FR2588859A1 - PROCESS FOR THE PRODUCTION OF 2,6-DI-HYDROXY PROPYL-2-NAPHTHALENE - Google Patents

Abstract

HEREBY DESCRIBES A PROCESS FOR THE PRODUCTION OF HIGHLY PURE DI- (HYDROXY-2-PROPYL-2) -2,6-NAPHTHALENE, WHICH INCLUDES: 1.OXYDATION OF 2,6-DIISOPROPYL-NAPHTHALENE BY MOLECULAR OXYGEN IN AQUEOUS SOLUTION ALKALI 2.A SEPARATION AND RECOVERY OF AQUEOUS SOLUTION OF ALKALI FROM THE REACTIONAL MIXTURE THUS OBTAINED 3.WASHING THE SOLID MATERIAL WITH WATER, WHICH ALLOWS TO REMOVE THE NAPHTHALENE DERIVATIVES HAVING A (OR) CARBOXYL GROUP (S), WHICH HAVE BEEN OBTAINED AS BY-PRODUCTS IN THE OXIDATION STEP, AND.APRES DISSOLUTION, UNDER HEATING, OF THE SOLID MATERIAL SO WASHED IN BENZENE OR AN ALKYLBENZENE WHICH HAS A ( OR S) (S) SIDE CHAINS (S) HAVING 1 TO 3 ATOMS OF CARBON, THE COOLING OF THE SOLUTION THUS PREPARED, WHICH ALLOWS TO SEPARATE THE DI (HYDROXY-2 PROPYL-2) -2,6 NAPHTHALENE.

Description

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PROCESS FOR THE PRODUCTION OF

  DI (HYDROXY-2 PROPYL-2) -2.6 NAPHTHALENE

  The present invention relates to a process for the production of highly pure di (2-hydroxy-2-propyl-2,6-naphthalene (hereinafter referred to as

  "2,6-DHPN"), which is a raw material for naphtha

  2,6-dienediol, used as monomer of aromatic polyesters, in particular aromatic polyesters

  having an ability to form liquid crystals.

  In recent years, various polymers have been developed as industrial plastics, and among these polymers, aromatic polyesters, in particular aromatic polyesters having a

  liquid crystal formation, attracted attention.

  As representative of aromatic polyesters exhibiting liquid crystalline ability, a three-component polymer, obtained from two components selected from terephthalic acid, hydroquinone and parahydroxybenzoic acid, has been described. a monomer consisting of a naphthalene derivative as

third component.

  Of the naphthalene derivative monomers, 2,6-naphthalenediol is an attractive monomer because the liquid crystalline polymer derived therefrom is excellent in physical properties, and terephthalic acid, which is available to good market,

  can be used as his comonomer.

  Although 2,6-naphthalenediol can be obtained by the process previously developed by the present inventors (Japanese Patent Application No. 60-123819 <1985 "), in which 2,6-DHPN is oxidized by the peroxide of hydrogen in acetonitrile or dioxane and in the presence of a mineral acid, the 2,6-DHPN used as starting material in the process must be highly pure and, at the same time, must be easily produced and

  effectively on an industrial scale.

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  Heretofore, as a method for converting an isopropyl substituted aromatic compound represented by the following formula (I) to an aromatic compound substituted by the 2-hydroxypropyl-2 group represented by the following formula (II), various methods have been described as follows:

CH3 CH3

Ar) I) Ar O (II) CH n CH3 / nt

3 3

  o Ar represents an aromatic ring and n represents the

integers i or 2.

  For example, (1) Japanese Patent Publication No. 39-19355 (1964) discloses a process for obtaining (2-hydroxy-2-propyl) benzene of 95% purity by oxidation of cumene in a 50% aqueous solution of sodium hydroxide, separation of an organic layer by liquid-liquid phase separation from the mixture

  reaction and distillation of the organic layer.

  However, in the case where this method is applied to the oxidation of 2,6-diisopropyl naphthalene, the 2,6-DHPN formed separates from the reaction mixture and, because its density is close to 1, the separation liquid-liquid is totally impossible. In addition, since 2,6-DHP boils at a high temperature, partial dehydration occurs during its distillation, thereby reducing

yield of 2,6-DHPN.

  On the other hand, (2) although Japanese Patent Publication No. 39-21242 (1964) discloses the oxidation of β-isopropylnaphthalene as an example, as far as the separation of the reaction products is concerned, there is only one

  general description of the implementation of the separation

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  liquid-liquid and there is no disclosure regarding the

  separation of J3- (2-hydroxy-2-propyl) naphthalene.

