FR2730731A1 - PROCESS FOR CARBOXYLATION OF AN AROMATIC ETHER - Google Patents

Abstract

A method for carboxylating a phenol ether, particularly guaiacol and guetol, wherein said phenol ether in salt form is reacted with carbon dioxide at a temperature below 150 DEG C in an aprotic, polar and basic organic solvent.

Description

PROCESS FOR CARBOXYLATION OF AN AROMATIC ETHER
The present invention relates to a carboxylation process of an aromatic ether.

 In a preferred variant, the invention relates to carboxylation of guaiacol (or 2-methoxyphenol) and guetol (or 2-ethoxyphenol).

 The carboxylation processes of phenols or phenol ethers having an industrial vocation, use carbon dioxide.

The carboxylation is carried out according to the reactions of Kolbe-Schmitt or
Marasse.

In the first case, the phenol or phenol ether is reacted in the form of a salt, usually sodium or potassium, with carbon dioxide, under pressure. An illustration of this type of reaction is given by
EP-A 327 221 which describes the carboxylation of sodium galacolate at 250 ° C under CO2 pressure. Such a method is suitable when it is desired to obtain 2-hydroxy-3-methoxybenzoic acid, that is to say carry out a carboxylation in the ortho position of the hydroxyl group.

It has also been proposed to conduct the reaction according to the conditions of
Marasse. Thus, O. BAISE et al [J. Org. Chem. 19. pp. 510 (1954)] have described obtaining 2-hydroxy-3-methoxybenzoic acid, by carboxylation at 2000C, of galacol by CO2, in the presence of an excess of potassium carbonate.

However, the yield obtained is not satisfactory because it is only 47%.

 The object of the present invention is to provide a carboxylation process in para of an aromatic ether to obviate the aforementioned drawbacks.

 It has now been found and this is the object of the present invention, a carboxylation method of an aromatic ether which comprises reacting said aromatic ether in salified form with carbon dioxide, said process being characterized in that the reaction is carried out at a temperature below 150 ° C. in an aprotic, polar and basic organic solvent.

In the following description of the present invention, the term "aromatic" is understood to mean the conventional notion of aromaticity as defined in the literature, in particular by Jerry MARCH, Advanced Organic Chemistry, 4th edition, John Wiley and
Sounds, 1992, pp. 40 and following.

 The term "aromatic ether" denotes an aromatic compound whose aromatic ring carries a hydroxyl group, a hydrogen atom in the para position of the OH group and a hydrogen atom directly attached to the aromatic nucleus. replaced by an ether group.

dans laquelle:
- A symbolise le reste d'un cycle formant tout ou partie d'un système
carbocyclique aromatique, monocyclique ou polycyclique, système
comprenant au moins un groupe OR': ledit reste cyclique pouvant porter un
ou plusieurs substituants,
- R représente un atome d'hydrogène ou un ou plusieurs substituants,
identiques ou différents,
- R' représente un radical hydrocarboné ayant de 1 à 24 atomes de
carbone, qui peut être un radical aliphatique acyclique saturé ou insaturé,
linéaire ou ramifié ; un radical cycloaliphatique saturé, insaturé ou
aromatique, monocyclique ou polycyclique; un radical aliphatique saturé ou
insaturé, linéaire ou ramifié, porteur d'un substituant cyclique,
- n est un nombre inférieur ou égal à 3.More specifically, the subject of the present invention is a process for the carboxylation of an aromatic ether of general formula (I):

in which:
- A symbolizes the remainder of a cycle forming all or part of a system
carbocyclic aromatic, monocyclic or polycyclic, system
comprising at least one OR 'group: said cyclic residue may carry a
or more substituents,
R represents a hydrogen atom or one or more substituents,
identical or different,
R 'represents a hydrocarbon radical having from 1 to 24 atoms of
carbon, which may be a saturated or unsaturated acyclic aliphatic radical,
linear or branched; a saturated, unsaturated cycloaliphatic radical or
aromatic, monocyclic or polycyclic; a saturated aliphatic radical or
unsaturated, linear or branched, carrying a cyclic substituent,
n is a number less than or equal to 3.

 In the present text, the groups of the R'-O- type in which R 'has the meaning given above are diagrammatically denoted by ether groups, R' thus representing both an acyclic or cycloaliphatic aliphatic radical, which is saturated. unsaturated or aromatic than a saturated or unsaturated aliphatic radical carrying a cyclic substituent.

