JPS6339831A - Method for purifying dihydroxynaphthalene - Google Patents

Abstract

PURPOSE:To purify the titled compound useful as a raw material for synthetic resins, synthetic fibers, drugs, agricultural chemicals, dye, etc., by crystallizing crude dihydronatphthalene by the use of a solvent system constituting of water and an aliphatic ketone or aliphatic alcohol. CONSTITUTION:In purifying low-purity dihydroxynaphthalene which is obtained by oxidizing diisopropylnaphthalene with O2 in the presence of a base, and subjecting the oxidation product to acidolysis to give low-purity dihydroxynaphthalene and purifying, thence, crystallization is carried out by the use of a mixed solvent of water or 3-4 Caliphatic ketone (especially preferably acetone) or a mixed solvent of water or 1-5C aliphatic alcohol (e.g. especially preferably methanol, ethanol or isopropanol). The amount of water is preferably 5-95 pts. wt. based on 100 pts. wt. mixed solvent in both the solvents.

Description

[Detailed Description of the Invention] Shakuwari Rigae Hokumonme! The present invention relates to a method for purifying dihydroxynaphthalene,
More specifically, the present invention relates to a method for purifying dihydroxynaphthalene using a specific solvent system.

Original technical background and its problems 71, dihydroxynaphthalene, such as 2,6-dihydroxynaphthalene,
It is a compound useful as a raw material for synthetic resins, synthetic fibers, medicines, pesticides, dyes, etc. It is known that dihydroxynaphthalene can be produced by oxidizing diisopropylnaphthalene with molecular oxygen in the presence of a base to produce diisopropylnaphthalene dihydroberoxide, which is then decomposed with an acidic catalyst such as sulfuric acid. .

By the way, for example, when 2,6-diisopropylnaphthalene is oxidized with molecular oxygen in the presence of a base, in addition to the target compound 2,6-diisopropylnaphthalene dihydroberoxide (hereinafter sometimes abbreviated as DHP), , as a by-product, 2-(2-hydroxy-2-propyl)-6-(2-hydroperoxy-2-propyl)naphthalene (hereinafter sometimes abbreviated as HH, P),
2゜6-bis(2-hydroxy-2-propylnaphthalene (hereinafter sometimes abbreviated as DCA), 2-isopropyl-6-(2-hydroxy-2-propyl)naphthalene (hereinafter sometimes abbreviated as MCA) carbinollopyl-6-(2-hydroperoxy-2-propyl) such as )
Large amounts of monohydroperoxides such as naphthalene (hereinafter sometimes abbreviated as MHP) are produced. Furthermore, when the oxidation reaction product of dihydroxynaphthalene containing HP and by-products is acid-decomposed in the presence of an acid catalyst such as sulfuric acid as described above, in addition to the target compound dihydroxynaphthalene, various acid-decomposed reactions are also produced. Products such as isopropylnaphthol are formed.

In this way, when dihydroxynaphthalene is oxidized with molecular oxygen in the presence of a base to form DHP, and this is acid-decomposed using an acidic catalyst such as @acid, the resulting reaction mixture contains the target compound dihydroxynaphthalene. In addition, various reaction by-products will often be present.

For this reason, research is being conducted to obtain dihydroxynaphthalene as the target compound with as high purity as possible from dihydroxynaphthalene, but none of the methods
Dihydroxynaphthalene cannot be produced in high purity. Therefore, it is necessary to provide a method for obtaining high purity dihydroxynaphthalene from impure and low purity dihydroxynaphthalene.

The present inventors conducted intensive research to obtain high-purity hydroxynaphthalene from low-purity hydroxynaphthalene obtained by oxidation of diisopropylnaphthalene and subsequent acid decomposition. The present invention was completed based on the discovery that it was only necessary to analyze the method.

Purpose of the Invention The present invention aims to solve the problems associated with the prior art as described above. It is an object of the present invention to provide a purification method for obtaining high purity dihydroxynaphthalene from low purity dihydroxynaphthalene at a high recovery rate.

2 Group Transition The method for purifying dihydroxynaphthalene according to the present invention is to oxidize diisopropylnaphthalene with molecular oxygen in the presence of a base and then decompose it with an acid. A mixed solvent with ~4 aliphatic ketones (A>, or water and a carbon number of 1
It is characterized in that the mixed solvent (B) with an aliphatic alcohol of 5 to 5 is used as a solvent for crystallization.

