FR2692889A1 - Oxidn. of aromatic cpds. substd. by oxidisable alkyl gps. and hydroxyl and/or alkoxy gps. - Google Patents

Abstract

The oxidn. of an aromatic cpd. substd. with an oxidisable alkyl gp. of formula (I) (where Y = an oxidisable gp.; n = 1-5, pref. 1,2 or 3; r = 1-24C hydrocarbon which may be satd. aliphatic, satd. cyclo-aliphatic (opt. unsatd. or aromatic) mono- or poly-cyclic, or satd. aliphatic with a cyclic substitutent; 2R gps. on 2 O atoms on vicinal C atoms (on the aromatic nucleus) may form a satd. ring (opt. unsatd. or aromatic) with 5-8 atoms) is effected in water or a mixt. of water + organic solvent in the presence of a solid catalyst consituted of an active phase deposited on a support, comprising Pd and Sn, Ge, Te or Cu.

Description

PROCESS FOR THE OXIDATION OF PHENOLIC COMPOUNDS CARRIING A
OXIDIZABLE ALKYLE GROUP
The present invention relates to a process for the oxidation of phenolic compounds carrying an oxidizable alkyl group.

 The invention relates to the preparation of aldehydes or hydroxyarornatic ketones.

 The invention relates more particularly to a process for the oxidation of cresols to corresponding hydroxybenzaldehydes.

 It is known according to EP-A 0 012 939, US-A 4 453 016 and US-A 4 471 140, to oxidize p-cresol1 by molecular oxygen, in the presence of sodium or potassium hydroxide and d 'A catalyst such as a cobalt, nickel, chromium or nickel compound which leads to the alkaline salts of p-hydroxybenzaldehyde.

 A preferred variant consists in using methanol as the reaction solvent and using cobalt salts as catalyst.

 Such processes use a large excess of sodium or potassium hydroxide, which leads to very concentrated and viscous reaction media.

In addition, to separate the p-hydroxybenzaldehyde formed, it is necessary to neutralize the excess base, which induces the formation of significant amounts of salts.

 To overcome these drawbacks, a process has been proposed (US Pat. No. 4,748,278) for isolating the p-hydroxybenzaldehyde formed, but this involves additional steps.

 Furthermore, it is described in JP-A 63 154 644, a process for the oxidation of p-cresol by oxygen, in the presence of a catalyst composed of cobalt acetate, cobalt bromide and acetate of manganese. The reaction is carried out in a mixture of acetic acid and acetic anhydride since it is necessary to protect the hydroxyl group by transforming it into an acetoxy group.

This process therefore has the disadvantage of requiring the protection of the hydroxyl group. In addition, the reaction is not selective for aldehyde because more acid is formed: the yield of acetoxybenzoic acid obtained being of the order of 80
The objective of the present invention is to provide an oxidation process, inter alia of cresols, a process which is carried out in a single step, which does not require the protection of the hydroxyl group and which makes it possible to obtain the aldehyde with good selectivity and good reaction yield.

 It has now been found, and this is what constitutes the object of the present invention, a process for the oxidation of phenolic compounds carrying an oxidizable alkyl group by oxidation of said compounds, by an oxidizing agent in the presence of a catalyst. characterized in that the catalyst is a solid catalyst consisting of an active phase deposited on a support comprising palladium optionally associated with another metallic element chosen from tin, germanium, tellurium and copper and that the reaction is carried out in water or in a mixture comprising water and an organic solvent.

 In the following description of the present invention, the term “phenolic compound with an oxidizable alkyl group” denotes an aromatic compound carrying at least one hydroxyl group and at least one oxidizable alkyl group.

 The term "oxidizable alkyl group *" means an alkyl group in which the carbon atom directly attached to the carbon atom of the aromatic nucleus carries at least two free hydrogen atoms.

dans ladite formule (I): - n est un nombre égal à 1,2 ou 3, - R1 et R2 représentent un atome d'hydrogène, - R3 représente l'un des groupes suivants:
un atome d'hydrogène, un radical alkyle ayant de 1 à 12 atomes de carbone, un radical phényle éventuellement substitué de formule

