WO2003064363A1

WO2003064363A1 - Method for the preparation of an aromatic aldehyde

Info

Publication number: WO2003064363A1
Application number: PCT/FR2003/000284
Authority: WO
Inventors: Roland Jacquot; Avelino Corma; Marcelo Eduardo Domine
Original assignee: Rhodia Chimie
Priority date: 2002-01-31
Filing date: 2003-01-30
Publication date: 2003-08-07
Also published as: FR2835251A1

Abstract

The invention relates to a method for preparing an aromatic aldehyde by oxidizing a hydroxymethyl compound. According to the inventive method for preparing an aromatic aldehyde by oxidizing a corresponding hydromethyl compound, said hydromethyl compound is reacted with formaldehyde or a formaldehyde generator in the presence of an effective quantity of a microporous solid of type zeolite β, containing silicon, tin, and/or titanium, and optionally aluminum. The invention particularly relates to the preparation of 3-methoxy-4-hydroxybenzaldehyde and 3-ethoxy-4-hydroxybenzaldehyde.

Description

PROCESS FOR THE PREPARATION OF AN AROMATIC ALDEHYDE.

The present invention relates to a process for the preparation of an aromatic aldehyde by oxidation of a hydroxymethylated compound.

The invention relates more particularly to the preparation of 3-methoxy-4-hydroxybenzaldehyde and 3-ethoxy-4-hydroxybenzaldehyde respectively called "vanillin" and "ethyl vanillin".

There are numerous methods in the literature for accessing aromatic aldehydes and more particularly their preparation by oxidation of a hydroxyalkylated compound.

In EP-A-0 934244, there has been described in particular the preparation of vanillin or 3-methoxy-4-hydroxybenzaldehyde according to a process which consists in reacting formaldehyde and guaiacol, in the presence of sodium hydroxide leading to a mixture comprising o-hydroxymethylgaiacol (OMG) and p-hydroxymethylgaiacol (PMG), then oxidizing said mixture with oxygen in the presence of a palladium catalyst and a bismuth co-catalyst and then eliminating in the products of oxidation the container, the carboxylic group located in the ortho position, thus making it possible to obtain vanillin with a very good reaction yield.

In the process described in EP-A-0 934244 which uses a homogeneous catalysis, there is selective oxidation of the hydroxymethyl and formyl group located in the ortho position of a hydroxyl group, into the carboxylic group and oxidation of the hydroxymethyl group situated in the position para, at most in formyl group.

The Applicant proposes a new process making it possible to obtain an aromatic aldehyde, according to a completely different process, using a different oxidizing system and a heterogeneous catalyst of a completely different nature.

More specifically, the subject of the present invention is a process for the preparation of an aromatic aldehyde by oxidation of a corresponding hydroxymethylated compound characterized in that the said hydroxymethylated compound is reacted with formaldehyde or a formaldehyde generator, in the presence an effective amount of a micro-porous solid of the β zeolite type comprising silicon, tin and / or titanium, optionally aluminum. It was surprisingly found that vanillin could be obtained by reacting p-hydroxymethylgaiacol (also known as vanillic alcohol) with formaldehyde, in the presence of the aforementioned micro-porous molecular sieve whereas one might have expected that the formaldehyde reacts on the free position ortho to the hydroxyl group and also leads to the hydroxymethylation of this position: the formaldehyde having, in the present invention, an oxidizing role.

In the following description of the present invention, the term "aromatic aldehyde" means an aromatic compound in which a hydrogen atom directly linked to the aromatic nucleus is replaced by a formyl group and by "aromatic compound", the classic notion of aromaticity as defined in the literature, in particular by Jerry MARCH, Advanced Organic Chemistry, 4 ^th edition, John Wiley and Sons, 1992, pp. 40 and following. By "hydroxymethylated aromatic compound" is meant an aromatic compound in which a hydrogen atom directly linked to the aromatic nucleus is replaced by a hydroxymethylated group.

The substrate involved in the process of the invention is an aromatic compound carrying at least one hydroxymethyl group, hereinafter called “hydroxymethyl compound”.

The aromatic ring carries at least one hydroxymethyl group but it can also carry one or more other substituents. Generally, by several substituents, less than four substituents are defined per aromatic ring.

Any substituent can be present as long as it does not interfere with the reaction of the invention. Examples of substituents are given below, but the list is in no way limiting.