According to the method for purifying dihydroxynaphthalene according to the present invention, low-purity dihydroxynaphthalene obtained by oxidation of diisopropylnaphthalene and subsequent acid decomposition is crystallized using a specific solvent system. Dihydroxynaphthalene can be recovered with a high recovery rate.

The method for purifying dihydroxynaphthalene according to the present invention will be specifically explained below.

The process according to the invention purifies dihydroxynaphthalene of low purity, which is obtained by oxidizing diimpropylnaphthalene with molecular oxygen in the presence of a base to give diisopropylnaphthalene dihydroberoxide. Obtained by acid decomposition of diisopropylnaphthalene dihydroberoxide in the presence of an acid catalyst.

The low-purity crude dihydroxynaphthalene purified in the present invention is obtained by the method described above. The reason for this is that the types of impurities contained in low-purity dihydroxynaphthalene obtained by oxidation of diisopropylnaphthalene and subsequent acid decomposition are completely different from those obtained by other processes. This is because the optimal purification method differs depending on the type of impurity contained.

In this way, even for dihydroxynaphthalene of the same low purity, the optimal purification method changes depending on the types of impurities contained.

The low-purity crude dihydroxynaphthalene purified in the present invention is obtained by oxidation of diisopropylnaphthalene and subsequent acid decomposition as described above.
As long as dihydroxynaphthalene can be obtained by the method described above, the solvent, acid catalyst, etc. used can be varied widely. An example of a specific method for producing dihydroxynaphthalene from diisopropylnaphthalene will be described in detail below.

The oxidation reaction of diisopropylnaphthalene is carried out by adding diisopropylnaphthalene to an aqueous base solution, mechanically mixing to form an emulsified state, and blowing a gas containing molecular oxygen into the emulsified state.

In the present invention, the diisopropylnaphthalene to be subjected to the oxidation reaction is 2,6-diisopropylnaphthalene, 2,7-diisopropylnaphthalene,
-diisopropylnaphthalene, 1°4-diisopropylnaphthalene, etc., among which 2,6-diisopropylnaphthalene is preferred.

As the base, an alkali metal compound is preferably used. Specifically, this alkali metal compound includes:
Examples include sodium hydroxide, potassium hydroxide, sodium carbonate, and potassium carbonate. The concentration of these alkali metal compounds in the aqueous solution is preferably 20% by weight or less. The amount of the aqueous base solution used in the reaction mixture is usually preferably 5 to 80% by weight, particularly preferably 20 to 70% by weight. When the amount of the aqueous base solution used is less than 5% by weight of the reaction mixture, the dispersion state of the reaction solution consisting of oily unreacted diisopropylnaphthalene and its oxidation products and the aqueous base solution is not good, and the emulsification state is insufficient. This has an adverse effect on the oxidation reaction. On the other hand, if the amount of the aqueous base solution used is more than 80% by weight, the emulsification state of the reaction system will deteriorate, which is not preferable. Further, in the oxidation reaction, the pH of the aqueous base solution is usually maintained in the range of 7 to 14.

Note that diisopropylnaphthalene and its oxidation product and the aqueous base solution can usually be sufficiently emulsified by mechanical stirring, but if necessary, for example,
Stirring may also be carried out in the presence of conventionally known emulsifiers such as stearic acid.

As the base, alkaline earth metal hydroxides such as calcium hydroxide, magnesium hydroxide, and strontium hydroxide can also be used. Among these, calcium hydroxide is particularly preferred. These alkaline earth metal hydroxides may be used alone or in combination with the alkali metal compounds.

As the molecular enzyme, oxygen gas may be used alone, but air is usually sufficient. The required amount of molecular oxygen is usually in the range of 5 to 15 t'l/hour in terms of oxygen gas per 100 g of diisopropylnaphthalene charged for the oxidation reaction, but is not particularly limited.

The reaction temperature is usually 80 to 150°C, preferably 90 to 150°C.
The temperature is 130°C, and the reaction time varies depending on conditions such as reaction temperature, but is usually 6 to 40 hours. The reaction rate of diisopropylnaphthalene is preferably 80% or more in order to increase the amount of dihydroperoxide produced.

The reaction is usually carried out under normal pressure, but can also be carried out under increased pressure or reduced pressure, if necessary.

