GB2192632A - Process for producing 2,6-dihydroxynaphthalene - Google Patents

Description

GB2192632A 1

SPECIFICATION

Process for producing 2,6-dihydroxynaphthalene The present invention relates to a process for producing 2,6- dihydroxynaphthalene, which is 5 utilized as a monomer in the production of aromatic polyesters having a capacity of forming liquid crystals.

Recently, in the development of various polymers known as the engineering plastics, aromatic polyesters, particularly the aromatic polyesters having a capacity of forming liquid crystals have attracted attention. 10 As the raw material of the polymer of aromatic polyesters, terephthalic acid, hydroquinone, p hydroxybenzoic acid and the like may be mentioned. In order to improve the physical and chemical properties of the aromatic polyesters, however, not only benzene derivatives but also naphthalene derivatives have come to be used as the raw material of the aromatic polyesters in recent years. 15 Of the naphthalenic raw materials, 2, 6-dihydroxynaphthalene has attracted attention as the monomer utilized in the production of the aromatic polyesters from the viewpoint that the physical properties of the liquid crystalline polymer derived frm 2,6dihydroxynaphthalene are excellent and that terephthalic acid used as the comonomer of the polymer is available at a low price. 20 However, since 2,6-dihydroxynaphthalene itself is not industrially produced at present, there is a problem that 2,6-dihydroxynaphthalene is not available at a low price.

As the process for producing 2,6-dihydroxynaphthalene, an old process has hitherto been known, wherein naphthalene or fl-naphthol is sulfonated and then the thus sulfonated product is subjected to alkali fusion, and such a process has been introduced in Beilstein's "Handbuch der 25 organischen Chemie". However, as is seen, for instance, in the description of Japanese Patent

Publication No. 56-77,254(1981), the by-production of the isomers other than the 2,6-isomer is inevitable according to this process and consequently, it is impossible to obtain the 2,6-isomer in a high yield. Furthermore, the yield of 2,6-dihydroxynaphthalene at the step of alkali fusion of sodium 2-naphthol-6-sulfonate is in the extent of 50% as is described in A.P. Kuriakose et al. in 30 J. Indian Chem. Soc., 43, 437(1966). Consequently, the yield of 2,6- dihydroxynaphthalene pro duced by the process comprising the steps of sulforiation of naphthalene or #-naphthol and of alkali fusion of the thus sulfonated product is extremely poor.

Further, since it is difficult to separate the 2,6-isomer and it is necessary to carry out a drainage treatment specific to the step of alkali fusion, there is a problem of a high production 35 cost. Namely, this process is industrially poor in practical use.

A process for producing hydroquinone from p-diisopropylbenzene while applying the principle in the production of phenol by the cumene process has hitherto been known [refer to Japanese Patent Publication No. 51-33 100(1976)].

A process has been proposed while applying the process to the production of 2,6-dihydroxy- 40 naphthalene. Namely, 2,6-diiso propyl naphtha I ene as the starting material is oxidized to obtain 2, 6-diisopropyinaphthalene dihydroperoxide and the thus obtained dihydroperoxide is converted into 2,6-dihydroxynaphthalene by acid decomposition [refer to Japanese Patent Applications Laid Open(KOKAI) Nos. 61-93 156(1986), 61-100 558(1986) and 61-191 638(1986)].

However, in this case, since it is difficult to separate the thus formed dihydroperoxide, even 45 this process cannot be regarded suitable industrially.

Still more, a process of converting aromatic carbinols represented by the formula:

CH 1 3 50 Ar-C - uh I CH 3 (wherein Ar represents an aromatic ring) into a compound represented by the formula: Ar-OH 55 has also been known. Namely the aromatic carbinol is oxidized with hydrogen peroxide in a solvent in the presence of a strong acid [for instance, refer to Japanese Patent Application Laid Open(KOKAI) No. 52-5 718(1977), Japanese Patent Publication No. 35-7 558(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, 743(1959)]. 60 However, the examples described in the literature concern processes for converting 2-hydroxy2-propylbenzene, p-d i (2-hyd roxy-2-propyl) benzene, p-(2-hydroxy-2propyl)-a, d-dimethylbenzyl hy droperoxide and the like into phenol or hydroquinone, and there has not been disclosed a process for converting the 2-hydroxy-2-propyl group which is directly bound to the naphthalene ring into the hydroxy group in the literature. 65 2 GB2192632A 2 By the way, even in the case where 2,6-di (2-hyd roxy-2-propyl) naphtha lene[herei nafter referred to as 2,6-DHPN1 is oxidized in the solvent used in the process described in the literature, it is impossible to produce industrially 2,6-dihydroxynaphthalene by the following reasons:

Namely, (1) 2,6-DHPN does not dissolve in the solvent, (2) in spite of the disappearance of 2,6-DHPN from the reaction system, 2,6-dihydroxynaphthalene is scarcely formed, (3) the solvent 5 itself reacts in the system or (4) the reaction velocity is small.

These facts are considered to be derived from the substantial difference of the physical and chemical properties between 2,6-dihydroxynaphthalene which is a naphthalene derivative and the carbinols disclosed in the literatures, which are benzene derivatives.

