 2,6-naphthalenediol obtained as described above is acetylated.

There are various methods for this acetylation, but crude 2,6-
The method in which naphthalene diol is heated together with acetic anhydride is most preferable because an extra substance is not mixed in the reaction system.

The amount of acetic anhydride used here may be excessive, or the amount of acetic anhydride may be slightly increased to use acetic acid as a solvent.

The reaction temperature for the heating is preferably 100 ℃ ~ 140 ℃,
The reaction time may be 30 minutes to 2 hours, and the reaction is completed in this time.

After completion of the reaction, the reaction product is allowed to cool, and 2,6-diacetoxynaphthalene is crystallized. Therefore, the formed crystal is filtered off.

The 2,6-diacetoxynaphthalene thus obtained has a high purity, but by recrystallizing it with a suitable solvent such as acetic acid, a highly pure 2,6-diacetoxynaphthalene can be obtained. be able to.

Effects of the Invention As described above, according to the present invention, 2,6-diisopropylnaphthalene derived from industrially easily available 2,
Using 6-naphthalenedicarbinol as a starting material, high-purity 2,6-diacetoxynaphthalene useful as a raw material for producing a liquid crystal polymer can be easily produced with high yield as shown in the following examples. Therefore, it can be said that it is useful for producing an aromatic polyester liquid crystal polymer.

The present invention and its effects will be specifically described below with reference to examples.

Example 1 2,6-naphthalenedicarbinol 50.0 g (0.205 mol) 92
Suspend it in 0 ml of acetonitrile, add 55% of 31% hydrogen peroxide solution and 50 g of 40% sulfuric acid-acetonitrile solution in this order, and react for 40 minutes under stirring in an oil bath maintained at 30 ° C. Let

After completion of the reaction, saturated saline was added to the reaction solution to separate the acetonitrile layer, and the acetonitrile layer was further washed until it became neutral. Then, this acetonitrile layer was dried over anhydrous sodium sulfate, and then acetonitrile was distilled off,
After drying, 34.8 g of crude 2,6-naphthalenediol was obtained. (Yield 96.0%) Next, a mixture of this crude 2,6-naphthalenediol 33.2 g (0.187 mol), acetic acid 15.0 g and acetic anhydride 44.9 g was added at 140 ° C.
The mixture was allowed to react for 90 minutes under stirring in an oil bath maintained at.
After completion of the reaction, the reaction solution was cooled, and the precipitated crystals were filtered out, washed with acetic acid and dried to obtain 41.8 g of white 2,6-diacetoxynaphthalene. (Yield 91.7%) This 2,6-diacetoxynaphthalene is a differential scanning calorimeter (DS
C, Mettler TA 3000 System) to measure the purity,
It was 99.81%.

The crystal mother liquor was concentrated to a purity of 91.3% (according to HPLC).
1.75 g of 2,6-diacetoxynaphthalene was obtained. When this is added to the 2,6-diacetoxynaphthalene obtained above, the total yield of 2,6-diacetoxynaphthalene is 95.2%.

Next, 41.0 g of 2,6-diacetoxynaphthalene with a purity of 99.81%
Was recrystallized from 61.5 g of acetic acid to obtain 39.3 g of highly pure 2,6-diacetoxynaphthalene. (Yield 95.8%) Purity is 1 by HPLC
It was 00% and DSC was 99.97%. From the mother liquor of recrystallization
Although 1.3 g of 2,6-diacetoxynaphthalene was recovered, the recrystallization yield was 99.0 when it was added to that obtained by the above recrystallization.
Reach%.

Example 2 40,70.0 g (0.287 mol) of 2,6-naphthalenedicarbinol
Suspend in 0 ml of acetonitrile, and in this suspension, 70.0 g of 31% hydrogen peroxide solution and 52.5 g of 40% sulfuric acid acetonitrile solution.
Were added in this order, and they were reacted by stirring for 30 minutes in an oil bath maintained at 30 ° C. After completion of the reaction, saturated saline was added to the reaction solution to separate the acetonitrile layer, and the acetonitrile layer was neutralized with sodium carbonate. Then, this acetonitrile layer was dried over anhydrous sodium sulfate, then acetonitrile was distilled off and dried to obtain crude 2,6-naphthalenediol 45.1
I got 4g. (Yield 98.5%) Next, 45 g of this 2,6-naphthalenediol was reacted with 23 g of acetic acid and 61 g of acetic anhydride in an oil bath kept at 140 ° C. for 90 minutes to cause a reaction. After the reaction was completed, the reaction solution was used as in Example 1.
The same treatment as described above was performed to obtain 60.6 g of 2,6-diacetoxynaphthalene having a DSC purity of 99.85%. (Yield 93.0%) Example 3 25 g of 2,6-naphthalenedicarbinol 10.0 g (0.041 mol)
The mixture was dispersed in 0 ml of acetonitrile, 15 g of 31% hydrogen peroxide and 30 g of 40% perchloric acid aqueous solution were added thereto, and the mixture was stirred at 30 ° C. for 30 minutes for reaction. After completion of the reaction, the same treatment as in Example 1 was carried out to obtain 6.7 g of crude 2,6-naphthalenediol. (Yield 9
6.5%) Next, a mixture of 6.0 g (0.035 mol) of this crude 2,6-naphthalenediol, 2.7 g of acetic acid and 7.9 g of acetic anhydride was stirred for 90 minutes in an oil bath kept at 140 ° C to react. It was After completion of the reaction, the reaction solution was treated in the same manner as in Example 1 to give white 2.
7.9 g of 6-diacetoxynaphthalene was obtained. (Yield 92.5%) The purity of this 2,6-diacetoxynaphthalene measured by DSC was 99.85%.