In the above oxidation reaction of diisopropylnaphthalene,
Preferably a reaction initiator is used. For example, α, α
・-azobis(cyclohexane-1-carbonitrile)
can be used as a reaction initiator. By using a reaction initiator, the induction period of the reaction can be shortened. The amount used is usually 0.00 parts per 100 parts by weight of the charged reaction mixture containing the raw material diimpropylnaphthalene.
The range is from 0.005 to 1 part by weight.

By the oxidation reaction of 2,6-diisopropylnaphthalene as diisopropylnaphthalene as explained above, in addition to 2,6-diisopropylnaphthalene dihydroperoxide (DHP>), 2-(
2-hydroxy-2-propyl)-6-(2-hydroperoxy-2-propyl)naphthalene (Hl-(P),
2. Carbinol-6- (2-hydroperoxy Monohydroperoxides such as -2-propyl)naphthalene (MHP>) are produced.

To determine the composition of the reaction product from the above oxidation reaction, separate the organic phase and aqueous phase after the reaction, extract the aqueous phase with ether, etc., and analyze the organic phase and ether extract using liquid chromatography. For example, unreacted diisopropylnaphthalene and oxidation reaction products DHP, HHP, DC
A. MHP, MCA, etc. can be quantified.

In the oxidation reaction of diisopropylnaphthalene, the reaction rate is preferably 80% or more, and the oxidation reaction mixture containing unreacted diisopropylnaphthalene, the above-mentioned dihydroperoxide, and by-products is subjected to the next acid decomposition reaction. usually,
Methyl isobutyl ketone (MIB) is added to the above oxidation reaction mixture.
A suitable amount of a suitable organic solvent such as K) is added, the organic phase containing the oxidation reaction mixture is separated from the aqueous phase, and this organic phase is used to carry out the subsequent acid decomposition. Hereinafter, this organic phase may be referred to as an acid-decomposed raw material.

Using the acid-decomposed raw material thus obtained, diisopropylnaphthalene dihydroberoxide contained therein is acid-decomposed in the presence of an acidic catalyst to produce dihydroxynaphthalene. In this case, since the acid-decomposed raw material contains the carbinols mentioned above as by-products of the oxidation reaction, hydrogen peroxide is allowed to coexist at the same time in the acid-decomposed reaction, and the by-products, carbinols, are Among them, HHP and D
It is preferable to oxidize CA to dihydroperoxides and simultaneously decompose the dihydroperoxides with an acid using an acidic catalyst, if necessary, since dihydroxynaphthalene can be obtained in high yield.

When the reaction rate of diisopropylnaphthalene is 80% or more, the yield of HHP and DCA in addition to DHP increases, but these HHP and DCA can be obtained by coexisting hydrogen peroxide at the same time during the acid decomposition reaction. When adopted, dihydroxynaphthalene can be obtained in high yield because it can be converted to DHP, and in this case, MH that does not contribute to the production of dihydroxynaphthalene is
This is preferred because the yield of P can be lowered. In particular, by controlling the reaction rate of diisopropylnaphthalene to 90% or more, more preferably 95% or more, the yield of dihydroxynaphthalene can be greatly increased.

As the above-mentioned hydrogen peroxide, in addition to hydrogen peroxide or an aqueous hydrogen peroxide solution, substances that generate hydrogen peroxide under reaction conditions, such as sodium peroxide and calcium peroxide, can be used. Preferably, an aqueous hydrogen solution is used. In particular, in the acid decomposition reaction, hydrogen peroxide can be used at a ratio of 0.9 to 2 mol, preferably 1.0 to 1.5 mol, per mol of the alcoholic hydroxyl group of the carbinol. dihydroxynaphthalene can be obtained in high yield. Further, when hydrogen peroxide is used under such conditions, it is possible to significantly suppress the production of by-products due to condensation of carbinols, which is preferable.

In addition, as the acidic catalyst in the acid decomposition reaction, Wt acid,
Inorganic acids such as hydrochloric acid and phosphoric acid, strong acidic ion exchange resins, solid acids such as silica gel and silica alumina, chloroacetic acid,
Organic acids such as methanesulfonic acid, benzenesulfonic acid and toluenesulfonic acid, and heteropolyacids such as phosphotungstic acid and phosphomolybdic acid are preferably used.

These acidic catalysts may be added to the reaction system as they are, or
Further, when these acidic catalysts have solubility, they can be dissolved in an appropriate inert solvent and added to the reaction system. The amount of acidic catalyst used depends on the type and reaction conditions, but is usually in the range of 0.05 to 10% by weight based on the total reaction mixture.

