EP0882005A1

EP0882005A1 - Phenol compound hydroxylation method

Info

Publication number: EP0882005A1
Application number: EP97904488A
Authority: EP
Inventors: Michel Costantini; Laurent Gilbert; Michel Spagnol
Original assignee: Rhodia Chimie SAS
Current assignee: Rhodia Chimie SAS
Priority date: 1996-02-09
Filing date: 1997-02-05
Publication date: 1998-12-09
Also published as: FR2744720B1; US6040484A; FR2744720A1; CN1210512A; JP2000509368A; WO1997029066A1

Abstract

A phenol compound hydroxylation method, specifically a phenol and phenol ether hydroxylation method using hydrogen peroxide, is disclosed. According to the phenol compound hydroxylation method using hydrogen peroxide, the reaction is performed in the presence of an effective amount of at least one bismuth or rare-earth salt of trifluoromethane sulphonic acid.

Description

PROCESS FOR HYDROXYLATION OF PHENOLIC COMPOUNDS

The subject of the present invention is a process for the hydroxylation of phenolic compounds and more particularly, a process for the hydroxylation of phenols and phenol ethers, with hydrogen peroxide.

Numerous processes for the hydroxylation of phenols are described in the state of the art.

Let us cite, among others, patent FR-A 2071 464 which relates to a very important industrial process for the hydroxylation of phenols and of phenol ethers.

Said method consists in carrying out the hydroxylation, with hydrogen peroxide, in the presence of a strong acid. Among these strong acids, sulfuric acid, paratoluene sulfonic acid, perchloric acid are the most used.

The hydroxylation of phenol carried out under the conditions described results in a mixture of hydroquinone and pyrocatechin, with predominance of the latter since the hydroquinone / pyrocatechin ratio most often varies between 0.3 and 0.7.

According to FR-A 2 266 683, an improvement has been proposed to this process which consists in carrying out the hydroxylation, in the presence of a ketone. This results in an improvement in the yield of the reaction with hydroquinone and pyrocatechin.

However, all the examples described lead to a greater quantity of pyrocatechol compared to that of hydroquinone.

The known methods therefore mainly lead to pyrocatechol.

It turns out that to meet the fluctuating market demand, it is important to have an industrial process allowing either to increase the production of hydroquinone formed compared to pyrocatechol, or to favor the quantity of pyrocatechin formed.

The Applicant has proposed in FR-A 2,667,598, a process making it possible to increase the quantity of hydroquinone formed relative to the quantity of pyrocatechin and to obtain, in its preferred variant, more hydroquinone than pyrocatechin.

Said method consists in carrying out the hydroxylation of phenol in the presence of an effective amount of a strong acid, said method being characterized in that the reaction is carried out in the presence of a ketone compound chosen from benzophenone and benzophenones of which the hydrogen atoms of the aromatic ring can be substituted by an electron donor group.

In accordance with the process described in FR-A 2,667,598, the presence of the ketone compound as selected, during the hydroxylation of the phenol plays on the regioselectivity of the reaction and of the hydroquinone / pyrocatechin ratios varying between 1.0 and 1.13 are advantageously obtained.

Continuing her research, the Applicant has found another process using original catalysis and making it possible to obtain good yields of diphenols and to control the selectivity of the reaction.

More specifically, the subject of the present invention is a process for the hydroxylation of a phenolic compound by hydrogen peroxide, said process being characterized in that the reaction is carried out in the presence of an effective amount of at least one rare earth or bismuth triflate.

A first variant of the process of the invention is to carry out the reaction in the presence of an organic solvent.

A second variant of the process of the invention consists in using a ketone compound as co-catalyst.

A third variant of the process of the invention is to use both the co-catalyst and the organic solvent.

According to the process of the invention, the hydroxylation of a phenolic compound is carried out in the presence of a catalyst chosen from rare earth or bismuth triflates.

By "rare earth or bismuth triflate" is meant a rare earth or bismuth salt of trifluoromethane sulfonic acid.

By "rare earth" is meant the lanthanides having an atomic number from 57 to 71 and yttrium as well as scandium. The present invention applies to phenolic compounds of general formula (I):

in said formula (I):

- Ri, R2, R3 and R4, identical or different, represent a hydrogen atom or any substituent,

- two groups Ri and R2 and / or R3 and R4 placed on two vicinal carbon atoms can form together and with the carbon atoms which carry them a ring,

- R 'represents a hydrogen atom or a hydrocarbon radical having from 1 to 24 carbon atoms, which can be a saturated acyclic aliphatic radical or unsaturated, linear or branched; a saturated or unsaturated, monocyclic or polycyclic cycloaliphatic radical; a saturated or unsaturated, linear or branched aliphatic radical, carrying a cyclic substituent.

By cyclic substituent is meant a saturated, unsaturated or aromatic carbocycle having, generally, from 4 to 7 carbon atoms, and preferably 6 carbon atoms.

The process of the invention applies to any phenolic compound corresponding to the general formula (I) and, more particularly, to the phenolic compounds of formula (I) in which R 'represents: a hydrogen atom

. a linear or branched alkyl radical having from 1 to 6 carbon atoms, preferably from 1 to 4 carbon atoms. and more particularly a methyl or ethyl radical,. a cyclohexyl radical,. a benzyl radical.

The phenolic compound of formula (I) can carry one or more substituents R-j, R2. R3 and R4. Examples of substituents are given below, but this list is in no way limiting. Any substituent can be present on the cycle as long as it does not interfere with the desired product.