The phenolic substrate which is oxidized, in accordance with the process of the invention, more particularly corresponds to the general formula (I):

in said formula (I): - n is a number equal to 1.2 or 3, - R1 and R2 represent a hydrogen atom, - R3 represents one of the following groups:
a hydrogen atom, an alkyl radical having from 1 to 12 carbon atoms, an optionally substituted phenyl radical of formula

in which R4 represents a hydrogen atom, an alkyl radical having
1 to 12 carbon atoms, an alkoxy radical having 1 to 10 carbon atoms
carbon, a hydroxyl group; m is a number equal to 0, 1, 2 or 3,
an alkoxy radical having from 1 to 10 carbon atoms,
a halogen atom,
a radical of the R5 - CO - X - type in which R5 represents a radical
linear or branched alkyl having from 1 to 10 carbon atoms, a radical
phenyl, a CF3- radical, an alkoxy radical having from 1 to 10 atoms
carbon or phenoxy and X represents a valential bond or an atom
oxygen.

 By halogen atom is meant more particularly a chlorine, bromine or fluorine atom.

The process of the invention applies very particularly to the substrates mentioned below: - o-cresol - p-cresol - m-cresol - 4-ethyl phenol - (2-methoxymethyl) phenol - 1,2-dihydroxy-4-methylbenzene - 4,4-dihydroxy diphenylmethane
The invention is entirely suitable for carrying out the oxidation of cresols and more especially for oxidizing p-cresol to p-hydroxybenzaldehyde and mcresol to m-hydroxybenzaldehyde.

 The process of the invention can be carried out in a solvent which can be water or a mixture of an organic solvent.

 In the following description of the present invention, the expression "reaction solvent" means water or a water / organic solvent mixture.

 The water can be water or an acidic, neutral or slightly basic aqueous solution.

Thus it is possible to envisage an aqueous solution of a mineral acid or an acid salt such as: Boric acid, Sulfuric acid, Potassium acetate, potassium carbonate, I ' sodium hydrogen sulfate,
Potassium hydrogen sulfate; an aqueous solution of a neutral salt, for example, potassium nitrate, potassium sulfate, magnesium sulfate; an aqueous solution of a mineral base or a basic salt such as: sodium hydroxide, potassium hydroxide, ammonium hydroxide, basic potassium carbonate.

 The concentration of the aqueous solution in acid, base or salt advantageously varies between 10-3 and 1 mole / liter.

 According to the process of the invention, water can be used as reaction solvent. In this case, in the absence of organic solvent, use is preferably made of an acidic, neutral or slightly basic aqueous solution as mentioned above.

 Also suitable for implementing the method of the invention, a water mixture! organic solvent.

 By organic solvent is meant a polar or apolar, protic or aprotic organic solvent.

 As examples of polar organic protic solvents suitable for the invention, mention may be made, inter alia, of carboxylic acids or their precursors and alcohols or polyols.

 The carboxylic acids which can be used can be mono- or polycarboxylic. These are compounds which do not exhibit unsatu rations.

They respond more particularly to the following general formula (II):
R-COOH (II) in said formula (II), R represents a hydrocarbon radical having from 1 to 24 carbon atoms which can be a linear or branched saturated acyclic aliphatic radical, a saturated or aromatic cycloaliphatic radical, monocyclic or polycyclic.

 Said radical R can carry another COOH functional group. It can also carry other substituents, for example, alkoxy or halogen insofar as they do not interfere in the reaction.

 R more particularly represents a linear or branched alkyl radical having from 1 to 4 carbon atoms, a cycloalkyl radical having from 5 to 7 carbon atoms or a phenyl radical.

As examples of carboxylic acids capable of being used in the process of the invention, there may be mentioned: aliphatic monocarboxylic acids such as acetic acid, propionic acid, butyric acid,
Valeric acid, Hexanoic acid; aliphatic dicarboxylic acids such as malonic acid, succinic acid, adipic acid; cycloaliphatic acids such as cyclopentane carboxylic acid, Cyclohexane carboxylic acid; Benzoic acid, Naphthoic acid, Phenylacetic acid.

 Among the abovementioned carboxylic acids, use is preferably made of acetic or propionic acid.

 As polar organic protic solvents which are suitable for the present invention, use may also be made of mono- or polyhydric alcohols.

The alcohols corresponding to the general formula (111) are chosen more particularly:
R'-OH (III) in said formula (III), R 'represents a hydrocarbon radical having from 1 to 24 carbon atoms which can be a linear or branched saturated acyclic aliphatic radical or a saturated, monocyclic cycloaliphatic radical.