As mentioned above, after the shielding reaction of diisopropylnaphthalene, diisopropylnaphthalene dihydroberoxide and byproducts are transferred from the reaction mixture into an organic solvent such as methyl isobutyl ketone, and an acid decomposition reaction is performed using this organic solvent as a reaction solvent. This is advantageous in practical terms. However, the reaction solvent is not limited to methyl isobutyl ketone, and if necessary, other inert organic solvents may be used, such as ketones such as acetone and methyl ethyl ketone, alcohols such as methanol and ethanol, acetic acid, Lower aliphatic carboxylic acids such as propionate, hydrocarbons such as benzene, toluene, xylene, hexane, and heptane, and mixtures thereof may also be used.

This acid decomposition reaction is performed at 0-100'C, preferably at 20-100'C.
It is carried out in the range of 80'C.

A step of adding an aromatic hydrocarbon such as cumene to the acid decomposition reaction mixture obtained as described above and extracting and removing by-products coexisting with dihydroxynaphthalene, and bringing the solution containing crude dihydroxynaphthalene into contact with activated carbon. After that, by going through a step of isolating crude dihydroxynaphthalene from this solution, some impurities can be removed to obtain crude dihydroxynaphthalene as a raw material to be used in the purification method of the present invention described later.

The aromatic hydrocarbon such as cumene may be added to the acid decomposition reaction mixture at any stage of isolating dihydroxynaphthalene, which is a necessary reaction product, by any appropriate method. can.

First, after the acid decomposition reaction is completed, the acidic catalyst contained in the resulting reaction mixture is neutralized with an aqueous alkaline solution, and then,
The organic solvent is distilled off to form two liquid phases, an aqueous phase and an oil phase, and then the oil phase is separated from the two liquid phases, and the organic solvent is roughly distilled off from the oil phase to produce a concentrated product. This is a method of adding aromatic hydrocarbons to According to this method, some of the reaction by-products are
The aromatic hydrocarbons are extracted, while the crude dihydroxynaphthalene precipitates out as crystals from the aromatic hydrocarbons.

The second is to add water to the concentrate obtained as described above to form a slurry containing dihydroxynaphthalene as a solid content,
After adding an aromatic hydrocarbon and heating to dissolve the solid content, the oil phase is extracted and the aqueous phase is cooled to precipitate crude dihydroxynaphthalene. On the other hand, some of the reaction by-products are extracted and removed to aromatic hydrocarbons.

Thus, by concentrating the acid decomposition reaction mixture and mixing it with aromatic hydrocarbons in the presence or absence of water, the reaction byproducts are partially extracted and removed to the aromatic hydrocarbons. , dihydroxynaphthalene from which most of the by-product inpropylnaphthol has been removed can be obtained as crude crystals. As aromatic hydrocarbons for this purpose, for example, benzene, toluene, xylene, trimethylbenzenes, cumene, cymene, diimpropylbenzene, etc. are preferably used.

The crude dihydroxynaphthalene thus obtained is
The purification method according to the present invention is a crude crystal with a purity usually as low as 20 to 60%, and contains impurities such as isopropylnaphthol, acetylnaphthol, tar, and aromatic hydrocarbons previously used as a solvent. refined by.

In the present invention, when refining this low-purity crude dihydroxynaphthalene, the crystallization solvent is a mixed solvent of water and an aliphatic ketone having 3 to 4 carbon atoms (A>), or a mixed solvent of water and an aliphatic ketone having 3 to 4 carbon atoms, or
A mixed solvent (B) with 5 to 5 aliphatic alcohols is used.

Examples of the aliphatic ketone having 3 to 4 carbon atoms used in the mixed solvent (A>) include acetone and methyl ethyl ketone.

In the mixed solvent (A) consisting of water and an aliphatic ketone having 3 to 4 carbon atoms as described above, water is contained in the mixed solvent (A>5 to 95 parts by weight, preferably 50 to 95 parts by weight in 100 parts by weight). The aliphatic ketone is preferably present in an amount of 95 to 5 parts by weight, preferably 50 to 5 parts by weight in the mixed solvent (A>100 parts by weight).

If the amount of water in the mixed solvent (A) is less than 5 parts by weight, the purity of the dihydroxynaphthalene obtained is very good, but the recovery rate is unfavorably lowered. On the other hand, if the amount of water in the mixed solvent (A) exceeds 95 parts by weight, the recovery rate of dihydroxynaphthalene will be good, but the purity will be significantly deteriorated, which is not preferable.

