FR2687663A1 - Process for the hydroxylation of phenol compounds - Google Patents

Abstract

The subject of the present invention is a process for the hydroxylation of phenol compounds which makes it possible to increase the amount of para isomer. The invention relates to a process for the hydroxylation of phenol compounds using hydrogen peroxide and in the presence of an effective amount of a strong acid and of a ketone compound, the said process being characterised in that the reaction is carried out in the presence of a polar aprotic organic solvent having a polarity such that its dielectric constant is less than approximately 20 and a basicity such that it has a "donor number" greater than or equal to 15 and less than 25.

Description

PROCESS FOR HYDROXYLATION OF PHENOLlOUS 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 by hydrogen peroxide.

 Many methods of hydroxylation of phenols are described in the state of the art.

 Let us mention, among others, the patent FR-A 2 071 464 which relates to a very important industrial process for the hydroxylation of phenols and phenol ethers.

 The method comprises performing hydroxylation with hydrogen peroxide in the presence of a strong acid. Among these strong acids, sulfuric acid, paratoluene sulphonic acid, perchloric acid are the most used.

 The hydroxylation of the phenol carried out under the conditions described leads to a mixture of hydroquinone and pyrocatechol, with predominance of it since the hydroquinone / pyrocatechol ratio most often varies between 0.3 and 0.7.

 It has been proposed, according to FR-A 2 266 683, an improvement to this process which consists in carrying out the hydroxylation in the presence of a ketone. This results in an improvement in the reaction yield of hydroquinone and pyrocatechol. However, all the examples described lead to a larger amount of pyrocatechol compared to that of hydroquinone.

 The known methods therefore lead mainly to pyrocatechol.

 It turns out that to respond to fluctuating market demand, it is important to have an industrial process to increase the production of hydroquinone formed relative to the amount of pyrocatechol.

 In the patent application FR 90/12345, there has been proposed a method for increasing the amount of hydroquinone formed relative to the amount of pyrocatechol and to obtain in its preferred embodiment, more hydroquinone than pyrocatechol.

dans laquelle R et R,, identiques ou différents représentent un atome d'hydrogène, un radical alkyle ayant de 1 à 4 atomes de carbone, un radical cyclohexyle, un radical phényle, au moyen de peroxyde d'hydrogène, en présence d'une quantité efficace d'un acide fort, ledit procédé étant caractérisé par le fait que la réaction est conduite en présence d'un composé cétonique répondant à la formule générale (II)

dans ladite formule (II) - R1 et R2 identiques ou différents représentent un atome d'hydrogène ou un groupe électro-donneur, - n1, n2 identiques ou différents est un nombre égal à 0, 1, 2 ou 3, - éventuellement les deux atomes de carbone situés en position a par rapport aux deux atomes de carbone portant le groupe -CO peuvent être liés ensemble par un lien valentiel ou par un groupe -CH2- formant ainsi un cycle cétonique qui peut être saturé mais aussi insaturé.The method comprises performing hydroxylation of phenolic compounds of the general formula (I):

in which R and R 2, which are identical or different, represent a hydrogen atom, an alkyl radical having from 1 to 4 carbon atoms, a cyclohexyl radical or a phenyl radical, by means of hydrogen peroxide, in the presence of a effective amount of a strong acid, said process being characterized in that the reaction is conducted in the presence of a ketone compound having the general formula (II)

in said formula (II) - R1 and R2, which are identical or different, represent a hydrogen atom or an electro-donor group, - n1, n2, which may be identical or different, is a number equal to 0, 1, 2 or 3, - optionally both carbon atoms located in position a with respect to the two carbon atoms bearing the -CO group can be bonded together by a valency bond or by a -CH 2 - group thus forming a ketone ring which can be saturated but also unsaturated.

"Electro-donating group" means a group as defined by HC BROWN in Jerry MARCH's book - Advanced Organic
Chemistry, chapter 9, pages 243 and 244 (1985).

 The electron-donor group is chosen so that it does not react under the conditions of acidity of the invention.

 Examples of electro-donating groups that are well suited to the invention described in FR / 90/12345 are the following: linear or branched alkyl radicals having from 1 to 4 carbon atoms, phenyl radical, and alkoxy radicals R 3 In which R 3 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 particularly adapted to the invention described in FR 90/12345, mention may be made most particularly of ketone compounds corresponding to the general formula (II) in which R1 and R2, which are identical or different, represent a hydrogen atom or an electro-donor group, preferably in position 4,4 'and n1, n2 identical or different are equal to 0 or 1.

 The ketone compounds of formula (II) in which R1 and R2, which are identical or different, represent a hydrogen atom are preferably used; a methyl, ethyl, tert-butyl or phenyl radical; a methoxy or ethoxy radical; a hydroxyl group, preferably in position 3,3 'or 4,4'.

As specific examples of ketones that can be used in the process of the invention described in FR 90/12345, mention may be made more particularly
- benzophenone
- 2-methylbenzophenone
2,4-dimethylbenzophenone
4,4'-Dimethylbenzophenone
2,2-dimethylbenzophenone
4,4'-Dimethoxybenzophenone
- fluorenone
- 4-hydroxybenzophenone
4-4-dihydroxybenzophenone
- 4-benzoyl biphenyl
According to the process described in FR 90/12345, the presence of the ketonic compound of formula (II) during the hydroxylation of the phenolic compound of formula (I) plays on the regioselectivity of the reaction and hydroquinone / pyrocatechin ratios varying between 1, 0 and 1.13 are advantageously obtained.

