MXPA96004036A

MXPA96004036A - Process for the preparation of a 4-hidroxibenzaldehido substitute

Info

Publication number: MXPA96004036A
Application number: MXPA/A/1996/004036A
Authority: MX
Inventors: Metivier Pascal; Maliverney Christian; Jouve Isabelle
Original assignee: Rhonepoulenc Chimie
Priority date: 1995-02-20
Filing date: 1996-02-14
Publication date: 1998-07-03

Abstract

The present invention relates to a process for the preparation of a substituted 4-hydroxybenzaldehyde, substituted at least in the 3-position by an alkoxy group, comprising the steps of attaching a substituted phenol compound, substituted at least in the 2-position by an alkoxy group and in which positions 4 and 6 are free, to a first carboxylation step in the 6-position, then to a hydroxymethylation step in the 4-position, followed by an oxidation step of the hydroxymethyl group to a formyl group , and finally to a final stage of decarboxylation

Description

PROCESS FOR THE PREPARATION OF A SUBSTITUTED 4-HIDR0XIBENZALDEHID0 The object of the present invention is a process for the preparation of a 4-hydroxybenzaldehyde having at least one substituent in the ortho position to the OH group. This refers more particularly to the preparation of 3-methoxy-4-hydroxybenzaldehyde and 3-ethoxy-4-hydroxybenzaldehyde, known respectively as COBO "vanillin" and "ethyl-vain 1 lina". Vanillin is obtained mainly from natural sources such as lignin, but a part is prepared chemically. Many methods of preparing the literature are described [Kirk-Othmer, Encyclopedia of Chemical Technology, ¿3, p. 1710, 3rd edition) and a number of them start from guaiacol or 2-raetoxy-phenol. Thus, mention can be made of the preparation of vanillin by the reaction of guaiacol and glyoxylic acid, the oxidation of the condensate by air and then the release of vanillin from the reaction mixture by acidification. The disadvantage of this process is that it uses glyoxylic acid, which is an expensive reagent. Another access route to vanillin according to the Reimer-Tiemann reaction comprises the reaction of guaiacol and chloroform in the presence of potassium hydroxide. Resin formation is a disadvantage of this preparation method. According to the Gatterman reaction, vanillin is synthesized by the reaction of hydrocyanic acid with guaiacol, in the presence of hydrochloric acid. In addition to the use of a reagent that is difficult to handle, this process has the disadvantage of not being selective, because vanillin is accompanied by isova ini 11 and o-vaipylin. A major difficulty present in the synthesis of vanillin is the selectively bind a formyl group? 1 guaiac in the position for a hydroyl group. Another problem to be solved is to provide a process that is competitive from an industrial point of view. The present invention provides a new process that makes it possible to overcome the aforementioned disadvantages, while satisfying the aforementioned requirements. A process for the preparation of a substituted 4-hydroxybenzaldehyde, substituted at least in the 3-position by an alkoxy group, has now been found, which constitutes the subject of interest of the present invention, characterized in that it comprises in holding a compound of substituted phenol, substituted at least in the 2-position by a lcoxy group and in which the 4 and 6-positions are free, to a first stage of the carboxylation in the 6-position, then to a hydro-ethyl-phase in position 4, followed by a step of oxidation of the hydroxymethyl group to a forallo group, and finally to a last stage of decarboxylation. The process of the invention is based on the preparation of the 2-hydroxybenzoic acids hydroxymethyl in the 5-position, and substituted at least in the 3-position by an alkoxy group, which are used as intermediates in the synthesis of hydroxybenzoic acids. -hydroxybenzalde substituted, substituted at least in the 3-position by an alkoxy group. Another object of the invention is the process for the oxidation of 2-hydrobenzoic acids hydroxymethyl in position 5 and substituted, at least in position 3, by an alkoxy group, to the corresponding formylated 2-hydroxybenzoic acids. The process of the invention is completely well suited for the preparation of vanillin. Of course, this makes it possible to selectively form the guaiac in the para position, successfully carrying out the carboxylation of guaiacol in position 6, the hydroxy ethalation followed by oxidation, which gives the formyl group in position 4 as a result, and finally the removal of the carboxyl group located in position b. This process is not only selective but also very coapetitive from an industrial point of view, because it uses cheap reagents. Although the process of the invention is highly suitable for the use of guaiacol and 2-ethoxyphenol, it is also suitable for other substituted phenol coapuestos. It is understood that "substituted phenol compound" means any aromatic compound in which the aromatic ring possesses a hydroxyl group, an alkoxy group in the 2-position, and other possible substituents, and in which positions 4 and 6 are free. Subsequently, in the present invention, "aromatics" is understood to mean the conventional notion of aromaticity as defined in the literature, in particular, by Jerry March, Advanced Organic Chemistry, 4 * edition, John Wiley and Sons, 1992, p. 40 et seq. The invention applies very particularly, among other substituted phenol compounds, to those corresponding to the general formula (I): in the above-mentioned formula (I) -Z, represents: a linear or branched alkoxy radical having from 1 to 12 carbon atoms, preferably from 1 to 4 carbon atoms, such as the methoxy, ethoxy, propoxy, isopropoxy, butoxy radicals , isobutoxy, sec-butoxy and tert-butoxy, -Z_ and Z-, which are identical or different, represent a hydrogen atom or one of the following groups: a linear or branched alkyl radical having from 1 to 2 carbon atoms; carbon, preferably 1 to 4 carbon atoms, such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, = ec-butyl or tert-butyl, a linear or branched alkenyl radical having from 2 to 12 carbon atoms, preferably from 2 to 4 carbon atoms, such as vinyl or allyl, a linear or branched alkoxy radical having from one to 12 carbon atoms, preferably from 1 to 4 carbon atoms, such as methoxy, ethoxy, propoxy, isopropoxy, butoxy, isobutoxy, sec-butoxy and tert-butoxy,. a phenyl radical, a halogen atom, preferably a fluorine, chlorine or bromine atom. The present invention does not exclude the presence on the aromatic ring of substituents of a different nature, as long as these do not interfere with the reactions of the process of the invention. The present invention preferably applies to the coapuestos of the formula (I) in which Z. represents a linear or branched alkoxy radical having from 1 to 6 carbon atoms, preferably from 1 to 4 carbon atoms, Z ~ and Z_ represent a hydrogen atom. Mention may be made, as examples of the substrates used in the process of the present invention. of guaiacol and 2-eto if enol, among others. According to the processes of the invention, the starting material is a substituted phenol compound which is preferably a compound corresponding to the formula (I). The reaction scheme of the process of the invention is given below to facilitate the understanding of the objective of the invention, without limiting the scope of the invention to the reaction scheme.

