GB2176188A

GB2176188A - Process for producing 2,6-naphthalenediol and 2,6-diacetoxynaphthalene

Info

Publication number: GB2176188A
Application number: GB08613759A
Authority: GB
Inventors: Takayuki Tanonaka; Takashi Yamauchi; Hiroyuki Enari
Original assignee: Kureha Corp
Current assignee: Kureha Corp
Priority date: 1985-06-07
Filing date: 1986-06-06
Publication date: 1986-12-17
Also published as: DE3618643A1; GB2176188B; FR2583040B1; DE3618643C2; GB8613759D0; FR2583040A1

Abstract

2,6-Naphthalenediol is produced by oxidizing 2,6-di(2-hydroxy-2-propyl)naphthalene in acetonitrile, 1,4-dioxane or a mixture thereof with hydrogen peroxide in the presence of an inorganic acid or a solid acid. 2,6-Diacetoxynaphthalene is prepared by acetylating the thus obtained 2,6-naphthalenediol.

Description

SPECIFICATION Process for producing 2,6-naphthalenediol and 2,6-diacetoxynaphthalene The present invention relates to a process for producing 2,6-naphthalenediol and highly pure 2,6-diacetoxynaphthalene which are utilized as the monomer of aromatic polyesters having an ability of forming liquid crystalline polymers.

In recent years, various engineering plastics have been developed, and as the plastics in this field, aromatic polyesters, particularly those having an ability of forming liquid crystalline polymers have attracted one's attention.

As the starting material for the aromatic polyesters having an ability of forming liquid crystalline polymers, terephthalic acid, hydroquione, p-hydroxybenzoic acid, etc. may be mentioned, however, in order to improve the physical and/or chemical properties of the aromatic polyesters, not only the benzene compounds but also naphthalene compounds have come to be required as the starting material thereof.

Of the naphthalene compounds, 2,6-naphthalenediol and 2,6-diacetoxynaphthalene have attracted one's attention from the view points that the physical properties of the liquid crystalline polymers obtained therefrom are excellent and terephthalic acid used as the comonomer thereof is available at low price.

Although 2,6-diacetoxynaphthalene is obtained by acetylation of 2,6-naphthalenediol, since 2,6-naphthalenediol is not produced industrially at present, there is a problem that 2,6-diacetoxynaphthalene is not available unexpensively.

In this connection, as the process for producing 2,6-naphthalenediol, a classic process has hitherto been known, wherein naphthalene or t3-naphthol is sulfonated and the thus sulfonated product is subjected to alkali fusion. Such a process has been described in Beilstein's "Handbuch der organischen Chemie". However, according to this process, for instance, as seen from Japanese Patent Publication No.

56-77254 (1981), by-production of the other isomers than 2,6-isomer is inevitable in sulfonation step, and accordingly, the 2,6-isomer cannot be obtained in a high yield. Further, in the alkali fusion step, for instance, as is described in A. P. Kuriakose et al. J. Indian Chem. Soc., 43, 437 (1966), since the yield of 2,6naphthalenediol is as low as 50 %, the total yield of 2,6-naphthalenediol in this process wherein naphthalene or p-naphthol is sulfonated and the thus sulfonated product is subjected to alkali fusion is extremely low.

In addition, it is necessary to provide the draining treatment in the step of alkali fusion and accordingly, there is a problem of increased cost. Namely, the process is industrially poor in practicality.

Besides, a process for producing hydroquinone from p-isopropylbenzene, while applying "the cumene process" has hitherto been known (Japanese Patent Publication No. 51-33100 (1976)) and the following process for producing 2,6-naphthalenediol could be considered from consideration of the process.

Namely, while applying the process to the production of 2,6-naphthalenediol, 2,6-diisopropylnaphthalene is oxidized to 2,6-di(2-hydroperoxy-2-propyl)-naphthalene, and the thus obtained dihydroperoxide is subjected to acid decomposition to be converted into 2,6-naphthalenediol.

However, in such a process, since the yield of the dihydroperoxide is poor as compared to that of the process for producing hydroquinone and it is difficult to isolate the thus formed dihydroperoxide, the above-mentioned process for producing 2,6-naphthalenediol cannot be said to be industrially suitable.