  In addition, in the method described in Japanese Patent Application Laid-Open (KOKAI) No. 58-162539 (1983), relating to the oxidation of cumene, to separate the oxidation products, the mixture The reaction mixture is extracted with ether after neutralization of the reaction mixture. However, it is impossible to separate the product from the unreacted substance, because

  that the dissolving power of the ether is too great.

  In addition, German Patent No. 1,233,839 discloses a method in which p-diisopropylbenzene is oxidized in bromobenzene and in the presence of a substantially anhydrous caustic alkali and p-di (2-hydroxy-2-propyl) benzene is separated by cooling the reaction product thus obtained. To carry out the method, it is necessary to carry out the oxidation in a specific solvent. Moreover, in the case where the method is applied to the oxidation of 2,6-diisopropyl naphthalene, since 2,6-DHPN has a high melting point and is poorly soluble in solvents. , it is very difficult to carry out the separation and purification of 2,6-DHPN by the method described, in other words, the described method is not

  practical for the production of 2,6-DHPN.

  In this connection, in the reaction in which an aromatic compound substituted with an isopropyl residue is oxidized in an aqueous alkali solution to obtain an aromatic compound substituted by the 2-hydroxypropyl-2 residue, it is inevitable that it is accompanied by of the unreacted starting material and by-products in addition to the intended product, and therefore the separation and

  the purification of the product are essential.

  As described above, it has been difficult to obtain 2,6DHPN advantageously at $ S5 on an industrial scale, by the application of the method.

  oxidation of isopropylbenzene and diisopropyl-

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  benzene, respectively, 2-hydroxy-2-propyl benzene and 2-di (2-hydroxypropyl) benzene, on the oxidation of

2,6-diisopropyl naphthalene.

  As a result of the present inventors' studies of the method for efficiently producing highly pure 2,6-DHPN, it has been discovered by the present inventors that highly pure 2,6-DHFPN can be efficiently obtained by the method comprising the steps of: (1) oxidizing 2,6-diisopropyl naphthalene in an aqueous solution of an alkali; (2) removing naphthalene derivatives having a carboxyl group (or groups) from the resulting reaction mixture; (3) recrystallizing the mixture thus obtained in benzene or an alkylbenzene which has a (or) side chain (s) having from 1 to 3 carbon atoms, which makes it possible to obtain 2,6-DHPN and, further, (4) recycling to the oxidation step the oxidation intermediates, such as 1 '(2-hydroxy-2-propyl) -2-isopropyl-naphthalene, etc. and unreacted 2,6-diisopropyl naphthalene in the mother liquor of recrystallization, and based on these findings, the present inventors

  have realized the present invention.

  In accordance with one aspect of the present invention, there is provided a process for producing 2,6-di (2-hydroxy-2-propyl) naphthalene comprising - oxidation of 2,6-diisopropyl naphthalene by molecular oxygen in an aqueous solution of an alkali, separating and recovering said aqueous alkali solution from the reaction mixture thus obtained, -washing the solid material obtained by separating the aqueous alkali solution, with water, so as to to eliminate naphthalene derivatives having a (or

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  carboxyl group (s), which are obtained as sub-

  products in the oxidation step, - the dissolution, under heating, of the solid material thus washed in benzene or an alkylbenzene, which has a (or) side chain (s) having from 1 to 3 atoms of carbon, and - the cooling of the solution thus formed, which makes it possible to

  separate 2-di (2-hydroxy-2-propyl) -2,6 naphthalene.

  The present invention relates to a method for efficiently producing highly pure 2,6-DHPN, which process comprises the steps of: (1) oxidizing 2,6-diisopropyl naphthalene in an aqueous solution of an alkali by means of molecular oxygen, (2) separating and recovering the aqueous alkali solution from the reaction mixture thus obtained, (3) washing the solid material obtained by separating the aqueous alkali solution with water, which allows eliminate naphthalene derivatives having a (or

  carboxyl group (s), which are obtained as sub-

  products in the oxidation step, (4) dissolve, under heating, the solid material thus washed in benzene or an alkylbenzene, which has a (or) side chain (s) having from 1 to 3 atoms of carbon, and then (5) cool the solution thus obtained, which allows

separate 2,6-DHPN.

  According to the present invention, firstly, 2,6-diisopropyl naphthalene is oxidized by molecular oxygen in an aqueous solution of an alkali. As the aqueous alkali solution used herein, an aqueous solution of 20 to 70% by weight, preferably 30 to 50% by weight, of sodium hydroxide or potassium hydroxide,

is preferred.