OM (10 With respect to the following description of the present invention, reference will be made to the formulas given below, without limiting the invention to the extracts defined by the given formulas. According to the process of the invention, a substituted phenol coapuesto of the formula (I) is carboxylated. in a first step, by reacting said substituted phenol compound, in the salted fora, with carbon dioxide. The substituted phenol coapuestos of this aforementioned take part in the process of the invention in the salified form. These are preferably salts of metal elements of the group (la) of the periodic classification. For the definition of the elements, reference is made later to the periodic classification of the elements, published in the Bulletin of the Chemical Society of France No. 1 (1966). From a practical and economic point of view, the sodium or potassium salts are used. In accordance with the processes of the invention, the substituted phenol compound in the salified form and the carbon dioxide are reacted. A salified form of a substituted phenol coapuesto prepared at the time of use can be used, but it is also possible to prepare it in situ by reaction of a substituted phenol compound with a base. A base, which may be organic or inorganic, is thus involved in the process of the invention. A strong base is preferably chosen, that is, a base having a pK greater than 12, where pK is. defined the co-logarithm of the dissociation constant of the measured base, in aqueous medium, at 25 ° C. Inorganic bases, such as alkali metal salts, preferably an alkali metal hydroxide which may be sodium or potassium hydroxide, or an alkali metal carbonate, preferably potassium carbonate, are particularly well suited for the implementation of the process of the invention. It is also possible to use a quaternary ammonium hydroxide. It is preferably used, as examples of quaternary ammonium hydroxide, hydroxides of teraalkyl ammonium or lithium benzylammonium, in which the identical or different alkyl radicals represent a linear or branched alkyl chain having from 1 to 12 carbon atoms, preferably from 1 to 6 carbon atoms. The tetramethylammonium hydroxide, the tetraethylammonium hydroxide or the tetrabutylammonium hydroxide are preferably chosen. It is also possible, according to the invention, to resort to the hydroxides of tyalkyl benzylammonium and in particular to the hydroxide of rime i 1 ammonium. For economic reasons, sodium hydroxide or potassium carbonate are preferably chosen from all bases. The concentration of the initial basic solution is not critical. The alkali metal hydroxide solution used generally has a concentration of - Il - and 50% by weight. The amount of the base introduced into the reaction mixture takes into account the amount necessary to salify the hydroxyl functional group of the substituted phenol compound. If the aforementioned compound has salifiable functional groups other than the hydroxyl group, the amount of base necessary to salify all the functional salivary functional groups is, therefore, introduced. The amount, of base, expressed with respect to the substituted phenol coapuesto, generally varies between 90 X and 120 Z of the stoichiometric amount. The substituted phenol compound is prepared in the salified form by reacting it with the base, at a temperature advantageously between 25 ° C and 100 ° C. Before introducing the carbon dioxide, the water formed by the salification reaction is removed by distillation at atmospheric pressure or under a reduced pressure of between 1 mm of mercury and atmospheric pressure, or by drying. When there is no more water in the mixture, carbon dioxide is introduced. Another alternative form of the process of the invention comprises the additional use of an anhydrous, alkali metal carbonate, preferably anhydrous potassium carbonate, which makes it possible to avoid the step of removing water (for example, from 5 to 100 mol%). of the substituted phenol coapuesto). The amount of carbon dioxide to be used, expressed by the molar ratio between the carbon dioxide and the substi tuted phenol, varies between 1 and 100, and more preferably between 1 and 2. The process of the invention is advantageously carried out at a temperature between 1 ° C and 250 ° C, preferably between 160 ° C and 200 ° C. This is generally implemented at atmospheric pressure, with carbon dioxide being bubbled into the reaction stream, which is maintained under agitation. It is also possible to carry out the reaction under a pressure of carbon dioxide varying between atmospheric pressure and about 100 bar. A pressure is preselected between 1 and 20. A preferred practical embodiment of the invention comprises the use of the substituted phenol compound and the base, and the removal of water, if necessary, by distillation and then the introduction of carbon dioxide. . This is a solid reaction / gas.