 The aromatic ether which is involved in the process of the invention corresponds to formula (I) in which R 'represents an acyclic aliphatic radical, saturated or unsaturated, linear or branched.

 More preferentially, R 'represents a linear or branched alkyl radical having from 1 to 12 carbon atoms, preferably from 1 to 6 carbon atoms: the hydrocarbon cat may be optionally interrupted by a heteroatom (for example, oxygen), by a functional group (for example -CO-) and / or a substituent (for example, a halogen).

 The acyclic aliphatic radical, saturated or unsaturated, linear or branched may optionally carry a cyclic substituent. By ring, is preferably meant a saturated carbocyclic ring, unsaturated or aromatic, preferably cycloaliphatic or aromatic, especially cycloaliphatic ring comprising 6 carbon atoms in the ring or benzene.

 The acyclic aliphatic radical may be linked to the ring by a valence bond, a heteroatom or a functional group and examples are given above.

The ring may be optionally substituted and, as examples of cyclic substituents, it is possible to envisage, among others, substituents such as
R whose meaning is specified for the formula (la).

 R 'may also represent a carbocyclic radical saturated or comprising 1 or 2 unsaturations in the ring, generally having 3 to 8 carbon atoms, preferably 6 carbon atoms in the ring; said cycle may be substituted with substituents such as R.

 R 'can also represent an aromatic carbocyclic radical, preferably monocyclic having generally at least 4 carbon atoms, preferably 6 carbon atoms in the ring; said cycle may be substituted with substituents such as R.

 The process of the invention is particularly applicable to aromatic ethers of formula (I) in which R 'represents a linear or branched alkyl radical having from 1 to 4 carbon atoms or a phenyl radical.

 Examples of preferred R 'radicals according to the invention include methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, tertbutyl or phenyl radicals.

 In the general formula (I) of the aromatic ethers, the residue A may represent the remainder of a monocyclic aromatic carbocyclic compound having at least 4 carbon atoms and preferably 6 carbon atoms or the remainder of a polycyclic carbocyclic compound which may consist of at least 2 aromatic carbocycles and forming between them ortho- or ortho- and peri-condensed systems or by at least 2 carbocycles of which at least one of them is aromatic and forming between them ortho- or ortho-systems. - and pericondensed.

The remainder A may carry one or more substituents on the aromatic ring.
Examples of substituents R are given below but this list is not limiting in nature. Any substituent may be present on the cycle as long as it does not interfere with the desired product.

 The remainder A can among others carry several alkoxy groups, it is possible according to the process of the invention to carboxylate polyalkoxylated compounds.

dans laquelle:
- n est un nombre inférieur ou égal à 3, de préférence égal à 0 ou 1,
- le radical R' représente un radical allyle, linéaire ou ramifié, ayant de 1 à
6 atomes de carbone, de préférence de 1 à 4 atomes de carbone, tel que
méthyle, éthyle, propyle, isopropyle, butyle, isobutyle, sec-butyle, tert-butyle
ou phényle,
- le ou les radicaux R représentent l'un des atomes ou groupes suivants::
un atome d'hydrogène,
un radical alkyle, linéaire ou ramifié, ayant de 1 à 6 atomes de
carbone, de préférence de 1 à 4 atomes de carbone, tel que méthyle,
éthyle, propyle, isopropyle, butyle, isobutyle, sec-butyle, tert-butyle,
un radical alkoxy linéaire ou ramifié ayant de 1 à 6 atomes de
carbone, de préférence de 1 à 4 atomes de carbone tel que les
radicaux méthoxy, éthoxy, propoxy, isopropoxy, butoxy, isobutoxy, sec
butoxy, tert-butoxy,
un atome d'halogène, de préférence un atome de fluor, chlore ou
brome, un radical trifluorométhyle.The process of the invention is more particularly applicable to aromatic ethers of formula (Ia):

in which:
n is a number less than or equal to 3, preferably equal to 0 or 1,
the radical R 'represents a linear or branched allyl radical having from 1 to
6 carbon atoms, preferably 1 to 4 carbon atoms, such as
methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, tert-butyl
or phenyl,
the radical or radicals R represent one of the following atoms or groups:
a hydrogen atom,
a linear or branched alkyl radical having from 1 to 6 carbon atoms
carbon, preferably 1 to 4 carbon atoms, such as methyl,
ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, tert-butyl,
a linear or branched alkoxy radical having from 1 to 6 carbon atoms
carbon, preferably from 1 to 4 carbon atoms, such as
radicals methoxy, ethoxy, propoxy, isopropoxy, butoxy, isobutoxy, dry
butoxy, tert-butoxy,
a halogen atom, preferably a fluorine, chlorine or
bromine, a trifluoromethyl radical.

the radicals R 'and R and the two successive atoms of the benzene ring
can form between them, a ring having from 5 to 7 atoms, comprising
possibly another heteroatom.

