JPH0667865B2 - Purification method of dihydroxynaphthalene - Google Patents

Description

TECHNICAL FIELD OF THE INVENTION The present invention relates to a method for purifying dihydroxynaphthalene,
More specifically, it relates to a method for purifying dihydroxynaphthalene using a specific solvent system.

Technical background of the invention and its problems Dihydroxynaphthalene, for example, 2,6-dihydroxynaphthalene, is a compound useful as a raw material for synthetic resins, synthetic fibers, pharmaceuticals, agricultural chemicals, dyes and the like. It is known that this dihydroxynaphthalene can be produced by oxidizing diisopropylnaphthalene with molecular oxygen in the presence of a base to give diisopropylnaphthalene dihydroperoxide, and subjecting this to acid decomposition with an acidic catalyst such as sulfuric acid.

By the way, for example, when 2,6-diisopropylnaphthalene is oxidized by molecular oxygen in the presence of a base, in addition to the target compound 2,6-diisopropylnaphthalene dihydroperoxide (hereinafter sometimes abbreviated as DHP),
As a by-product, 2- (2-hydroxy-2-propyl) -6- (2-hydroperoxy-2-propyl) naphthalene (hereinafter sometimes abbreviated as HHP) and 2,6-bis (2-hydroxy) -2-Propylnaphthalene (hereinafter DCA
Abbreviated as "), 2-isopropyl-6- (2
-Hydroxy-2-propyl) naphthalene (hereinafter sometimes abbreviated as MCA) or other carbinols or 2
-Isopropyl-6- (2-hydroperoxy-2-propyl) naphthalene (hereinafter sometimes abbreviated as MHP)
A large amount of monohydroperoxides such as is produced. Moreover, when the oxidation reaction product of dihydroxynaphthalene containing DHP and by-products as described above is acid-decomposed in the presence of an acid catalyst such as sulfuric acid, various acid decomposition reactions other than the target compound dihydroxynaphthalene are carried out. Products such as isopropyl naphthol are produced.

In this way, dihydroxynaphthalene is oxidized by molecular oxygen in the presence of a base to form DHP, which is acid-decomposed with an acidic catalyst such as sulfuric acid. In addition, various reaction byproducts are present in large amounts.

For this reason, studies have been conducted to obtain dihydroxynaphthalene, which is a target compound with a purity as high as possible from dihydroxynaphthalene.
Dihydroxynaphthalene cannot be obtained in high purity. Therefore, it is necessary to provide a method for obtaining high-purity dihydroxynaphthalene from low-purity dihydroxynaphthalene containing impurities.

The inventors of the present invention have conducted diligent research to obtain high-purity hydroxynaphthalene with high recovery from low-purity hydroxynaphthalene obtained by oxidation of diisopropylnaphthalene and subsequent acid decomposition. The present invention has been completed by finding that it should be analyzed.

OBJECT OF THE INVENTION The present invention is intended to solve the problems associated with the prior art as described above, and is obtained by oxidation of diisopropylnaphthalene with molecular oxygen in the presence of a base and subsequent acid decomposition. It is an object of the present invention to provide a purification method for obtaining high-purity dihydroxynaphthalene with a high recovery rate from the low-purity dihydroxynaphthalene obtained.

SUMMARY OF THE INVENTION A method for purifying dihydroxynaphthalene according to the present invention is a method for purifying low-purity dihydroxynaphthalene obtained by oxidation of diisopropylnaphthalene with molecular oxygen in the presence of a base and subsequent acid decomposition. Mixed solvent with aliphatic ketone of (A), or water and carbon number 1
It is characterized in that a mixed solvent (B) with an aliphatic alcohol of ~ 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 the oxidation of diisopropylnaphthalene and the subsequent acid decomposition is crystallized using a specific solvent system, so that high purity is obtained. Dihydroxynaphthalene can be recovered at a high recovery rate.

DETAILED DESCRIPTION OF THE INVENTION The method for purifying dihydroxynaphthalene according to the present invention will be specifically described below.

What is purified by the process according to the present invention is low-purity dihydroxynaphthalene, which is obtained by oxidizing diisopropylnaphthalene with molecular oxygen in the presence of a base to give diisopropylnaphthalene dihydroperoxide. It is obtained by acidolysis of dihydroperoxide in the presence of an acid catalyst.