On the other hand, a process wherein a compound represented by the formula:

wherein Ar represents an aromatic ring, is oxidized in a solvent by hydrogen peroxide in the presence of a strong acid into a phenolic compound represented by the formula, Ar-OH, has been also known (for instance, refer to Japanese Patent Application Laying-Open (KOKAI) No. 52-5718 (1977), Japanese Patent Publication No. 35-7558 (1960), British Patent No. 910,735, TSUNODA and KATO J. Chem. Soc. Japan, 80 (7), 689 (1959) and M.S. Kharasch et al. J. Org. Chem., 15, 748 and 775 (1950)).However, the reaction disclosed in the references are processes for converting (2-hydroxy-2-propyl)benzene, p-di(2-hydroxy-2propyl)benzene, 1-(2-hydroxy-2-propyl)-4-(2-hydroperoxy-2-propyl)benzene, etc. into phenol or hydroquinone, and there is no disclosure concerning the process for converting a compound having naphthalene ring such as di(2-hydroxy-2-propyl)naphthalene, etc. into naphthalenediols in the references.

In this connection, it is substantially impossible to obtain 2,6-naphthalenediol profitably in industrial scale from 2,6-di(2-hydroxy-2-propyl)naphthalene (hereinafter referred to as 2,6-DHPN) by the process disclosed in the references due to the following reason.

Namely, in oxidizing 2,6-DHPN in the solvent used in the process disclosed in the references (1) 2,6 DHPN does not dissolve in the solvent described in the references, (2) in spite of the disappearance of 2,6-DHPN from the reaction system, 2,6-naphthalenediol is scarcely formed, (3) the solvent itself reacts in the system or (4) the reaction rate is very low.

The above-mentioned facts are considered to be due to the remarkable difference of the physical and/ or chemical properties between the naphthalene compound (2,6-DHPN) and the benzene compound ((2hydroxy-2-propyl)-benzene, etc.).

As a result of the present inventors' studies on the industrially profitable process for producing 2,6naphthalenediol and 2,6-diacetoxynaphthalene, it has been found by the present inventors that (1) 2,6naphthalenediol can be profitably produced by using 2,6-DHPN as the starting material, which is available from 2,6-diisopropylnaphthalene which is easily available in an industrial scale and subjecting 2,6 DHPN to oxidation under specified conditions, and (2) 2,6-diacetoxynaphthalene of a high purity can be produced in a high yield by further acetylating the thus obtained 2,6-naphthalenediol, and based on the findings, the present inventors have attained the present invention.

In a first aspect of the present invention, there is provided a process for producing 2,6-naphthalenediol, which comprises oxidizing 2,6-di(2-hydroxy-2-propyl)naphthalene in acetonitrile, 1,4-dioxane or a mixture thereof with hydrogen peroxide in the presence of an inorganic acid or a solid acid.

In a second aspect of the present invention, there is provided a process for producing 2,6-diacetoxynaphthalene of a high purity, which comprises (1) oxidizing 2,6-di(2-hydroxy-2-propyl)naphthalene in acetonitrile, 1,4-dioxane or a mixture thereof with hydrogen peroxide in the presence of an inorganic acid, thereby obtaining 2,6-naphthalenediol and (2) acetylating the thus obtained 2,6-naphthalenediol to obtain 2,6-diacetoxynaphthalene of a high purity.

The present invention relates to (1) a process for producing 2,6-naphthalenediol by oxidizing 2,6-di(2hydroxy-2-propyl)naphthalene in acetonitrile, 1,4-dioxane or a mixture thereof with hydrogen peroxide in the presence of an inorganic acid or a solid acid and (2) a process for producing 2,6-diacetoxynaphthalene by acetylating 2,6-naphthalenediol obtained by the process shown in (1).

2,6-Di(2-hydroxy-2-propyl)naphthalene used as the starting material according to the present invention can be easily obtained by applying the known process for producing dimethylphenylcarbinoi from cumene to 2,6-diisopropylnaphthalene.

It is important in the present invention to use acetonitrile, 1,4-dioxane or a mixture thereof as the solvent in oxidizing 2,6-di(2-hydroxy-2-propyl)naphthalene (referred to as 2,6-DHPN) into 2,6-naphthalenediol. As has been described, in the case of using another solvent in the above-mentioned reaction, it is difficult to obtain 2,6-naphthalenediol profitably in an industrial scale. For instance, ketones such as acetone, isobutyl methyl ketone, etc. used as the solvent in the Japanese Patent Publication No. 52-5718 (1977) are not inert to the reaction and accordingly, in the case of using such a solvent in the present reaction, although 2,6-naphthalenediol is formed, a large amount of by-products derived from ketone is formed.