 When n is greater than or equal to 1, the radicals R 'and R and the two successive atoms of the benzene ring may be linked together by an alkylene, alkenylene or alkenylidene radical having from 2 to 4 carbon atoms to form a saturated heterocycle, unsaturated or aromatic having 5 to 7 carbon atoms. One or more carbon atoms may be replaced by another heteroatom, preferably oxygen. Thus, the R 'and R radicals may represent a methylene dioxy or ethylene dioxy radical.

 The process of the invention is particularly applicable to aromatic ethers of formula (Ia) in which n is equal to 1, the radicals R and R 'both representing identical or different alkoxy radicals. It is more preferable to aromatic ethers of formula (la) in which n is 0, the radical R 'representing an alkoxy radical.

By way of illustration of compounds corresponding to formula (I), mention may be made more particularly of:
monoethers such as galacol, 3-methoxyphenol, guetol, 3
ethoxyphenol, 2-isopropoxyphenol, 3-isopropoxyphenol, 2-methoxy
5-methylphenol, 2-methoxy-6-methylphenol, 2-methoxy-6-tert
butylphenol, 3-chloro-5-methoxyphenol, 2,3-dimethoxy-5-methylphenol,
2-ethoxy-5- (1-propenyl) phenol, 2-methoxy-1-naphthol,
diethers such as 2,3-dimethoxyphenol, 2,6-dimethoxyphenol and 3,5-dimethoxyphenol.

 The compounds to which the process according to the invention is more particularly applicable are galacol and guetol.

 The aromatic ethers are involved in the process of the invention in salified form. These are preferably salts of the metal elements of group (Ia) of the periodic table or of an ammonium salt.

For the definition of elements, reference is made hereinafter to the Periodic Table of Elements published in the Bulletin of the Chemical Society of
France, No. 1 (1966).

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

 According to the process of the invention, a polar aprotic organic solvent having certain characteristics of polarity and basicity is used; the presence of said solvent for improving the regio-selectivity of the reaction.

 Several imperatives preside over the choice of the organic solvent.

 A first characteristic of the organic solvent is that it is aprotic and stable in the reaction medium.

 By aprotic solvent is meant a solvent which in Lewis's theory has no protons to release.

 Solvents which are not stable in the reaction medium or which are capable of reacting under the reaction conditions are excluded from the present invention.

 According to the invention, a polar organic solvent is used.

 According to the invention, an organic solvent is chosen which has a dielectric constant greater than or equal to 15. The upper limit is not critical. It is preferred to use an organic solvent having a high dielectric constant, preferably between 25 and 75.

 In order to determine whether the organic solvent meets the dielectric constant conditions set out above, reference can be made, inter alia, to the tables of the work: Techniques of Chemistry, U - Organic solvents - p. 536 and following, 3rd edition (1970).

 Another condition governing the choice of the solvent is that it must meet certain characteristics of basicity. Indeed, said solvent must be basic.

To determine whether a solvent meets this requirement, its basicity is assessed by reference to the "donor number". A polar organic solvent is chosen having a donor number greater than 20, preferably greater than or equal to 25. The upper limit is not critical. An organic solvent having a donor number between 25 and 75 is preferably chosen.

With regard to the requirements concerning the basicity of the organic solvent to be used, it will be recalled that the "donor or donor number nimber designated abbreviated DN, gives an indication of the nucleophilic character of the solvent and reveals its ability to give its doublet
In Christian REINHARDT's book, Solvents and Solvent Effects in
Organic Chemistry - VCH p.19 (1988)], we find the definition of "donor number" which is defined as the negative (-bH) of the enthalpy (KcaVmol) of the interaction between the solvent and the pentachlowre of antimony, in a dilute solution of dichloroethane.