The process of the invention applies more preferably to the phenolic compounds of formula (I) in which:

- R-j, R2, R3 and R4, identical or different, represent RQ, one of the following 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, sec-butyl, tert-butyl,

. a linear or branched alkenyl radical having from 2 to 6 carbon atoms, preferably from 2 to 4 carbon atoms, such as vinyl, allyl,

. 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, radicals. an acyl group having from 2 to 6 carbon atoms,. a radical of formula:

-R5-OH

-R5-COOR6

-R5-X in said formulas, R5 represents a valence bond or a divalent hydrocarbon radical, linear or branched, saturated or unsaturated, having from 1 to 6 carbon atoms such as, for example, methylene, ethylene, propylene, isopropylene, isopropylidene; BQ represents a hydrogen atom or a linear or branched alkyl radical having from 1 to 6 carbon atoms; X symbolizes a halogen atom, preferably a chlorine, bromine or fluorine atom.

- R-j, R2, R3 and R4, identical or different, represent R7, one of the following more complex radicals:

. a saturated or unsaturated carbocyclic radical having from 4 to 7 carbon atoms, preferably a cyclohexyl radical,. a radical of formula

in which R5 represents a valential bond or a divalent, linear or branched, saturated or unsaturated hydrocarbon radical having from 1 to 6 carbon atoms such as, for example, methylene, ethylene, propylene, isopropylene, isopropylidene and RQ having the meaning given above and m is an integer from 0 to 4,. a radical - R5 - A - Rg in which R5 has the meaning given above, Rg represents a linear or branched alkyl radical having

1 to 6 carbon atoms or a radical of formula

and A symbolizes one of the following groups: ^Q

- O -, - COO -, - OCOO -, - S0 ₉ -, - C0 - N

R9 in these formulas, Rg represents a hydrogen atom or an alkyl radical having from 1 to 4 carbon atoms, a cyclohexyl or phenyl radical.

- two groups Ri and R2 and / or R3 and R4 placed on two vicinal carbon atoms can form together and with the carbon atoms which carry them an unsaturated or aromatic carbocycle having from 4 to 7 carbon atoms and, preferably, 6 carbon atoms,

Among the compounds of formula (I), use is more particularly made of those corresponding to formula (I) in which: - R 'represents a hydrogen atom - Rj, R2, R3 and R4, identical or different, represent one of the following groups:

. a hydrogen atom,

. an alkyl radical, linear or branched having from 1 to 4 carbon atoms ,. . a linear or branched aikoxy radical having from 1 to 4 carbon atoms,. a hydroxyl group,. a halogen atom,. a -CFg group. a cyclohexyl radical,. a phenyl radical,

- two groups R- | and R2 and / or R3 and R4 placed on two vicinal carbon atoms can form together and with the carbon atoms which carry them a benzene ring.

Even more preferably, the compounds of formula (I) are chosen in which R ′ represents a hydrogen atom and one of the radicals R- | , R2, R3 and R4 represents a hydroxyl group, a methyl radical or a methoxy radical and the other 3 represent a hydrogen atom.

By way of illustration of phenolic compounds of formula (I) capable of being used in the process of the invention, there may be mentioned more particularly:

- those corresponding to formula (I) in which R-j, R2, R3 and R4 represent a hydrogen atom, such as phenol or anisole,

- those corresponding to formula (I) with a substituent on the benzene ring, such as o-cresol, m-cresol, p-cresol, 2-methoxyphenol, 2-ethylphenol, 3-ethylphenol, 2-propylphenol, 2-sec-butylphenol, 2-tert-butylphenol, 3-tert-butylphenol, 4-tert-butylphenol, 2-methoxyphenol, 3-methoxyphenol, 4-methoxyphenol, salicylate methyl, 2-chlorophenol, 3-chlorophenol, 4-chlorophenol,

- Those corresponding to formula (I) with two substituents on the benzene ring, such as 2,3-dimethylphenol, 2,5-dimethylphόnol, 2,6-dimethylphenol,

3,5-dimethyphenol, 2,3-dichlorophenol, 2,5-dichlorophenol, 2,6-dichlorophenol, 3,5-dichlorophenol, 2,6-ditert-butylphenol, 3,5-ditert- butylphenol,

- those corresponding to formula (I) with three substituents on the benzene ring, such as 2,3,5-trimethylphenol, 2,3,6-trimethylphenol, 2,3,5-trichlorophenol, 2,3 , 6-trichlorophenol,

- those corresponding to formula (I) in which Ri and R2 form a benzene ring, such as 1-hydroxynaphthalene, - those corresponding to formula (I) in which R- | represents a radical of type R7, such as 2-phenoxyphenol, 3-phenoxyphenol.

Among the phenolic compounds of formula (I) which may be used in the process of the invention, there may be mentioned, without limitation, phenol, o-cresol, m-cresol, p-cresol.

Regarding the rare earth triflate used as a catalyst, it is more particularly a rare earth chosen from lanthanides, yttrium scandium and their mixtures, preferably lanthanides such as lanthanum, cerium, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium and lutetium and their mixtures.

It is possible to use a mixture of ceric rare earths including the elements La, Ce, Pr, Nd, and / or of yttric rare earths comprising Y, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu. In the process of the invention, the following rare earths are more particularly envisaged: lanthanum, ytterbium, lutetium and / or scandium.

Rare earth triflates are known products which are described in the literature, in particular in US-A-3,615,169. They are generally obtained by reaction of rare earth oxide and trifluoromethanesulfonic acid. According to a variant of the process of the invention, the catalyst is advantageously prepared in situ by reacting trifluoromethanesulfonic acid and a source of rare earth.