  In the case where the concentration of the aqueous alkali solution is less than 20% by weight, the oxidation rate of 2,6-diisopropyl naphthalene in the

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  naphthalene having a carboxyl group (or groups) (hereinafter

  referred to as "naphthalene acids"

  the carboxyl product is increased, thereby reducing the yield of the desired 2,6-DHPN product, and therefore such a condition is not preferred. In addition, where the concentration of the aqueous alkali solution is greater than 70% by weight, there is no practical advantage in improving the

yield of 2,6-DHPN.

  The amount of the aqueous alkali solution used herein is preferably from 1 to 20 ml, more preferably from 2 to 10 ml per 1 g of the starting material, 2,6-diisopropyl naphthalene. and, in the case where an amount of less than 1 ml is used per 1 g of 2,6-diisopropyl naphthalene, it is difficult to obtain a favorable contact between 2,6-diisopropyl

  naphthalene and oxygen by stirring.

  The molecular oxygen used in the oxidation is pure oxygen or a gaseous mixture prepared by dilution

of pure oxygen with an inert gas.

  Although the oxidation reaction proceeds more rapidly as the oxygen partial pressure increases, in practice, an oxygen partial pressure greater than 1.96 x 104 Pa <0.2 kg / cm) in the manometer, preferably 4.90 x 10 to 294.20 x 10 Pa (0.5 to 30 kg / cm2) gauge is sufficient. In addition, in the case where molecular oxygen is used after mixing with an inert gas, the total pressure of the gas mixture is not particularly limited; however, as a rule the reaction proceeds rapidly under a total pressure of from 9.81 x 104 to 294.20 x 104 Pa.

(1 to 30 kg / cm2) on the manometer.

  Although the reaction rate and the reaction time are decided by consideration of the other reaction conditions, the reaction temperature is preferably from 60 to 200 ° C, more preferably

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  preferably, from 80 to 150 ° C, and the reaction time is preferably from 1 to 50 hours, more preferably

prefered, from 10 to 30 hours.

  Heretofore, in the oxidation of cumene in the presence of an alkali, there was a method for carrying out the reaction in the presence of a catalytic amount of manganese naphthenate (Japanese Patent Publication No. 39-19355). 1964)); however, in the reaction according to the present invention, the presence of a heavy metal salt, such as manganese and cobalt, is not favorable, because the presence of such a heavy metal causes the increase

  by-products and staining of 2,6-DHPN.

  In addition, with respect to the material of the reaction vessel, those corroded by a concentrated aqueous alkali solution should be avoided, and it is preferable to use a reaction vessel in which the portion exposed to the aqueous solution

  concentrated alkali or nickel.

  In the oxidation of 2,6-diisopropyl naphthalene, the first step of oxidation of 2,6-diisopropyl naphthalene to (2-hydroxy-2-propyl) -2-n-6-propyl-naphthalene (hereinafter referred to as " mono (hydroxypropyl) naphthalene "), proceeds rapidly; however, the second step of oxidation of mono (hydroxypropyl) naphthalene to 2,6-DHPN proceeds slowly, and it is in practice difficult to complete the oxidation of 2,6-diisopropyl naphthalene to 2,6-DHPN, Therefore, the reaction mixture of the oxidation reaction contains intermediates, such as mono (hydroxypropyl) naphthalene, and by-products, such as 2-acetyl-6-isopropyl-naphthalene, 2-acetyl-hydroxy 2-propyl-2) -6-naphthalene and an alkali salt of naphthalenecarboxylic acids, etc. as well as the targeted substance, 2,6-DHPN, and 2,6-diisopropyl

naphthalene which did not react.

  In this respect, naphthalenecarboxylic acids, 2-acetyl-6-isopropyl naphthalene and 2-acetyl

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  (2-Hydroxypropyl-2) -6 naphthalene are by-products that can not be converted to 2,6-DHPN. 2,6-DHPN, the

  2,6-diisopropyl naphthalene, the intermediates and sub-

  products are solids at room temperature and do not dissolve in a concentrated aqueous alkali solution, and therefore, in the present invention,

  retrieves 2,6-DHPN, intermediates and sub-

  produced by subjecting the reaction mixture to solid-liquid separation, thereby removing the aqueous alkali solution. After adjusting the concentration of the aqueous alkali solution thus recovered to a value of 70% by weight, the aqueous solution of alkali thus adjusted can be reused in the oxidation step of the

2,6-diisopropyl naphthalene.