In addition, in the case of using a lower alcohol such as methanol, ethanol, 2-propanol, etc. as the solvent, the reaction rate is very small and in addition, the selectivity in reaction is low and accordingly, it is impossible to obtain 2,6-naphthalenediol in a high yield.

Furthermore, in the case of using a lower fatty acid such as acetic acid, propionic acid, etc. as the solvent, although 2,6-DHPN disappears from the reaction system, 2,6-naphthalenediol is scarcely formed because of the preferential side reactions. In addition, in the case of using a hydrocarbon as the solvent, since the solubilities of 2,6-DHPN and 2,6-naphthalenediol (which is the reaction product) in such a solvent are very small, it is impossible to obtain 2,6-naphthalenediol in a high yield.

According to the present invention, acetonitrile, 1,4-dioxane or a mixture thereof is used as the solvent in an amount of 3 to 30 ml, preferably 5 to 20 ml to one gram of 2,6-DHPN, and into the mixture of 2,6 DHPN and the solvent, hydrogen peroxide and the inorganic acid are added dropwise to initiate the reaction.

As the inorganic acid used in the present invention, sulfuric acid or perchloric acid is preferred, and as sulfuric acid, it is preferred to use concentrated sulfuric acid, however, diluted sulfuric acid of not less than 10 % may be used.

In addition, in the case of using concentrated sulfuric acid, it may be added to the reaction system after being diluted with an aqueous solution of hydrogen peroxide or the solvent, and in the case of using perchioric acid, it is preferable to use the commerciallized aqueous solution thereof such as 70 /O, 60 % or 40 % of perchloric acid.

It is preferable to use the inorganic acid in an amount of 0.1 to 4 times by weight of the amount of 2,6 DHPN, more preferably 0.2 to 3 times by weight.

In the case of using the acid in an amount of below 0.1 times by weight of the amount of 2,6-DHPN, the reaction does not complete, and on the other hand, in the case of using the acid in an amount of over 4 times by weight of the amount of 2,6-DHPN, the selectivity in reaction is low and the low selectivity becomes the cause of coloration of the reaction product. Namely, the two cases are not preferable.

As the solid acid used in the present invention, acid-type ion-exchange resins, preferably those having sulfonic acid groups (-SO3H), may be used. It is preferable to use the solid acid in an amount of 0.1 to 5 9, more preferably 0.2 to 3 g per one g of 2,6-DHPN.

As hydrogen peroxide used according to the present invention, the commerciallized aqueous 30 % solution is preferable and hydrogen peroxide may be used in an amount of from 2 to 10 mols, preferably from 2 to 3 mols to one mol of 2,6-DHPN.

In the case of using below 2 mols of hydrogen peroxide to one mol of 2,6-DHPN, the conversion ratio of 2,6-DHPN into 2,6-naphthalenediol is low, and on the other hand, in the case of using over 10 mols to one mol of 2,6-DHPN, the coloration of the reaction product is remarkable. Namely, the above-mentioned two cases are not preferable.

In adding both the inorganic acid and hydrogen peroxide to the mixture of 2,6-DHPN and the solvent by a method of dropping, etc., it is preferable to add a mixture thereof or add the inorganic acid after the addition of hydrogen peroxide.

In the case of adding the inorganic acid in preference to hydrogen peroxide, olefin is formed by the dehydration of 2-hydroxy-2-propyl group of 2,6-DHPN, and the olefin further reacts to form impurities, and accordingly, such a mode of addition is not preferable.

The reaction temperature of the process for producing 2,6-naphthalenediol according to the present invention may be selected in the range of from room temperature to 80"C, however, a temperature of from 30 to 60"C is preferable, and although the reaction period depends on the amount of 2,6-DHPN, the solvent, the inorganic acid or the solid acid and hydrogen peroxide used in the reaction and the reaction temperature, the reaction ordinarily completes within from 10 min to 3 hours.