The nature of the compounds providing the various elements used for the preparation of the catalyst of the invention is not critical. The rare earth elements can be provided in the form of a metal or in the form of an inorganic derivative such as an oxide or a hydroxide. It is possible to use a mineral salt preferably, nitrate, sulfate, oxysulfate, halide, oxyhalide, silicate, carbonate, orthophosphate or an organic derivative, preferably oxalate, acetylacetonate; alcoholate and even more preferably methylate or ethylate; carboxylate and even more preferably acetate.

Preferably, nitrates, chlorides and / or sulfates of rare earths are used, such as cerium, lanthanum, praseodymium, neodymium, samarium, gadolinium, rytterbium and ryttrium. As examples of compounds capable of being used for the preparation of the catalysts of the invention, there may be mentioned in particular:. yttrium (III) chloride,. lanthanum chloride (III), . neodymium (III) chloride,

. samarium chloride (III),

. ytterbium (III) chloride.

The bismuth salts of trifiic acid described in patent application PCT / FR96 / 01488 can also be used in the process of the invention. A method of preparing bismuth triflate is given below.

According to the method of the invention, it is possible according to a variant of the invention to use a polar aprotic organic solvent having certain characteristics of polarity and basicity; the presence of said solvent being able to improve the yield and the regioselectivity of the reaction.

A first class of solvents suitable for the invention are polar and not very basic organic solvents, that is to say having a polarity such that its dielectric constant is greater than or equal to 20 and a basicity such that it has a "number donor "less than 25. Another type of solvent also suitable for the invention are organic solvents which are not very polar but basic, that is to say having a polarity such that its dielectric constant is less than about 20 and a basicity such that 'it has a "donor number" greater than or equal to 15 and less than 25.

Several requirements govern the choice of 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 theory has no protons to release.

Excluded from the present invention are solvents which are not stable in the reaction medium and which degrade either by oxidation or by hydrolysis. As examples of reaction solvents which are not suitable for the invention, mention may be made of ester type solvents derived from carboxylic acids such as in particular methyl or ethyl acetate, methyl or ethyl phthalate, methyl benzoate etc. The organic solvents suitable for carrying out the process of the invention must meet certain requirements in terms of their polarity and their basicity which is characterized by the donor number.

A first class of organic solvents which are entirely suitable for carrying out the process of the invention are polar and not very basic organic solvents.

In accordance with the invention, an organic solvent is chosen which has a dielectric constant greater than or equal to 20. The upper bound does not is not critical. It is preferred to use an organic solvent having a high dielectric constant, preferably between 25 and 75.

The organic solvent having the aforementioned polarity characteristics must also satisfy certain basicity conditions. Indeed, said solvent should not be too 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 less than 25, preferably less than or equal to 20. The lower limit has no critical character. An organic solvent preferably having a donor number between 2 and 17 is chosen.

With regard to the other class of solvents claimed, the characteristics of said solvents are defined below.

The solvents belonging to this category are organic solvents which are not very polar but basic. An organic solvent is chosen in accordance with the invention which has a dielectric constant of less than about 20. The lower limit has no critical character. It is preferred to use an organic solvent having a low dielectric constant, preferably between 2 and 15.

As regards its basicity, it must be such that it has a "donor number" greater than or equal to 15 and less than 25. An organic solvent preferably having a donor number between 15 and 25 is chosen.

In order to determine whether the organic solvent meets the conditions of dielectric constant set out above, one can refer, among others, to the tables of the work: Techniques of Chemistry, H - Organic solvents - p. 536 and following, ^3rd edition (1970).

With regard to the requirements concerning the basicity of the organic solvent to be used, reference is made to the definition of "donor number" given previously.

As examples of polar, aprotic organic solvents which meet the aforementioned basicity characteristics, which can be used in the process of the invention, there may be mentioned more particularly:

- nitro compounds such as nitromethane, nitroethane, 1-nitropropane, 2-nitropropane or their mixtures, nitrobenzene,

- alphatic or aromatic nitriles such as acetonitrile, propionitrile, butanenitrile, isobutanenitrile, benzonitrile, benzyl cyanide,

- tetramethylene sultone (sulfolane),

- propylene carbonate.

It is also possible to use a mixture of solvents. Among the abovementioned solvents, acetonitrile is preferably used.

As regards the other class of solvents claimed, examples of slightly polar and basic aprotic solvents which can be used in the process of the invention are given below:

- aliphatic, cycloaliphatic or aromatic ether-oxides and, more particularly, diethyl ether, dipropyl ether, diisopropyl ether, dibutyl ether, methyltertiobutyl ether, dipentyl ether, diisopentyl oxide, ethylene glycol dimethyl ether (or 1,2-dimethoxyethane), diethylene glycol dimethyl ether (or 1,5-dimethoxy-3-oxapentane), dioxane, tetrahydrofuran,

- neutral phosphoric esters such as, in particular, tri-methyl phosphate, triethyl phosphate, butyl phosphate, triisobutyl phosphate, tripentyl phosphate, - ethylene carbonate.

It is also possible to use a mixture of solvents.

According to another variant of the process of the invention, the hydroxylation of the phenolic compound is carried out, in the presence of a ketone compound and more particularly those corresponding to formula (II):

R _a - CO - X - R _b (II)

in said formula (II):

- R and R _b , identical or different, represent hydrocarbon radicals having from 1 to 30 carbon atoms or together form a divalent radical, optionally substituted by one or more halogen atoms or functional groups stable under the conditions of the reaction,

- X represents a valence bond, a group -CO-, a group -CHOH or a group - (R) - _n representing an alkylene group preferably having from 1 to 4 carbon atoms and n is an integer chosen between 1 and 16.