 Continuing its research, the Applicant has perfected the invention described in FR 90/12345 and found that even higher hydroquinone / pyrocatechine ratios could be obtained by adding to the reaction mixture a small amount of an organic solvent, protic, having certain characteristics of polarity and basicity.

dans laquelle R et R,, identiques ou différents représentent un atome d'hydrogène, un radical alkyle ayant de 1 à 4 atomes de carbone, un radical cyclohexyle, un radical phényle, au moyen de peroxyde d'hydrogène et en présence d'une quantité efficace d'un acide fort et d'un composé cétonique, ledit procédé étant caractérisé par le fait que la réaction est conduite en présence d'un solvant organique, aprotique, polaire, présentant une polarité telle que sa constante diélectrique est inférieure à environ 20 et une basicité telle qu'il possède un "nombre donneur" supérieur ou égal à 15 et inférieur à 25.More specifically, the subject of the present invention is a process for the hydroxylation of phenolic compounds of general formula (I):

in which R and R 2, which are identical or different, represent a hydrogen atom, an alkyl radical having from 1 to 4 carbon atoms, a cyclohexyl radical or a phenyl radical, by means of hydrogen peroxide and in the presence of a effective amount of a strong acid and a ketone compound, said process being characterized in that the reaction is conducted in the presence of an aprotic, polar organic solvent having a polarity such that its dielectric constant is less than about And a basicity such that it has a "donor number" greater than or equal to 15 and less than 25.

 It has now been found that the presence of a solvent having the characteristics as previously defined makes it possible to increase the hydroquinone / pyrocatechol ratio in favor of hydroquinone.

 Thus, according to the present invention ratios of the order of 1.1 and higher can be obtained.

 It should be noted that the choice of the organic solvent to be used is quite critical and that it is important to use an aprotic organic solvent, slightly polar and basic. Thus, if an aprotic organic solvent of high polarity and strong basicity such as dimethylformamide or N-methylpyrrolidone is used, the desired effect is not obtained.

 Furthermore, it was unexpectedly found that this solvent effect chosen according to the invention, whatever the nature of the ketone compound.

 Thus, it becomes possible, according to the method of the invention, to very easily adapt the amount of hydroquinone to the needs of the market by simply adding the appropriate organic solvent.

 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 the theory of
Lewis does not have any protons to release.

 Also excluded from the present invention are solvents which are not stable in the reaction medium and which degrade either by oxidation or by hydrolysis. By way of 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 ...

 A second characteristic of the organic solvent is that it has a certain polarity. According to the invention, an organic solvent is chosen which has a dielectric constant of less than about 20. The lower limit is not critical.

It is preferred to use an organic solvent having a low dielectric constant, preferably between 2 and 15.

 In order to determine whether the organic solvent meets the dielectric constant condition set forth above, reference may be made, inter alia, to the tables of the work: Techniques of Chemistry, II - Organic Solvents - p. 536 and following, 3rd edition (1970).

 A third characteristic of the organic solvent is that it has a basicity such that it has a "donor number" greater than or equal to 15 and less than 25. The upper limit is not critical. An organic solvent having a donor number between 15 and 25 is preferably chosen.

 With regard to the requirements relating to the basicity of the organic solvent to be used, it will be recalled that the "donor number" or "donor number", abbreviated as DN, gives an indication of the nucleophilic character of the solvent and reveals its ability to give his doublet.

In the work of Christian REINHARDT, [Solvents and Solvent
Effects in Organic Chemistry - VCH p.19 (1988)], we find the definition of the "donor number" which is defined as the negative (-BH) of the enthalpy (Kcal / mol) of the interaction between the solvent and antimony pentachloride in a dilute solution of dichloroethane.

 Examples of polar aprotic solvents having the abovementioned characteristics which can be used in the process of the invention include, in particular, aliphatic, cycloaliphatic or aromatic ether-oxides and, more particularly, diethyl ether, dipropyl ether, diisopropyl ether, dibutyl ether, methyl tert-butyl ether, dipentyl ether, diisopentyl ether, ethylene glycol dimethyl ether (or 1,2-dimethoxy ethane) , dimethyl ether of diethylene glycol (or 1,5-dimethoxy-3-oxa-pentane), dioxane, tetrahydrofuran, neutral phosphoric esters such as, in particular, trimethyl phosphate, triethyl phosphate, butyl phosphate, triisobutyl phosphate, tripentyl phosphate, - ethylene carbonate.

 It is also possible to use a mixture of solvents.

 According to the process of the invention, a polar aprotic organic solvent is used during the process of hydroxylation of the phenolic compound of formula (I) carried out in the presence of a strong acid and a ketone compound.

Since the solvent effect is observed irrespective of the nature of the ketone compound used, it is therefore possible to use any ketone compound and more particularly those corresponding to formula (II)
Ra - CO - X - Rb (II) in said formula (II) - Ra and Rb, which may be 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 atoms halogen or functional groups which are stable under the conditions of the reaction, X represents a valency bond, a group -CO-, a group -CHOH or a group - + RAnZ R representing an alkylene group preferably having from 1 to 4 atoms of carbon and n is an integer selected from 1 to 16.