Thus, the process of the invention is well suited to apply to hydroxymethylated compounds corresponding to the following formula (I):

in said formula (I):

- x is an integer between 0 and 4,

- R, identical or different, represents: . a hydrogen atom,

. an alkyl group, linear or branched, having from 1 to 6 carbon atoms, preferably from 1 to 4 carbon atoms, such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, tert-butyl,. a linear or branched alkoxy group having from 1 to 6 carbon atoms, preferably from 1 to 4 carbon atoms such as methoxy, ethoxy, propoxy, isopropoxy, butoxy or a phenoxy group,. a group of formula:

-R OH -R ₁ -COOR ₂

-R OCOR ₂ -R CHO -R., - CO-N (R ₂ ) ₂ -RX -R ^ CFs in said formulas, R ₁ represents a valence bond or a divalent, linear or branched, saturated or unsaturated hydrocarbon group, having from 1 to 6 carbon atoms such as, for example, methylene, ethylene, propylene, isopropylene, isopropylidene; the groups R _{2, which are} identical or different, represent a hydrogen atom or a linear or branched alkyl group having from 1 to 6 carbon atoms; X symbolizes a halogen atom, preferably a chlorine, bromine or fluorine atom.

- two R groups placed on two vicinal carbon atoms can form together and with the carbon atoms which carry them a benzene ring,

- two R groups placed on two vicinal carbon atoms can form together and with the carbon atoms which carry them, a ring having 5 to 7 atoms, comprising a heteroatom.

When x is greater than or equal to 2, two R groups and the two successive atoms of the aromatic ring can be linked together by an alkylene, alkenylene or alkenylidene group having from 2 to 4 carbon atoms to form a saturated, unsaturated or aromatic heterocycle having 5 to 7 carbon atoms. One or more carbon atoms can be replaced by another heteroatom, preferably oxygen. Thus, the R groups can represent a methylenedioxy or ethylenedioxy group.

In formula (I), R preferably represents one of the following groups or functions:

. a hydrogen atom, . a hydroxyl group,

. an alkyl group, linear or branched, having from 1 to 4 carbon atoms,

. a linear or branched alkoxy group having from 1 to 4 carbon atoms,

. a methylenedioxy or ethylenedioxy group. Even more preferably, the hydroxymethylated aromatic compounds of formula (I) are chosen in which the groups R which are identical or different, are a hydrogen atom, a hydroxyl group, a methyl or ethyl group, a methoxy or ethoxy group.

In formula (I), x is preferably equal to 1 or 2. The present invention is particularly applicable to the compounds used alone or in mixture, corresponding to the following formulas:

in said formulas, R represents an alkyl or alkoxy group having from 1 to 4 carbon atoms, preferably a methyl or ethyl group. As preferred examples of substrates capable of being used in the process of the invention, there may be mentioned, among others:

- o-hydroxymethylphenol,

- p-hydroxymethylphenol,

- o-hydroxymethylgaiacol, - p-hydroxymethylgaiacol,

- o-hydroxymethylguetol;

- p-hydroxymethylguetol.

Formaldehyde or any formaldehyde generator such as, for example, trioxane or paraformaldehyde used in the form of linear polyformaldehydes of indifferent degree of polymerization, preferably having a number of units (CH ₂ O), of between 8, may be used. and 100 patterns,

Formaldehyde can be used in the form of an aqueous solution whose concentration is not critical. It can vary between 15 and 50% by weight: commercial solutions are preferably used, the concentration of which is approximately 20 to 40% by weight.

The amount of formaldehyde expressed in moles of formaldehyde per mole of hydroxymethyl compound can vary within wide limits. The formaldehyde / hydroxymethyl compound molar ratio can vary between 5 and 90% and preferably between 15 and 75%. A characteristic of the process of the invention is to use a catalyst which is a micro-porous molecular sieve of the β zeolite type in which part of the silicon atoms are substituted with tin and / or titanium, optionally with aluminum.

The catalyst involved in the process of the invention corresponds to an empirical formula, after calcination which is as follows:

(Al _w Si _1-yz Sn _y Ti _z ) O ₂ (II) in said formula (II): - w is a number between 0 and 0.2, preferably between 0 and 0.1 and even more preferably between 0 and 0.05,

- y is a number between 0 and 0.1, preferably between 0 and 0.06 and even more preferably between 0 and 0.03,

- z is a number between 0 and 0.1, preferably between 0 and 0.06, - y and z cannot be simultaneously equal to 0.

