EP0927153A1

EP0927153A1 - Method for the carboxylation on an aminonaphtol

Info

Publication number: EP0927153A1
Application number: EP97940212A
Authority: EP
Inventors: Murièle MICHEL
Original assignee: Rhodia Chimie SAS
Current assignee: Rhodia Chimie SAS
Priority date: 1996-09-10
Filing date: 1997-09-10
Publication date: 1999-07-07
Also published as: FR2753194B1; FR2753194A1; JP2001504089A; WO1998011055A1

Abstract

The invention concerns a method for the carboxylation on an aminonaphtol and more particularly of 5-amino-1-naphtol which consists in preparing an aminonaphtol salt by reacting aminonaphtol and a base, and then in carrying out the carboxylation of the resulting salt characterised in that the aminonaphtol salt is prepared in an organic solvent having a boiling point less than 160 °C and forming an azeotropic mixture with water; the water is eliminated by azeotropic distillation and carbon dioxide is introduced so as to obtain the carboxylic compound.

Description

CARBOXYLATION PROCESS OF AN AMINONAPHTOI

The present invention relates to a process for the carboxylation of an aminonaphthol in order to prepare hydroxynaphthoic acids and derivatives. In a preferred variant, the invention relates to the carboxylation of 5-aminonaphthol in order to prepare 1-hydroxy-5-amino-2-naphthoic acid.

It is known in the literature that the carboxylation of an aminophenol is considered to be difficult.

Indeed, it generally proves necessary to protect the amino function, to carry out the carboxylation according to the Kolbe-Schmitt reaction, under high carbon dioxide pressure, then in a subsequent step, to remove the protection of the amino function. . The process is complicated because in 3 steps and expensive

It should be noted that the carboxylation reaction presents implementation difficulties since the medium must be anhydrous and it is difficult to obtain an anhydrous salt without shielding the reactor.

It has now been found, and this is what constitutes the object of the present invention, a process for the carboxylation of an aminonaphthol, which consists in preparing a salt of aminonaphthol by reaction of the aminonaphthol and of a base, then carrying out the carboxylation of the salt obtained, characterized in that the aminonaphthol salt is prepared in an organic solvent having a boiling point below 160 ° C and forming an azeotrope with water; that water is removed by azeotropic distillation and then carbon dioxide is introduced, in order to obtain the carboxylated compound.

An advantageous variant of the process of the invention consists in gradually introducing the base into the reaction medium comprising the aminonaphthol and the organic solvent, while eliminating the water from the medium as it is introduced and formed.

The process of the invention has many advantages. It can be run without shielding the reactor. The solvent used in the salification reaction and in the carboxylation reaction being the same, the two reactions can be linked together and carried out in the same reactor. In addition, the difficulty of working in an anhydrous medium is circumvented by the implementation of the preferred variant of continuous introduction of the base and simultaneous distillation of water.

In the present text, the term "aminonaphthol" denotes a naphthalene compound, one of the aromatic rings of which carries a hydroxyl group, and of which one of the hydrogen atoms of one of the aromatic rings is replaced by an optionally substituted amino group.

More specifically, the subject of the present invention is a process for the carboxylation of an aminonaphthol of general formula (I):

in which :

- n is a number from 0 to 3,

- p and p ', identical or different, represent a number equal to 0 or 1,

- p or p ', is at least equal to 1, - Ri represents:

. a hydrogen atom,

. an alkyl radical optionally carrying one or more halogen atoms having from 1 to 30 carbon atoms,

. an alkoxy radical having from 1 to 30 carbon atoms,. an aryl radical having from 6 to 30 carbon atoms,

. an OH group,

. an NH2 group,

. a NO2 group,

. a COOH group,. an SO3H group,

. a group R3-CO-NH, R ₃ having the meaning given for R,

. a group R ₃ -S0 ₂ -NH, R3 having the meaning given for R ₄ ,

- R2 represents:

. a hydrogen atom,. an RY group with Y = COO, SO2 and R ₄ represents an alkyl radical optionally carrying one or more halogen atoms having from 1 to 30 carbon atoms or an aryl radical having from 6 to 30 carbon atoms. If the radical (s) R ^ have a hydrocarbon chain, this can be optionally interrupted by a heteroatom (for example, oxygen or nitrogen), by a functional group and / or carrying a substituent (for example, a halogen, a trifluoromethyl group or an ester function).