 In formula (II), Ra and Rb are more particularly linear or branched alkyl radicals, linear or branched alkenyl radicals, cycloalkyl or cycloalkenyl radicals containing from 4 to 6 carbon atoms, monounsaturated aryl radicals, and or polycyclic, in the latter case, the cycles forming between them an ortho- or ortho- and peri-condensed system or being linked together by a valency bond, - arylalkyl or arylacenyl radicals, - Ra and Rb may together form an alkylene radical or alkenylene having from 3 to 5 carbon atoms, optionally substituted by a lower carbon alkyl radical or a cycloalkyl or cycloalkenyl radical having 4 to 6 carbon atoms; 2 to 4 carbon atoms of the alkylene or alkenylene radicals may be part of one or two benzene rings optionally substituted with 1 to 4 hydroxyl groups and / or alkyl and / or alkoxy low carbon condensation.

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

 The hydrocarbon radicals mentioned above may be substituted with 1 or more, preferably 1 to 4, low carbon condensation alkyl groups or functional groups such as hydroxyl groups, low carbon alkoxy groups, hydroxycarbonyl groups, and alkyloxycarbonyl groups having 1 to 4 carbon atoms. carbon atoms in the alkyl group, a nitrile group, -SO3H, nitro or with one or more halogen atoms, and especially chlorine and bromine.

 Preferably, Ra and Rb are more particularly 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 comprising from 4 to 10 carbon atoms. with 6 carbon atoms, - phenyl radicals optionally substituted with 1 to 4 alkyl and / or hydroxyl and / or alkoxy groups, - phenylalkyl or phenylacenyl radicals containing 1 (or 2) to 10 carbon atoms in the aliphatic part, and still more particularly from 1 (or 2) to 5 carbon atoms in the aliphatic portion, - Ra and Rb may together form an alkylene or alkenylene radical having from 3 to 5 carbon atoms, optionally substituted by 1 to 4 low alkyl radicals. carbon condensation.

As specific examples of ketones which may be used in the process of the invention, mention may be made, more particularly, of acetone, butanone-2, methylisopropylketone, pivalone, pentanone-2 and pentanone-3. 4-methylpentanone-2-dimethyl-3,3-butanone-2-hexanone-2-hexanone-3-heptanone-2-heptanone-4-octanone-2-octanone 3 - nonanone-2 - nonanone-5 - pentadecanone-8 - methyl-2 hexanone-3 - methyl-5 hexanone-2 - methyl-5 hexanone-3 - dimethyl-2,4 pentanone-3 - 5-methylheptanone-3-methylvinylketone-mesityl oxide-penten-1-one-3-penten-3-one-2-hexen-5-one-2-methyl-5-hexene-3 one-2-methyl-6-heptene-5-one-2-diacetyl-diacetone-alcohol-acetoin-butanedione-2,3-pentanedione-2,4-1-hexanedione-2,5-la dicyclohexylketone - methylcyclohexylketone - acetophenone - n-propiophenone - n-butyrophenone - isobutyrophenone - n-valerophenone - 2-methylacetophenone - 2,4-dimethylacetophenone - phenylvinylketone - benzophenone - 2-methylbenzophenone - 2,4-dimethylbenzophenone - 4,4'-dimethyl benzophenone - 2,2'-dimethylbenzophenone - 4,4'-dimethoxybenzophenone - 4-hydroxybenzophenone - 4,4'-dihydroxybenzophenone - 4-benzoylbiphenyl - benzoin - 4-dihydroxy Benzoin - 2,4-dimethylbenzoin - 4,4'-dimethylbenzoin - 4,4'-dimethoxybenzoin - 4,4'-difluorobenzoin - α-methoxybenzoin - ethoxy benzoin - deoxybenzoin - 4-hydroxy-deoxybenzoin - 4-methyl-deoxybenzoin - 4-methoxy-deoxybenzoin - 4,4-dimethoxy-deoxybenzoin - 4,4'-difluoro-deoxybenzoin - ss-phenylpropiophenone - dibenzylketone - o-phenylvalerophenone - 1,1-diphenylpropanone-2 - 1,3-diphenylpropanone - benzalacetone - benzalacetophenone benzyl - cyclopentanone - 2-methylcyclopentanone - cyclohexanone - 2-methylcyclohexanone - 3,3,5,5-tetramethylcyclohexanone - 2-cyclopentenone - 2-cyclohexenone - a-isophorone - ss -isophorone - cyclohexenyl-cyclohexanone - a-indanone - ss-indanone - a-tetralone - fluorenone
Among all the above-mentioned ketones, the ketone compounds which themselves have a para-orienting effect as evidenced in the patent application FR 90/12345 are preferably used.

dans ladite formule (IIa) : - R1 et R2 identiques ou différents représentent un atome d'hydrogène ou un groupe électro-donneur, - n1, n2 identiques ou différents est un nombre égal à 0, 1, 2 ou 3, - éventuellement les deux atomes de carbone situés en position a par rapport aux deux atomes de carbone portant le groupe -CO peuvent être liés ensemble par un lien valentiel ou par un groupe -CH2- formant ainsi un cycle cétonique qui peut être saturé mais aussi insaturé.Thus, the ketone compounds of general formula (IIa) are particularly used.

in said formula (IIa): R1 and R2, which are identical or different, represent a hydrogen atom or an electro-donor group; n1, n2, which may be identical or different, is a number equal to 0, 1, 2 or 3; two carbon atoms located in position a with respect to the two carbon atoms bearing the -CO group can be bonded together by a valency bond or by a -CH 2 - group thus forming a ketone ring which can be saturated but also unsaturated.