After the reaction is over, for instance, an aqueous saturated solution of sodium chloride is added to separate the organic layer, and after washing the organic layer with the aqueous saturated solution of sodium chloride, the solvent is distilled off from the organic layer to obtain 2,6-naphthalenediol in a yield of higher than 75 %, preferably higher than 90 %.

2,6-Diacetoxynaphthalene is obtained by subjecting the thus obtained 2,6-naphthalenediol to acetylation.

Although there are various processes of acetylation, the process of heating 2,6-naphthalenediol together with acetic anhyderide is most preferable for obtaining highly pure 2,6-diacetoxynaphthalene.

Acetic anhydride may be used in excess and also a mixture of a small excess of acetic anhydride and acetic acid may be used in acetylation.

The reaction temperature of acetylation is preferably 100 to 140"C, and the reaction is carried out for 30 min to 2 hours, the reaction completing within the above-mentioned period.

After the reaction is over, the reaction mixture is allowed to cool, is filtered to collect the crystals of 2,6-diacetoxynaphthalene.

Although the purity of the thus collected 2,6-diacetoxynaphthalene is higher than 98 %, it is possible to obtain 2,6-diacetoxynaphthalene of a purity of higher than 99.5 % by recrystallizing the thus obtained crystals from a suitable solvent, for instance, acetic acid.

As has been described above, according to the present invention, while using, as the starting substance 2,6-DHPN which is easily available from 2,6-diisopropylnaphthalene which is industrially easily available, it has been possible to obtain 2,6-naphthalenediol and 2,6-diacetoxynaphthalene of a purity of higher than 95 %, which are useful as the starting substances for producing aromatic polyesters having an ability of forming liquid crystals, in high yields as will be seen in the following Examples.

The present invention will be more precisely explained while referring to the following non-limitative examples.

Example 1: In 25 ml of acetonitrile, 1.0 g (4.1 mmol) of 2,6-DHPN was suspended, and 1.3 ml of an aqueous 31 % solution of hydrogen peroxide and 0.9 ml of an aqueous 70 % solution of perchloric acid were successively added, and the thus formed mixture was stirred for 10 min in an oil bath kept at 30"C.

After the reaction was over, an aqueous saturated solution of sodium chloride was added to the reaction mixture to separate the layer of acetonitrile, and the layer of acetonitrile was washed repeatedly with the saturated solution of NaCI until the layer of acetonitrile became neutral. After drying the layer of acetonitrile over anhydrous sodium sulfate, acetonitrile was distilled off, and the residue was dried to obtain 0.63 g of crude 2,6-naphthalenediol in a yield of 96.0 %.

Example 2: In 127 ml of acetonitrile, 5.0 g (20.5 mmol) of 2,6-DHPN were suspended, and 6.7 ml of an aqueous 31 % solution of hydrogen peroxide and 10.2 ml of a 40 % solution of sulfuric acid in acetonitrile were successively added to the suspension.

The thus formed mixture was stirred for 30 min in an oil bath kept at 30"C.

After the reaction was over, the reaction mixture was treated in the same manner as in Example 1 to obtain 3.17 g of crude 2,6-naphthalenediol in a yield of 96.7 %.

Example 3: In 2 g of acetonitrile, 0.1 g (0.41 mmol) of 2,6-DHPN was suspended, and 0.15 g of an aqueous 31 % solution of hydrogen peroxide and 0.3 g of an aqueous 40 % solution of perchloric acid were successively added to the suspension.

The thus formed mixture was stirred for 30 min at 30 C.

As a result of examining the reaction mixture by high performance liquid chromatography (HPLC), it was found that 2,6-naphthalenediol was nearly quantitatively formed therein.

Example 4: Into a mixture of 0.2 g (0.82 mmol) of 2,6-DHPN, 2 g of 1,4-dioxane and 0.35 g of an aqueous 31 % solution of hydrogen peroxide, 0.5 g of an aqueous 40 % solution of perchloric acid was added dropwise under stirring at 40"C and the thus formed mixture was further stirred for 30 min at 40"C.

As a result of examining the reaction mixture by HPLC, it was found that 2,6-naphthalenediol was formed in a yield of 98 %.