Under the circumstances, as a result of the present inventors' study concerning the industrially 10 feasible process for producing 2,6-dihydroxynaphthalene, it has been found out that 2,6-dihy droxynaphthalene represented by the following formula(iii) can be advantageously produced by using 2,6-DHPN represented by the following formula(I1) and derived from 2,6-diisopropyina phthalene represented by the following formulafl) which is easily available industrially, as the starting material, namely, by oxidizing 2,6-DHPN under the specified conditions, 2,6-dihydroxyna- 15 phthalene of the formula(lil) can be advantageously produced, and on the basis of the finding, the present invention has been attained.

CH 3 20 )- c,' 1 HC \ H 3 C'-- /Y CH 3 - 25 CH H c 1 31 c -OH H-C 0 0 1 1 3 H 3 c 30 OH H 0 35 Namely, the object of the present invention is to provide a process for advantageously and industrially producing 2,6-dihydroxynaphthalene which is useful as the raw material for producing 40 the so-called liquid crystal polymer which has a capacity of forming liquid crystals.

In an aspect of the present invention, there is provided a process for producing 2,6-dihydroxy naphthalene, which process comprises the step of oxidizing 2,6-di(2- hydroxy-2-propyl)naphthal- ene with hydrogen peroxide and acetonitrile, 1,4-dioxane or a mixture thereof in the presence of an inorganic acid of an amount not less than 0.001 time by weight and less than 0.1 time by 45 weight to the amount of the 2,6-di(2-hydroxy-2-propyi) naphthalene. Ik The feature of the present invention lies in producing 2,6- dihydroxynaphthalene by oxidizing 2,6-DHPN of the formula (11) with hydrogen peroxide in acetonitrile, 1,4- dioxane or a mixture thereof in the presence of a specified amount of an inorganic acid.

The compound, 2,6-DHPN, represented by the formula (11), which is used as the starting 50 substance in the present invention, is easily available by applying a known method for producing dimethylphenylcarbinol from cumene to 2,6-diisopropyinaphthalene.

According to the present invention, in oxidizing the starting substance, 2,6-DHPN, to convert it to 2,6-dihydroxynaphthalene, it is suitable to use acetonitrile, 1,4- dioxane or a mixed solvent thereof as the reaction solvent in an amount of from 7 to 25 times by volume to the weight of 55 the starting substance (mi/g).

Although the present inventors formerly proposed that the oxidation of 2, 6-DHPN is carried out in the reaction solvent [refer to Japanese Patent Application No. 60- 123,819(1985)], since the added amount of the inorganic acid in the reaction system is too much, a rapid generation of heat is caused in the reaction and consequently, there was a fear of inability to control the 60 reaction temperature.

in order to solve this problem, the present invention discloses, by reducing the amount of the inorganic acid, which is added to the reaction system, to a specifically limited range and increasing the concentration of hydrogen peroxide which is used for oxidation as well as the use of the above-mentioned solvent, the control of the reaction temperature is possible. 65 3 GB2192632A 3 Namely, in the present invention, the oxidation of the starting substance, 2,6-DHPN, is carried out by adding not less than 0.001 time and less than 0.1 time by weight, preferably from 0.005 to 0.05 time by weight of the inorganic acid to the amount of 2,6-DHPN and an aqueous solution of hydrogen peroxide of a concentration of not less than 60% to a solution of 2,6 DHPN in acetonitrile, 1,4-dioxane or a mixture thereof, and by such an operation, the reaction 5 temperature is controlled to the preferred temperature, whereby it is possible to convert 2,6 DHPN rapidly into 2,6-dihydroxynaphthalene.

As the inorganic acid, sulfuric acid and perchloric acid may be used, and the inorganic acid is dropped together with hydrogen peroxide in the 2,6-DHPN solution. In the case where the amount of the added inorganic acid is less than 0.001 time by weight, the reaction is not 10 completed, and on the other hand, in the case where the amount thereof is more than 0.1 time by weight, the selectivity becomes poor and coloration of the product is caused.

Furthermore, it is preferable to use hydrogen peroxide in an amount of from 2 to 3 moles to the starting subs ' tance. In the case where the amount used is too small, the conversion rate of the starting substance is poor, and on the other hand, in the case where the amount used is too 15 much, the coloration of the product becomes remarkable.

In adding the inorganic acid and hydrogen peroxide to the starting substance, it is preferable - to mix the inorganic acid and hydrogen peroxide and then to drop the thus formed mixture onto the starting substance, or after dropping hydrogen peroxide onto the starting substance, it is preferable to drop the inorganic acid thereonto. 20 In the case where the inorganic acid is added in advance, olefin is formed by dehydration of the starting substance and the olefin further reacts to cause the reduction in the production of the objective, and consequently, such an operation is undesirable.

The reaction temperature in the present invention is preferably not lower than 60'C and not higher than the boiling point of the solution, and although the reaction time depends on the 25 reaction temperature, the reaction is completed usually within 30 min.