Examples of the aliphatic alcohol having 1 to 5 carbon atoms used in the mixed solvent (B) include methanol, ethanol, isopropanol, n-propanol, butanol, and amyl alcohol.

In a mixed solvent (B) consisting of water and an aliphatic alcohol having 1 to 5 carbon atoms as described above, water is 10% of the mixed solvent (B).
5 to 95 parts by weight in 0 parts by weight, preferably 40 to 90 parts by weight 1
The aliphatic alcohol is preferably present in an amount of 95 to 5 parts by weight, preferably 60 to 100 parts by weight, per 100 parts by weight of the mixed solvent (B).

If the amount of water in the mixed solvent (B) is less than 5 parts by weight, the recovery rate of dihydroxynaphthalene decreases, which is not preferable. On the other hand, if the amount of water passing through the mixed solvent (B) exceeds 95 parts by weight, the purity of dihydroxynaphthalene will deteriorate, which is not preferable.

The crystallization operation of dihydroxynaphthalene using the above-mentioned crystallization solvent is carried out according to a conventional method, but usually 5 to 40 parts by weight of low-purity dihydroxynaphthalene crude crystals are added to 100 parts by weight of the above-mentioned solvent. and this solvent at 60
This is carried out by heating to a temperature of ~100'C to dissolve dihydroxynaphthalene, and then cooling the resulting solution to about room temperature to precipitate dihydroxynaphthalene. Such a crystallization operation can be repeated many times if necessary.

Effects of the Invention According to the method for purifying dihydroxynaphthalene according to the present invention, 1q of low-purity crude dihydroxynaphthalene produced by oxidation of diisopropylnaphthalene and subsequent acid decomposition is crystallized using a specific solvent system. , high purity dihydroxynaphthalene can be recovered with a high recovery rate.

EXAMPLES The present invention will be explained below with reference to Examples, but the present invention is not limited to these Examples.

Example 1 A 500rni autoclave (SUS
316L) were charged with 75 g of 2.6-diisopropylnaphthalene, 75 g of a 4.5% aqueous sodium hydroxide solution, and 0.1 g of α,α·-bis(cyclohexane-1-carbonitrile), and the reaction temperature was 100°C and the pressure was to 5'
While vigorously stirring the contents with j/crAG, air was pumped out for 20 minutes. The reaction was carried out for 9 hours by blowing at a rate of ft/hr. The reaction rate of 2,6-diisopropylnaphthalene is 9
It was 9.5%.

Methyl isobutyl ketone 15 is added to the obtained oxidation reaction product.
After adding 07, the oil phase (methyl isobutyl ketone phase) and water phase were separated. The composition of the oxidation products contained in this oil phase was determined by liquid chromatography analysis.
6.5% by weight H1-IP
13.4 type mouth %DCA
6J heavy! %MHP
2.7 Handling% MCA
1.6 weight% other (numerator is 212).

) 7.6% by weight.

Next, 28.3 g of an acetone solution containing 1.7% by weight sulfuric acid was placed in a 1 g capacity glass reaction vessel equipped with a rotary stirrer, a reflux condenser, an acid decomposition raw material supply pipe, and an acidic catalyst solution supply pipe.
The reaction vessel was placed on a water bath at a temperature of 65°C. When the acetone starts to reflux due to heating, a methyl isobutyl ketone solution (oil phase) of the oxidation product is added from the acid decomposition raw material supply pipe to 2369.60% hydrogen peroxide solution 17.
Feed of a mixture of 29 and 73 g of acetone was started.

Simultaneously with the start of supply of this acid decomposition raw material, supply of acetone solution 433 containing 1.7% sulfuric acid was also started from the acidic catalyst solution supply pipe, and the supply was finished one hour later. The feed amounts of the decomposition raw material and the acetone solution of sulfuric acid were determined using a small metering pump. After this, the reaction was further carried out for 3 hours.

The acid decomposition reaction described above was carried out twice, and the resulting reaction mixtures were combined. As a result of liquid chromatography analysis, the composition of the acid decomposition reaction product was as follows: 2.6-dihydroxynaphthalene 9.6% by weight 6-ituprobyl-2-naphthol 2.0% by weight 2.6-dihydroxynaphthalene 0.
1ii% Others (assuming the molecular weight is the same as 6-piprovir-2-naphthol) 4.0% by weight.