 As mentioned above, said ketone compounds are the subject of the patent application FR 90/12345 which is incorporated by reference in the present application.

 According to the process of the invention, a polar aprotic organic solvent intervenes during the process of hydroxylation of the phenolic compound of formula (I) carried out in the presence of a strong acid and a ketone compound.

 The amount of organic solvent to be used is determined in such a way 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 amount of solvent to be added is chosen according to the basicity of the solvent. The amount of solvent used will be even lower than its basicity will be stronger.

In other words, an amount located towards the lower limit of the previously defined range will be chosen when the solvent has a high basicity.

 The ketone compound of formula (II) which has previously been defined is used in a quantity 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 hydrogen peroxide. In practice, the amount of ketone compound is most often between 0.05 and 1.0 mole per mole of hydrogen peroxide.

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

 Aqueous solutions being commercially more readily available are preferably used.

The concentration of the aqueous solution of hydrogen peroxide, although not critical in itself, is chosen so as to introduce as little water as possible into the reaction medium. An aqueous solution of hydrogen peroxide of at least 20% by weight of
H2O2 and preferably about 70%.

 The amount of hydrogen peroxide can be up to 1 mole of H 2 O 2 per 1 mole of phenolic compound of formula (I).

 However, it is preferable to obtain an industrially acceptable yield of using 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 rate, the initial content of the water medium is limited to 20% by weight and preferably to 10% by weight.

 The weight contents indicated are expressed relative to the phenolic compound mixture of formula (I) / hydrogen peroxide / water.

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

 In the process of the invention, a strong acid is involved. By strong acid is meant in the present invention, an acid having a pKa in water of less than -0.1 and, preferably, less than -1.0.

 PKa is defined as the ionic dissociation constant of the acid / base pair, when water is used as the solvent.

 Among the acids corresponding to this definition, it is preferable to use those which are stable with respect to oxidation by hydrogen peroxide.

 Mention may more particularly be made of halogenated or non-halogenated oxyacids such as sulfuric acid, pyrosulphuric acid, perchloric acid, nitric acid, halosulfonic acids such as fluorosulphonic acid, chlorosulphonic acid or acid. trifluoromethanesulfonic acid, methanesulfonic acid, ethanesulfonic acid, ethanedisulphonic acid, benzenesulphonic acid, benzenedisulphonic acids, toluenesulphonic acids, naphthalenesulphonic acids and naphthalenesulphonic acids.

 Among these acids, perchloric acid, trifluoromethanesulphonic acid, para-toluenesulphonic acid, chlorosulphonic acid, fluorosulphonic acid and methanesulphonic acid are preferably used.

 In particular, perchloric acid or trifluoromethanesulphonic acid is chosen.

 The amount of acid expressed as the ratio of the number of proton equivalents to the number of moles of hydrogen peroxide can vary between about 1.10-4 and about 1.0.

 A preferred variant of the process of the invention consists in choosing a H + / H2O2 ratio of between 1.10-3 and 0.1.

 A preferred variant of the process of the invention consists in adding a complexing agent for the metal ions present in the medium since these are detrimental to the smooth running of the process of the invention, in particular in the case of phenols where the yields of hydroxylation are low. Therefore, it is preferable to inhibit the action of metal ions.

 The metal ions that are detrimental to the progress of the hydroxylation are transition metal ions and more particularly iron, copper, chromium, cobalt, manganese and vanadium ions.

 The metal ions are provided by the reagents and in particular the aromatic compounds and the equipment used. To inhibit the action of these metal ions, it suffices to conduct the reaction in the presence of one or more stable complexing agents with respect to hydrogen peroxide and giving complexes that can not be decomposed by the strong acids present and in which the metal can no longer exert chemical activity.

 By way of nonlimiting examples of complexing agents, it is possible to use, in particular, the various phosphoric acids such as, for example, orthophosphoric acid, metaphosphoric acid, pyrophosphoric acid, polyphosphoric acids, phosphonic acids such as (1-hydroxyethylidene) diphosphonic acid, phosphonic acid, ethylphosphonic acid, phenylphosphonic acid.

 It is also possible to use the esters of the abovementioned acids and, more particularly, orthophosphates of mono- or dialkyl, mono- or dicycloalkyl, mono- or dialkylaryl, for example ethyl phosphate, or of diethyl, hexyl phosphate, cyclohexyl phosphate, benzyl phosphate.

 The amount of complexing agent depends on the content of the reaction medium in metal ions.

 The amount of complexing agent, expressed as the number of moles of complexing agent per mole of hydrogen peroxide, advantageously varies between 0.0001 and 0.01.

 Another alternative embodiment of the process of the invention consists in conducting the process for the hydroxylation of phenolic compounds of general formula (I) by means of hydrogen peroxide, in the presence of an effective amount of a sodium salt. an alkali metal or alkaline earth metal of a strong acid, an effective amount of at least one phosphorus oxy acid, an effective amount of at least one ketone compound having the general formula (II), said process being characterized in that the reaction is conducted in the presence of a polar aprotic solvent as previously defined.