 As examples of polar aprotic organic solvents having the above-mentioned basic characteristics, which can be used in the process of the invention, mention may be made more particularly of linear or cyclic carboxamides such as N, N-dimethylacetamide (DMAC). N, N-diethylacetamide, dimethylformamide (DMF), diethylformamide or 1-methyl-2-pyrrolidinone (NMP); dimethylsulfoxide (DMSO) hexamethylphosphoric acid (H M PT); tetramethylurea.

 It is also possible to use a mixture of solvents.

 Among the abovementioned solvents, use is preferably made of linear or cyclic carboxamides.

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

 It is determined in such a way that the concentration of the substrate in the organic solvent is preferably between 1 and 50% by weight and more preferably between 10 and 40%.

 According to the process of the invention, the aromatic ether in salified form and the carbon dioxide are reacted in an organic solvent as defined.

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

 Thus, in the process of the invention, there is a base which can be inorganic or organic.

 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 measured base, in an aqueous medium, at 250 ° C.

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

 It is also possible to use a quaternary ammonium hydroxide.

 As examples of quaternary ammonium hydroxide, preference is given to the use of tetraalkylammonium or trialkylbenzylammonium hydroxides, the identical or different alkyl radicals of which represent a linear or branched alkyl chain having from 1 to 12 carbon atoms, preferably from 1 to 12 carbon atoms. at 6 carbon atoms.

Tetramethylammonium hydroxide is preferably chosen,
Tetraethylammonium hydroxide or tetrabutylammonium hydroxide.

 It is also possible according to the invention to use trialkylbenzylammonium hydroxides and especially trimethylbenzylammonium hydroxide.

 For economic reasons, one chooses from all bases, preferentially sodium or potassium hydroxide.

 The concentration of the basic starting solution is not critical. The alkali metal hydroxide solution used has a concentration generally of between 10 and 50% by weight.

 The amount of base introduced into the reaction medium takes into account the amount necessary to salify the hydroxyl function of the aromatic ether.

 If said compound has salifiable functions other than the hydroxyl group, then the amount of base necessary to salify all salifiable functions is introduced.

 Generally, the amount of base expressed relative to the aromatic ether varies between 90 and 120% of the stoichiometric amount.

 The aromatic ether in salified form is prepared by reacting it with the base at a temperature advantageously between 25 ° C and 100 ° C.

 Before introducing the carbon dioxide, the water formed during the salification reaction is removed by distillation at atmospheric pressure or at a reduced pressure of between 1 mm of mercury and atmospheric pressure or by drying. When there is no more water in the medium, carbon dioxide is introduced.

 The amount of carbon dioxide to be employed expressed by the molar ratio between the carbon dioxide and the aromatic ether varies between 1 and 100, and more preferably between 1 and 2.

 The process of the invention is advantageously carried out at a temperature below 150 ° C., and preferably below 120 ° C. In order to obtain a better selectivity of the reaction, the reaction temperature is chosen between 90 ° C. and 110 ° C.

 It is generally carried out under atmospheric pressure, by bubbling carbon dioxide into the stirred reaction medium.

 It is also possible to conduct the reaction under pressure of carbon dioxide ranging between atmospheric pressure and about 100 bar. A pressure of between 1 and 20 is preferred.

 A preferred embodiment of the invention is to use the solvent, the aromatic ether, the base, to remove the water by distillation and then to introduce the carbon dioxide.

 In a last step, the para-carboxylated aromatic ether is recovered from the reaction medium, in a manner known per se.

 At the end of the reaction, the pH is brought to between 5.0 and 8.0, by addition of 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 unreacted aromatic ether decants. It is removed by separation of the organic and aqueous phases.

 The residual aqueous solution is acidified to an internal pH of 3, preferably of between 1 and 2, by addition of an acidic aqueous solution as previously described in order to precipitate the substituted 4-hydroxybenzoate acid.

 The acid obtained is recovered from the reaction medium according to conventional solid / liquid separation techniques, preferably by filtration.

 The process of the invention provides easy access to 4-hydroxybenzoic acids whose aromatic ring carries at least one ether group, which can be used as intermediates for the production of the corresponding 4-hydroxybenzaldehydes, by reducing the carboxylic function in aldehyde function.

 In order to carry out the reduction of the 4-hydroxybenzoic acid obtained according to the invention to the corresponding aldehyde, it is possible in particular to use the process described in EP-A-0 539 274. The process described consists of carrying out the reduction with hydrogen, in phase. steam and in the presence of a rutheniumtin-type bimetallic catalyst.