 Said radical R ′ can carry another functional group OH. It can also carry other substituents, for example, alkoxy or halogen as long as they do not interfere in the reaction.

 R 'more particularly represents a linear or branched alkyl radical having from 1 to 4 carbon atoms, a cycloalkyl radical having from 5 to 7 carbon atoms.

 As examples of mono- or polyhydroxylated alcohols which may be used in the process of the invention, there may be mentioned: aliphatic monoalcohols such as methanol, ethanol, propanol, butanol, sec-butanol , tert-butanol, pentanol, hexanol; aliphatic dialcohols such as ethylene glycol, diethylene glycol, propylene glycol; cycloaliphatic alcohols such as cyclopentanol, cyclohexanol.

Among the various aforementioned alcohols, the preferred alcohols are methanol,
Ethanol, tert-butanol.

Also suitable for the implementation of the process of the invention, aprotic polar organic solvents and there may be mentioned more particularly: - nitro compounds such as nitromethane, nitroethane, 1-nitro propane, 2-nitro propane or their mixtures, nitrobenzene, - aliphatic or aromatic nitriles such as acetonitrile, propionitrile, butanenitrile, isobutanenitrile, benzonitrile, benzyl cyanide, - tetramethylene sulfone (sulfolane),
Among the abovementioned solvents, acetonitrile is preferably used.

It is also possible to use in the process of the invention, slightly polar aprotic solvents such as in particular: - aliphatic, cycloaliphatic or aromatic ether-oxides and, more particularly, diethyl ether, dipropyl ether, Diisopropyl ether,
Dibutyl oxide, methyl tertiobutyl ether, dipentyl oxide, diisopentyl oxide, ethylene glycol dimethyl ether (or 1,2-dimethoxy ethane), diethylene glycol dimethyl ether (or 1,5-dimethoxy oxa- 3 pentane), dioxane, tetrahydrofuran, - neutral phosphoric esters such as, in particular, trimethyl phosphate, triethyl phosphate, tributyl phosphate, triisobutyl phosphate, tripentyl phosphate, - carbonate ethylene.

 Dioxane is preferably used.

 According to the process of the invention, the oxidation of the phenolic substrate can be carried out in a water / organic solvent mixture.

 The amount of water in the water / organic solvent mixture can vary widely. Thus, the weight ratio between water and the organic solvent can vary between 0.05 and 0.95, and preferably between 0.20 and 0.80.

 One of the characteristics of the process of the invention is that there is always water in the reaction mixture.

 The water / phenolic substrate molar ratio to be oxidized can vary between 20 and 1000 and is preferably around 100.

 The concentration of the phenolic substrate to be oxidized in the reaction solvent can vary within wide limits. Thus, it can be between 0.01 mole and 5 moles of phenolic substrate per liter of reaction solvent and preferably from 0.05 to 1.0 mole per liter.

 According to the present invention, a solid catalyst is used which comprises at least the metallic element palladium, this being able to be associated with other metallic elements chosen from tin, germanium, tellurium and copper. It is therefore possible to use bi- or tri-metallic catalysts.

 As examples of catalysts which are very suitable for the present invention, mention may be made of catalysts comprising the following elements: palladium, palladium-tin, palladium-germanium, palladium-copper, palladium-tellurium, palladium-tellurium-copper, palladium-tin-copper .

 Advantageously, catalysts based on palladium-tin, palladium-germanium are used.

 The aforementioned metal elements are implemented on a support, the nature of which may be variable. This is how the present invention may be suitable, in particular, active charcoals, silica gels, silica alumina mixtures, alumina, clays, bauxite, magnesia and diatomaceous earth.

 For a good implementation of the process of the invention, the preferred carbon supports are generally activated by a well-known treatment carried out with nitric acid.

 The active phase consisting of palladium optionally added with another metallic element as mentioned above generally represents at most 20% of the weight of the solid catalyst although higher contents can be used.

 With regard to the minimum content, the active phase represents at least 0.1% of the weight of the solid catalyst.

 The amount of active phase in the catalyst can vary widely, it preferably represents from 0.05 to 10 k of the weight of the solid catalyst.

 When the catalyst has additional metallic elements, the amount of these is such that the molar ratio between the palladium and the other metallic elements is preferably between 0.01 and 10, and even more preferably between 0.1 and 5.0.