After the reaction is over, for instance, an aqueous saturated saline solution is added to the thus obtained reaction mixture, whereby the organic layer is separated. Then, the organic layer is washed with an aqueous saturated saline solution and the solvent was distilled off from the organic layer to obtain the crude 2,6-dihydroxynaphthalene. 30 By recrystallizing the thus obtained crude 2,6-dihydroxynaphthalene from a suitable solvent, for instance, acetic acid, it is possible to obtain the purified 2,6- dihydroxynaphthalene.

According to the process of the present invention, it is possible to produce 2,6-dihydroxyna phthalene which is useful as the raw material for producing the liquid crystal polymer, advantage ously in a high yield as shown in the following Examples while using 2,6- DHPN which is derived 35 from the industrially and easily available 2,6-di iso pro pyIna phthalene, as the starting material.

Consequently, the process of the present invention is useful in the production of the liquid crystal polymer of aromatic polyesters.

The present invention is explained more in detail in the following Examples; however, it should be recognized that the scope of the present invention is not restricted to these Examples. 40 EXAMPLE 1: -

Into 240ml of acetonitrile, 10.0g(41mmol) of 2,6-DHPN were dissolved at 70'C, and 4ml of an aqueous 70% solution of hydrogen peroxide were added to the thus formed solution. Then, a solution. of 0. 1 g of concentrated sulfuric acid in 1 0ml of acetonitrile was added to the thus formed mixture, and the whole mixture was reacted under agitation for 20 min in an oil bath 45 kept at 70'C. After the reaction was over, an aqueous saturated saline solution was added to the liquid reaction mixture and after separating the acetonitril layer, the thus obtained acetonitrile layer was washed with an aqueous saturated saline solution until the acetonitrile layer became neutral. After separating the acetonitrile layer, the solvent was distilled off from the acetonitrile layer and the residue was dried to obtain 6.6g of crude 2,6- dihydroxynaphthalene (yield:99%). 50 EXAMPLE 2:

The reaction was carried out in the same manner as in Example 1 except for using 1,4 dioxane instead of acetonitrile in Example 1. On quantitatively analyzing the thus obtained reaction mixture with the high performance liquid chromatography, 2,6- dihydroxynaphthalene was 55 obtained (yield:99%).

COMPARATIVE EXAMPLE Into 50ml of acetonitrile, 10.1g(41mmol) of 2,6-DHPN were suspended, and after adding 10ml of an aqueous 31% solution of hydrogen peroxide to the thus formed suspension, the thus 60 formed mixture was stirred in an oil bath kept at 30'C.

On adding a solution of 5g of concentrated sulfuric acid in 10ml of acetonitrile to the thus stirred mixture, the mixture became transparent at a time and then began to be turbid, and although the dropl:iing of the diluted sulfuric acid was stopped, the temperature of the reaction mixture rose suddenly beyond control and the reaction mixture bumped. 65 4 GB2192632A 4

Claims (8)

1. CLAIMS. 1. A process for producing 2,6-dihydroxynaphthalene, which process

   comprises oxidizing 2,6d i(2-hydroxy-2-propyl) naphthalene with hydrogen peroxide in acetonitrile, 1,4-dioxane or a mix- ture thereof in the presence of not less than 0.00 1 times by weight but less than 0. 1 times by 5 weight, based on the weight of the 2,6-di(2-hydroxy-2-propyi)naphthalene, of an inorganic acid.
2. 2. A process according to claim 1, wherein said inorganic acid is sulfuric acid or perchloric acid.
3. 3. A process according to claim 1 or 2, wherein the oxidation of said 2,6di(2-hydroxy-2- propyl)naphthalene is carried out by using hydrogen peroxide in an amount of from 2 to 3 times 10 by mole the amount of the 2,6-di(2-hydroxy-2-propyl) naphthalene.
4. 4. A process according to any one of the preceding claims, wherein the oxidation of said 2,6-di (2-hydroxy-2-propyl) naphthalene is carried out at a temperature of not lower than 60'C but not higher than the boiling point of the solution of the 2,6-di (2- hydroxy-2-propyl) naphthalene in.

   acetonitrile or 1,4-dioxane. 15
5. 5. A process according to any of the preceding claims, wherein the oxidation of said 2,6 di (2-hydroxy-2-propyl) naphthalene is carried out in the presence of from 0.005 to 0.05 times by weight, based on the weight of the 2,6-di (2-hyd roxy-2-propyl) naphthalene, of the inorganic acid.
6. 6. A process according to any one of the preceding claims, wherein the concentration of the 2Q aqueous hydrogen peroxide solution is not lower than 60% by weight. 20
7. 7. A process for the preparation of 2,6-dihydroxynaphthalene, said process being substan tially as hereinbefore described in Example 1 or 2.
8. 8. An aromatic polyester produced from 2,6-dihydroxynaphthalene prepared by a process as claimed in any one the preceding claims.

   Published 1988 at The Patent Office, State House, 66/71 High Holborn, London WC1R 4TP. Further copies may be obtained from The Patent Office, Sales Branch, St Mary Cray, Orpington, Kent BR5 3RD. Printed by Burgess & Son (Abingdon) Ltd. Con. 1/87.