The zeolitic catalysts are prepared according to a hydrothermal crystallization process of a reaction medium comprising a source of tin and / or titanium, a source of silicon, a structuring agent, optionally a source of aluminum, an mobilizing agent OH ^" or F ^" , possibly hydrogen peroxide and water.

Many sources of the silicon element with oxidation state +4 can be used. By way of example, mention may be made of silicas in the form of hydrogels, aerogels, xerogels, colloidal suspensions, silicas resulting from precipitation from solutions of soluble silicates or from hydrolysis of silicic esters as Si (OCH ₃ ) ₄ , Si (OC ₂ H ₅ ) ₄ . Hydrolysable tetravalent silicon compounds such as silicon halides or the like can also be used.

The source of silicon is preferably chosen from alkylsilicates, tetraethylsilicate being that which is most preferred. Among the sources of titanium, there may be mentioned, by way of example, titanium oxides and hydroxides, crystallized or amorphous, tetravalent titanium compounds which can be hydrolyzed such as halides (TiCl ₄ ), organic derivatives of titanium, such as, for example, alkyl o-titanates, preferably tetraethyl o-titanate or tetrabutyl o-titanate, soluble titanium salts such as TiOSO ₄ , TiOCI ₂ , (NH ₄ ) ₂ TiO (C ₂ O ₄ ) ₂ .

Among the sources of tin, mention may in particular be made of tin halides, preferably SnCl ₄ , tin alkoxides, metallic tin, alkali or alkaline earth metal stannates, alkyltin-type compounds.

As sources of aluminum, there may be mentioned, but not limiting, alumina, aluminum ides and alkoxides, aluminum sulfates or nitrates or halides.

As structuring agents, mention may be made of tetraalkylammonium ions such as tetraethylammonium ions; dialkylbenzylammonium ions such as dimethylbenzylammonium ion; bis-piperidunium ions such as the 4,4'-trimethylene-bis (N-benzyl-N-methylpiperidinium) ion. These ions can be provided in the form of compounds of the hydroxide or halide type, preferably chloride or bromide. Mention may also be made of aza-polycyclic compounds such as 1, 4-diazabicyclo-2,2,2-octane.

A first preferred variant of the process of the invention consists in using a micro-porous molecular sieve of the β zeolite type with tin and / or titanium.

Another variant of the process of the invention is to use a micro-porous molecular sieve of the zeolite β Ti + Al or Sn + Al type.

A particularly preferred catalyst for the implementation of the process of the invention is a micro-porous molecular sieve of the β zeolite type with tin corresponding to an empirical formula, after calcination which is as follows:

[If _1-y Sn _y ] O ₂ (IIA) in said formula (IIA), y is between 0.001 and 0.1, preferably between 0.001 and 0.06 and even more preferably between 0.001 and 0.03.

Said catalyst is known and is described in particular in EP-A 1 010667. It is obtained according to a process which consists in a hydrothermal process which involves the formation of a reaction mixture by mixing the desired sources of tin, silicon, optionally titanium, optionally aluminum, an organic structuring agent, water, optionally hydrogen peroxide and a source of fluoride, in any order to give the desired mixture. It is also necessary that the pH of the mixture is in the range of about 7.5 to 9.5. If necessary, the pH of the mixture can be adjusted by adding HF and / or NH ₄ F. Hydrogen peroxide can be added in order to form a complex with the titanium and to keep it in solution. The reaction mixture is heated to a temperature of from about 90 ° C to about 200 ° C, and preferably from about 120 ° C to about 180 ° C, for a period of from about 2 days to 50 days, and preferably from about 10 days to about

25 days, in a hermetically sealed reactor under autogenous pressure. After the allotted time, the mixture is filtered to isolate the solid product which is washed with demineralized water and air dried.

In order to promote crystallization, it is preferable to add crystals of zeolite β as seeds in the reaction mixture. These crystals can be added in the form of a dry solid, of a suspension in a suitable liquid, for example water, an alcohol or a pre-organized gel, that is to say a gel containing germs. A preferred β zeolite germ is a germ prepared according to the teachings of Spanish patent application No. P9501552 or US 6,306,364, in particular Example 1. The germs comprise aluminum but preferably in very small quantities. The Si / Ai ratio is advantageously chosen between 1000 and 2000.

The isolated molecular sieve is characterized in that it has an X-ray diffraction pattern of a β zeolite.