 The amount of catalyst to be used relative to the phenolic substrate to be oxidized can vary within wide limits. Thus, the amount of catalyst expressed by the molar ratio between the metal element (s) and the phenolic compound carrying an oxidizable alkyl group can vary between 0.01 and 0.001, preferably between 0.05 and 0.01.

 To prepare the supported catalyst useful for carrying out the process of the present invention, recourse may be had to conventional techniques, known in themselves, for the preparation of supported metal catalysts. Reference may be made, in particular, to the preparation of the various catalysts for the work: [J. F. LEPAGE "Contact catalysis *, design, preparation and implementation of industrial catalysts, Technip Edition (1978) 1.

 The catalyst can be prepared, for example, by introducing a support into a solution which is prepared by dissolving at least one suitable compound of the chosen element (s); the active element (s) are deposited on the support by distilling off the solvent and the contact mass thus obtained is subjected to reduction by means of a stream of hydrogen or by a reducing compound such as hydrazine, methanol or formaldehyde.

 According to another conventional mode of preparation, the deposition of the compound or compounds providing the active elements on the support is carried out by precipitating the compounds in a manner known per se and by subjecting the contact mass thus obtained to a reduction by means, in particular, hydrogen, hydrazine, methanol or formaldehyde.

 Other methods of preparation are also possible, in particular the impregnation of a support by means of a solution of the appropriate compound (s), in the presence of an organic reducing agent as mentioned above.

 The deposition on the support of several metal elements can of course be carried out simultaneously or successively.

 The nature of the compounds providing the metallic elements used for the preparation of the catalysts of the invention is not critical.

 Metals themselves can be used such as palladium, tin, germanium, tellurium and copper.

By way of examples of compounds which can be used for the preparation of the catalysts of the invention, there may be mentioned in particular: palladium oxide hydrated or not, palladium dioxide, palladium nitrate,
Palladium acetate. As regards additional metallic elements, it is possible to use, inter alia, oxides, nitrates, carboxylates, alcoholates of tin, germanium, tellurium or copper or organometallic compounds in which the abovementioned metals are linked to an atom of hydrogen and / or alkyl radicals preferably having from 1 to 4 carbon atoms. The preferred salts are the following: tin II compounds such as tin acetate II, tin octoate II, tin ethylhexanoate; tellurium monoxide or trioxide; Germanium oxide, germanium ethylate, tetrabutylgermanium; Cuprous oxide, cupric oxide, cupric sulfate, cupric acetate, cu ivic methylate.

 The size of the catalyst particles is generally between 0.1 and 1.0 mm, it being understood that larger or smaller dimensions can also be used. The size of the particles as mentioned above depends on the procedure chosen.

 As mentioned above, the phenolic compounds carrying an oxidizable alkyl group are oxidized in a reaction solvent as defined in the presence of a solid catalyst defined above and an oxidizing agent.

 The reaction is advantageously carried out in the liquid phase, by suspending the solid catalyst in the reaction medium comprising the phenolic compound carrying an oxidizable alkyl group, the reaction solvent and an oxidizing agent.

 As oxidizing agents capable of being used in the process of the invention, there may be mentioned in particular, hydrogen peroxide, peracetic acid, tert-butyl hydroperoxide, cyclohexyl hydroperoxide.

 The hydrogen peroxide is advantageously used in its commercial form, namely an aqueous solution whose concentration is around 70%.

 The amount of oxidizing agent introduced can vary widely. Generally, it is equal to the stoichiometric amount or even in slight excess of 20% compared to the stoichiometric amount.

 As oxidizing agents, use is preferably made of molecular oxygen or a gas containing it.

 This gas can be pure oxygen or oxygen diluted with an inert gas, for example nitrogen or a rare gas, preferably argon. We can therefore use air.

 The quantity of oxygen to be used is not critical insofar as it is such that neither the feed gases, nor any gas phase capable of appearing in the reaction zone is in the range of the explosive compositions , taking into account the other parameters or reaction conditions chosen. The quantity of oxygen can be in excess or in defect with respect to the stoichiometry of the reaction, with respect to the substrate to be oxidized.

 The reaction pressure varies between atmospheric pressure and around 200 bar. A pressure between 1 and 100 bar is preferred.

 The process of the invention can be carried out at atmospheric pressure, by bubbling pure oxygen, at a flow rate, for example, from 1 to 50 liters / hour.