In formula (II), R and R ^ more particularly represent:

- linear or branched alkyl radicals,

- linear or branched alkenyl radicals,

- cycloalkyl or cycloalkenyl radicals containing from 4 to 6 carbon atoms,

- mono- or polycyclic aryl radicals; in the latter case, the cycles forming between them an ortho- or ortho- and pericondensed system or being linked together by a valential bond, - arylalkyl or arylacenyl radicals,

- R _a and R _D can together form an alkylene or alkenylene radical containing from 3 to 5 carbon atoms, optionally substituted by an alkyl radical with low carbon condensation or by a cycloalkyl or cycloalkenyl radical having 4 to 6 carbon atoms; 2 to 4 carbon atoms of the alkylene or alkenylene radicals which may be part of one or two benzene rings optionally substituted by 1 to 4 hydroxyl and / or alkyl and / or aikoxy groups with low carbon condensation.

In the following description of the invention, the term “low carbon alkyl group” means a linear or branched alkyl group generally having from 1 to 4 carbon atoms.

The abovementioned hydrocarbon radicals can be substituted by 1 or more, preferably 1 to 4, low carbon condensation alkyl groups or functional groups such as hydroxyl groups, low carbon condensation aikoxy, hydroxycarbonyls, alkyloxycarbonyls comprising from 1 to 4 carbon atoms in the alkyl group, a nitrile group, -SOgH, nitro or by one or more halogen atoms, and in particular of chlorine and bromine. Preferably, R _a and R _D more particularly represent:

- linear or branched alkyl radicals having from 1 to 10 carbon atoms, - linear or branched alkenyl radicals having from 2 to 10 carbon atoms,

- cycloalkyl or cycloalkenyl radicals containing from 4 to 6 carbon atoms,

- phenyl radicals optionally substituted with 1 to 4 alkyl and / or hydroxyl and / or aikoxy groups,

- phenylalkyl or phenylacenyl radicals containing 1 (or 2) to 10 carbon atoms in the aliphatic part, and more particularly still from 1 (or 2) to 5 carbon atoms in the aliphatic part,

- R and Ru can together form an alkylene or alkenylene radical containing 3 to 5 carbon atoms, optionally substituted by 1 to 4 alkyl radicals with low carbon condensation.

As specific examples of ketones which can be used in the process of the invention, there may be mentioned, more particularly:

- acetone, - butanone-2

- methylisopropylketone

- pivalone

- pentanone-2 - pentanone-3

- 4-methyl-pentanone-2

- 3,3-dimethyl-butanone-2

- hexanone-2 - hexanone-3

- heptanone-2

- heptanone-4

- octanone-2

- octanone-3 - nonanone-2

- nonanone-5

- pentadecanone-8

- 2-methyl-hexanone-3

- 5-methyl hexanone-2 - 5-methyl hexanone-3

- 2,4-dimethyl-pentanone-3

- 5-methyl heptanone-3

- methylvinylketone

- mesityl oxide - pentene-1 one-3

- pentene-3 one-2

- hexene-5 one-2

- 5-methyl-hexene-3 one-2

- 6-methyl-5-heptene one-2 - diacetyl

- diacetone-aicool

- acetolne

- butanedione-2,3

- pentanedione-2,4 - hexanedione-2,5

- dicyclohexylketone

- methylcyclohexylketone

- acetophenone

- n-propiophenone - n-butyrophenone

- isobutyrophenone

- n-valerophenone

- 2-methyl acetophenone - 2,4-dimethyl acetophenone

- phenylvinylketone

- benzophenone

- 2-methyl benzophenone - 2,4-dimethyl benzophenone

- ladimethyl-4,4 'benzophenone

- ladimethyl-2,2'benzophenone

- ladimethoxy-4,4'benzophenone

- 4-hydroxy benzophenone - 4-dihydroxy benzophenone

- 4-benzoyl biphenyl

- ia benzoïne

- 4,4 'dihydroxy benzoin

- 2,4-dimethyl benzoin - 4,4-dimethyl benzoin

- 4,4 'dimethoxy benzoin

- difluoro-4,4'benzoin

- benzoin α-methoxy

- α-ethoxy benzoin - deoxybenzoin

- 4-hydroxy deoxybenzoin

- 4-methyl deoxybenzoin

- 4-methoxy deoxybenzoin

- 4,4 'dimethoxy deoxybenzoin - 4,4' difluoro deoxybenzoin

- β-phenylpropiophenone

- dibenzylketone

- δ-phenylvalerophenone

- diphenyl-1,1 propanone-2 - diphenyl-1,3 propanone

- benzalacetone

- benzalacetophenone

- benzile

- cyclopentanone - 2-methyl cyclopentanone

- cyclohexanone

- 2-methyl cyclohexanone

- tetramethyl-3,3,5,5 cyclohexanone - cyclopentene-2 one

- cyclohexene-2 one

- α-isophorone

- β-isophorone - cyclohexenyl-cyclohexanone

- α-indanone

- β-indanone

- α-tetralone

- fluorenone Thus, use is made, in particular, of ketone compounds of the dialkylketone type corresponding to formula (II) in which R _a and Rt represent a linear or branched alkyl radical having from 1 to 8 carbon atoms and to alkylphenones that is to say R _a represents a linear or branched alkyl radical having from 1 to 6 carbon atoms and Rb represents a phenyl radical. As more specific examples of dialkylketones and alkylphenones, mention may be made of pentanones, acetophenone and n-valerophenone.