At the end of the reaction, the substituted phenol compound, which possesses a carboxylate group in the 6-position, is then recovered and dissolved in water at a concentration ranging between 5 and 50% by weight. The solution is brought to a pH of between about 6 and 10, preferably in the region of 7 by the addition of an acid. Any acid can be used but, for economic reasons, it is preferable to use inorganic acids with encionales, preferably hydrochloric acid or sulfuric acid. The concentration of the acid used is not critical. This preferably corresponds to the concentration of the commercial form, for example at 37 X by weight for hydrochloric acid and 92 or 96% for sulfuric acid. A two-phase mixture is then obtained, composed of an organic phase comprising the unreacted substituted phenol compound and, on the other hand, an aqueous phase comprising the desired product, namely the salt of the substituted 2-hydroxybenzoic acid less in the 3-position by an alkoxy group, which is represented by the formula (II) in which Z., Z_ and Z- have the meanings given above, and M represents a hydrogen atom and / or a metal cation of the group (the) This is subsequently known, simply as "hydroxybenzoic acid salt". The two phases are separated and the aqueous phase is collected. It should be noted that it will not depart from the scope of the present invention at the beginning of the hydroxybenzoic acid salt of the formula (II), prepared at the time of use. In a subsequent step, the reaction of hydroxymethyl ion in the para position to the OH group is carried out by reaction of the acid salt obtained above, with formaldehyde, optional-presence in the presence of a base. It is possible to use formaldehyde or any formaldehyde generator, such as, for example, trioxane or for formaldehyde form in the form of linear polymers, in which the degree of polymerization is not significant, preferably having a number of units (CH-0) of between 8 and 100 units. Said reagent is generally used in the form of an aqueous solution having a concentration of less than 50 Z by weight, preferably between 20 and 50 Z by weight. The amount of ormaldehyde, expressed as moles of formaldehyde per mole of hydroxy-1-benzoic acid salt, can vary within wide limits. The molar ratio of ormaldehyde / s to benzoic acid, advantageously falls between 0.5 and 3.0. It is possible to carry out the reaction in the presence of a base. The bases mentioned above are completely very suitable. The amount of base used, expressed by the ratio of the number of moles of base to the number of moles of hydroxybenzoic acid salt, can vary 0 between 0 and 2, and preferably between 0 and 1.1. The base can be used without distinction in solid fora or COBO an aqueous solution. The temperature of the reaction can vary from 50 ° C to 100 ° C, and preferably from 60 ° C to 80 ° C. The process is preferably carried out under the autogenous pressure of the reactants, in order to avoid the possible losses of parafmaldehyde, which can be gaseous at the reaction temperatures. It is preferable to carry out the reaction under a controlled atmosphere of inert gases, such as nitrogen or rare gases, for example argon. The duration of the reaction can be highly variable. This falls more frequently between 30 minutes 5 and 24 hours, preferably between 4 hours and 8 hours.