 Another variant of the invention consists in working under pressure, in an autoclave. In this case, dilute oxygen is used, preferably air, under a pressure advantageously of the order of 80 to 100 bar.

 The reaction temperature is generally between 40 ° C. and 200 ° C., and preferably between 50 ° C. and 120 ° C.

 From a practical point of view, the reactor is loaded in any order: the reaction solvent, the solid catalyst and the phenolic substrate to be oxidized.

 In the case where the oxidizing agent is in liquid form, it is introduced at the same time as the other reagents.

 The reaction medium is stirred and heated to the chosen reaction temperature. When the oxidizing agent is in gaseous form, molecular oxygen or a gas containing it is then sent.

 At the end of the reaction, the solid catalyst is separated by conventional solid / liquid separation techniques, preferably by filtration or by decantation. The oxidized compound obtained, aldehyde or ketone, is recovered by any suitable means, for example, by distillation of the reaction solvent.

 The examples which follow illustrate the invention without however limiting it.

 In Examples 1 to 11, the apparatus used is always the same. It is a 100 ml glass flask, fitted with effective central stirring, a condenser, an oxygen supply by a dip tube. Heating is provided by an oil bath.

In the examples, the abbreviations have the following meaning:
number of moles of phenolic substrate transformed
Conversion rate = ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~
number of moles of phenolic substrate introduced
number of moles of aldehyde formed
Selectivity =
number of moles of phenolic substrate transformed
The percentages given in the examples are expressed by weight.

EXAMPLE 1
a) Treatment of the carbon black used as a support
Activated carbon black supplied by CECA SA, type 3S and with a BET surface area of 1150 m 2 / g (100 g) is suspended in an aqueous solution of nitric acid at 30% (600 ml). The mixture is brought to reflux for 2 hours. The aqueous solution is removed by filtration and the carbon black is washed with demineralized water until a pH of the washing waters is equal to 4.

The carbon black is dried at 90 ° C., under reduced pressure of 20 mm of mercury.

b) Preparation of the catalyst containing palladium and germanium
In an autoclave of. 300 ml, carbon black (10 g), thus treated, is loaded, suspended in toluene (150 ml), then tetrabutylgermanium (6.02 g, 20 mmol) and palladium acetate (1 , 08 g, 4.42 mmol)
The mixture is heated to 80ex for 2 hours, with effective stirring under 20 kg / cm 2 of hydrogen.

 The autoclave is cooled, the catalyst recovered by filtration under argon and dried under reduced pressure of 20 mm of mercury.

c) Oxidation of p-cresol
The catalyst (1 g) thus prepared was reacted according to the procedure given below.

The following are loaded into the reactor:
- 10 ml of acetic acid,
- 40 ml of water,
- 0.98 g (10 mmol) of potassium acetate,
- 1.1 g (10 mmol) of p-cresol,
- 1 g of catalyst as prepared palladium / germanuim on carbon.

 It is specified and this is valid for all the examples that the acetic acid used is 99% acetic acid.

Stirred, heated at 1 00C for two hours, admitting oxygen at the rate of 5 liters / hour.

 The reactor is cooled and the content determined by high pressure liquid chromatography (HPLC).

 The conversion of p-cresol is 50%.

 0.8 mmol of p- (hydroxymethyl) phenol is obtained, 2.2 mmol of phydroxybenzaldehyde and 0.3 mmol of p-hydroxybenzoic acid.

EXAMPLE Ne 2
In this example, palladium deposited on carbon black is used as catalyst.

 The catalyst was obtained by precipitation of palladium from palladium chloride according to a well-known technique described in the work: [J. F. LEPAGE "Contact catalysis", design, preparation and implementation of industrial catalysts, Technip Edition (1978) 1.

The following are loaded into the reactor:
- 10 ml of acetic acid,
- 40 ml of water,
- 0.98 g (10 mmol) of potassium acetate,
- 1.1 g (10 mmol) of p-cresol,
- lg of catalyst, namely palladium on carbon black (3S)
comprising 5% by weight of palladium.

 Stirred, heated at 100ex for two hours, admitting oxygen at the rate of 5 liters / hour.

 The reactor is cooled and the content determined by high pressure liquid chromatography (HPLC).

 The conversion of p-cresol is 60%.