Among all the ketone compounds corresponding to formula (II), particular use is made of ketone compounds corresponding to the following formula (IIa):

^{© O} in said formula (Ha):

- R and R _{d, which are} identical or different, represent a hydrogen atom or a substituent, preferably an electron donor group,

- n ₁ , n "identical or different is a number equal to 0, 1, 2 or 3, - optionally the two carbon atoms located in position a with respect to the two carbon atoms carrying the group -CO can be linked together by a valential bond or by a group -CHg- thus forming a ketone cycle which can be saturated but also unsaturated.

The substituent is chosen so that it does not react under the acidity conditions of the invention. It is preferably an electron donor group.

The term “electron donor group” is understood to mean a group as defined by HC BROWN in the work of Jerry MARCH - Advanced Organic Chemistry, chapter 9, pages 243 and 244 (1985). Examples of substituents which are very suitable for the invention are the following: - linear or branched alkyl radicals having from 1 to 4 carbon atoms,

- the phenyl radical,

- the aikoxy Rio - O radicals in which R-J O represents a linear or branched alkyl radical having from 1 to 4 carbon atoms or the phenyl radical, - the hydroxyl group,

- the fluorine atom.

As examples of ketone compounds which are particularly suitable for the invention, mention may very particularly be made of ketone compounds corresponding to the general formula (Ha) in which R and R _d , which are identical or different, represent a hydrogen atom or a substituent as mentioned above , preferably in position 4,4 'and n ₁ , n ₂ identical or different are equal to 0 or 1. Preferably, ketone compounds corresponding to the formula (IIa) are used in which R _Q and R ^, which are identical or different, represent a hydrogen atom; a methyl, ethyl, tert-butyl, phenyl radical; a methoxy or ethoxy radical; a hydroxyl group, preferably in the 3.3 ′ or 4.4 ′ position. As specific examples of ketones which can be used in the process of the invention, there may be mentioned more particularly:

- benzophenone

- 2-methyl benzophenone - 2,4-dimethyl benzophenone

- 4,4 'dimethyl benzophenone

- 2,2-dimethyl benzophenone

- 4,4 'dimethoxy benzophenone

- 4-hydroxy benzophenone - 4-dihydroxy benzophenone

- 4-benzoyl biphenyl

In accordance with the process of the invention, hydrogen peroxide, a catalyst optionally an organic solvent and / or a ketone compound is used during the hydroxylation process of the phenolic compound of formula (I).

The hydrogen peroxide used according to the invention can be in the form of an aqueous solution or an organic solution.

Preferably, aqueous solutions being commercially more readily available are used. The concentration of the aqueous hydrogen peroxide solution, although not critical in itself, is chosen so as to introduce as little water as possible into the reaction medium. Generally an aqueous solution of peroxide is used hydrogen at least 20% by weight of H2O2 and preferably around 70%.

The amount of hydrogen peroxide can range up to 1 mole of H2O2 per 1 mole of phenolic compound of formula (I). It is however preferable, in order to obtain an industrially acceptable yield, to use a molar ratio of hydrogen peroxide / phenolic compound of formula (I) of 0.01 to 0.3 and, preferably, of 0.05 to 0.10.

In order to have a sufficient reaction speed, the initial water content of the medium is limited to 10% by weight and, preferably, to 5% by weight. The weight contents indicated are expressed relative to the mixture of phenolic compound of formula (1) / hydrogen peroxide / water.

This initial water corresponds to the water introduced with the reagents and in particular with the hydrogen peroxide.

The amount of catalyst expressed by the ratio between the number of moles of triflate and the number of moles of hydrogen peroxide advantageously varies between 10 ^-4 and 10 ' ¹ , preferably between 10 ^{* 3} and 5.10 ^-3 .

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

Thus, during the use of a polar but not very basic organic solvent, it is determined so that the molar ratio between the number of moles of organic solvent and the number of moles of phenolic compound of formula (I) varies between 0.1 and 2.0, preferably between 0.25 and 1.0.

If a weakly polar and basic organic solvent is used, the quantity used is determined so that the molar ratio between the number of moles of organic solvent and the number of moles of phenolic compound of formula (I) varies between 0.01 and 0.25, preferably between 0.025 and

0.15.

The ketone compound of formula (II) which has been previously defined intervenes in an amount defined below. Generally, the amount of the ketone compound of formula (II) expressed in moles per mole of hydrogen peroxide varies between 1.10 ^"3 mole and 10. It is not necessary to exceed 1.0 mole of ketone compound per mole of peroxide In practice, the amount of ketone compound is most often between 0.05 and 1.0 mole per mole of hydrogen peroxide In accordance with the process of the invention, the hydroxylation of the compound is carried out. phenolic of formula (I) at a temperature which can be between 45 ° C. and 150 ° C. A preferred variant of the process of the invention consists in choosing the temperature between 50 ° C and 80 ° C.

The reaction is advantageously carried out at atmospheric pressure.

From a practical point of view, the method according to the invention is simple to implement continuously or discontinuously.

Preferably, the following different reagents are introduced in any order, phenolic compound of formula (I), catalyst, ketone compound of formula (II), organic solvent.

The reaction medium is brought to the desired temperature and then the hydrogen peroxide solution is added gradually.

At the end of the reaction, the unconverted phenolic compound and the ketone compound of formula (II) are separated from the hydroxylation products by the usual means, in particular by distillation and are returned to the reaction zone.

Examples of the invention are given below.

Examples 1 to 11 which follow illustrate the invention without however limiting it.

Test a is a comparative example. In the examples, the following abbreviations mean:

number of moles of hydrogen peroxide processed

TT =% number of moles of hydrogen peroxide introduced

number of moles of hydroquinone formed

RT _HQ =% number of moles of hydrogen peroxide transformed

number of moles of pyrocatechol formed

RT _pc =% number of moles of hydrogen peroxide transformed

EXEMP1ES.