 According to the invention, it is thus possible to prepare vanillin and ethyl vanillin by reducing, respectively, p-vanillic acid and 4-hydroxy-3-ethoxybenzoic acid, by carrying out the above-mentioned method.

 The following examples illustrate the invention without limiting it.

In the examples, the yields mentioned correspond to the following definition:
number of moles of 4hydroxy-Omethoxybenzoic acid formed
Yield: RR =
number of moles of sodium galacolate introduced
EXAMPLES
The following is the operating protocol which is repeated in the various examples.

1 - Synthesis of Potassium GaPacolate
62.05 g (0.5 mol) of galacol and 50 ml of toluene are charged to a 1000 ml three-necked flask equipped with a central stirrer, a vigorous column and a 100 ml dropping funnel.

 97.8 g of a 28.6% by weight aqueous solution of potassium hydroxide are poured in at 0 hrs.

 There is formation of a white precipitate suspended in the medium.

 It is heated under reflux: the medium is homogeneous greenish color.

 The water / toluene azeotrope is distilled off. After distilling 91% of the water engaged and formed, the medium is pasty: stirring is difficult.

 Cooled under a stream of nitrogen.

 It is filtered on sintered glass n 4. The precipitate is washed with 50 ml x 2 of anhydrous toluene marketed by Aldrich.

 Dry at constant weight in an oven at 100 ° C. under 1-2 mm of mercury.

 We grind in a mortar.

75.61 g of a fine precipitate of brown color are recovered. The yield is 100
It is stored in a desiccator containing phosphoric anhydride P205-2 Synthesis of sodium guaiacolate
62.09 g (0.5 mol) of guaiacol and 500 ml of toluene are charged to a 1000 ml three-necked flask equipped with a central stirrer, a vigorous column and a 100 ml dropping funnel.

 At 65.2 g of a 30.8% by weight aqueous solution of sodium hydroxide is poured in at room temperature.

 There is formation of a white precipitate suspended in the medium.

 It is heated under reflux. The water / toluene azeotrope is distilled: 13.5 / 86.5% at 84 ° C.

 After distilling the water engaged and formed, the medium is pasty: stirring is difficult.

 Cooled under a stream of nitrogen.

 It is filtered on sintered glass n 4. The precipitate is washed with 50 ml × 2 of anhydrous toluene marketed by Aldrich.

 Dry to constant weight, in an oven at 1000C under 1-2 mm of mercury.

 We grind in a mortar.

 68.18 g of precipitate are recovered in the form of fine white needles. The yield is 93.3%.

 It is stored in a desiccator containing phosphoric anhydride.

3 - Carboxylation of sodium galacolate under pressure of Cg,
Charge in a Burton Corbelin 50 ml reactor in hastelloy B2, equipped with a blade turbine, 2.79 g (19.1 mmol) of anhydrous sodium galacolate, with 20 ml of anhydrous 1-methyl-2-pyrrolidinone. marketed by
Aldrich.

 The reactor is purged with a stream of CO2. There is a slight exotherm.

 The mixture is heated at 100 ° C. for 7 hours while maintaining the CO2 pressure at 20 bar.

 After cooling the reactor to ambient temperature, 20 ml of water are added.

 A solution of 5 N hydrochloric acid is poured until a pH of about 2.0 is reached. There is precipitation.

 Acetonitrile is added to make the reaction medium homogeneous.

High performance liquid chromatography is used: Lichro column
Cart RP 18-5 μm, 250/4 mm marketed by Merck - eluent: 800 ml
H2O / 200 ml CH3CN / 3.5 ml H3PO4 - flow rate: 1 ml.mn-1 - UV detection 240 pm ambient temperature.

4 - Carboxylation of potassium guaiacolate under a stream of CO2 at atmospheric pressure
In a 100 ml tricolor equipped with a glass impeller, a CO2 inlet plunger tube and an ascending straight refrigerant, 5.33011 g (32.7 mmol) dry anhydrous potassium gaiacolate was charged. with 30 ml of anhydrous 1-methyl-2-pyrrolidinone marketed by Aldrich.

 The mixture is heated to 100 ° C. under a flow of CO2 having a flow rate of approximately 3.0 I.h -1 for 7 hours.

 It is rapidly cooled to room temperature by an ice-water bath.

20 ml of water are added.

 A solution of 5 N hydrochloric acid is poured until a pH of about 2.0 is reached. There is precipitation.