 0.18 mmol of p- (acetoxymethyl) phenol is obtained, 1.11 mmol of phydroxybenzaldehyde and 0.2 mmol of p-hydroxybenzoic acid.

EXAMPLE Ne 3
a) Preparation of the catalyst containing palladium and tin.

In a balloon te! as previously described, we load:
- 400 ml of acetic acid,
- 2.44 9 (10 mmol) of palladium acetate Pd (OAc) 2,
- 9.8 g (100 mmol) of potassium acetate,
- 20 g of carbon black treated according to the procedure of example N ′ 1.

The mixture is stirred for 15 minutes at room temperature and then 16.1 g (40 mmol) of tin ethylhexanoate II are added
It is heated for 4 hours at 110 ° C. with stirring.

 The flask is cooled, the catalyst collected by filtration under argon, washed with 2 times 50 ml of acetic acid and dried at 50C under 20 mm of mercury. The catalyst contains 4.3% by weight of palladium, and 2% by weight of tin.

b) Oxidation of p-cresol
The catalyst (1.0 g) thus prepared is reacted according to the procedure used for example N "2.

 The conversion of p-cresol and 96%.

 0.3 mmol of p- (hydroxymethyl) -phenol is obtained, 5.2 mmol of phydroxybenzaldehyde, 1 mmol of p-hydroxybenzoic acid.

EXAMPLE # 4
The catalyst (0.5 g) prepared in Example Ne 3 is reacted according to the procedure used for Example N "2 except that the reaction is carried out in a mixture of 30 ml of acetic acid and 20 ml of water.

 The reaction temperature is 100 ° C.

 The conversion of p-cresol is 87%.

 0.9 mmol of p- (acetoxymethyl) phenol are obtained, 5.6 mmol of phydroxybenzaldehyde and 0.75 mmol of p-hydroxybenzoic acid.

EXAMPLE Ne 5
The catalyst (0.5 g) prepared in Example N 3 is reacted according to the procedure used for Example N 2 except that the reaction is carried out in a mixture of 20 ml of methanol and 30 ml of an aqueous solution of sulfuric acid at pH = 1.

 The reaction temperature is 80 C.

 The conversion of p-cresol is 80%.

 5.4 mmol of p-hydroxybenzaldehyde and 0.7 mmol of methyl phydroxybenzoate are obtained.

EXAMPLE # 6
The catalyst (1 g) prepared in Example N '3 is reacted according to the procedure used for Example N' 2, except that the acetic acid is replaced by tertiobutanol and that the reaction temperature is 80 C.

 The conversion of p-cresol is 50%.

 2.2 mmol of p-hydroxybenzaldehyde and 0.2 mmol of phydroxybenzoic acid are obtained.

EXAMPLE # 7
In this example, a palladium / copper-tin catalyst prepared from a palladium / copper on carbon catalyst manufactured by
Engelhard containing 53% by weight of palladium, 1.5% by weight of copper and 53% by weight of water.

We charge:
- 2 g of a palladium / copper on carbon catalyst,
- 20 ml of acetic acid,
- 30 ml of water,
- 1.02 g (9.4 mmol) of p-cresol,
- 0.9 g (2.25 mmol) of ethyl ethylhexanoate il,
It is heated for 2 hours at 100 ° C. with stirring and admitting oxygen at the rate of 5 liters / hour.

 The conversion of p-cresol is 70%.

 2.9 mmol of p-hydroxybenzaldehyde and 0.8 mmol of phydroxybenzoic acid are obtained.

EXAMPLE # 8
a) Preparation of the catalyst containing palladium. tellurium and copper
Dissolve in a 30% aqueous solution of nitric acid:
- 1.63 g (7.3 mmol) of palladium acetate, Pd (OAc) 2,
- 0.105 g (0.66 mmol) of tellurium dioxide TeO2,
- 4 g (20 mmol) of copper acetate Cu (OAc) 2, H2O,
Carbon black (15 g) treated according to Example N "1 is suspended in this solution. The solvent is evaporated off under reduced pressure and the solid thus obtained is dried at 80" C under reduced pressure of 20 mm of mercury. .

 The catalyst is reduced for 2 hours at 200 "C and 2 hours at 400" C by a stream of nitrogen (60 liters / hour) saturated with methanol.