As the low-purity crude dihydroxynaphthalene purified by the present invention, the one obtained by the above method is used. This is because the low-purity dihydroxynaphthalene obtained by the oxidation of diisopropylnaphthalene and the subsequent acid decomposition and the low-purity dihydroxynaphthalene obtained by another process are different in the types of impurities contained therein. This is because the optimum purification method differs depending on the type of impurities contained.
Thus, even with the same low-purity dihydroxynaphthalene, the optimum purification method changes depending on the type of impurities contained.

The low-purity crude dihydroxynaphthalene purified by the present invention is obtained by the oxidation of diisopropylnaphthalene and the subsequent acid decomposition as described above.
If dihydroxynaphthalene is obtained by the above method, for example, the solvent, acid catalyst, etc. used can be widely varied. 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 it into an emulsified state, and blowing a gas containing molecular oxygen into it.

In the present invention, examples of diisopropylnaphthalene used in the oxidation reaction include 2,6-diisopropylnaphthalene, 2,7-diisopropylnaphthalene, and 1,4-diisopropylnaphthalene. Among them, 2,6-diisopropylnaphthalene is preferable.

An alkali metal compound is preferably used as the base. As the alkaline metal compound, specifically,
Sodium hydroxide, potassium hydroxide, sodium carbonate,
Examples thereof include 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 preferably accounts for 5 to 80% by weight of the reaction mixture, and more 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 oily unreacted diisopropylnaphthalene and its oxidation product and the reaction solution consisting of the aqueous base solution are not well dispersed and the emulsified state is insufficient. And adversely affect the oxidation reaction. On the other hand, when the amount of the aqueous base solution used is more than 80% by weight, the emulsified state of the reaction system is deteriorated, which is not preferable. In addition, in the oxidation reaction, the pH of the aqueous base solution is usually maintained in the range of 7 to 14.

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

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

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

The reaction temperature is usually 80 to 150 ° C, preferably 90 to 130 ° C, and the reaction time is usually 6 to 40 hours, though it varies depending on conditions such as reaction temperature. The reaction rate of diisopropylnaphthalene is The amount is preferably 80% or more in order to increase the production amount of peroxide. The reaction is
Usually, it is carried out under normal pressure, but if necessary, it may be carried out under pressure or under reduced pressure.

In the above oxidation reaction of diisopropylnaphthalene,
A reaction initiator is preferably 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 0.0 per 100 parts by weight of the charged reaction mixture containing the raw material diisopropylnaphthalene.
The range is from 05 to 1 part by weight.

In addition to 2,6-diisopropylnaphthalene dihydroperoxide (DHP), as a by-product, 2- (2-hydroxy-2-hydroxy-2-hex-2-ene) is obtained by the oxidation reaction of 2,6-diisopropylnaphthalene as diisopropylnaphthalene as described above. Propyl) -6- (2-hydroperoxy-2-propyl) naphthalene (HHP), 2,6-bis (2
-Hydroxy-2-propyl) naphthalene (DCA), 2
-Carbinols such as isopropyl-6- (2-hydroxy-2-propyl) naphthalene (MCA), or 2-isopropyl-6- (2-hydroperoxy-2)
A monohydroperoxide such as -propyl) naphthalene (MHP) is formed.

In order to obtain the composition of the reaction product by the above-mentioned oxidation reaction, after the reaction, the organic phase and the aqueous phase are separated, the aqueous phase is extracted with ether, and the organic phase and the ether extract are analyzed by liquid chromatography. For example, unreacted diisopropylnaphthalene and oxidation reaction products DHP, HHP, DCA, 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 dihydroperoxide and the by-product is subjected to the next acid decomposition reaction. Usually, an appropriate amount of an appropriate organic solvent such as methyl isobutyl ketone (MIBK) is added to the above-mentioned oxidation reaction mixture, the organic phase containing the oxidation reaction mixture is separated from the aqueous phase, and this organic phase is used to Disassemble. Hereinafter, this organic phase may be referred to as an acid decomposition raw material.