From a practical point of view, the reaction is easily carried out by charging the hydroxybenzoic acid salt and formaldehyde, and optionally a base, to the equipment and then by treatment of the reaction mixture with stirring, to the temperature desired for the duration necessary for the termination of the reaction. The order of introduction of the reagents is not critical and can therefore be different. At the end of the reaction, an acid is obtained 2-hyd rox ibenzoic which is hydrox imet i side in the 5-position and which is substituted at least in the 3-position by an alkoxy group, which preferably corresponds to the formula (III) in which Z., Z » and Z- have the meanings given above, and M represents a hydrogen atom and / or a metal cation of the group (la). According to an alternative and preferred form of the process of the invention, the obtained compound n < it is separate but it is directly oxidized. A preferred oxidation method of the invention, which constitutes yet another objective of the present invention, comprises the oxidation of 2-hydroxy-benzoic acid which is hydroxylated at the position, and which is substituted at least in the 3-position. by an alkoxy group, in the liquid phase, using molecular oxygen or a gas containing it, the oxidation being carried out in an aqueous medium containing an alkaline agent, in the presence of a catalyst based on platinum or palladium, optionally in the presence of a co-catalyst based on a bismuth derivative. As regards the noble metals used for the catalysis of the reaction, in this case platinum and palladium, these may have various forms such as coao, for example: platinum black, palladium black, platinum oxide, palladium oxide or the noble metal itself deposited on various supports, such as carbon black, calcium carbonate, aluminas and activated silicas or equivalent materials. Catalytic bodies based on carbon black are particularly suitable. The amount of this catalyst to be used, expressed as the weight of the platinum or palladium with respect to that of hydroxymethylbenzoic acid 2-h idrox acid, may vary from 0.01 to 4 Z, and preferably from 0.04 to 2 Z. co-catalyst and, more particularly, use is generally made of an inorganic or organic bismuth derivative in which the bismuth atom has an oxidation number greater than zero, for example equal to 2, 3, 4 or 5. The Waste combined with bismuth is not critical, as long as it satisfies this condition. The cocatalyst can be soluble or insoluble in the reaction mixture. Illustrative cocatalyst compounds which can be used in the process according to the present invention are: bismuth oxides, bismuth hydroxides, salts of inorganic hydrocides, such as chloride, bromide, iodide, sulfide, selenide and bisauto telluride, salts of inorganic oxyacids, such as sulfur, sulfate, nitrite, nitrate, phosphite, phosphate, pyrophosphate, carbonate, perchlorate, antimonate, assassin, selenite and bismuth selenate, or salts of oxyacids derived from transition metals, such COBO vanadate , niobiate, tantalate, chromate, molybdate, tungstate and bismuth permanganate. The salts of inorganic aliphatic or aromatic acids such as acetate, propionate, benzoate, salicylate, oxalate, tartarate, lactate and bisauto citrate or phenoxides, such as gallate and bisauto pyrogalate, are also other suitable co-replacements. These salts and phenoxides can also be bismuth salts. It is possible to make use, like other inorganic and organic compounds, of binary combinations of bis-muto with elements such as phosphorus and arsenic, hete-ropolyacids containing bismuth, and their salts; Aliphatic and aromatic bisautins are also appropriate. Mention may be made, as specific examples, of: - COBO oxides: Bio, Bi-0-, Bi-O ^. or Bi205, - as hydroxides: Bi (OH) -, - COBO salts of inorganic hydrocides: bis-auto BiCl- chloride, bismuth bromide BiBr-, bismuth iodide Bile_, bismuth sulfide Bi-S., Bismuth selenide Bi2Se ~ bismuth telluride Bi2Te ~, - coao salts of inorganic oxyacids: bisauto basic sulfite Bi »(S0«) _. Bi-0- .5H20, bis-mute neutral sulfate Bi_ (S04) -, bismutyl sulfate (BiOJHSO ^, bismutyl nitrite (BiO) NO., - 0.5H20, neutral bismuth nitrate Bi (O ^) ~. 5H20, bismuth and magnesium nitrate 2Bi (.03) 3.3Mg (N03) 2.24H20, bismutyl nitrate (BiO) N03, bismuth phosphite BiY PO-H) - .3H20, bismuth neutral phosphate BiPO ,, bismuth pyrophosphate Bi, (P207) ~, bismutyl carbonate (BiO CO- • 0.05H20, bismuth neutral perchlorate Bi (CIO,) _ .5H20, bismutile perchlorate (BiO) ClO ,, bismuth antimonate BiSbO, bismuth neutral arsenate Bi (AsO ^) -, bismutyl arsenate (BiO) As04.5H20 or bismuth selenite Bi ^ SeO-Y, - as salts of oxyacides derived from transition metals: bismuth vanadate BiVO bismuth mobiate 4 BiNbO bismuth tantalate BiTaO ^, bismuth neutral chromate Bi2 (Cr04), bismutyl dichromate (BiO) 2Cr207, chromate acid <ie Dismuco H (Bi0) Cr04, bismuthyl-potassium chromate K (BiO) Cr04, bismuth molybdate BiYMoO ^ Y, BiYWO bismuth tungstate, Y, bismuth-sodium molybdate NaBi (MoO,) 2 or bismuth basic permanganate Bi202 (0H) Mn04, - COBO salts of organic acids aliphatic or aromatic: bismuth acetate Bi (CHO -) -, bismutyl propionate (Bi0) C-H502, basic bismuth benzoate C6H5C02Bi (OH) 2, bismutyl salicylate C6H4C02 (BiO) (OH) bismuth oxalate (C204) -Bi2, bismuth tartrate Bi2 (C4H406) 3-6H20. Bismuth ijctate (C6HQ05) 0Bi .7H20 or bismuth citrate YH-OjBi, - COBO phenoxides: basic bismuth gallate C_H707Bi or bismuth basic pyrogamate C & H -, (OH (OBi) (OH)) Coao other inorganic compounds or organic compounds which are also suitable may be mentioned: bisauto phosphide BiP, bismuth arsenide Bi-As-, sodium bismutate NaBi03, thiocyanic acids of bismuth H2lBi (CMS) 5l or H3 (Bi (CNS) 6J and their sodium salts and potassium, trimethylbismutin Bi (CH3) 3 ot rifeni Ibismutin Bi (C6H5) 3.