 Strong acid salt is understood to mean an acid having a pka in water of less than -0.1 and preferably less than -1.0.

 Among the salts of the acids corresponding to this definition, it is preferable to use the alkali metal or alkaline earth metal salts of acids which are stable with respect to oxidation by hydrogen peroxide.

 Thus, the alkali metal or alkaline earth metal salts of the above strong acids are quite suitable.

 The term "alkali metal salts" means the neutral salts of the previously defined acids of lithium, sodium, potassium, rubidium and cesium.

 It is most often preferred to use the sodium or potassium salts and even more preferably, for economic reasons, the sodium salts.

 Among these various salts, there may be mentioned, among the preferred, disodium sulphate, sodium perchlorate, sodium trifluoromethanesulphonate, sodium paratoluenesulphonate, sodium chlorosulphonate, sodium fluorosulphonate, sodium methanesulphonate.

 By alkaline earth metal salts is meant in the present text the neutral salts of the previously defined acids of beryllium, magnesium, calcium, strontium and barium.

 It is most often preferred to use the magnesium, calcium and barium salts.

 Among these different alkaline earth metal salts, use will preferably be made of calcium sulphate, magnesium sulphate, calcium perchlorate, magnesium perchlorate, calcium trifluoromethanesulphonate, magnesium trifluoromethanesulphonate, paratoluenesulphonate and the like. calcium, magnesium paratoluenesulfonate, calcium paratoluenesulfonate, magnesium paratoluenesulfonate, calcium fluorosulfonate, magnesium fluorosulfonate, calcium methanesulfonate, magnesium methanesulfonate.

 Mixtures of several alkali or alkaline earth metal salts may be used.

 Alkali or alkaline earth metal salts can also be prepared in situ, for example by loading stoichiometric amounts of acid and oxide or hydroxide of these metals.

 Phosphorus oxacids are more particularly acid-function compounds of phosphorus at oxidation state 5.

 It is also possible to use compounds with an acid function of phosphorus at oxidation state 3, which will be oxidized in the medium by hydrogen peroxide into corresponding compounds of phosphorus V; but this is not of particular interest, while having the disadvantage of consuming a portion of the hydrogen peroxide.

 Among these oxides of phosphorus V, there may be mentioned, for example, orthophosphoric acid, metaphosphoric acid, pyrophosphoric acid, polyphosphoric acids, phosphonic acids such as (1-hydroxyethylidene) diphosphonic acid, phosphonic acid, ethylphosphonic acid, phenylphosphonic acid.

 The most commonly used are, for practical and economic reasons, orthophosphoric acid, pyrophosphoric acid and (1-hydroxyethylidene) diphosphonic acid.

 The amount of alkali or alkaline earth metal salt used in the process of the invention may vary within wide limits.

 Generally, this amount is expressed in molar ratio of alkali metal salt or alkaline earth metal / hydrogen peroxide. This ratio is most often between 0.001 and 0.10 and preferably between 0.005 and 0.05.

 The amount of phosphorus oxyacid expressed in phosphorus oxyacid / hydrogen peroxide molar ratio is most often between 0.001 and 0.20 and preferably between 0.05 and 0.10.

 As regards the conditions of use of hydrogen peroxide and the ketone compound corresponding to formula (II), these correspond to that described above.

 According to the process of the invention, the hydroxylation of the phenolic compound of formula (I) is carried out at a temperature which can be between 450C and 1500C.

 A preferred variant of the process of the invention consists in choosing the temperature between 450 ° C. and 750 ° C.

 The reaction is advantageously carried out under atmospheric pressure.

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

 In a preferred manner, the order of the following reagents is selected, the phenolic compound of formula (I), the polar aprotic organic solvent, optionally the complexing agent, the strong acid and then the ketone compound of formula (II) are introduced. .

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

 At the end of the reaction, the unprocessed 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.

 Among the phenolic compounds of formula (I) which may be used in the process of the invention, mention may be made, without limitation, of phenol, anisole, orthocresol, paracresol, metacresol and tert-butyl. 4-phenol, 2-methoxyphenol, 4-methoxyphenol.

 The present process is particularly suitable for the preparation of hydroquinone and pyrocatechol from phenol.

 The following examples illustrate the invention without limiting it.

In the examples, the following abbreviations mean
number of moles of hydrogen peroxide transformed
TT =
number of moles of hydrogen peroxide introduced
number of moles of hydroquinone formed RTHQ =%
number of moles of hydrogen peroxide transformed
number of moles of pyrocatechin formed
PSTN =
number of moles of hydrogen peroxide transformed
EXAMPLES
The following is the operative protocol which will be followed in all the examples.

In a 100 ml glass flask equipped with a central stirrer, a condenser, a dropping funnel and a thermometer,
47 g (0.50 mol) of phenol,
xg of a ketone compound of formula (II).

 Next, 4 g of polar aprotic solvent and 3 g of perchloric acid are introduced.

 The different quantities (x, y and z) can be determined from the indications given in the summary tables.

 The reaction mixture is brought to the selected reaction temperature 750C while maintaining stirring at 1200 rpm.

 The aqueous solution of hydrogen peroxide 70.5% by weight is introduced via the dropping funnel in 2 minutes in an amount also specified in the following tables.

 The reaction mixture is stirred at 750 ° 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 determined by iodometry and the diphenols formed are determined by high performance liquid chromatography.