Example 5: After adding dropwise a mixture of 0.3 g of concentrated sulfuric acid and 0.3 g of an aqueous 31 % solution of hydrogen peroxide to a mixture of 0.2 g (0.82 mmol) of 2,6-DHPN and 1.5 g of 1,4-dioxane, the thus formed mixture was stirred for 30 min at 30"C.

As a result of examining the reaction mixture by HPLC, it was found that 2,6-naphthalenediol was formed in a yield of 99 %.

Example 6: In 23 ml of acetonitrile, 1 g (4.1 mmol) of 2,6-DHPN was suspended, and 1.3 ml of an aqueous 31 % solution of hydrogen peroxide and 2 g (dry) of AMBERLITE 200C (H-type) (made by ORGANO Inc., Tokyo, Japan) were successively added into the thus obtained suspension.

The thus formed mixture was stirred for 2 hours at 50"C.

As a result of examining the reaction mixture by HPLC, 2,6-naphthalenediol was formed in a yield of 93 %.

Example 7: In 920 ml of acetonitrile, 50.0 g (0.205 mol) of 2,6-DHPN were suspended, and 55 g of an aqueous 31 % solution of hydrogen peroxide and 50 g of a 40 % solution of sulfuric acid in acetonitrile were successively added to the thus formed suspension. The thus formed mixture was stirred for 40 min in an oil bath kept at 30"C.

After the reaction was over, an aqueous saturated solution of sodium chloride was added to the reaction mixture to separate the organic layer, and the organic layer was washed repeatedly with the aqueous saturated solution of sodium chloride until the organic layer became neutral. After drying the organic layer over anhydrous sodium sulfate, acetonitrile was distilled off therefrom, and the residue was dried to obtain 34.8 g of 2,6-naphthalenediol in a yield of 96.0 %.

Thereafter, a mixture of 33.2 g (0.187 mol) of the thus obtained 2,6-naphthalenediol, 15.0 g of acetic acid and 44.9 g of acetic anhydride was stirred for 90 min in an oil bath kept at 140"C. After the reaction was over, the reaction mixture was cooled to room temperature and the thus precipitated crystals were collected by filtration, washed with acetic acid and dried to obtain 41.8 g of 2,6-diacetoxynaphthalene of white in color in a yield of 91.7 %.

As a result of examining the purity of the thus obtained 2,6-diacetoxynaphthalene by a differential scanning calorimeter (DSC, Mettler TA 3000 System), the purity was 99.81 %.

In addition, 1.75 g of 2,6-diacetoxynaphthalene of the purity of 91.3 % (by a high performance liquid chromatography) were further obtained from the mother liquor. Namely, the combined yield of 2,6-diacetoxynaphthalene becomes 95.2 %.

Subsequently, 41.0 g of 2,6-diacetoxynaphthalene of the purity of 99.81 % were recrystallized from 61.5 g of acetic acid to obtain 39.3 g of 2,6-diacetoxynaphthalene of the high purity of 100 % (by HPLC) and 99.97 % (by DSC) in a recovery of 95.8 %. In addition, from the mother liquor of recrystailization, 1.3 g of 2,6-di-acetoxynaphthalene were further obtained, and therefore the combined recovery became 99.0 %.

Example 8: In 400 ml of acetonitrile, 70.0 g (0.287 mol) of 2,6-DHPN were suspended, and 70.0 g of an aqueous 31 % solution of hydrogen peroxide and 52.5 g of a 40 % solution of sulfuric acid in acetonitrile were successively added to the thus formed suspension, and the mixture was stirred for 30 min in an oil bath kept at 30 C.

After the reaction was over, an aqueous saturated solution of sodium chloride was added to the reaction mixture to separate the acetonitrile layer. After neutralizing the acetonitrile layer with sodium carbonate and then drying the thus neutralized acetonitrile layer over anhydrous sodium sulfate, acetonitrile was distilled off from the layer to obtain 45.14 g of 2,6-naphthalenediol in a yield of 98.5 %.

Subsequently, 45 g of the thus obtained 2,6-naphthalenediol were acetylated with 23 g of acetic acid and 61 g of acetic anhydride in the same manner as in Example 7 to obtain 60.6 g of 2,6-diacetoxynaphthalene of the purity of 99.85 % (by DSC) in a yield of 93.0 %.