In order to activate the zeolite, that is to say active for adsorption or for catalytic reactions, it is necessary to remove the structuring agent and the fluoride. This is generally achieved by calcination in air of the molecular sieve at a temperature of about 300 ° C to about 1000 ° C for a time sufficient to remove essentially all of the structuring agent and the fluoride, which takes from about 1 to about 10 a.m. After calcination, the solid retains its crystallinity.

The β zeolite involved in the process of the invention is a microporous solid. The size of its pores generally varies between 5 and 7 Å, and preferably between 5.6 and 6.6 Å. [Cf. Atlas of Zeolite Framework Types of C. Baerlocher et al, Elsevier 5 ^th edition (2001)]. Another type of catalyst suitable for the invention is a micro-porous molecular sieve of the titanium β zeolite type corresponding to an empirical formula, after calcination which is as follows:

[If _1-z Tiz] O ₂ (IIB) in said formula (MB), z is between 0.001 and 0.1, preferably between 0.001 and 0.06.

A process for the preparation of such a catalyst is described by T. Blasco et al [J. Phys. Chem. B, 102, 75, 1998].

As other zeolites capable of being used in the process of the invention, mention may be made of β zeolites comprising titanium and tin. They can be represented by the formula (IIC):

[Si _1-yz Sn _y Tiz] O ₂ (IIC) in said formula (IIC): - y is a number greater than 0, between 0.001 and 0.1, preferably between 0.001 and 0.06, and even more preferably between 0.001 and 0.03,

- Z is a number greater than 0, between 0.001 and 0.1, preferably between 0.001 and 0.06.

It is also possible to use a titanium catalyst comprising silicon, aluminum which can be represented by the empirical formula, after calcination which is as follows:

(Al _w Si _1-z Ti ₂ ) O ₂ (IID) in said formula (IID):

w is a number greater than 0, between 0.001 and 0.2, preferably between 0.001 and 0.1, and even more preferably between 0.001 and 0.05,

- Z is a number between 0.001 and 0.1, preferably between 0.001 and 0.06.

Another type of catalyst suitable for the process of the invention are zeolites comprising silicon, aluminum and tin which can be represented by the empirical formula, after calcination which is as follows:

(Al _w Si _1-y Sn _y ) O ₂ (IIE) in said formula (IIE):

- y is a number greater than 0, between 0.001 and 0.1, preferably between 0.001 and 0.06, and even more preferably between 0.001 and 0.03.

For the preparation of said catalysts, reference may be made to the work of T. Blasco et al, J. Am. Chem. Soc, 115, (1993), p. 11806 - 11813. Among the various catalysts mentioned above, a Sn β zeolite is more preferably chosen, preferably corresponding to formula (IIA) in which y is between 0.001 and 0.06 and even more preferably between 0.001 and 0.03.

In accordance with the process of the invention, a catalyst of the zeolitic type as described above is used during the oxidation reaction. The amount of this catalyst to be used, expressed by weight of catalyst relative to the hydroxymethyl compound can vary between 10 and 75%, preferably between 20 and 50%.

A variant of the process of the invention consists in carrying out the oxidation reaction in an organic solvent.

The organic solvent is chosen so that it is inert under the reaction conditions.

Thus, aliphatic, cycloaliphatic or aromatic ether oxides can be used and, more particularly, dipropyl ether, diisopropyl ether, dibutyl ether, methyltertiobutylether, dimethylether of ethylene glycol (or glyme) , dimethyl ether of diethylene glycol (or diglyme); phenyl oxide; dioxane, tetrahydrofuran (THF); esters such as methyl benzoate, methyl terephthalate, methyl adipate, dibutyl phthalate; aliphatic or aromatic nitriles such as acetonitrile, propionitrile, benzonitrile; linear or cyclic carboxamides such as N, N-dimethylacetamide (DMAC), dimethylformamide (DMF), diethylformamide or 1-methyl-2-pyrrolidinone (NMP).

The amount of organic solvent is determined so that the weight concentration of the hydroxymethylated compound in the liquid phase is usually between 2% and 40%, preferably between 5% and 20%.

In accordance with the invention, the hydroxymethyl compound and formaldehyde are reacted hot, in the presence of the microporous molecular sieve. The oxidation temperature is preferably chosen in a temperature range from 40 ° C to 120 ° C, preferably between 60 ° C and 100 ° C.

We generally operate at atmospheric pressure, but we can work at slightly lower or higher pressures.

According to a preferred variant of the process of the invention, the process of the invention is carried out under a controlled atmosphere of inert gases. One can establish an atmosphere of rare gases, preferably argon, but it is more economical to use nitrogen.