In the case where the radical R 1 represents a ring such as benzene or the like, it is possible that there are substituents on this ring. Any substituent can be present. It is most often a lower alkyl radical

C1-C4, a lower aikoxy radical C1-C4, a hydroxyl group, a nitro group and / or a halogen atom, in particular fluorine or chlorine.

The process of the invention applies very particularly to the aminonaphthols of formula (I) in which: - n is equal to 0 or 1,

- p and p ', identical or different, represent a number equal to 0 or 1,

- p qu p ', is at least equal to 1,

- R-- represents one of the following atoms or groups:

. a hydrogen atom,. an alkyl radical, linear or branched, having from 1 to 6 carbon atoms, preferably from 1 to 4 carbon atoms, such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, tert-butyl,

. a linear or branched aikoxy radical having from 1 to 6 carbon atoms, preferably from 1 to 4 carbon atoms such as the methoxy, ethoxy, propoxy, isopropoxy, butoxy, isobutoxy, sec-butoxy, tert-butoxy radicals,

. a COOH group,

. a methylsulfoamino group,

. an acetamido group,. a halogen atom, preferably a fluorine, chlorine or bromine atom, a trifluoromethyl radical,

- R2 represents:

. a hydrogen atom,

. an R5Y group with Y = COO, SO2 and R ₅ represents an alkyl radical having from 1 to 12 carbon atoms, a trifluoromethyl radical, an optionally substituted phenyl or benzyl radical. By way of illustration of compounds corresponding to formula (I), there may be mentioned more particularly:

- 5-amino-1 -naphthol, - 4-amino-1 -naphthol,

- 4-amino-2-naphthol,

- 3-amino-2-naphthol,

- 1-amino-2-naphthol, - 8-amino-1-naphthol-3,6-disulfonic acid,

- 8-amino-1-naphthol-5-sulfonic acid,

- 1-amino-2-naphthol-4-sulfonic acid,

- 1-amino-2-naphthol-6-sulfonic acid, - 6-amino-4-hydroxy-2-naphthalenesulfonic acid,

- 7-amino-4-hydroxy-2-naphthalenesulfonic acid,

- 4-amino-5-hydroxy-3- (4-nitrophenylazo) -2,7-naphthalenedisulfonic acid,

- 5-amino-1,4-dihydroxynaphthalene,

- 5-amino-4-chloro-1-naphthol, - 5-amino-4-ethoxy-1 -naphtol,

- 4,5-diamino-1-naphthol,

- 6-amino-1-naphthol,

- 6-acetamido-1-naphthol,

- 6-tert-butylamido-l -naphthol. In the list aciαes implemented may optionally be in a salified form, in particular in the form of sodium or potassium salt.

In accordance with the process of the invention, in the first step, the aminonaphthol salt in suspension in an organic solvent is prepared. According to a characteristic of the process of the invention, an organic solvent is used, the characteristic of which is to have a boiling temperature below 160 ° C., and to form an azeotrope with water.

As examples of organic solvents suitable for the invention, mention may in particular be made of benzene, preferably alkylbenzenes, toluene, o xylene, m-xylene, p-xylene and their mixtures or isopropanol. It is also possible to use a mixture of organic solvents. Among the aforementioned solvents, toluene is preferably used.

The amount of organic solvent to be used is determined according to the nature of the organic solvent chosen.

It is determined so that the concentration of the substrate in the organic solvent is preferably between 10 and 30% by weight.