 Acetonitrile is added to make the reaction medium homogeneous.

High performance liquid chromatography is used: Lichro column
Cart RP 18 - 5 μm, 250/4 mm marketed by Merck - eluent: 800 ml
H20 / 200 ml CH3CN / 3.5 ml H3PO4 - flow rate: 1 ml.mn-1 - UV detection 240 m room temperature.

Examples 1 to 6
Comparative test
A series of tests is carried out by reproducing the operating protocol given above, using 1-methyl-2-pyrrolidinone, polar and basic solvent and by varying the reaction temperature, the pressure and the nature of the starting galacolate.

 The operating conditions and the results obtained are recorded in Table (I).

Table (I)

Ref. <SEP> Nature <SEP> of <SEP> solvent <SEP> Pressure <SEP> Temperature <SEP> Guaiacolate <SEP> Time <SEP> RR <SEP> para <SEP> RR <SEP> ortho <SEP> Selectivity
<tb> ex. <SEP> (bar) <SEP> (C) <SEP> (h) <SEP> (%) <SEP> (%) <SEP> p / p + o
<tb> (%)
<tb> 1 <SEP> 1-methyl-2- <SEP> 1 <SEP> 100 <SEP> Na <SEP> 6 <SEP> h <SEP> 50 <SEP> 2.6 <SEP> 0.6 <SEP> 81
<tb> pyrrolidinone
<tb> 2 <SEP> 1-methyl-2- <SEP> 20 <SEP> 100 <SEP> Na <SEP> 7 <SEP> h <SEP> 10 <SEP> 31.6 <SEP> 6.0 <SEP> 84
<tb> pyrrolidinone
<tb> 3 <SEP> 1-methyl-2- <SEP> 1 <SEP> 137 <SEP> Na <SEP> 6 <SEP> h <SEP> 42 <SEP> 6.7 <SEP> 3.7 <SEP> 64
<tb> pyrrolidinone
<tb> 4 <SEP> 1-methyl-2 <SEP> 1 <SEP> 100 <SEP> K <SEP> 7 <SEP> h <SEP> 25 <SEP> 20.5 <SE> 2.5 <SEP > 89
<tb> pyrrolidinone
<tb> 5 <SEP> 1-methyl-2- <SEP> 20 <SEP> 100 <SEP> K <SEP> 6 <SEP> h <SEP> 57 <SEP> 7.6 <SEP> 0.8 <SEP> 90
<tb> pyrrolidinone
<tb> 6 <SEP> 1-methyl-2- <SEP> 1 <SEP> 125 <SEP> K <SEP> 7 <SEP> h <SEP> 40 <SEP> 9.3 <SE> 2,2 <SEP> 81
<tb> pyrrolidinone
<tb> a <SEP> 1-methyl-2- <SEP> 20 <SEP> 170 <SEP> Na <SEP> 6 <SEP> h <SEP> 32 <SEP> 1.9 <SEP> 39.2 <SEP> 5
<tb> pyrrolidinone
<Tb>
It is noted that a reaction temperature that is too high reduces the selectivity of the reaction.

Exemptions 7 and 8
Comoative tests b to d
In both Examples 7 and 8 which follow, the carboxylation reaction of guaiacol is carried out in polar and basic aprotic solvents, such as N, N-dimethylformamide (Example 7) and N, N-dimethylacetamide (Example 8).

Comparative examples of embodiments of the carboxylation of guaiacol are given in various solvents which are not suitable for the invention:
protic solvent such as butanol (test b),
aprotic, slightly polar and slightly basic solvent such as toluene (test c),
aprotic, slightly polar and basic solvent such as pyridine (test d).

 The operating conditions and the results obtained are recorded in Table (II).

Table (II)