EXAMPLES 1 TO 10
Comparative tests a to d
In this series of examples, various solvents chosen in accordance with the invention have been used, namely di-n-propyl ether: Example 1, methyltertiobutyl ether: Examples 2 and 3, dimethoxy-1 Ethane: Example 4, tetrahydrofuran: Examples 5 and 6, dioxane: Examples 7 and 8, triethyl phosphate: Example 9, tributyl phosphate: Example 10

 The examples are conducted according to the previously defined operating protocol.

All the conditions and the results obtained are collated in the following table (I).
HYDROXYLATION OF PHENOL BY H2O2 / HClO4 / KETONE COMPOUND OF FORMULA (II)

Ref. <SEP> Compound <SEP> ketone <SEP> (II) <SEP> Solvent <SEP> organic <SEP> Ratio <SEP> molar <SEP> Ratio <SEP> molar <SEP> Duration <SEP> TT <SEP> RTHQ <SEP> PSTN <SEP> Report
<tb> [ratio <SEP> molar <SEP> [ratio <SEP> molar <SEP> H2O2 / PHENOL <SEP> HClO4 / H2O2 <SEP> HQ / PC
<tb> compound <SEP> ketone <SEP> (II) / <SEP> solvent <SEP> organic /
<tb> H2O2] <SEP> phenol]
<tb> 1 <SEP> benzophenone <SEP> oxide <SEP> of <SEP> di <SEP> n-propyl <SEP> 5,25.10-2 <SEP> 1,1.10-2 <SEP> 100mn <SEP> 99 , 5 <SEP> 45 <SEP> 42 <SEP> 1.07
<tb> (0.97) <SEP> (0.25)
<tb> 2 <SEP> Benzophenone <SEP> Methyl Tertiobutyl Ether <SEP> 5.5.10-2 <SEP> 1.3.10-2 <SEP> 40mn <SEP> 100 <SEP> 45 <SEP> 42 <SEP> 1.07
<tb> (0.91) <SEP> (0.025)
<tb> 3 <SEP> Benzophenone <SEP> Methyltertiobutyl Ether <SEP> 5.0.10-2 <SEP> 1.2.10-2 <SEP> 60mn <SEP> 100 <SEP> 40 <SEP> 35.5 <SEP> 1 13
<tb> (1,0) <SEP> (0,062)
<tb> 4 <SEP> benzophenone <SEP> 1,2-dimethoxy <SEP> ethane <SEP> 5,0.10-2 <SEP> 1,15.10-2 <SEP> 45mn <SEP> 99.5 <SEP> 46 <SEP> 42.5 <SEP> 1.08
<tb> (0.99) <SEP> (0.12)
<tb> 5 <SEP> benzophenone <SEP> tetrahydrofuran <SEP> 4,95.10-2 <SEP> 1,15.10-2 <SEP> 90mn <SEP> 100 <SEP> 41 <SEP> 38.5 <SEP> 1 , 06
<tb> (0.97) <SEP> (0.12)
<tb> 6 <SEP> benzophenone <SEP> tetrahydrofuran <SEP> 5.2.10-2 <SEP> 1.15.10-2 <SEP> 110mn <SEP> 100 <SEP> 44.5 <SEP> 40.5 <SEP > 1.10
<tb> (0.96) <SEP> (0.25)
<tb> 7 <SEP> benzophenone <SEP> dioxane <SEP> 4.95.10-2 <SEP> 1.3.10-2 <SEP> 60mn <SEP> 100 <SEP> 45 <SEP> 42.5 <SEP> 1 , 06
<tb> (0.97) <SEP> (0.12)
<tb> 8 <SEP> benzophenone <SEP> dioxane <SEP> 5.3.10-2 <SEP> 1.25.10-2 <SEP> 120mn <SEP> 100 <SEP> 48 <SEP> 41.0 <SEP> 1 17
<tb> (0.95) <SEP> (0.25)
<tb> 9 <SEP> benzophenone <SEP> phosphate <SEP> of <SEP> triethyl <SEP> 5.25.10-2 <SEP> 1.40.10-2 <SEP> 60mn <SEP> 100 <SEP> 42.5 <SEP> 37.5 <SEP> 1.13
<tb> (1,0) <SEP> (0,083)
<tb> 10 <SEP> benzophenone <SEP> phosphate <SEP> of <SEP> tributyl <SEP> 5.0.10-2 <SEP> 1.15.10-2 <SEP> 60mn <SEP> 100 <SEP> 45 <SEP > 41.5 <SEP> 1.08
<tb> (1.0) <SEP> (0.025)
<tb> Table I (continued)
HYDROXYLATION OF PHENOL BY H2O2 / HClO4 / KETONE COMPOUND OF FORMULA (II)