From a practical point of view, the method according to the invention is simple to implement. The formaldehyde and the hydroxymethyl compound are charged and the zeolitic catalyst is added and the mixture is heated.

When working batchwise, the reaction time is generally between 0.5 and 15 hours. According to another embodiment, the hydroxymethylated compound can be dissolved in an appropriate solvent, for example acetonitrile, and then introduced continuously during the reaction.

A preferred embodiment of the invention consists in gradually introducing the hydroxymethylated compound optionally in an organic solvent into the reaction medium comprising formaldehyde and the catalyst.

It is also possible to implement the process of the invention in a continuous mode in a tubular reactor comprising the solid catalyst placed in a fixed bed.

The reagents can be introduced separately or as a mixture into the reactor. They can also be introduced into a solvent as mentioned above.

The residence time of the material flow on the catalytic bed varies, for example, between 15 min and 10 hours, and preferably between 30 min and 5 hours.

The aromatic aldehyde obtained is recovered in a conventional manner. If necessary, the organic solvent is removed and then the aldehyde is separated by extraction with the aid of a suitable solvent, for example methyl isobutyl ketone.

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

In the examples, the transformation rate (TT) corresponds to the ratio between the number of moles of substrate transformed and the number of moles of substrate used.

The yield (RR) corresponds to the ratio between the number of moles of product formed and the number of moles of substrate used.

EXAMPLES:

Example 1 This example illustrates the synthesis of a stannosilicate with a β zeolite structure.

30 g of tetraethyl orthosilicate (TEOS) and 32.99 g of tetraethylammonium hydroxide (TEAOH, 35% by weight) are added to a container.

After 90 minutes, a solution of 0.43 g of SnCl _4, 6H ₂ O (purity = 98%) in 2.75 g of water and the mixture was stirred until the ethanol formed by the hydrolysis of TEOS has evaporated.

To the transparent solution, 3.2 g of HF is added (concentration of HF in water equal to 48% by weight) and a thick paste is obtained. Finally, a suspension of 0.36 g of dealuminized β zeolite seeds (Si / Ai ratio of 1000) in 1.75 g of water is added.

The final composition of the gel is described by the following formula:

SiO ₂ ; 0.27 (TEA) ₂ O; 0.008 SnO ₂ ; 0.54 HF; 7.5 H ₂ O This paste is loaded into stainless steel autoclaves with a Teflon jacket and heated to 140 ° C. and allowed to react for 11 days with stirring.

After 11 days, the product is recovered by filtration and is revealed by an X-ray diffraction analysis to have the structure of the β zeolite and to have a crystallinity of approximately 95%.

A chemical analysis also shows that the product contains 1.6% by weight of tin.

The product is calcined at 580 ° C. for 3 hours and it retains its crystallinity.

Example 2

This example illustrates the synthesis of a titanosilicate with a β zeolite structure.

In a container, 40 g of TEOS and 2.54 g of titanium tetraethylate are added and to this solution, 45.38 g of TEAOH (35%) and 6.40 g of hydrogen peroxide (35%) are added. .

The mixture is stirred until the ethanol formed by the hydrolysis of TEOS has evaporated.

To this solution, 4.50 g of HF (48%) is added and a thick paste is obtained.

Finally, a suspension of 0.48 g of dealuminized β zeolite seeds in 2.3 g of water is added.

The final composition of the gel is described by the following formula:

SiO ₂ ; 0.28 (TEA) ₂ O; 0.0035 TiO ₂ ; 0.56 HF; 0.34 H ₂ O ₂ ; 7.5 H ₂ O This paste is loaded into stainless steel autoclaves with a teflon jacket and heated to 140 ° C. for 7 days with stirring.

After this time, the product is recovered by filtration to give a product which contains silicon and titanium in the frame and has the X-ray diffraction pattern of the β zeolite. The crystallinity of the product measured from its X-ray diffraction spectrum is approximately 100%.

Part of this sample is analyzed and shows that it contains 3.2% by weight of titanium. After calcination at 580 ° C, the molecular sieve of the titanosilicate type retains its crystallinity.

Example 3 This example illustrates the synthesis of a stannotitanosilicate with a β zeolite structure.

In a container, 45 g of TEOS and 0.98 g of titanium tetraethylate are added and, to this solution, 50.47 g of TEAOH (35%) and 7.12 g of hydrogen peroxide (35%) are added. . Then, a solution of 0.64 g of SnCl, 5H ₂ O (98%) in

2.5 g of water.