Ref. <SEP> Nature <SEP> of <SEP> solvent <SEP> Pressure <SEP> Temperature <SEP> Gaiacolate <SEP> Time <SEP> RR <SEP> para <SEP> RR <SEP> ortho <SEP> Selectivity
<tb> ex. <SEP> (bar) <SEP> (C) <SEP> (h) <SEP> (%) <SEP> (%) <SEP> p / p + o
<tb> (%)
<tb> 7 <SEP> N, N-dimethylformamide <SEP> 20 <SEP> 100 <SEP> Na <SEP> 7 <SEP> h <SEP> 00 <SEP> 12.0 <SEP> 1.9 <SEP > 86
<tb> 8 <SEP> N, N-dimethylacetamide <SEP> 20 <SEP> 100 <SEP> Na <SEP> 7 <SEP> h <SEP> 00 <SEP> 27.5 <SEP> 5.1 <SEP > 84
<tb> b <SEP> 1-butanol <SEP> 20 <SEP> 100 <SEP> Na <SEP> 7 <SEP> h <SEP> 00 <SEP> 7.5 <SEP> 0 <SEP> 0
<tb> c <SEP> toluene <SEP> 20 <SEP> 100 <SEP> Na <SEP> 7 <SEP> h <SEP> 00 <SEP> 4.4 <SEP> 8.8 <SEP> 33
<tb> d <SEP> pyridine <SEP> 20 <SEP> 100 <SEP> Na <SEP> 7 <SEP> h <SEP> 00 <SEP> 1.2 <SEP> 9.6 <SEP> 11
<Tb>
It appears from the comparison of the results obtained that the selectivity of the carboxylation reaction in para is very good under the conditions of the invention but very bad in the comparative tests.

Claims (25)

A process for carboxylating an aromatic ether which comprises reacting said aromatic ether in salified form with carbon dioxide, said process being characterized by conducting the reaction at a temperature below 150 ° C, in a polar and basic aprotic organic solvent. 2- Process according to claim 1 characterized in that the aromatic ether has the general formula (I):

 in which:  - A symbolizes the remainder of a cycle forming all or part of a system  carbocyclic aromatic, monocyclic or polycyclic, system  comprising at least one OR 'group: said cyclic residue may carry a  or more substituents,  R represents a hydrogen atom or one or more substituents,  identical or different,  R 'represents a hydrocarbon radical having from 1 to 24 atoms of  carbon, which may be a saturated or unsaturated acyclic aliphatic radical,  linear or branched; a saturated, unsaturated cycloaliphatic radical or  aromatic, monocyclic or polycyclic; a saturated aliphatic radical or  unsaturated, linear or branched, carrying a cyclic substituent,  n is a number less than or equal to 3. 3- Process according to one of claims 1 and 2 characterized in that the aromatic ether has the general formula (I) wherein R 'represents: - a saturated or unsaturated, linear or branched, acyclic aliphatic radical of preferably a linear or branched alkyl radical having from 1 to 12 carbon atoms, preferably from 1 to 6 carbon atoms: the hydrocarbon chain may optionally be interrupted by a heteroatom, a functional group and a carrier of a substituent, a linear or branched, saturated or unsaturated, acyclic aliphatic radical bearing an optionally substituted cyclic substituent: said acyclic radical may be linked to the ring by a valency bond, a heteroatom or a functional group, a saturated carbocyclic radical or comprising 1 or 2 unsaturations in the ring, generally having 3 to 8 carbon atoms, preferably 6 carbon atoms in the ring; said cycle being substitutable. an aromatic carbocyclic radical, preferably monocyclic, generally having at least 4 carbon atoms, preferably 6 carbon atoms in the ring; said cycle being substitutable. 4. Process according to claim 1, characterized in that the aromatic ether has the general formula (I) in which R 'represents a linear or branched alkyl radical having from 1 to 4 carbon atoms, preferably a methyl radical or a phenyl radical. 5. Process according to one of Claims 1 to 4, characterized in that the aromatic ether corresponds to the general formula (I) in which the residue A represents the residue of a monocyclic aromatic carbocyclic compound having at least 4 atoms. of carbon and preferably 6 carbon atoms or the remainder of a polycyclic carbocyclic compound: the residue A may carry one or more substituents on the aromatic ring. 6. Process according to one of claims 1 to 5 characterized in that the aromatic ether corresponds to formula (la):