Ref. <SEP> Compound <SEP> ketone <SEP> (II) <SEP> Solvent <SEP> organic <SEP> Ratio <SEP> molar <SEP> Ratio <SEP> molar <SEP> Duration <SEP> TT <SEP > RTHQ <SEP> PSTN <SEP> Report
<tb> [ratio <SEP> molair <SEP> [ratio <SEP> molar <SEP> H2O2 / PHENOL <SEP> HClO4 / H2O2 <SEP> HQ / PC
<tb> compound <SEP> ketone <SEP> (II) / <SEP> solvent <SEP> organic /
<tb> H2O2] <SEP> phenol]
<tb> a <SEP> benzophenone <SEP> without <SEP> 4.9.10-2 <SEP> 1.35.10-2 <SEP> 3 <SEP> min <SEP> 100 <SEP> 43 <SEP> 42 <SEP > 1.02
<tb> (1,0)
<tb> b <SEP> benzophenone <SEP> dimethylformamide <SEP> 5.0.10-2 <SEP> 1.50.10-2 <SEP> 120 <SEP> min <SEP> 21.5 <SEP> 16 <SEP> 33 , 5 <SEP> 0.48
<tb> (1.0) <SEP> (0.25)
<tb> c <SEP> benzophenone <SEP> hexamethylenephos- <SEP> 5.1.10-2 <SEP> 1.25.10-2 <SEP> 120 <SEP> min <SEP> 9.0 <SEP> 0.5 <SEP> 3.5 <SEP> 0.14
<tb> (0.98) <SEP> phoramide
<tb> (0.115)
<tb> d <SEP> benzophenone <SEP> methanol <SEP> 5.1.10-2 <SEP> 1.25.10-2 <SEP> 85mn <SEP> 100 <SEP> 37 <SEP> 39 <SEP> 0.95
<tb> (0.98) <SEP> (0.24)
<Tb>
By way of comparison, the results obtained when conducting the process of the invention - test a: in the absence of an organic solvent, - test b and c: in the presence of benzophenone and in the presence of a organic solvent having a high dielectric constant such as dimethylformamide (test b) and hexamethylenephosphoramide (test c), test d: in the presence of benzophenone and a protic solvent such as methanol.

 Examination of Table (I) clearly shows that the presence of a polar organic solvent as defined according to the invention promotes the formation of hydroquinone.

EXAMPLES 11 and 12
Comparative tests e and f
A series of tests are carried out using the diisopropyl ether as the organic solvent.

All operating conditions and results are recorded in the following Table (II)
Two tests without organic solvent were also conducted for comparison.

 It is noted that the presence of the organic solvent makes it possible to increase the amount of hydroquinone formed.

Table II
HYDROXYLATION OF PHENOL BY H2O2 / HClO4 / KETONE COMPOUND OF FORMULA (II)

Ref. <SEP> Compound <SEP> ketone <SEP> (II) <SEP> Solvent <SEP> organic <SEP> Ratio <SEP> molar <SEP> Ratio <SEP> molar <SEP> Duration <SEP> TT <SEP> RTHQ <SEP> PSTN <SEP> Report
<tb> [ratio <SEP> molar <SEP> [ratio <SEP> molar <SEP> H2O2 / PHENOL <SEP> HClO4 / H2O2 <SEP> HQ / PC
<tb> compound <SEP> ketone <SEP> (II) / <SEP> solvent <SEP> organic /
<tb> H2O2] <SEP> phenol]
<tb> 11 <SEP> benzophenone <SEP> oxide <SEP> of <SEP> diisopropyl <SEP> 5.1.10-2 <SEP> 0.6.10-2 <SEP> 120 <SEP> min <SEP> 100 <SEP > 45.5 <SEP> 41.5 <SEP> 1.10
<tb> (0.975) <SEP> (0.125)
<tb> 12 <SEP> benzophenone <SEP> oxide <SEP> of <SEP> diisopropyl <SEP> 5.0.10-2 <SEP> 1.35.10-2 <SEP> 90 <SEP> mn <SEP> 98 <SEP > 44.0 <SEP> 40.5 <SEP> 1.09
<tb> (1.0) <SEP> (0.25)
<tb> e <SEP> without <SEP> oxide <SEP> of <SEP> diisopropyl <SEP> 5.0.10-2 <SEP> 1.45.10-2 <SEP> 230 <SEP> mn <SEP> 99.5 <SEP> 38 <SEP> 43 <SEP> 0.88
<tb> (0.125)
<tb> f <SEP> without <SEP> oxide <SEP> of <SEP> diisopropyl <SEP> 5.0.10-2 <SEP> 1.45.10-2 <SEP> 375 <SEP> min <SEP> 96 <SEP > 34 <SEP> 36.5 <SEP> 0.93
<tb> (0,50)
<Tb>
EXAMPLES 13 AND 14
COMPARATIVE TEST q
In the following two examples, a different ketone compound was used in comparison with the previous examples.

 It is acetophenone.

 For comparison, the results of the tests are given in the absence of organic solvent (test g).

All conditions and results obtained are collated in the following table (III) Table III
HYDROXYLATION OF PHENDL BY H2O2 / HClO4 / KETONE COMPOUND OF FORMULA (II)