It is generally desirable not to exceed 50% in order to avoid agitation problems. The aminonaphthol which is involved in the process of the invention is in salified form. They are preferably the salts of the metallic elements of group (la) of the periodic table or an ammonium salt. For the definition of the elements, reference is made below to the Periodic Table of the Elements published in the Bulletin of the Chemical Society of France, n ° 1 (1966).

From a practical and economical point of view, sodium or potassium salts are used.

It is possible to use a salified form of an aminonaphthol prepared extemporaneously but it is also possible to prepare it in situ by reacting the aminonaphthol and the base.

There is therefore involved, in the process of the invention, a base which is preferably an inorganic base.

A strong base is preferably chosen, that is to say a base having a pKb greater than 12: the pKb being defined as the cologarithm of the dissociation constant of the base measured, in aqueous medium, at 25 ° C.

Particularly suitable for carrying out the process of the invention, inorganic bases such as the alkali metal salts, preferably an alkali metal hydroxide which may be sodium or potassium hydroxide.

For economic considerations, one chooses from all the bases, preferably sodium or potassium hydroxide. The concentration of the basic starting solution is not critical. The alkali metal hydroxide solution used has a concentration generally between 10 and 50% by weight.

The amount of base introduced into the reaction medium takes account of the amount necessary to salify the hydroxyl function of aminonaphthol. If the said compound has salifiable functions other than the hydroxyl group, the quantity of base necessary to salify all the salifiable functions is therefore introduced.

Generally, the amount of base expressed relative to aminonaphthol varies between 90 and 100% of the stoichiometric amount. Aminonaphthol is prepared in salified form by reacting it with the base at a temperature advantageously between room temperature and 200 ° C, preferably between 50 ° C and 160 ° C. By "ambient temperature" is meant a temperature generally between 15 ° C and 25 ° C. According to a preferred variant of the process of the invention, the salification step is carried out under a controlled atmosphere of inert gases. One can establish an atmosphere of rare gases, preferably argon, but it is more economical to use nitrogen. A preferred variant of the process of the invention consists in gradually introducing the base into the reaction medium comprising the aminonaphthol and the organic solvent, while removing water from the medium as it is introduced and formed. After elimination of the last traces of water, a variant of the invention consists in introducing an alkali metal carbonate.

By "alkali metal" is meant an element from group (1a) of the periodic table of elements, preferably sodium or potassium.

More particularly, potassium carbonate is used, preferably used in solid form.

The amount of carbonate used preferably represents from 0 to 50% by mole of substrate and even more preferably from 10 to 30% by mole.

In accordance with the process of the invention, the aminonaphthol in salified form and the carbon dioxide are reacted in an organic solvent te! qu π defined. The quantity of carbon dioxide to be used, expressed by the molar ratio between carbon dioxide and aminonaphthol varies between 1 and 50, and more preferably between 1 and 2.

The process of the invention is advantageously carried out at a temperature between 100 ° C and 200 ° C, preferably between 100 ° C and 180 ° C. It is possible to carry out the reaction under pressure of carbon dioxide varying between atmospheric pressure and about 100 bar. We prefer a pressure between 1 and 20.

Carbon dioxide, in the form of a sweep, can be used to control the atmosphere at the start of the reaction. Continuing her research, the Applicant has found that it is desirable to conduct the salification and carboxylation reactions, in the presence of a reducing compound in order to reduce the secondary oxidation reactions.

The reducing compounds which can be used are of varied nature.

As reducing compounds which are suitable in the context of the present process, mention may be made, by way of nonlimiting examples, of inorganic or organic sulfur compounds; organic phosphorus compounds; hydrazines.

Preferably, the alkali metal salts of sulfur acids are used in which the sulfur is at an oxidation state of 2+ to 4+, such as the alkali metal salts of sulfurous acid, thiosulfuric acid, l dithionous acid. Generally, for practical and economic reasons, the alkali metal salts indicated above are sodium salts.