Next, 150 g of the above acid decomposition reaction mixture was taken, and in order to neutralize the sulfuric acid contained in it, the pH of the solution was
A 2% aqueous sodium carbonate solution was gradually added until H was about 4. Thereafter, the following concentration operation was performed in order to remove acetone and methyl isobutyl ketone contained in the acid decomposition reaction mixture. That is, first, acetone was distilled off under normal pressure using a rotary evaporator to form two liquid phases consisting of an aqueous phase and an oil phase, and then the oil phase and the aqueous phase were separated. The separated oil phase was again distilled off to remove methyl isobutyl ketone using a rotary evaporator to obtain a condensate. However, the distillation of methyl isobutyl ketone was stopped just before crystal precipitation started.

This concentrate contains 2,6-hydroxynaphthalene 21.
6% by weight and 6-isopropyl-2-naphthol4.
It contained 4% by weight.

Next, 500m equipped with stirrer, thermometer, reflux condenser and concentrate dripping port! ! A volume separable flask was charged with 290 g of cumene and placed on a water bath at a temperature of 70'C. The concentrate 693 was gradually dropped into this flask to precipitate crystals. After the dropwise addition was completed, the temperature of the hot water bath was gradually lowered to further precipitate crystals, and finally the mixture was cooled to room temperature to sufficiently precipitate crystals.

Thereafter, the crystals were filtered and dried to obtain 237 crude crystals of 2,6-dihydroxynaphthalene (2.6-dihydroxynaphthalene crystallization recovery rate: 80%).

The crude crystals thus obtained contained 50.7% by weight of 2,6-hydroxynaphthalene and 6-isoprobyl-
2-Naphthol 0. % by weight, and most of the rest was cumene.

1 part of a water-acetone mixed solvent containing 10 parts by weight of the low-purity 2,6-hydroxynaphthalene crude crystals thus obtained in a ratio of 90 parts by weight of water and 1 part by weight of acetone.
The mixture was added to 32 parts by weight, and the temperature was raised to 80'C with heating and stirring to dissolve the 2,6-dihydroxynaphthalene crude crystals.

This solution was then cooled to 5°C to precipitate crystals,
The obtained crystals were filtered out from the filtrate.

The purity and recovery rate of the obtained 2,6-dihydroxynaphthalene were determined by weighing the thus obtained crystals and measuring the purity by gas chromatography.

The results are shown in Table 1.

Example 2 In Example 1, low-purity 2
, 6-dihydroxynaphthalene was purified.

The results are shown in Table 1.

Example 3 In the same manner as in Example 1 except that a water-acetone mixed solvent containing 20 parts by weight of water and 80 parts by weight of acetone was used as the crystallization solvent,
, 6-dihydroxynaphthalene was purified.

The results are shown in Table 1.

Example 4 In the same manner as in Example 1, except that a water-acetone mixed solvent containing 10 parts of water and 90 parts by weight of acetone was used as the crystallization solvent, low-purity 2
, 6-dihydroxynaphthalene was purified.

The results are shown in Table 1.

Comparative Example 1 In Example 1, except that water was used as the crystallization solvent,
In the same manner as in Example 1, low purity 2,6-hydroxynaphthalene was purified.

The results are shown in Table 1.

Comparative Example 2 Low-purity 2,6-hydroxynaphthalene was purified in the same manner as in Example 1, except that acetone was used as the crystallization solvent.

The results are shown in Table 1.

In Example 1, low-purity 2,6-hydroxynaphthalene was purified.

The purity of the obtained 2,6-hydroxynaphthalene was 92
%, and the recovery rate was 95%.

Claims (5)

[Claims] (1) Low-purity dihydroxynaphthalene obtained by oxidation of diisopropylnaphthalene with molecular oxygen in the presence of a base and subsequent acid decomposition in a mixed solvent (A) of water and an aliphatic ketone having 3 to 4 carbon atoms. , or a mixed solvent (B) of water and an aliphatic alcohol having 1 to 5 carbon atoms is used as a solvent to crystallize dihydroxynaphthalene. (2) The method according to claim 1, wherein the aliphatic ketone having 3 to 4 carbon atoms is acetone. (3) The method according to claim 1, wherein water is present in an amount of 5 to 95 parts by weight in 100 parts by weight of the mixed solvent (A). (4) C1-5 aliphatic alcohol is methanol,
The method according to claim 1, wherein ethanol or isopropanol is used. (5) The method according to claim 1, wherein water is present in an amount of 5 to 95 parts by weight in 100 parts by weight of the mixed solvent (B).