Ref. <SEP> Compound <SEP> ketone <SEP> (II) <SEP> Solvent <SEP> organic <SEP> Ratio <SEP> molar <SEP> Ratio <SEP> molar <SEP> Duration <SEP> TT <SEP> RTHQ <SEP> PSTN <SEP> Report
<tb> [ratio <SEP> molar <SEP> [ratio <SEP> molar <SEP> H2O2 / PHENOL <SEP> HClO4 / H2O2 <SEP> HQ / PC
<tb> compound <SEP> ketone <SEP> (II) / <SEP> solvent <SEP> organic /
<tb> H2O2] <SEP> phenol]
<tb> 13 <SEP> acetophenone <SEP> oxide <SEP> of <SEP> diisopropyl <SEP> 5.25.10-2 <SEP> 1.15.10-2 <SEP> 16 <SEP> min <SEP> 100 <SEP > 37 <SEP> 49 <SEP> 0.76
<tb> (0.93) <SEP> (0.12)
<tb> 14 <SEP> acetophenone <SEP> oxide <SEP> of <SEP> diisopropyl <SEP> 5.1.10-2 <SEP> 1.20.10-2 <SEP> 90 <SEP> mn <SEP> 100 <SEP > 40.5 <SEP> 47 <SEP> 0.86
<tb> (1.0) <SEP> (0.25)
<tb> g <SEP> acetophenone <SEP> without <SEP> 5.1.10-2 <SEP> 1.25.10-2 <SEP> 2 <SEP> min <SEP> 100 <SEP> 34.5 <SEP> 49 <SEP> 0.70
<tb> (0.975)
<Tb>
Examination of Table (III) clearly demonstrates that the presence of a polar organic solvent as defined according to the invention promotes the formation of hydroquinone.

Claims (10)

1 - Process for hydroxylation of phenolic compounds of general formula (I):

 in which R and Ro, which are identical or different, represent a hydrogen atom, an alkyl radical having from 1 to 4 carbon atoms, a cyclohexyl radical or a phenyl radical, by means of hydrogen peroxide and in the presence of a quantity effective method of a strong acid and a ketone compound, said method being characterized by the fact that the reaction is conducted 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. 2 - Process according to claim 1 characterized in that the polar organic solvent has a dielectric constant of between 2 and 15. 3 - Method according to one of claims 1 and 2 characterized in that the polar organic solvent has a donor number between 15 and 25. 4 - Process according to one of claims 1 to 3 characterized in that the polar organic solvent is selected from aliphatic ether, cycloaliphatic or aromatic, the neutral phosphoric esters, ethylene carbonate. 5 - Process according to one of claims 1 to 4 characterized in that the polar organic solvent is selected from the following solvents: diethyl ether, dipropyl oxide, diisopropyl oxide, dibutyl, methyl tert-butyl ether, dipentyl ether, diisopentyl ether, ethylene glycol dimethyl ether (or 1,2-dimethoxy ethane), diethylene glycol dimethyl ether (or 1,5-dimethoxy-3-oxa-pentane), dioxane, tetrahydrofuran, trimethyl phosphate, triethyl phosphate, butyl phosphate, triisobutyl phosphate, tripentyl phosphate, ethylene carbonate. 6 - Process according to one of claims 1 to 5, characterized in that the ketone compound used corresponds to formula (II)  Ra - CO - X - Rb (II) in said formula (II): - Ra and Rb, which are 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 which are stable under the conditions of the reaction, X represents a valency bond, a -CO- group, a -CHOH group or an R + n- group, R representing an alkylene group preferably having 1 at 4 carbon atoms and n is an integer selected from 1 to 16. 7 - Process according to claim 6, characterized in that the ketone compound used corresponds to formula (II) in which Ra and Rb 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 rings forming between them an ortho- or ortho- and peri-condensed system or being linked together by a valency bond, - arylalkyl or arylacenyl radicals, - Ra and Rb may together form an alkylene or alkenylene radical having from 3 to 5 carbon atoms optionally substituted with a lower carbon alkyl radical or a cycloalkyl or cycloalkenyl radical having 4 to 6 carbon atoms; 2 to 4 carbon atoms of the alkylene or alkenylene radicals may be part of one or two benzene rings optionally substituted with I to 4 hydroxyl groups and / or alkyl and / or alkoxy low carbon condensation. 8 - Process according to one of claims 1 to 7, characterized in that the ketone compound used corresponds to formula (IIa)

 in said formula (IIa): R1 and R2, which are identical or different, represent a hydrogen atom or an electro-donor group; n1, n2, which may be identical or different, is a number equal to 0, 1, 2 or 3; two carbon atoms located in position a with respect to the two carbon atoms bearing the -CO group can be bonded together by a valency bond or by a -CH 2 - group thus forming a ketone ring which can be saturated but also unsaturated. 9 - Process according to one of claims 1 to 8 characterized in that the ketone compound used is chloisi among acetone, dimethyl-3,3 butanone-2, methylvinylketone, mesityl oxide, the 2,4-dimethylpentanone-3, diacetyl, dicyclohexylketone, acetophenone, benzophenone, 2-methylbenzophenone, 2,4-dimethylbenzophenone, 4,4'-dimethylbenzophenone, dimethyl-2, Benzophenone, 4,4'-dimethoxybenzophenone, 4-hydroxybenzophenone, 4-dihydroxybenzophenone, 4-benzoylbiphenyl, benzoin, 4,4'-dihydroxybenzoin, dimethylbenzophenone, 2,4 benzoin, 4,4'-dimethylbenzoin, 4,4'-dimethoxybenzoin, 4,4'-difluorobenzoin, α-methoxybenzoin, α-ethoxybenzoin, deoxybenzoin, 4-hydroxy-deoxybenzoin, 4-methyl-deoxybenzoin, 4-methoxy-deoxybenzoin, 4,4'-dimethoxy-deoxybenzoin, 4,4'-difluoro-deoxybenzoin, benzalacetone, benzil, cyclohexyl xanone, α-isophorone, cyclohexenylcyclohexanone, fluorenone. 10 - Process according to one of claims 1 to 9 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.