Example 4 2,6-naphthalenedicarbinol 20.0 g (0.082 mol), 1,
A mixture of 200 ml of 4-dioxane and 35 g of 31% hydrogen peroxide was stirred at 40 ° C., 50 g of 40% perchloric acid aqueous solution was added dropwise thereto, and the reaction was further continued for 30 minutes after the addition. Saturated saline was added to the obtained reaction solution to separate the dioxane layer, and this dioxane layer was washed until it became neutral. Then
After the dioxane layer was dried over anhydrous sodium sulfate, dioxane was distilled off and dried to obtain crude 2,6-naphthalenediol 1
Obtained 3.5 g. (Yield 97.8%) Next, 13.0 g of this crude 2,6-naphthalenediol was mixed with 5.9% of acetic acid.
g and 17.6 g of acetic anhydride were stirred in an oil bath kept at 140 ° C. for 90 minutes to cause a reaction. After completion of the reaction, the reaction solution was treated in the same manner as in Example 1 to obtain 17.5 g of 2,6-diacetoxynaphthalene having a DSC purity of 99.82%.

Example 5 25 g of 2,6-naphthalenedicarbinol 10.0 g (0.041 mol)
Suspend in 0 ml of acetonitrile, add 13 ml of 31% hydrogen peroxide solution and 9 ml of 70% perchloric acid aqueous solution in this order, and stir for 30 minutes in an oil bath maintained at 30 ° C to react. Let After completion of the reaction, the reaction solution was treated in the same manner as in Example 1 to obtain 6.6 g of crude 2,6-naphthalenediol. (Yield 95.6%) Next, 6.0 g of this crude 2,6-naphthalenediol was reacted with 2.7 g of acetic acid and 7.9 g of acetic anhydride in an oil bath kept at 140 ° C. for 90 minutes with stirring. After the completion of the reaction, the reaction solution was treated in the same manner as in Example 1 to obtain 8.0 g of 2,6-diacetoxynaphthalene having a DSC purity of 99.85%.

Next, acetonitrile and 1,4-as solvent for acid decomposition reaction
The case where a substance other than dioxane is used is shown as a comparative example.

Comparative Example 1 The reaction was carried out by the same procedure as in each of the above-mentioned Examples except that acetic acid was used instead of acetonitrile as a solvent. When the obtained reaction liquid was analyzed by gas chromatography,
Despite the disappearance of 2,6-naphthalenedicarbinol, the formation of 2,6-naphthalenediol was not observed.

Comparative Example 2 2,6-naphthalenedicarbinol 0.1 g (0.41 mmol),
To a mixture of 2 g of ethanol and 0.2 g of 31% hydrogen peroxide, add 30
At 70 ° C, 0.1 g of 70% aqueous solution of perchloric acid was added and reacted. After 30 minutes from the start of the reaction, formation of 2,6-naphthalenediol was not observed. After further reaction for 2 hours, it was found that 2,6-naphthalenediol was produced in a yield of 55%, but many by-products were observed by gas chromatography.

Comparative Example 3 A mixture of 0.1 g of 2,6-naphthalenedicarbinol, 2.0 g of n-heptane and 0.2 g of 31% hydrogen peroxide solution was added with 0.1 g of 70% perchloric acid aqueous solution and reacted at 30 ° C. for 30 minutes. Tacit, 53.1%
It was found that 2,6-naphthalenediol was produced in a yield of 2,6, but the purity of 2,6-naphthalenediol on gas chromatography was 52%, and many by-products were observed. It was

Comparative Example 4 2,6-naphthalenedicarbinol 0.1 g, benzene 2.0 g and
A mixture of 0.2 g of 31% hydrogen peroxide and 70% aqueous solution of perchloric acid
0.1g was added and it was made to react at 30 degreeC. 30 minutes after starting the reaction,
The production of 2,6-naphthalenediol reached 45.7%, but black insoluble matter of unknown structure was observed in the reaction solution.

Comparative Example 5 Crude 2,6-naphthalenediol was produced in the same manner as in Example 1 and recrystallized from acetic acid.

Recrystallization was repeated 3 times with 3 times the amount of acetic acid to the crude 2,6-naphthalenediol, and the DSC purity of the obtained crude 2,6-naphthalenediol was 98.8%. The recovery rate was about 50%. In addition, an attempt was made to recover secondary crystals from the recrystallized mother liquor, but when the mother liquor was concentrated, it became tar-like, and it was impossible to recover 2,6-naphthalenediol from the mother liquor.

Next, it is shown as a reference example that acetone is not suitable as a solvent because it is not inactive in this reaction system.

Reference Example To 20 ml of acetone, 1.0 g of 31% hydrogen peroxide solution and 2.0 g of 70% aqueous perchloric acid solution were added and stirred at 30 ° C. for 30 minutes, whereupon a white precipitate was formed. This precipitate has an irritating odor and seems to be a condensation product of acetone, and acetone is not inactive in this reaction system,
It was found to be unsuitable as a reaction solvent.

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Claims (2)

[Claims] 1. α, α, α ′, α ′,-tetramethyl-2,6
-Oxidation of naphthalenedimethanol with hydrogen peroxide in acetonitrile or 1,4-dioxane in the presence of an inorganic acid to give 2,6-naphthalenediol, which is then acetylated. A method for producing high-purity 2,6-diacetoxynaphthalene characterized by: 2. The production method according to claim 1, wherein the inorganic acid is sulfuric acid or perchloric acid.