  In the solid material obtained by the solid-liquid separation, are contained several compounds mentioned above, and therefore, in the present invention, the intended product, 2,6-DHPN, is isolated from the material

  solid according to the following steps of the procedure.

  Thus, although the naphthalenecarboxylic acids present in the solid material do not dissolve in a concentrated aqueous alkali solution, they dissolve in a dilute aqueous alkali solution, and therefore the naphthalenecarboxylic acids can be separated by washing with water. the solid matter with water. The washing with water is preferably carried out until

the filtrate becomes neutral.

  After drying the washed solid material obtained by separation of the naphthalenecarboxylic acids, the dried solid material is dissolved in benzene or an alkylbenzene by heating at a temperature ranging from 70 to C, preferably from 100 to 130 C, and at cooling of the solution thus obtained up to a temperature ranging from 10 to 40 ° C, preferably from 20 to 30 ° C, practically only 2,6-DHPN is precipitated. The 2,6-DHPN thus precipitated is

separated and collected.

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  In the next step, by distilling off the organic solvent from the solution from which the 2,6-DHPN has been separated, a mixture containing mainly mono (hydroxypropyl) naphthalene is obtained, and therefore in the present invention, the mono (hydroxypropyl) naphthalene thus obtained is recycled to the oxidation step of 2,6-diisopropyl naphthalene, which

  allows reuse in conversion to 2,6-DHPN.

  As alkylbenzenes, those having 1 or 2 side chains having 1 to 3 carbon atoms, especially toluene, xylene, cumene, etc. can be given as examples. In addition, since the solubility of 2,6-DHPN in benzene and these alkylbenzenes is highly dependent on the temperature thereof, it is preferable to dissolve the solid material by heating at a temperature of from 70 to 150 ° C. C, more preferably, from 100 to 130C. The recovery of 2,6-DHPN in the recrystallization becomes greater than

% by doing this.

  The benzene or alkylbenzene is preferably used in an amount of from 1 to 30 ml, more preferably from 2 to 5 ml, per 1 g of the solid material. In the present invention, removal of the naphthalenecarboxylic acids after separation and recovery of the aqueous alkali solution and treatment with benzene or alkylbenzene can be carried out in this order, however, both steps can be carried out.

to be performed simultaneously.

  Thus, water and benzene or alkylbenzene are added to the solid material obtained by the separation of the aqueous alkali solution, and the mixture thus formed is heated with stirring, thereby dissolving the naphthalenecarboxylic acids in the layer. aqueous and other compounds in the organic layer, to effect the separation. After separating the aqueous layer and washing the organic layer with warm water, the layer

  organic is cooled to separate 2,6-DHPN.

  As has been described, according to the present invention, the yield of 2,6-DHPN, which is the object of the present invention, can be increased by recycling the intermediates which are present in the reactional mixture obtained by oxidation of diisopropyl -2.6 naphthalene in the oxidation step, which allows them to

  submit again to oxidation.

  Furthermore, by the use of benzene or an alkylbenzene as a solvent for recrystallization, it is

  possible to obtain 2,6-DHPN with high purity.

  Furthermore, since 2,6-diisopropyl naphthalene which did not react in the reaction mixture obtained by oxidation of 2,6-diisopropylnaphthalene with molecular oxygen in an aqueous alkali solution, the 2,6 -DHPN, the intermediates and by-products hardly dissolve in the concentrated aqueous solution of alkali, it is possible to separate and recover the aqueous alkali solution and use it repeatedly. The present invention will be explained in more detail with reference to non-limiting Examples as follows. Example 1: In a nickel autoclave with a capacity of 1.5 liters, equipped with a powerful stirrer, a condenser with

  reflux and a gas inlet tube, 250 g of diisopropylene

  2,6-naphthalene pyl, 240 g of sodium hydroxide and 560 g of water were introduced, and the substances thus introduced were stirred for 20 hours at 140 ° C., while gaseous oxygen was supplied. substances at a flow rate of 5 1 / hour and that the internal pressure of

  the autoclave at 98.07 x 104 Pa (10 kg / cm2) at the manometer.

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  In the next step, the autoclave was cooled to remove the contents. and the aqueous solution of sodium hydroxide was recovered in an amount of 642 g by filtration of the contents. By acid treatment of the thus recovered alkali solution with dilute sulfuric acid, no turbidity was observed in the alkali solution, which shows that the alkali solution

  contained few organic substances.