Thus, sodium dithionite, sodium hydrogen sulfite, sodium sulfite, sodium thiosulfate are particularly suitable. As reducing compounds, hydrazine hydrochloride can also be used.

Examples of organic sulfur compounds that may be mentioned include organic sulfides such as thionanisole, diphenyl sulfide, phenyl and 4-chlorophenyl sulfide, di (4-chlorophenyl) sulfide,

Di (2-hydroxy-4,6-ditertiobutylphenyl), di (4-hydroxy-3,5-dimethylphenyl) sulfide, di (2-hydroxy-3,5-ditertiobutylphenyl) sulfide, phenyl sulfide and cyclohexyl, phenyl and butyl sulfide, 4-chlorophenyl and hexyl sulfide, 4-methylphenyl and dodecyl sulfide, benzyl and octyl sulfide, 4-methoxyphenyl sulfide and d 'ethyl, IR iî. phenyl and stearyl suide, dihexyl sulfide, ethyl sulfide and hexyl sulfide, dioctyl sulfide, propyl and 4-methylcyclohexyl sulfide, methyl sulfide and 4-chlorocyclohexyl.

As examples of organic phosphorus compounds, mention may be made of organic phosphites such as triphenyl phosphite, 0 tris phosphites (chlorophenyl), tris phosphites (dichlorophenyl), tris phosphites (trichlorophenyl), phosphite trimethyl, triethyl phosphite, tributyl phosphite, trioctyl phosphite, tris (nonylphenyl) phosphites, 2,4-ditertiobutylphenyl phosphite, tribenzyl phosphite, tris (phenethyl) phosphite, phosphite tris (2-ethoxyethyl), tricyclohexyl phosphite; organic phosphinites such as methyl diphenylphosphinite; phosphines such as triphenylphosphine, diphenylmethylphosphine, diphenylethylphosphine, diethylphenylphosphine, tributylphosphine.

The amount of reducing compound used is generally small. It most often represents from 0.1 to 5% of the weight of the aminonaphthol and preferably about 1%.

If the two salification and carboxylation reactions are not chained in the same reactor, it may be desirable to add reducing compound, in the same proportions, before the carboxylation. From a practical point of view, the method can be implemented according to two preferred modes. A first embodiment consists in putting the substrate (possibly a reducing compound) in suspension in the solvent. The base is preferably added in aqueous solution.

The mixture is heated in order to remove the water by azeotropic distillation. Optionally, an alkali metal carbonate is introduced.

The medium is then brought to the chosen carboxylation temperature.

The carbon dioxide is introduced at the desired pressure and maintained until there is no more consumption of carbon dioxide.

The duration of the reaction is obviously variable depending on the nature of the substrate. It usually varies between 1 and 8 hours.

Another embodiment of the invention is to put the substrate (optionally a reducing compound) in the organic solvent, to bring the suspension obtained to the reflux temperature of the solvent.

Then, the base is gradually introduced, in aqueous solution, while αis iiani gradually the azeotrope water / organic solvent so as to eliminate the water continuously.

Optionally, an alkali metal carbonate is introduced.

Carboxylation is then carried out as previously described.

An aminonaphthol carrying a carboxylate group is obtained. It is located in position 2 or 4 with respect to a hydroxyl group in position α and in position 1, 3 or 6 with respect to a hydroxyl group in position β.

The product is suspended in the solvent which comprises the substrate and the product obtained.

The product is separated according to conventional solid / liquid separation techniques, preferably by filtration.

In a last step, the carboxylated aminonaphthol is recovered from the reaction medium, in a manner known per se.