To this solution, 5 g of HF (48%) are added and a thick paste is obtained.

Finally, a suspension of 0.94 g of dealuminized β zeolite seeds in 3 g of water is added.

The final composition of the gel is described by the following formula: SiO ₂ ; 0.28 (TEA) ₂ O; 0.02 TiO ₂ ; 0.008 SnO ₂ ; 0.56 HF; 0.34 H ₂ O ₂ ; 7.5 H ₂ O

This paste is loaded into stainless steel autoclaves with a teflon jacket and heated to 140 ° C. for 18 days with stirring.

After this time, the product is recovered by filtration to give a product which contains silicon, titanium and tin in the frame and has the X-ray diffraction pattern of the β zeolite.

The crystallinity of the product measured from its X-ray diffraction spectrum is approximately 95%.

Part of this sample is analyzed and shows that it contains 0.6% by weight of titanium and 1.5% by weight of tin. After calcination at 580 ° C., the molecular sieve of the stannotitanosilicate type retains its crystallinity.

Example 4

This example illustrates the synthesis of a stannoaluminosilicate with a β zeolite structure.

40 g of TEOS and 35.75 g of TEAOH (35%) are added to a container.

Then a solution of 0.55 g of SnCI ₄ , 5H ₂ O (98%) in 2.5 g of water is also added. After 60 minutes, a solution of 0.21 g of metallic aluminum in 10 g of TEAOH is added and the mixture is stirred until the ethanol formed by the hydrolysis of TEOS has evaporated.

To this solution, 4.53 g of HF (48%) is added and a thick paste is obtained.

Finally, a suspension of 0.47 g of dealuminized β zeolite seeds in 2.5 g of water is added.

The final composition of the gel is described by the following formula:

SiO ₂ ; 0.28 (TEA) ₂ O; 0.008 SnO ₂ ; 0.02 AI ₂ O ₃ ; 0.57 HF; 7.5 H ₂ O This paste is loaded into stainless steel autoclaves with a teflon jacket and heated to 140 ° C. for 10 days with stirring.

After this time, the product is recovered by filtration and has the X-ray diffraction pattern of the β zeolite and a crystallinity of approximately 100%.

A chemical analysis of the material shows that the product contains 1.9% by weight of tin and has an Si / Ai ratio of 27.

The product is calcined at 580 ° C. for 3 hours and its crystallinity is approximately 90%.

Example 5 This example illustrates the synthesis of a titanoaluminosilicate with a β zeolite structure.

30 g of TEOS and 0.82 g of titanium tetraethylate are added to a container and 28.15 g of TEAOH (35%) and 4.73 g of hydrogen peroxide (35%) are added to this solution . After 60 minutes, a solution of 0.039 g of metallic aluminum in 6 g of water is added and the mixture is stirred until the ethanol formed by the hydrolysis of TEOS has evaporated.

The final composition of the gel is described by the following formula:

SiO ₂ ; 0.28 (TEA) ₂ O; 0.025 TiO ₂ ; 0.005 AI ₂ O ₃ ; 0.34 H ₂ O ₂ ; 6.5 H ₂ O The gel is loaded into stainless steel autoclaves with a teflon jacket and heated to 140 ° C. for 4 days with stirring.

After this time, the product is recovered by centrifugation to give a product which contains silicon, titanium and aluminum in the frame and has the X-ray diffraction pattern of the β zeolite. The crystallinity of the product measured from its X-ray diffraction spectrum is approximately 90%.

Part of this sample is analyzed and shows that it contains 2.4% by weight of titanium and has an Si / Al ratio of 70. After calcination at 580 ° C, the titanoaluminosilicate molecular sieve retains its structure.

Example 6 In this example, the catalytic activities of the samples prepared in examples 1, 2, 3, 4 and 5 are compared with respect to the selective oxidation of vanillic alcohol to vanillin using aqueous formaldehyde as agent. oxidant.

Thus, 50 mg of vanillic alcohol and 2 g of aqueous formaldehyde (24.9% by weight solution) are homogenized with stirring, and the mixture is heated to temperatures between 80 and 100 ° C., and the a small aliquot part is taken (time zero).

Then, the reaction mixture is added all at once in a 2 ml glass microreactor (fully closed) equipped with a magnetic stirrer and immersed in a thermostate bath which contains only the catalyst (15 to 20 mg).