  Then, the solid material obtained by filtration was washed with water until the filtrate became neutral. By adjusting the pH of the washings to 3 with dilute sulfuric acid, a white precipitate was obtained. The precipitate was extracted with acetate

  of ethyl to give 23.3 g of naphthalene

carboxylic.

  In the next step, by drying the solid material thus washed, 248 g of a dried, white cake were obtained. After dissolving the cake in 3000 ml of toluene by heating at 110 ° C, the resulting solution was cooled to room temperature to precipitate needle-like crystals. By collecting the needle-like crystals on a filter and drying the crystals thus collected, 142 g of 2,6-DHPN

  with a purity of 97.9% were obtained. By recrystall

  the 2,6-DHPN thus obtained is obtained with 430 ml of toluene,

  136 g of almost pure 2,6-DHPN were obtained.

  By distilling off the toluene from the toluene solution remaining after the separation of 2,6-DHPN, a mixture consisting mainly of 2% (2-hydroxy-2-propyl) -isopropyl-6-naphthalene is formed by oxidation intermediate. , (hereinafter referred to as "the mixture

  Intermediates were obtained in an amount of 84.8 g.

  The composition of the intermediate mixture was as follows. 7.8% by weight of 2,6-diisopropyl naphthalene, 0.5% by weight of 2-acetyl-2-isopropyl naphthalene, 86.1% by weight of 2-hydroxy-2-propyl-2-isopropyl-6-naphthalene , 1% by weight of 2,6-DHPN, and

  0.5% by weight of 2-acetyl-2-hydroxy-2-propyl-6-naphthalene.

  Therefore, the yields of the products obtained by the oxidation reaction are respectively as follows. 2.7 mole% 2,6-diisopropyl naphthalene, 0.2% mole 2-acetyl-2-isopropyl-naphthalene, 28.7% mole 2-hydroxy-2-propyl-2-isopropyl Naphthalene, 49.1 mol% 2,6-DHPN, 0.2 mol% 2-acetyl-2-hydroxy-2-propyl-naphthalene, and

  9.0 mol% of naphthalenecarboxylic acids.

  Since the naphthalenecarboxylic acids were obtained in the form of a mixture, their weight

  Molecular average was assumed to be 220.

EX'RMPLE '2:

  In a nickel autoclave with a capacity of 1 ml, equipped with a powerful stirrer, a condenser with

  reflux and a gas inlet tube, 10 g of diiso-

  2,6-propyl-naphthalene and 100 g of an aqueous solution of 50% sodium hydroxide were introduced, and the contents of the autoclave was stirred for 22 hours at 120 ° C, while the pressure of the autoclave at 49.03 x 104 Pa (5 kg / cm2) on the manometer and introducing a gas mixture of 21% oxygen and 79%

nitrogen, at a rate of 5 1 / hour.

  In the next step, after recovering 77 g of the aqueous solution of sodium hydroxide by filtration of the reaction mixture, the solid material thus obtained was washed with 450 ml of water to obtain 23 g of a white cake and wet. After being dried, the wet cake was dissolved in 120 ml of toluene by heating to 110 ° C., and the solution thus formed was cooled to room temperature.

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  ambient, to precipitate crystals similar to needles. By filtration and drying of the needle-like crystals, 4.57 g of 2,6-DHPN with a purity of 96.5% was obtained. The crystals contained nothing more than 1 '(2-hydroxy-2-propyl) -2-isopropyl-6

naphthalene as impurity.

  After distilling off toluene of the remaining toluene solution after separation of 2,6-DHPN, the mixture of intermediates having the following composition was

  was obtained in an amount of 4.55 g.

  13.4% by weight of 2,6-diisopropyl naphthalene, 0.2% by weight of 2-acetyl-6-isopropyl naphthalene, 79.0% by weight of (2-hydroxy-2-propyl) -2-isopropyl- 6 naphthalene, 6.9%. by weight of 2,6-DHPN, and

  0.5%. by weight of 2-acetyl-2-hydroxy-2-propyl-6-naphthalene.

  In addition, by adjusting the pH of the washing solutions to 3, a white precipitate was obtained. By extraction from

  precipitated with ethyl acetate, 0.8 g of naphthalene

carboxylic acid has been obtained.

EXEXPLE: 3

  In the same autoclave as used in Example 2, 12 g of 2,6-diisopropyl naphthalene, 60 g of sodium hydroxide and 60 g of water were introduced, and the contents of the autoclave was stirred. for 22 hours at 'C, while maintaining the internal pressure of the autoclave at 49.03 x 104 Pa (5 kg / cm2) at the manometer and that

  oxygen was introduced at a rate of 3 l / hour.