In order to obtain the product in acid form, it is suspended in water and the pH is brought below 6, preferably between 2.0 and 5.0, by adding an aqueous solution of a mineral acid such as for example hydrochloric, sulfuric or nitric acid. Hydrochloric acid or sulfuric acid are preferred. The concentration of the acid is not critical. It preferably corresponds to the concentration of the commercial form, for example, 37% by weight for hydrochloric acid, 92 or 96% for sulfuric acid. The acid obtained is recovered from the reaction medium according to conventional solid / liquid separation techniques, preferably by filtration. The carboxylated compound is obtained in acid form. It is possible to very easily prepare the esters of the acid obtained, in particular the C1-C4 alkyl esters and the aryl esters, preferably phenyl.

The process of the invention allows easy access to 1-hydroxy-5-amino-2-naphthoic acid.

An exemplary embodiment of the invention is given, given by way of illustration, without limitation.

In the example, the yield mentioned corresponds to the following definition:

number of moles of naphthoic acid formed

Yield: RR =% number of moles of aminonaphthol introduced

Example 1

23.9 g (150 mmol) of 5-amino-1-naphthol and 218 g (252 ml) of toluene are charged into a 300 ml Burton Corbelin® reactor equipped with a distillation system.

It is heated to reflux.

An aqueous 50% potash solution (16.8 g) is introduced gradually, the water being distilled simultaneously.

At the end of the pouring, the mixture is allowed to reflux for 1 hour to remove the last traces of water.

It is heated to 170 ° C. Carbon dioxide is introduced until a pressure of 10 bar is obtained. It is heated to 170 ° C for 3 hours, maintaining the pressure at 10 bar.

After the reactor has cooled to room temperature, the reaction medium is filtered.

The cake obtained is suspended in water (10%) and acidified to pH = 3 using a 96% sulfuric acid solution.

After filtration and drying, 24.4 g of product with 90% purity are obtained. The yield of 1-hydroxy-5-amino-2-naphthoic acid is 72% relative to aminonaphthol.

Example 2

In a glass reactor of 1 liter equipped with a stirrer, a Dean-Stark® distillation assembly and an addition funnel are introduced: - 55.1 g or 0.345 mol of 5-amino-1-naphthol,

- 0.5 g of sodium dithionite and

- 470 ml or 407 g of toluene (50 ml of toluene are also introduced into the base of the Dean-Stark® assembly). The agitation is started and the medium is inerted with nitrogen.

The medium is heated to toluene reflux and then poured in 2 hours, 40.3 g of a 49.3% potash solution or 0.3598 mol of potash; the water supplied being distilled simultaneously.

The mixture is again heated at reflux for 2 hours in order to completely dry the medium, then the latter, after cooling to room temperature, is transferred into a 1 liter autoclave equipped with a Ruchston® turbine. 0.2 g of sodium dithionite is added to the medium.

After starting the stirring, the autoclave is purged with carbon dioxide and the medium is heated to 150 ° C. Carbon dioxide is then injected into the autoclave over a period of

1 hour 30 so that the relative pressure is between 8 and 10 bar.

The introduction of carbon dioxide is stopped and the medium is further heated to 175 ° C for 3 hours; during this period the relative pressure is approximately 9 bar.

After the autoclave has cooled to room temperature, the medium is filtered on a No. 3 frit glass and 84.1 g of product are obtained (by mass):

- 5% toluene, - 15.4% 5-amino-1-naphthol,

- 57.7% of potassium 5-amino-1-hydroxy-2-naphthoate which corresponds to a 100% isolated yield of 58% in this product.

Example 3 Into a 1 liter glass reactor equipped with a stirrer, a Dean-Stark® distillation assembly and an addition funnel are introduced:

- 75.0 g or 0.471 mol of 5-amino-1-naphthol,

- 0.6 g of sodium dithionite and

- 640 ml or 555 g of toluene (50 ml of toluene are also introduced into the base of the Dean-Stark® assembly).

The agitation is started and the medium is inerted with nitrogen. The medium is heated to toluene reflux and then poured over 3 hours, 55.0 g of a 49.6% potassium hydroxide solution, ie 0.491 mol of potassium hydroxide; the water supplied being distilled simultaneously.