Example 9: In 250 ml of acetonitrile, 10.0 g (0.041 moi) of 2,6-DHPN were dispersed, and 15 g of an aqueous 31 % solution of hydrogen peroxide and 30 g of an aqueous 40 % solution of perchloric acid were added to the thus formed dispersion, and the thus formed mixture was stirred for 30 min at 30"C. After the reaction was over, the reaction mixture was treated as in Example 7 to obtain 6.7 g of 2,6-naphthalenediol in a yield of 96.5 %.

Subsequently, 6.0 g (0.035 mol) of the thus obtained 2,6-naphthalenediol were acetylated with 2.7 g of acetic acid and 7.9 g of acetic anhydride in the same manner as in Example 7 to obtain 7.9 g of 2,6diacetoxynaphthalene of white in color in a yield of 92.5 %.

The purity of the thus obtained 2,6-diacetoxynaphthalene was 99.85 % (by DSC).

Example 10: A mixture of 20.0 g (0.082 mol) of 2,6-DHPN, 200 ml of 1,4-dioxane and 35 g of an aqueous 31 % solution of hydrogen peroxide was stirred at 40"C, and 50 g of an aqueous 40 % solution of perchloric acid were added dropwise, and the thus formed mixture was stirred for further 30 min after completion of the addition. After the reaction was over, the reaction mixture was treated as in Example 7 to obtain 13.5 g of 2,6-naphthalenediol in a yield of 97.8 %.

In the same manner as in Example 7, 13.0 g of the thus obtained 2,6-naphthalenediol were acetylated with 5.9 g of acetic acid and 17.6 g of acetic anhydride to obtain 17.5 g of 2,6-diacetoxynaphthalene of the purity of 99.82 % (by DSC).

Example 11: In 250 ml of acetonitrile, 10.0 g (0.041 mol) of 2,6-DHPN were suspended, and 13 ml of an aqueous 31 % solution of hydrogen peroxide and 9 ml of an aqueous 70 % solution of perchloric acid were successively added to the thus formed suspension. The thus formed mixture was stirred for 30 min in an oil bath kept at 30"C. After the reaction was over, the reaction mixture was treated as in Example 7 to obtain 6.6 g of 2,6-naphthalenediol in a yield of 95.6 /O.

In the same manner as in Example 7, 6.0 g of the thus obtained 2,6-naphthalenediol were acetylated with 2.7 g of acetic acid and 7.9 g of acetic anhydride to obtain 8.0 g of 2,6-diacetoxynaphthalene of the purity of 99.85 % (by DSC).

Example 12: In 23 ml of acetonitrile, 1 g (4.1 mmol) of 2,6-DHPN was suspended, and 1.3 ml of an aqueous 31 % solution of hydrogen peroxide and 2 g (dry) of AMBERLITE 200C (H-type) (made by ORGANO Inc., Tokyo, Japan) were successively added into the thus obtained suspension.

The thus formed mixture was stirred for 2 hours at 50 C.

In the same manner as in Example 7, 6.0 g of the thus obtained 2,6-naphthalenediol were acetylated with 2.7 g of acetic acid and 7.9 g of acetic an hydride to obtain 7.9 g of 2,6-diacetoxynaphthalene of the purity of 99.80 % (by DSC).

Comparative Examples 1 to 3: In the same manner as in Examples 1 to 3, each of the three reactions was carried out except for using acetic acid instead of using acetonitrile in Examples 1 to 3. On analyzing the thus obtained reaction mixture by gas-chromatography, any formation of 2,6-naphthalenediol was not recognized, although 2,6 DHPN disappeared from the reaction mixture.

Comparative Example 4: Into a mixture of 0.1 g (0.41 mmol) of 2,6-DHPN, 2 g of ethanol and 0.2 g of an aqueous 31 % solution of hydrogen peroxide, 0.1 g of an aqueous 70 % solution of perchloric acid was added and stirring was started to initiate the reaction. After 30 min from the initiation of the reaction, any formation of 2,6-naphthalenediol was not recognized. After subjecting the mixture to reaction further for 2 hours, it was found that 2,6-naphthalenediol was formed in a yield of 55 %. On examining the reaction mixture by gaschromatography, formation of a number of by-products was recognized.

Comparative Example 5: Into a mixture of 0.1 g of 2,6-DHPN, 2.0 g of n-heptane and 0.2 g of an aqueous 31 % solution of hydrogen peroxide, 0.1 g of an aqueous 70 % solution of perchloric acid was added, and the thus formed mixture was stirred for 30 min at 30"C.