 Then it is treated for 15 hours at 3000C with nitrogen (60 liters / hour) containing 2% oxygen and again reduced for 2 hours at 200 "C and 2 hours at 400" C with a stream of nitrogen saturated with methanol.

b) Oxidation of p-cresol
A test was carried out with the catalyst (1 g) thus prepared.

The following are loaded into the reactor:
- 1 g of catalyst,
- 20 ml of acetic acid,
- 30 ml of water,
- 1.22 9 (11.3 mmol) of p-cresol.

 It is heated for 2 hours at 1000C by stirring and admitting oxygen at the rate of 5 liters / hour.

 The conversion of p-cresol is 50%.

 2.9 mmol of p-hydroxybenzaldehyde and 0.3 mmol of phydroxybenzoic acid are obtained.

EXAMPLE # 9
The catalyst (0.5 g) prepared in Example N 3 is reacted according to the procedure used for Example N 2 except that the reaction is carried out in a mixture of 25 ml of water and 25 ml of dioxane.

 The reaction temperature is 90 ° C.

 The conversion of p-cresol is 60%.

 1.2 mmol of p- (hydroxymethyl) phenol and 3.3 mmol of phydroxybenzaldehyde are obtained.

EXAMPLE 10
In this example, the reaction is carried out in a two-phase medium.

 The catalyst (0.5 g) prepared in Example N 3 is reacted according to the procedure used for Example N 2 except that the reaction is carried out in a mixture of 25 ml of chlorobenzene, 12.5 ml of acetic acid and 12.5 ml of water.

 The conversion of p-cresol is 35%.

 1.6 mmol of p- (hydroxymethyl) phenol and 1.0 mmol of phydroxybenzaldehyde are obtained.

EXAMPLE 11
In this example, the reaction is carried out using hydrogen peroxide as the oxidant.

The catalyst (1.0 g) prepared in Example N 3 is loaded into the reactor as well as:
- 25 ml of water,
- 25 ml of acetic acid,
- 25 mmol of hydrogen peroxide
- 10 mmoles of p-cresol,
- 10 mmol of potassium acetate.

 Stir and heat 2 hours at 100ex.

 The conversion of hydrogen peroxide is 100% and that of p-cresol 84%.

 3.0 mmol of p-hydroxybenzaldehyde and 2.7 mmol of phydroxybenzoic acid are obtained.

EXAMPLE NO 12
In this example, the reaction is carried out under pressure.

The catalyst (0.5 g) prepared in Example N 3 is loaded into a 150 ml autoclave as well as:
- 25 ml of water,
- 25 ml of acetic acid,
- 10 mmoles of p-cresol,
- 10 mmol of potassium acetate.

 The autoclave is pressurized with 40 bar of air containing by volume, 20% oxygen and 80% nitrogen and heated at 130 ° for 2 hours.

 The autoclave is cooled and brought back to atmospheric pressure.

 The conversion of p-cresol is 100%.

 6.8 mmol of p-hydroxybenzaldehyde and 1 mmol of p hydroxybenzoric acid are obtained.

Claims (19)

1 - Process for the oxidation of phenolic compounds carrying an oxidizable alkyl group by oxidation of said compounds with an oxidizing agent in the presence of a catalyst characterized in that the catalyst is a solid catalyst consisting of an active phase deposited on a support comprising palladium optionally associated with another metallic element chosen from tin, germanium, tellurium and copper and the reaction is carried out in water or in a mixture comprising water and an organic solvent. 2- A method according to claim 1 characterized in that the phenolic substrate which is oxidized corresponds to the general formula (I):

 in said formula (I): - n is a number equal to 1, 2 or 3, - R1 and R2 represent a hydrogen atom, - R3 represents one of the following groups:  a hydrogen atom,  an alkyl radical having from 1 to 12 carbon atoms, an optionally substituted phenyl radical of formula