The operating protocol which will be followed in all the examples is given below.

The phenol is charged into a 100 ml glass flask fitted with a central stirrer, a condenser, a dropping funnel and a thermometer. the catalyst, rare earth or bismuth triflate, optionally the ketone compound of formula (II), the solvent.

The different quantities used are indicated in the attached summary tables. The reaction mixture is brought to the chosen reaction temperature, ie

75 ° C, while keeping it stirred at 1200 rpm.

Is introduced via the dropping funnel, in 2 minutes, the aqueous solution of hydrogen peroxide at 70.5% by weight in an amount also specified in the following tables. The reaction mixture is kept under stirring at 75 ° C. for the period mentioned in the following tables.

The reaction mixture is then cooled and the reaction products are assayed: the residual hydrogen peroxide is assayed by iodometry and the diphenols formed are assayed by high performance liquid chromatography.

EXAMPLES 1 TO 6 Comparative test a

In this series of examples, various catalysts have been used, namely:

- ytterbium triflate: examples 1, 5 and 6,

- lanthanum triflate: example 2,

- scandium triflate: example 3, - lutetium triflate: example 4.

The tests are carried out according to the operating protocol previously defined. All the conditions and the results obtained are collated in the following table (I):

By way of comparison, the results obtained are given when the process of the invention is carried out in the presence of magnesium triflate (test a).

Examination of Table (I) clearly shows that the presence of the catalyst, the ketone and the organic solvent as defined leads to the best yield and para-selectivity results.

EXAMPLE 7

In this example, less catalyst, scandium triflate, was used.

The comparison of Examples 7 and 3 shows that the reduction in the amount of catalyst leads to an increase in the yield and in the selectivity of the reaction in favor of hydroquinone.

The test is carried out according to the operating protocol previously defined. All the conditions and the results obtained are collated in the following table (II):

EXAMPLE 8

In this example, the influence of the organic solvent has been demonstrated.

The comparison of Examples 8 and 1 shows that the use of a solvent leads to an increase in the yield and the selectivity of the reaction in favor of hydroquinone.

The test is carried out according to the operating protocol previously defined. All the conditions and the results obtained are collated in the following table (III):

EXAMPLES 9 and 10

In the examples which follow, a different ketone compound is used, namely acetophenone. The tests are carried out according to the operating protocol previously defined.

All the conditions and the results obtained are collated in the following table (IV):

TABLE IV

KO o βv

ro ro

TABLE V

e o

K "

EXAMPLE 11

In this example, bismuth triflate is used as catalyst. The latter can be prepared as follows:

0.44 g of triphenylbismuth PhβBi (1 mmol) and 10 are introduced into a 250 ml flask, purged with argon and equipped with an air inlet connected to a calcium chloride tube. ml anhydrous dichloromethane. The solution is cooled to -78 ° C. 0.44 g of triflic acid (2.9 mmol) is added using a syringe.

A yellow coloration appears.

The reaction mixture is allowed to return to room temperature. The solid obtained is filtered under argon and washed with dry dichloromethane in order to remove the traces of triflic acid. The powder is introduced into a two-necked bottle and dried under reduced pressure (18 mm of mercury), under argon, for 1 hour.

The use of said catalyst for hydroxylating phenol is carried out according to the operating protocol previously defined.

All the conditions and the results obtained are collated in table (V) above.

Claims

1 - Process for the hydroxylation of a phenolic compound with hydrogen peroxide, characterized in that the reaction is carried out in the presence of an effective amount of at least one rare earth or bismuth triflate.

2 - Process according to claim 1 characterized in that the catalyst used is a triflate of a rare earth chosen from lanthanides, yttrium scandium and their mixtures, preferably lanthanides such as lanthanum, cerium , praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium and lutetium and their mixtures.

3 - Process according to claim 1 characterized in that the catalyst used is a triflate of ceric rare earths in a mixture including the elements La, Ce, Pr, Nd and / or yttric rare earths in mixture comprising Y, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu.

4 - Process according to claim 1 characterized in that the catalyst used is a triflate of a rare earth chosen from lanthanum, ytterbium, lutetium and / or scandium.

5 - Method according to one of claims 1 to 4 characterized in that the reaction is carried out in the presence of an organic solvent.

6 - Process according to claim 5 characterized in that the reaction is carried out in the presence of an organic, aprotic, polar solvent, having a polarity such that its dielectric constant is greater than or equal to 20 and a basicity such that it has a "donor number" less than 25.

7 - Process according to claim 6 characterized in that the polar organic solvent has a dielectric constant between 25 and 75.

8 - Method according to one of claims 6 and 7 characterized in that the polar organic solvent has a donor number less than or equal to 20, preferably between 2 and 17. 9 - Method according to one of claims 6 to 8 characterized in that the polar organic solvent is chosen from nitro compounds, aliphatic or aromatic nitriles, tetramethylene sulfone, propylene carbonate.

10 - Method according to one of claims 6 to 9 characterized in that the polar organic solvent is chosen from the following solvents: nitromethane, nitroethane, 1-nitropropane, 2-nitropropane or their mixtures, nitrobenzene, acetonitrile, propionitrile, butanenitrile, isobutanenitrile, benzonitrile, benzyl cyanide, tetramethylene sulfone (sulfolane), propylene carbonate.

11 - Method according to one of claims 6 to 10 characterized in that the amount of solvent used is such that the molar ratio between the number of moles of organic solvent and the number of moles of phenolic compound of formula (I ) varies between 0.1 and 2.0, preferably between 0.25 and 1.0.