Using the acid-decomposing raw material thus obtained, diisopropylnaphthalene dihydroperoxide contained therein is acid-decomposed in the presence of an acidic catalyst to produce dihydroxynaphthalene. In this case, since the above-mentioned carbinols are contained in the acid decomposition raw material as a by-product of the oxidation reaction, hydrogen peroxide is allowed to coexist in the acid-decomposition reaction at the same time, so that the by-product carbinols are present. Of these, if necessary, a method of oxidizing HHP and DCA to dihydroperoxides, and simultaneously subjecting this dihydroperoxide to acid decomposition with an acidic catalyst, dihydroxynaphthalene can be obtained in high yield. Therefore, it is preferable.

When the reaction rate of diisopropylnaphthalene is 80% or more, the yields of HHP and DCA as well as DHP are increased,
The HHP and DCA can be converted into DHP when a method of coexisting hydrogen peroxide at the same time in the acid decomposition reaction is adopted, and thus dihydroxynaphthalene can be obtained in a high yield, and In this case, the yield of MHP that does not contribute to the production of dihydroxynaphthalene can be lowered, which is preferable. Particularly, by setting the reaction rate of diisopropylnaphthalene to 90% or more, more preferably 95% or more, the yield of dihydroxynaphthalene can be further increased.

As the hydrogen peroxide, in addition to hydrogen peroxide or a hydrogen peroxide solution, substances that generate hydrogen peroxide under reaction conditions, such as sodium peroxide and calcium peroxide, can be used. It is preferable to use an aqueous hydrogen solution. In particular, in the acid decomposition reaction, hydrogen peroxide is used in a proportion of 0.9 to 2 mol, preferably 1.0 to 1.5 mol, per mol of the alcoholic hydroxyl group of the carbinols, so that the desired yield of dihydroxynaphthalene can be increased. You can get at a rate. Further, it is preferable to use hydrogen peroxide under such conditions, because at the same time, the production of by-products due to the condensation of carbinols can be significantly suppressed.

In addition, as the acidic catalyst in the acid decomposition reaction, inorganic acids such as sulfuric acid, hydrochloric acid and phosphoric acid, strongly acidic ion exchange resins, solid acids such as silica gel and silica alumina, chloroacetic acid, methanesulfonic acid, benzenesulfonic acid and toluenesulfone. Organic acids such as acids and heteropoly acids such as phosphotungstic acid and phosphomolybdic acid are preferably used. These acidic catalysts may be added to the reaction system as they are, or when these acidic catalysts are soluble, they may be dissolved in an appropriate inert solvent and added to the reaction system. The amount of the acidic catalyst used depends on the kind and reaction conditions, but is usually in the range of 0.05 to 10% by weight based on the total reaction mixture.

As described above, after the oxidation reaction of diisopropyl naphthalene, diisopropyl naphthalene dihydroperoxide and by-products are transferred from the reaction mixture into an organic solvent such as methyl isobutyl ketone, and the acid decomposition reaction can be performed using this organic solvent as a reaction solvent. It is practically advantageous. However, the reaction solvent is not limited to methyl isobutyl ketone at all, and if necessary, other inert organic solvents such as acetone, ketones such as methyl ethyl ketone, alcohols such as methanol and ethanol, acetic acid and propione. Lower aliphatic carboxylic acids such as acids,
Hydrocarbons such as benzene, toluene, xylene, hexane, heptane, etc. can also be used, or mixtures thereof.

This acid decomposition reaction is carried out in the range of 0 to 100 ° C, preferably 20 to 80 ° C.

To the acid decomposition reaction mixture obtained as described above, a step of adding an aromatic hydrocarbon such as cumene to extract and remove by-products coexisting with dihydroxynaphthalene, and contacting a solution containing crude dihydroxynaphthalene with activated carbon After that, a step of isolating the crude dihydroxynaphthalene from this solution may be performed to remove some impurities to obtain crude dihydroxynaphthalene as a raw material to be used in the purification method of the present invention described later.

The time point at which the aromatic hydrocarbon such as cumene is added to the acid decomposition reaction mixture may be determined by an appropriate method at any stage of isolating the reaction product dihydroxynaphthalene, and for example, the following method can be used. .

First, after completion of the acid decomposition reaction, the acidic catalyst contained in the obtained reaction mixture is neutralized with an alkaline aqueous solution, and then,
The organic solvent is distilled off to obtain two liquid phases, an aqueous phase and an oil phase. Then, the oil phase is separated from the two liquid phases, and the organic solvent is further distilled off from the oil phase to obtain a concentrated aromatic compound. It is a method of adding hydrocarbons. According to this method, a part of the reaction by-product is
Extracted into aromatic hydrocarbons, while crude dihydroxynaphthalene precipitates as crystals from the aromatic hydrocarbons.