After 6 hours, the micro-reactor is removed from the thermostate bath (final time).

The sample is filtered and 20 mg of the final mixture are placed in 0.85 g of acetonitrile.

The solution obtained is analyzed by high performance liquid chromatography, by high performance liquid chromatography (HPLC) coupled with mass spectrometry (MS) and the reaction products are identified by gas chromatography (GC) coupled with mass spectrometry and HPLC-MS, and compared with standard compounds available.

The TT and the RR of several catalysts after six hours of reaction are presented in table (I):

Table (I)

Example 7 This example illustrates the catalytic activity of the Sn-β molecular sieve prepared in Example 1 with respect to the oxidation of vanillic alcohol to vanillin using aqueous formaldehyde as the oxidizing agent and with a slow addition substrate dissolved in acetonitrile.

Thus, 2 g of aqueous formaldehyde (24.9% by weight solution) are introduced into a 5 ml glass micro-reactor (completely closed) equipped with a magnetic stirrer and immersed in a thermostate bath which contains only the catalyst (15 to 20 mg), and it is heated to temperatures between

80 and 100 ° C.

Then, a well homogenized solution of 50 mg of vanillic alcohol in 1 g of acetonitrile is slowly added to the reaction system using a micro-syringe infusion pump (addition rate = 150 μl / h).

After 6 hours, the micro-reactor is removed from the thermostate bath (final time). The sample is filtered and 20 mg of the final mixture are placed in 0.5 g of acetonitrile. The solution obtained is analyzed by HPLC, HPLC-MS and the reaction products are identified by CG-MS and HPLC-MS, and they are compared with standard compounds available. The TT and the RR obtained for the catalyst sample after six hours of reaction are presented in table (II):

Table (II)

Claims

claims

1 - Process for the preparation of an aromatic aldehyde by oxidation of a corresponding hydroxymethylated compound characterized in that said hydroxymethylated compound is reacted with formaldehyde or a formaldehyde generator, in the presence of an effective amount of a micro-porous solid of the β zeolite type comprising silicon, tin and / or titanium, optionally aluminum.

2 - Process according to claim 1 characterized in that the hydroxymethylated compound corresponds to the following formula:

in said formula (I):

- x is an integer between 0 and 4, - R, identical or different, represents:

. a hydrogen atom,

-R OH -R COOR ₂

-R OCOR ₂ -R ^ CHO -R ₁ -CO-N (R ₂ ) ₂ -RX -R CF ₃ in said formulas, R ₁ represents a valence bond or a divalent, linear or branched, saturated or unsaturated hydrocarbon group, having from 1 to 6 carbon atoms ^" such as, for example, methylene, ethylene, propylene, isopropylene, isopropylidene; the groups R ₂ identical or different represent a hydrogen atom or a linear or branched alkyl group having from 1 to 6 carbon atoms; X symbolizes a halogen atom, preferably a chlorine, bromine or fluorine atom,

3 - Method according to one of claims 1 and 2 characterized in that the hydroxymethylated compound corresponds to formula (I) in which R represents one of the following groups or functions:

. a hydrogen atom,. a hydroxyl group,

. an alkyl group, linear or branched, having from 1 to 4 carbon atoms,

. a linear or branched alkoxy group having from 1 to 4 carbon atoms,

. a methylenedioxy or ethylenedioxy group.

4 - Method according to one of claims 1 to 3 characterized in that the hydroxymethylated compound corresponds to formula (I) in which the identical or different R groups are a hydrogen atom, a hydroxyl group, a methyl group or ethyl, a methoxy or ethoxy group.

5 - Method according to one of claims 1 to 4 characterized in that the hydroxymethylated compound corresponds to formula (I) in which x is equal to 1 or 2.

6 - Method according to one of claims 1 to 5 characterized in that the

in said formulas, R represents an alkyl or alkoxy group having from 1 to 4 carbon atoms, preferably a methyl or ethyl group. 7 - Method according to one of claims 1 to 6 characterized in that the hydroxymethylated compound is chosen from:

- o-hydroxymethylphenol,

- p-hydroxymethylphenol, - o-hydroxymethylgaiacol,

- p-hydroxymethylgaiacol,

- Po-hydroxymethylguetol;

- p-hydroxymethylguetol.

8 - Process according to claim 1 characterized in that one uses formaldehyde or any formaldehyde generator preferably, trioxane or paraformaldehyde used in the form of linear polyformaldehydes of indifferent degree of polymerization, preferably having a number of patterns (CH ₂ O) between 8 and 100 patterns.