12 - Process according to claim 5 characterized in that the reaction is carried out in the presence of an organic solvent, aprotic, polar, having a polarity such that its dielectric constant is less than about 20 and a basicity such that it has a "donor number" greater than or equal to 15 and less than 25.

13 - A method according to claim 12 characterized in that the polar organic solvent has a dielectric constant between 2 and 15.

14 - Method according to one of claims 12 and 13 characterized in that the polar organic solvent has a donor number between 15 and 25.

15 - Method according to one of claims 12 to 14 characterized in that the polar organic solvent is chosen from aliphatic, cycloaliphatic or aromatic ether-oxides, neutral phosphoric esters, ethylene carbonate.

16 - Method according to one of claims 12 to 15 characterized in that the polar organic solvent is chosen from the following solvents: diethyl ether, dipropyl ether, diisopropyl ether, dibutyl, methyltertiobutylether, dipentyl oxide, diisopentyl oxide, ethylene glycol dimethyl ether (or 1,2-dimethoxyethane), diethylene glycol dimethyl ether (or 1,5-dimethoxy-3-oxapentane), dioxane, tetrahydrofuran, trimethyl phosphate, triethyl phosphate, phosphate butyl, triisobutyl phosphate, tripentyl phosphate, ethylene carbonate.

17 - Method according to one of claims 12 to 16 characterized in that the amount of solvent used is such that the molar ratio between the number of moles of organic solvent and the number of moles of phenolic compound of formula (I ) varies between 0.01 and 0.25, preferably between 0.025 and 0.15.

18 - Method according to one of claims 1 to 17 characterized in that the reaction is carried out in the presence of a ketone compound.

19 - Process according to claim 18 characterized in that the ketone compound used corresponds to formula (II):

R _a - CO - X - R _b (II)

in said formula (II):

- R and Ru, identical or different, represent hydrocarbon radicals having from 1 to 30 carbon atoms or together form a divalent radical, optionally substituted by one or more halogen atoms or functional groups stable under the conditions of the reaction, - X represents a valence bond, a group -CO-, a group -CHOH or a group - (R) - _n representing an alkylene group preferably having from 1 to 4 carbon atoms and n is an integer chosen between 1 and 16 .

20 - Process according to claim 19 characterized in that the ketone compound used corresponds to formula (II) in which R _Q and R _b represent:

- linear or branched alkyl radicals,

- linear or branched alkenyl radicals,

- cycloalkyl or cycloalkenyl radicals containing from 4 to 6 carbon atoms,

- mono- or polycyclic aryl radicals; in the latter case, the cycles forming between them an ortho- or ortho- and pricondensed system or being linked together by a valential bond, - arylalkyl or arylacenyl radicals,

- R _a and Rb may together form an alkylene or alkenylene radical containing from 3 to 5 carbon atoms, optionally substituted by an alkyl radical with low carbon condensation or by a cycloalkyl or cycloalkenyl radical having 4 to 6 carbon atoms; 2 to 4 carbon atoms of the alkylene or alkenylene radicals which may be part of one or two benzene rings optionally substituted by 1 to 4 hydroxyl and / or alkyl and / or aikoxy groups with low carbon condensation.

21 - Method according to one of claims 1 to 20 characterized in that the ketone compound used is chosen from ketone compounds of dialkylketone type corresponding to formula (II) in which R _a and Rb represent a linear alkyl radical or branched having from 1 to 8 carbon atoms and to alkylphenones corresponding to formula (II) in which R _a represents a linear or branched alkyl radical having from 1 to 6 carbon atoms and Rb represents a phenyl radical.

22 - Method according to one of claims 1 to 21 characterized in that the ketone compound used corresponds to the formula (IIa):

- R and R ^, which are identical or different, represent a hydrogen atom or a substituent, preferably an electron donor group,

- n ₁ , n "identical or different is a number equal to 0, 1, 2 or 3, - optionally the two carbon atoms located in position a with respect to the two carbon atoms carrying the group -CO can be linked together by a valential bond or by a group -CHp- thus forming a ketone cycle which can be saturated but also unsaturated.

23 - Process according to claim 22 characterized in that the ketone compound corresponds to the general formula (Ha) in which R and R ^, identical or different, represent:

- linear or branched alkyl radicals having from 1 to 4 carbon atoms,

- a phenyl radical, - aikoxy radicals R-10-O- in which R-JO represents a linear or branched alkyl radical having from 1 to 4 carbon atoms or the phenyl radical, - the hydroxyl group,

- a fluorine atom.

24 - Method according to one of claims 22 and 23 characterized in that the ketone compound corresponds to the general formula (Ha) in which R and R ,, identical or different, represent a hydrogen atom or an electro- group donor in position 4,4 'and n ^, ng identical or different are equal to 0 or 1.

25 - Method according to one of claims 22 to 24 characterized in that the ketone compound corresponding to the general formula (IIa) in which R- and R ^, identical or different, represent a hydrogen atom; a methyl, ethyl, tert-butyl, phenyl radical; a methoxy or ethoxy radical; a hydroxyl group, preferably in the 3.3 ′ or 4.4 ′ position.