 wherein R4 represents a hydrogen atom, an alkyl radical having from 1 to 12 carbon atoms, an alkoxy radical having from 1 to 10 carbon atoms, a hydroxyl group; m is a number equal to 0, 1, 2 or 3, an alkoxy radical having from 1 to 10 carbon atoms, a halogen atom,  a radical of the R5 - CO - X - type in which R5 represents a linear or branched alkyl radical having from 1 to 10 carbon atoms, a phenyl radical, a CF3 radical -, an alkoxy radical having from 1 to 10 carbon atoms  carbon or phenoxy and X represents a valential bond or an atom  oxygen. 3- Method according to one of claims 1 and 2 characterized in that the phenolic substrate is chosen from: - o-cresol - p-cresol - m-cresol - 4-ethyl phenol - ( 2-methoxymethyl) phenol - 1,2-dihydroxy-4, 4-methylene benzene - 4,4-dihydroxy 'diphenylmethane 4 - Method according to one of claims 1 to 3 characterized in that the phenolic substrate is o cresol, p-cresol or m-cresol. 5 - Method according to one of claims 1 to 4 characterized in that the reaction solvent is water or an acidic, neutral or slightly basic aqueous solution optionally mixed with an organic solvent. 6- Method according to one of claims 1 to 5 characterized in that the reaction solvent comprises an aqueous solution of a mineral acid or an acid salt such as: boric acid, sulfuric acid, L ' potassium acetate, potassium carbonate, sodium hydrogen sulfate, potassium hydrogen sulfate; an aqueous solution of a neutral salt, for example, potassium nitrate, potassium sulfate, magnesium sulfate; an aqueous solution of a mineral base or a basic salt such as: sodium hydroxide, potassium hydroxide, ammonium hydroxide, basic potassium carbonate. 7- Method according to one of claims 1 to 6 characterized in that the reaction solvent comprises a polar or apolar, protic or aprotic organic solvent chosen from: mono- or polycarboxylic acids or their precursors; mono- or polyhydroxylated alcohols; nitro compounds, aliphatic or aromatic nitriles; tetramethylene sulfone; aliphatic, cycloaliphatic or aromatic ether-oxides; neutral phosphoric esters; ethylene carbonate. 8- Process according to one of Claims 1 to 7, characterized in that the reaction solvent comprises an organic solvent chosen from: Acetic or propionic acid, methanol, ethanol, tert-butanol, acetonitrile, dioxane. 9- Method according to one of claims 1 to 8 characterized in that the amount of water in said water / organic solvent mixture varies so that the weight ratio between water and organic solvent can vary between 0, 05 and 0.95, and preferably between Q, 20 and 0.80. 10 - Method according to one of claims 1 to 9 characterized in that the water / phenolic substrate molar ratio to be oxidized varies between 20 and 1000 and is preferably around 100.  1 1 - Method according to one of claims 1 to 10 characterized in that the concentration of the phenolic substrate to be oxidized, in the reaction solvent varies between 0.01 mole and 5 moles of phenolic substrate per liter of reaction solvent and preferably between 0.05 and 1.0 mole per liter. 12- Method according to one of claims 1 to 1 1 characterized in that the catalyst comprises the following elements. palladium, palladium-tin, palladium-germanium, palladium-copper, palladium-tellurium, palladium-tellurecopper, palladium-tin-copper. 13 - Method according to one of claims 1 to 12 characterized in that the catalyst is a catalyst based on palladium-tin or palladiumgermanium. 14- Method according to one of claims 1 to 13 characterized in that the metal elements of the catalyst are deposited on a support chosen from active carbon, silica gels, silica-alumina mixtures, alumina, clays , bauxite, magnesia and diatomaceous earth. 15 - Process according to claim 14 characterized in that the metallic elements of the catalyst are deposited on activated carbon. 16 - Method according to one of claims 1 to 15 characterized in that the active phase consisting of palladium possibly added with another metallic element represents from 0.1 to 20%, preferably from 0.5 to 10% of the weight of solid catalyst. 17 - Method according to one of claims 1 to 16 characterized in that the molar ratio between the palladium and the other metallic elements is preferably between 0.01 and 10, and even more preferably between 0.1 and 5 , 0. 18- Method according to one of claims 1 to 17 characterized in that the amount of catalyst expressed by the molar ratio between the metal element (s) and the phenolic compound carrying an oxidizable alkyl group varies between 0.01 and 0.001 , preferably between 0.05 and 0.01. 19- Method according to one of claims 1 to 18 characterized in that the oxidizing agent is hydrogen peroxide or molecular oxygen or a gas containing it. 20 - Method according to one of claims 1 to 19 characterized in that the reaction pressure is between atmospheric pressure and about 200 bar, preferably between 1 and 100 bar. 21 - Method according to one of claims 1 to 20 characterized in that the reaction temperature is between 40 C and 200 "C, and preferably between 50" C and 120 C.