9 - Process according to claim 8 characterized in that the molar formaldehyde / hydroxymethyl compound molar ratio varies between 5 and 90% and preferably between 15 and 75%.

10 - Process according to claim 1 characterized in that the catalyst corresponds to the empirical formula, after calcination which is as follows:

(Al _w Si _1-yz Sn _y Ti _z ) O ₂ (II) in said formula (II):

- w is a number between 0 and 0.2, preferably between 0 and 0.1 and even more preferably between 0 and 0.05,

- z is a number between 0 and 0.1, preferably between 0 and 0.06,

- y and z cannot be equal to 0 simultaneously.

11 - Process according to claim 1 characterized in that the catalyst is a Sn β zeolite corresponding to the empirical formula, after calcination which is as follows:

[If _1-y Sn _y ] O ₂ (IIA) in said formula (IIA), y is between 0.001 and 0.1, preferably between 0.001 and 0.06 and even more preferably between 0.001 and 0.03. 12 - Process according to claim 1 characterized in that the catalyst is a Ti β zeolite corresponding to the empirical formula, after calcination which is as follows:

[Siι. _z τyθ ₂ (IIB) in said formula (IIB), z is between 0.001 and 0.1, preferably between 0.001 and 0.06.

13 - Process according to claim 1 characterized in that the catalyst is a β zeolite comprising titanium and tin corresponding to the empirical formula, after calcination which is as follows:

[Sii-y-z Sny TiJOg (IIC) in said formula (IIC):

- y is a number greater than 0, between 0.001 and 0.1, preferably between 0.001 and 0.06, and even more preferably between 0.001 and 0.03,

14 - Process according to claim 1 characterized in that the catalyst is a Ti + Al β zeolite corresponding to the empirical formula, after calcination which is as follows:

(Al _w Siι _-z Ti _z ) O ₂ (IID) in said formula (IID):

- w is a number greater than 0, between 0.001 and 0.2, preferably between 0.001 and 0.1, and even more preferably between

0.001 and 0.05,

- Z is a number between 0.001 and 0.1, preferably between 0.001 and 0.06.

15 - Process according to claim 1 characterized in that the catalyst is a Sn + Al β zeolite corresponding to the empirical formula, after calcination which is as follows:

in said formula (IIE): - w is a number greater than 0, between 0.001 and 0.2, preferably between 0.001 and 0.1, and even more preferably between 0.001 and 0.05, - y is a number greater than 0, between 0.001 and 0.1, preferably between 0.001 and 0.06, and even more preferably between 0.001 and 0.03.

16 - Process according to claim 1 characterized in that the catalyst is a Sn β zeolite preferably corresponding to the formula (IIA) in which y is between 0.001 and 0.06 and even more preferably between 0.001 and 0.03.

17 - Method according to one of claims 1 to 16 characterized in that the amount of this catalyst to be used, expressed by weight of catalyst relative to the hydroxymethylated compound varies between 10 and 75%, preferably between 20 and 50%.

18 - Method according to one of claims 1 to 17 characterized in that the oxidation temperature is chosen in a temperature range from 40 ° C to 120 ° C, preferably between 60 ° C and 100 ° C.

19 - Method according to one of claims 1 to 18 characterized in that the reaction is carried out in an organic solvent.

20 - Process according to claim 19 characterized in that the organic solvent is chosen from aliphatic, cycloaliphatic or aromatic ether-oxides and, more particularly, dipropyl ether, diisopropyl ether, dibutyl ether, methyltertiobutylether, dimethylether of ethylene glycol (or glyme), dimethylether of diethylene glycol (or diglyme); phenyl oxide; dioxane, tetrahydrofuran (THF); esters such as methyl benzoate, methyl terephthalate, methyl adipate, dibutyl phthalate; aliphatic or aromatic nitriles such as acetonitrile, propionitrile, benzonitrile; linear or cyclic carboxamides such as N, N-dimethylacetamide (DMAC), dimethylformamide (DMF), diethylformamide or 1-methyl-2-pyrrolidinone (NMP).

21 - Method according to one of claims 1 to 20 characterized in that the hydroxymethylated compound optionally in an organic solvent is added to the reaction medium comprising formaldehyde, the catalyst, optionally an organic solvent. 22 - Method according to one of claims 1 to 21 characterized in that the aromatic aldehyde obtained is vanillin or ethylvanillin.