 in which:  n is a number less than or equal to 3, preferably equal to 0 or 1,  the radical R 'represents a linear or branched alkyl radical having from 1 to  6 carbon atoms, preferably 1 to 4 carbon atoms, such as  methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, tert-butyl  or phenyl,  the radical or radicals R represent one of the following atoms or groups:  a hydrogen atom,  . a linear or branched alkyl radical having from 1 to 6 carbon atoms  carbon, preferably 1 to 4 carbon atoms, such as methyl,  ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, tert-butyl,  . a linear or branched alkoxy radical having from 1 to 6 carbon atoms  carbon, preferably from 1 to 4 carbon atoms, such as  radicals methoxy, ethoxy, propoxy, isopropoxy, butoxy, isobutoxy, dry  butoxy, tert-butoxy,  a halogen atom, preferably a fluorine, chlorine or  bromine, a trifluoromethyl radical.  the radicals R 'and R and the two successive atoms of the benzene ring  can form between them, a ring having from 5 to 7 atoms, comprising  possibly another heteroatom. 7- Process according to claim 6 characterized in that the aromatic ether has the formula (la) in which n is greater than or equal to 1, the radicals R 'and R and the two successive atoms of the benzene ring can be linked between them with an alkylene, alkenylene or alkenylidene radical having 2 to 4 carbon atoms to form a saturated, unsaturated or aromatic heterocycle having 5 to 7 carbon atoms in which one or more carbon atoms may be replaced by a heteroatom, preferably oxygen: the R 'and R radicals preferably forming a methylene dioxy or ethylene dioxy radical. 8- Method according to one of claims 1 and 7 characterized in that the aromatic ether has the formula (la) in which n is equal to 0, the radical R 'represents an alkoxy radical. 9 - Process according to claim 1 and 2 characterized in that the aromatic ether is galacol or guétol. 10 - Process according to one of claims 1 to 9 characterized in that the polar organic solvent has a dielectric constant greater than or equal to 15, preferably between 25 and 75.  II - Process according to one of claims 1 to 10 characterized in that the polar organic solvent has a donor number greater than 20, preferably greater than or equal to 25, preferably between 25 and 75. 12 - Process according to one of claims 1 to 11 characterized in that the polar organic solvent is selected from linear or cyclic carboxamides; dimethylsulfoxide (DMSO); hexamethylphosphoric acid (HMPT); tetramethylurea. 13 - Process according to claim 12, characterized in that the polar organic solvent is chosen from N, N-dimethylacetamide (DMAC), N, N'-ethylacetamide, dimethylformamide (DMF), diethylformamide or 1-methyl-2-pyrrolidinone ( NMP). 14 - Method according to one of claims 10 to 13 characterized in that the amount of solvent is determined such that the concentration of the substrate in the organic solvent is preferably between 1 and 50% by weight and more preferably between 10 and 40%. 15 - Process according to one of claims 1 to 14 characterized in that the aromatic ether is in salified form, preferably in the form of the metal elements of the group (la) of the periodic table, preferably salts of sodium or potassium or an ammonium salt. 16 - Process according to claim 15, characterized in that the aromatic ether in salified form is prepared by reacting said compound with a base, preferably sodium or potassium hydroxide or a quaternary ammonium hydroxide, and then eliminating the water formed during salification. 17 - Process according to claim 16 characterized in that the amount of base expressed relative to the aromatic ether varies between 90 and 120% of the stoichiometric amount. 18 - Method according to one of claims 16 and 17 characterized in that the temperature of the salification reaction is between 250C and 100 "C. 19 - Process according to one of claims 1 to 18, characterized in that the amount of carbon dioxide to be implemented expressed by the molar ratio between carbon dioxide and the aromatic ether varies between 1 and 100, and more preferably between 1 and 2. 20 - Process according to one of claims 1 to 19 characterized in that the temperature at which the carboxylation takes place is an internal temperature at 120 "C, preferably between 90 C and 110 C. 21 - Method according to one of claims 1 to 20 characterized in that the carbon dioxide pressure varies from atmospheric pressure and about 100 bar, preferably between 1 and 20 bar. 22 - Process according to one of claims 1 to 21 characterized in that it implements the solvent, the aromatic ether, the base, which is removed water by distillation and that one introduces carbon dioxide. 23 - Method according to one of claims 1 to 22, characterized in that the carboxylated aromatic ether is recovered in para, from the reaction medium. 24. Use of 4-hydroxybenzoic acids whose aromatic ring carries at least one ether group obtained according to the method described in one of claims 1 to 23, as intermediates for the production of the 4 corresponding hydroxybenzaldehydes. 25- Use of p-vanillic acid and 4-hydroxy-3-ethoxybenzoic acid obtained according to the process described in one of claims 1 to 23, as intermediates for the manufacture respectively of vanillin and ethyl vanillin . 26- Use according to one of claims 24 and 25 characterized in that the reduction of the carboxylic function in aldehyde function is carried out by hydrogen, in the vapor phase and in the presence of a bimetallic catalyst ruthenium / tin type.