Secondly, water is added to the concentrate obtained as described above to form a slurry containing dihydroxynaphthalene as a solid content,
Aromatic hydrocarbons are added to this, the solid content is dissolved by heating, the oil phase is extracted, and the aqueous phase is cooled to precipitate crude dihydroxynaphthalene. On the other hand, a part of the reaction by-product is extracted and removed to aromatic hydrocarbon.

Thus, by concentrating the acid decomposition reaction mixture and mixing it with an aromatic hydrocarbon in the presence or absence of water, the reaction by-products are partially extracted and removed to the aromatic hydrocarbon. It is possible to obtain dihydroxynaphthalene in which most of the by-product isopropylnaphthol is removed as crude crystals. As the aromatic hydrocarbon for this purpose, for example, benzene, toluene, xylene, trimethylbenzenes, cumene, cymen, diisopropylbenzene and the like are preferably used.

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

In the present invention, when purifying this low-purity crude dihydroxynaphthalene, a mixed solvent (A) of water and an aliphatic ketone having 3 to 4 carbon atoms or water and 1 carbon atom is used as a crystallization solvent.
A mixed solvent (B) with an aliphatic alcohol of ~ 5 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) composed of water and the above-mentioned aliphatic ketone having 3 to 4 carbon atoms, water is 5 to 95 parts by weight, preferably 50 to 95 parts by weight, in 100 parts by weight of the mixed solvent (A). It is desirable that the aliphatic ketone is present in an amount of 95 to 5 parts by weight, preferably 50 to 5 parts by weight, in 100 parts by weight of the mixed solvent (A).

When 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 remarkably reduced, which is not preferable. On the other hand, if the amount of water in the mixed solvent (A) exceeds 95 parts by weight, the recovery of dihydroxynaphthalene will be good, but the purity will be markedly 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, amyl alcohol and the like.

In the mixed solvent (B) consisting of water and the above-mentioned aliphatic alcohol having 1 to 5 carbon atoms, water is the mixed solvent (B) 100
It is desirable that it is present in an amount of 5 to 95 parts by weight, preferably 40 to 90 parts by weight, and the aliphatic alcohol is 95 to 5 parts by weight, preferably 60 to 1 part by weight, in 100 parts by weight of the mixed solvent (B).
It is preferably present in an amount of 0 parts by weight.

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

The crystallization operation of dihydroxynaphthalene using the crystallization solvent as described above is carried out according to a conventional method. Usually, about 5 to 40 parts by weight of low-purity crude dihydroxynaphthalene crystals are mixed with 100 parts by weight of the solvent. , This solvent 60 ~ 100
It is carried out by heating to a temperature of ° C to dissolve dihydroxynaphthalene, and then cooling the obtained solution to about room temperature to precipitate dihydroxynaphthalene.
Such crystallization operation can be repeated as many times as necessary.

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

The present invention will be described below with reference to examples, but the present invention is not limited to these examples.

Example 1 A 500 ml capacity autoclave (made of SUS 316L) equipped with a rotary stirrer, a gas blowing tube, a thermometer and a reflux condenser.
To the reaction mixture, 75 g of 2,6-diisopropylnaphthalene, 75 g of 4.5% sodium hydroxide aqueous solution and 0.1 g of α, α′-bis (cyclohexane-1-carbonitrile) were charged, and the reaction temperature was adjusted.
Air was blown in at a rate of 20 / hour while stirring the contents for strengthening at 100 ° C. and a pressure of 5 kg / cm ² G to carry out a reaction for 9 hours. The reaction rate of 2,6-diisopropylnaphthalene is 9
It was 9.5%.

150 g of methyl isobutyl ketone was added to the resulting oxidation reaction product.
After adding, the oil phase (methyl isobutyl ketone phase) and the aqueous phase were separated. The composition of the oxidation products contained in this oil phase is
As a result of liquid chromatography analysis, DHP 6.5% by weight HHP 13.4% by weight DCA 6.3% by weight MHP 2.7% by weight MCA 1.6% by weight Others (molecular weight is 212) 7.6% by weight.