  In the next step, after cooling the autoclave, its contents were removed and filtered for

  recover 90 g of the aqueous solution of sodium hydroxide.

  The solid material remaining on the filter was dissolved by heating at 100 ° C in 500 ml of water and 150 ml of xylene, and the aqueous layer was separated from the organic layer. The organic layer (xylene) was washed twice with, in each case, 100 ml of hot water. Leaving the layer of

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  Xylene is cooled to room temperature and needle-like crystals precipitated. By collecting the needle-like crystals and drying them, 7.18 g of 2,6-DHPN with a purity of 98.9% was obtained with a yield of 51.4 mol%.

EXAMPLE 4

  In this example, the aqueous alkali solution recovered from the reaction mixture and the mixture of intermediates were recycled to the oxidation stage of the reaction mixture.

  2,6-diisopropyl naphthalene for reuse.

  In the same autoclave as used in Example 2, 10 g of 2,6-diisopropyl naphthalene, 30 g of sodium hydroxide and 70 g of water were introduced, and the contents of the autoclave was stirred. for 22 hours at 120 ° C, while maintaining the internal pressure of the autoclave at 49.03 x 104 Pa (5 kg / cm5) at the manometer and that

  oxygen was introduced at a rate of 5 l / hour.

  In the next step, the reaction mixture was treated in the same manner as in Example 2 to obtain 6.75 g of 2,6-DHPN with a purity of 97.5%, 2.48 g of the mixture of intermediates, 1.26 g of naphthalenecarboxylic acids and 80.6 g of the aqueous solution

recovered sodium hydroxide.

  Then 7.91 g of 2,6-diisopropyl naphthalene and 19.4 g of 30% aqueous sodium hydroxide solution were added to 2.25 g of the resulting mixture of intermediates and 80.6 g. g of the aqueous solution of sodium hydroxide thus recovered, and the mixture thus formed was subjected to reaction in the same manner as in Example 2, to obtain, as second pass products, 6.80 g of

  2,6-DHPN of 97.0% purity, 2.45 g of the reaction mixture

  mediums, 1.32 g of naphthalenecarboxylic acids and 78.3 g

  of the aqueous solution of sodium hydroxide recovered.

  In the next step, 7.99 g of 2,6-diisopropyl naphthalene and 21.7 g of the 30% aqueous solution of sodium hydroxide were added to 2.14 g of the mixture.

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  78.3 g of the dense aqueous solution of sodium hydroxide recovered, the two solutions having been obtained in the second pass, and the mixture thus formed was reacted under the same conditions as in EXAMPLE 2 By treating the reaction mixture in the same manner as in Example 2, 6.73 g of 2,6-DHPN with a purity of 97.3% were obtained as third pass products. 2.49 g of the mixture of intermediates, 1.30 g of naphthalenecarboxylic acids and 78.2 g of the aqueous solution

recovered sodium hydroxide.

Claims (4)

  1 - Process for the production of di (2-hydroxy-2-propyl) -2,6-naphthalene, characterized in that it comprises: -oxydopropin-2,6-naphthalene oxidation by molecular oxygen in a solution aqueous phase of an alkali, -the separation and recovery of said aqueous alkali solution from the reaction mixture thus obtained, -washing the solid material obtained by removing the aqueous alkali solution, with water, so to eliminate the naphthalene derivatives having a carboxyl group, which are obtained as by-products in the oxidation step, -the dissolution. under heating, the solid material thus washed, in benzene or in an alkylbenzene which has a (or) side chain (s) having 1 to 3 carbon atoms, and -the cooling of the solution as well as formed, which allows   separate 2-di (2-hydroxy-2-propyl) -2,6 naphthalene. -   2 - Process according to claim 1, characterized in that is recycled to the oxidation stage of 2,6-diisopropyl naphthalene, the aqueous solution of alkali recovered and a mixture obtained from the organic solution of which 2-hydroxy-2-hydroxypropyl-2,6-naphthalene was separated, allowing reuse in oxidation.   3 - Process according to claim 1, characterized in that the aqueous solution of alkali is an aqueous solution at 20-to 70% by weight of sodium hydroxide or potassium hydroxide.   4 - Process according to claim 1, characterized   in that the alkylbenzene is toluene or xylene.   - Process according to claim 1, characterized in that the oxidation is carried out in a container nickel reaction.