The mixture is again heated at reflux for 2 hours in order to completely dry the medium, then the latter, after cooling to room temperature, is transferred into a 1 liter autoclave equipped with a Ruchston® turbine.

19.5 g, ie 0.1415 mol of dry potassium carbonate and 0.3 g of sodium dithionite, are added to the medium.

After starting the stirring, the autoclave is purged with carbon dioxide and the medium is heated to 170 ° C.

Carbon dioxide is then introduced into the autoclave over a period of

I hour 30 so that the relative pressure is between 10 and

I I bar.

The introduction of carbon dioxide is stopped and the medium is heated to 180 ° C. for 2 hours; during this period . _α relative pressure is around 11 to 12 bar.

After the autoclave has cooled to room temperature, the medium is filtered on a No. 3 frit glass and then dried on a rotary evaporator at 55 ° C. for 2 hours 30 minutes at 20 mbar and 129 g of product containing ( en masse):

- 0.6% toluene,

- 14.9% 5-amino-1-naphthol

- 78.2% of potassium 5-amino-1-hydroxy-2-naphthoate which corresponds to a 100% isolated yield of 88% in this product.

Claims

1 - Process for the carboxylation of an aminonaphthol, which consists in preparing a salt of aminonaphthol by reaction of the aminonaphthol and of a base, then in carrying out the carboxylation of the salt obtained, characterized in that the salt is prepared aminonaphthol in an organic solvent having a boiling point below 160 ° C and forming an azeotrope with water; that water is removed by azeotropic distillation and then carbon dioxide is introduced, in order to obtain the carboxylated compound.

2 - Process according to claim 1 characterized in that the aminonaphthol corresponds to the general formula (I):

in which: - n is a number from 0 to 3,

- p and p ', identical or different, represent a number equal to 0 or 1,

- p or p ', is at least equal to 1,

- R- _| represented :

. a hydrogen atom,. an alkyl radical optionally carrying one or more halogen atoms having from 1 to 30 carbon atoms,

. an aikoxy radical having from 1 to 30 carbon atoms,

. an aryl radical having from 6 to 30 carbon atoms _"

. an OH group,. an NH2 group,

. a NO2 group,

. a COOH group,

. an SO3H group,

. a group R3-CO-NH, R3 having the meaning given for R,. a group R3-SO2-NH, R3 having the meaning given for R ₄ ,

- R ₂ represents:

. a hydrogen atom,

. an RY group with Y = COO, SO2 and R ₄ represents an alkyl radical optionally bearing one or more halogen atoms having from 1 to 30 carbon atoms or an aryl radical having from 6 to 30 carbon atoms.

3 - Method according to one of claims 1 and 2 characterized in that the aminonaphthol corresponds to the general formula (I) in which:

- n is equal to 0 or 1,

- p and p ', identical or different, represent a number equal to 0 or 1,

- p or p ', is at least equal to 1,

- Ri represents one of the following atoms or groups:. a hydrogen atom,

. an alkyl radical, linear or branched, having from 1 to 6 carbon atoms, preferably from 1 to 4 carbon atoms, such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, tert-butyl,

. a COOH group,

. a methylsulfoamino group,. an acetamido group,

. a halogen atom, preferably a fluorine, chlorine or bromine atom, a trifluoromethyl radical,

- R2 represents:

. a hydrogen atom,. an R ₅ Y group with Y = COO, SO ₂ and R ₅ represents an alkyl radical having from 1 to 12 carbon atoms, a trifluoromethyl radical, an optionally substituted phenyl or benzyl radical.