It was found that 2,6-naphthalenediol was formed in a yield of 53.1 %, however, on examining the reaction product by gas-chromatography, formation of a number of by-products was recognized.

Comparative Example 6: Into a mixture of 0.1 g of 2,6-DHPN, 2.0 g of benzene and 0.2 g of an aqueous 31 % solution of hydrogen peroxide, 0.1 g of an aqueous 70 % solution of perchloric acid was added, and the thus formed mixture was stirred at 30"C to initiate the reaction. After 30 min from the initiation of the reaction, the formation of 2,6-naphthalenediol was very small and accordingly, the reaction was continued for further 5 hours. The yield of 2,6-naphthalenediol was 45.7 %, however, precipitation of an insoluble matter black in color and unknown in structure was recognized in the reaction mixture.

Comparative Example 7: In the same manner as in Example 7, 2,6-naphthalenediol was produced and it was recrystallized from acetic acid as follows.

In spite of repeating the recrystallization three times while using acetic acid in an amount of 3 times by weight of the amount of 2,6-naphthalenediol, the purity of the thus obtained, recrystallized 2,6-naphthalenediol was 98.8 % (by DSC) and the recovery was about 50 %.

In addition, it was attempted to obtain second crop from the mother liquor, however, the mother liquor changed into a tarry matter when condensed, and accordingly, the recovery of 2,6-naphthalenediol from the mother liquor was impossible.

Reference Example Into 20 ml of acetone, 1.0 g of an aqueous 31 % solution of hydrogen peroxide and 2.0 g of an aqueous 70 % solution of perchloric acid were added, and the mixture was stirred for 30 min at 30"C to obtain a white precipitate. The thus obtained precipitate had a stimulative odor and was considered to be a condensate of acetone. It was found that acetone was not inert in the reaction system according to the present invention and that acetone is not suitable as the reaction solvent therein.

Claims

1. Process for producing 2,6-naphthalenediol, which process comprises oxidizing 2,6-di(2-hydroxy-2propyl)-naphthalene in acetonitrile, 1 ,4-dioxane or a mixture thereof with hydrogen peroxide in the presence of an inorganic acid or a solid acid.

2. A process according to Claim 1, wherein said acetonitrile, 1,4-dioxane or a mixture thereof is used in an amount of 3 to 30 ml per gram of 2,6-di(2-hydroxy-2-propyl)naphthalene.

3. A process according to Claim 1 or 2, wherein said inorganic acid is sulfuric acid or perchloric acid.

4. A process according to any one of the preceding claims, wherein said inorganic acid is used in an amount by weight which is from 0.1 to 4 times the amount of 2,6-di(2-hydroxy-2-propyl)naphthalene.

5. A process according to Claim 1 or 2, wherein said solid acid is an ion-exchange resin having sulfonic acid groups.

6. A process according to any one of Claims 1, 2 and 5, wherein said solid acid is used in an amount by weight which is from 0.1 to 5 times the amount of said 2,6-di(2-hydroxy-2-propyl)-naphthalene.

7. A process according to any one of the preceding claims, wherein the oxidation is carried out by using 2 to 10 mols of hydrogen peroxide per mol of 2,6-di(2-hydroxy-2-propyl)naphthalene.

8. A process for producing 2,6-diacetoxynaphthalene, which process comprises acetylating 2,6-naphthalenediol which has been prepared by a process as claimed in any one of the preceding claims.

9. A process according to Claim 8, wherein the acetylation is carried out in acetic anhydride or a mixture of acetic anhydride and acetic acid.

10. A process according to Claim 8 or 9, wherein the acetylation is carried out at a temperature of 100 to 1400C for 30 min to 2 hours.

11. A process for producing 2,6-naphthalenediol, said process being substantially as hereinbefore described in any one of Examples 1 to 12.

12. A process for producing 2,6-diacetoxynaphthalene, said process being substantially as hereinbefore described in any one of Examples 7 to 12.

13. An aromatic polyester which has been prepared from 2,6-naphthalenediol or 2,6-diacetoxynaphthalene produced by a process as claimed in any one of Claims 1 to 7 or any one of Claims 8 to 10 and 12 respectively.