Next, 28.3 g of an acetone solution containing 1.7% by weight sulfuric acid was charged into a 1-volume 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, and the temperature was 65 ° C. The reaction vessel was placed on the bath. When acetone began to reflux by heating, 236 g of a methyl isobutyl ketone solution (oil phase) of the above-mentioned oxidation product, 17.2 g of 60% hydrogen peroxide solution and acetone 7 from the acid decomposition raw material supply pipe.
Feeding of 3 g of mixture was started. At the same time when the supply of the acid decomposition raw material was started, 43 g of an acetone solution containing 1.7% sulfuric acid was also started to be supplied from the acidic catalyst solution supply pipe, and the supply was finished after 1 hour. The supply amounts of the decomposition raw material and the acetone solution of sulfuric acid were determined by a small metering pump. After that, the reaction was further performed for 3 hours.

The above-mentioned acid decomposition reaction was performed twice, and the obtained reaction mixtures were combined. As a result of liquid chromatography analysis, the composition of the acid decomposition reaction product was found to be 2,6-dihydroxynaphthalene 9.6% by weight 6-isopropyl-2-naphthol 2.0% by weight 2,6-diisopropylnaphthalene 0.1% by weight Others (molecular weight 6- Same as isopropyl-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 therein, a 2% sodium carbonate aqueous solution was gradually added until the pH of the solution became about 4. . Then, 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 with a rotary evaporator to obtain two liquid phases consisting of an aqueous phase and an oil phase, and then the oil phase and the aqueous phase were separated. Separated oil phase is again on rotary evaporator
It was kept under a reduced pressure of 20 to 30 mmHg to distill off methyl isobutyl ketone to obtain a concentrate. However, the distillation of methyl isobutyl ketone was stopped just before the start of crystal precipitation.

The concentrate is 21.6% by weight of 2,6-dihydroxynaphthalene and 4.4% by weight of 6-isopropyl-2-naphthol.
Was included.

Next, in a 500 ml separable flask equipped with a stirrer, a thermometer, a reflux condenser and a concentrate dropping port, cumene 290 was added.
After being charged with g, it was placed on a hot water bath at a temperature of 70 ° C. Into this flask, 60 g of the above concentrate was gradually added dropwise to precipitate crystals. After completion of dropping, the temperature of the hot water bath was gradually lowered to further precipitate crystals, and finally cooled to room temperature to sufficiently precipitate crystals.

After that, the crystals were separated by filtration and dried to obtain 23 g of 2,6-dihydroxynaphthalene crude crystals (2,6-dihydroxynaphthalene crystallization recovery rate 80%). The crude crystals thus obtained were 50.7% by weight of 2,6-dihydroxynaphthalene and 6
-Containing 0.7% by weight of isopropyl-2-naphthol, the balance was mostly cumene.

10 parts by weight of low-purity crude 2,6-dihydroxynaphthalene crystals thus obtained were mixed with 90 parts by weight of water and acetone.
It is added to 132 parts by weight of a water-acetone mixed solvent containing 10 parts by weight, and heated to 80 ° C. with heating and stirring for 2,6
-Crude crystals of dihydroxynaphthalene were dissolved.

Thereafter, this solution was cooled to 5 ° C. to precipitate crystals, and the obtained crystals were filtered out from the filtrate.

The crystals thus obtained were weighed and the purity was measured by gas chromatography to determine the purity and the recovery rate of the obtained 2,6-dihydroxynaphthalene.

The results are shown in Table 1.

Example 2 In the same manner as in Example 1 except that a water-acetone mixed solvent containing 50 parts by weight of water and 50 parts by weight of acetone was used as the crystallization solvent, 6-
Purification of dihydroxynaphthalene was performed.

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-
Purification of dihydroxynaphthalene was performed.

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 by weight of water and 90 parts by weight of acetone was used as the crystallization solvent, a low-purity 2, 6-
Purification of dihydroxynaphthalene was performed.

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-dihydroxynaphthalene was purified.

The results are shown in Table 1.

Comparative Example 2 Low-purity 2,6-dihydroxynaphthalene 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.

Example 5 In Example 1, the procedure of Example 1 was repeated except that a water-methanol mixed solvent containing 80 parts by weight of water and 20 parts by weight of methanol was used as the crystallization solvent.
Purification of 6-dihydroxynaphthalene was performed.

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

Claims (5)

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