- Method according to claim 1 characterized in that the aminonaphthol st chosen from:

- 5-amino-1-naphthol,

- 4-amino-1-naphthol,

- 4-amino-2-naphthol,

- 3-amino-2-naphthol, - 1-amino-2-naphthol,

- 8-amino-1-naphthol-3,6-disulfonic acid,

- 8-amino-1-naphthol-5-sulfonic acid,

- 1-amino-2-naphthol-4-sulfonic acid, - 1-amino-2-naphthol-6-sulfonic acid,

- 6-amino-4-hydroxy-2-naphthalenesulfonic acid,

- 7-amino-4-hydroxy-2-naphthalenesulfonic acid,

- 4-amino-5-hydroxy-3- (4-nitrophenylazo) -2,7-naphthalenedisulfonic acid, - 5-amino-1, 4-dihydroxynaphthalene,

- 5-amino-4-chloro-1-naphthol,

- 5-amino-4-ethoxy-1-naphthol,

- 4,5-diamino-1-naphthol,

- 6-amino-1-naphthol, - 6-acetamido-1-naphthol,

- 6-tert-butylamido-1-naphthol.

5 - Method according to one of claims 1 to 4 characterized in that the organic solvent is benzene, preferably alkylbenzenes, toluene, o-xylene, m-xylene, ie p- xylene and mixtures thereof or isopropanol.

6 - Process according to claim 5 characterized in that the amount of organic solvent is determined so that the concentration of the substrate in the organic solvent is between 10 and 30% by weight.

7 - Method according to one of claims 1 to 6 characterized in that the aminonaphthol is in salified form, preferably in the form of metallic elements of group (la) of the periodic table, preferably of sodium salts or potassium.

8 - Process according to claim 7 characterized in that the aminonaphthol in salified form is prepared by reacting said compound with a base, preferably a sodium or potassium hydroxide.

9 - Method according to claim 8 characterized in that the amount of base expressed relative to the aminonaphthol varies between 90 and 100% of the stoichiometric amount.

10 - Method according to one of claims 7 to 9 characterized in that the base is added and that the water is removed by azeotropic distillation. 11 - Method according to one of claims 7 to 9 characterized in that the base is added gradually while removing the water as and by azeotropic distillation.

12 - Method according to one of claims 7 to 11 characterized in that the temperature of the salification reaction is between room temperature and 200 ° C, preferably between 50 ° C and 160 ° C.

13 - Method according to one of claims 7 to 12 characterized in that one adds an alkali metal carbonate, preferably, potassium carbonate.

14 - Method according to one of claims 7 to 13 characterized in that the amount of alkali metal carbonate expressed in molar percentages relative to the aminonaphthol used is from 0 to 50%, preferably from 10 to 30% .

15 - Method according to one of claims 1 to 14 characterized in that the amount of carbon dioxide to be used expressed by the molar ratio between carbon dioxide and aminonaphthol varies between 1 and 50, and more preferably between 1 and 2.

16 - Method according to one of claims 1 to 15 characterized in that the temperature at which the carboxylation takes place is a temperature between 100 ° C and 200 ° C, preferably between 100 ° C and 180 ° C.

17 - Method according to one of claims 1 to 16 characterized in that the carbon dioxide pressure varies from atmospheric pressure and about 100 bar, preferably between 1 and 20 bar.

18 - Method according to one of claims 1 to 17 characterized in that one adds a reducing compound during salification and carboxylation.

19 - Process according to claim 18 characterized in that the reducing compound is a mineral or organic sulfur compound; an organic phosphorus compound; a hydrazine.

20 - Process according to claim 19 characterized in that the reducing compound is chosen from the alkali metal salts of sulfur acids in which the sulfur is at an oxidation state of 2+ to -, such as the salts of alkali metals of sulfurous acid, thiosulfuric acid, dithionous acid.

21 - Process according to claim 20 characterized in that the reducing compound is chosen from sodium dithionite, sodium hydrogen sulphite, sodium sulfite and sodium thiosulfate.

22 - Method according to one of claims 1 to 21 characterized in that the carboxylated aminonaphthol is recovered from the reaction medium.