26 - Method according to one of claims 1 to 25 characterized in that the ketone compound used is chosen from: acetone, 3,3-dimethyl-butanone-2, methylvinyl ketone, mesityl oxide, 2,4-dimethyl-pentanone-3, diacetyl, dicyclohexyl ketone, acetophenone, benzophenone, 2-methyl benzophenone, 2,4-dimethyl benzophenone, 4,4-dimethyl benzophenone, dimethyl-2 , 2 'benzophenone, 4,4-dimethoxy benzophenone, 4-hydroxy benzophenone, 4-4 dihydroxy benzophenone, 4-benzoyl biphenyl, benzoin, 4,4-dihydroxy benzoin, dimethyl -2.4 benzoin, dimethyl-4.4 'benzoin, dimethoxy-4.4' benzoin, difluoro-4.4 'benzoin, α-methoxy benzoin, α-ethoxy benzoin, deoxybenzoin, 4-hydroxy deoxybenzoin, 4-methyl deoxybenzoin, 4-methoxy deoxybenzoin, 4,4-dimethoxy deoxybenzoin, 4,4-difluoro-deoxybenzoin, benzalacetone, benzile, cy clohexanone, α-isophorone, cyclohexenylcyclohexanone, fluorenone.

27 - Method according to one of claims 1 to 27 characterized in that the phenolic compound responds to l (I):

in said formula (I): - Rj, R2, R3 and R4, identical or different, represent a hydrogen atom or any substituent,

- two groups R-j and R2 and / or R3 and R4 placed on two vicinal carbon atoms can form together and with the carbon atoms which carry them a ring,

- R 'represents a hydrogen atom or a hydrocarbon radical having from 1 to 24 carbon atoms, which can be a saturated or unsaturated, linear or branched acyclic aliphatic radical; a saturated or unsaturated, monocyclic or polycyclic cycloaliphatic radical; a saturated or unsaturated, linear or branched aliphatic radical, carrying a cyclic substituent.

28 - Process according to claim 27 characterized in that the phenolic compound corresponds to the general formula (I) in which:

- R- |, R2, R3 and R4, identical or different, represent Rn, one of the following 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, sec-butyl, tert-butyl,. a linear or branched alkenyl radical having from 2 to 6 carbon atoms, preferably from 2 to 4 carbon atoms, such as vinyl, allyl,. 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, radicals. an acyl group having from 2 to 6 carbon atoms,

. a radical of formula:

-R5-OH -R5-COOR6

-R5-X - ^R 5-CF ₃ in said formulas, R5 represents a valence bond or a divalent hydrocarbon radical, linear or branched, saturated or unsaturated, having from 1 to 6 carbon atoms such as, for example, methylene, ethylene , propylene, isopropylene, isopropylidene; Rβ represents a hydrogen atom or a linear or branched alkyl radical having from 1 to 6 carbon atoms; X symbolizes a halogen atom, preferably a chlorine, bromine or fluorine atom. - Rj, R2, R3 and R4, identical or different, represent R7, one of the following more complex radicals:

. a saturated or unsaturated carbocyclic radical having from 4 to 7 carbon atoms, preferably a cyclohexyl radical,

. a radical of formula

in which R5 represents a valential bond or a divalent, linear or branched, saturated or unsaturated hydrocarbon radical having from 1 to 6 carbon atoms such as for example, methylene, ethylene, propylene, isopropylene, isopropylidene and RQ- having the meaning given above and m is an integer from 0 to 4,

. a radical - R5 - A - Rs in which R5 has the meaning given above, RQ represents a linear or branched alkyl radical having

1 to 6 carbon atoms or a radical of formula

^{^} and A symbolizes one of the following groups:

- O -, - COO -, - OCOO -, - SOo -, - CO - N -,

I

- two groups Ri and R2 and / or R3 and R4 placed on two vicinal carbon atoms can form together and with the carbon atoms which carry them an unsaturated or aromatic carbocycle having from 4 to 7 carbon atoms and, preferably, 6 carbon atoms.

29 - Method according to one of claims 27 and 28 characterized in that the phenolic compound corresponds to the general formula (I) in which:

- the radical R 'represents one of the following groups:

. a hydrogen atom. a linear or branched alkyl radical having from 1 to 4 carbon atoms,

. a cyclohexyl radical,. a benzyl radical,

- Rj, R2, R3 and R4, identical or different, represent one of the following groups:. a hydrogen atom, . an alkyl radical, linear or branched having from 1 to 4 carbon atoms ,.

. a linear or branched aikoxy radical having from 1 to 4 carbon atoms,

. a hydroxyl group,

. a halogen atom,. a -CFg group

. a cyclohexyl radical,

. a phenyl radical, - two R- groups | and R2 and / or R3 and R4 placed on two vicinal carbon atoms can form together and with the carbon atoms which carry them a benzene ring.

30 - Method according to one of claims 27 to 29 characterized in that the phenolic compound corresponds to the general formula (I) in which R 'represents a hydrogen atom and one of the radicals R ^, R2, R3 and R4 represents a hydroxyl group, a methyl radical or a methoxy radical and the other 3 represent a hydrogen atom.

31 - Process according to claim 27 characterized in that the phenolic compound is phenol, anisole, o-cresol, m-cresol and p-cresol.

32 - Method according to one of claims 1 to 31 characterized in that the amount of catalyst expressed by the ratio between the number of moles of triflate and the number of moles of hydrogen peroxide varies between 10 ^-4 and 10 ^_1 preferably between 10 ' ³ and 5.10 ^-3 .

33 - Method according to one of claims 1 to 32 characterized in that the molar ratio ^ Op / phenolic compound of formula (I) is between 0.01 and 0.3, preferably between 0.05 and 0 , 10.

34 - Method according to one of claims 1 to 33 characterized in that the amount of ketone compound of formula (I) is between 1.10 mole and 10 moles per mole of hydrogen peroxide and even more preferably between 0.05 and 1.0 mole.

35- Method according to one of claims 1 to 34 characterized in that one operates at a temperature between 45 ° C and 150 ° C, preferably between 50 ° C and 80 ° C.