The bismuth derivatives which are preferably used to carry out the process of the present invention are: oxides, bismuth, bismuth hydroxides, bismuth or bismutyl salts of inorganic hydrocarbons, bismuth or bismuthyl salts of inorganic oxyacids, bismuth or bismutyl salts of organic aliphatic or aromatic acids, and bismuth or bismuthyl phenoxides. A group of co-catalysts which are particularly suitable for carrying out the invention, is composed of: bismuth oxides i20-, and Bi20, bismuth hydroxide Bi (0H), bismuth neutral sulphate BiYSO.Y , bismuth chloride BiCl », bismuth bromide BiBr .., bismuth iodide Bil-, neutral bismuth nitrate, Bi (03) 3 • H 0, bismutyl nitrate BiO (N03), bismutyl carbonate (BiO) C0- * 0.5H-0, bismuth acetate Bi (CHO-),. or bisrautyl salicylate C6H4C02 (Bi0) (0H). The amount of co-catalyst used, expressed Q by the amount of metallic bismuth contained in the co-catalyst with respect to the weight of the noble metal used, may vary within wide limits. For example, this amount can be as small as 0.1 Z and can reach the weight of the noble metal used, and even e. Exceed it without disadvantage.

More particularly, this amount is chosen so that 10 to 900 ppm by weight of metallic bismuth are introduced into the oxidation mixture with respect to the hydroxymethyl 2-hydroxybenzoic acid. In this regard, larger amounts of co-catalyst, of the order of 900 to 1500 ppm, can naturally be used, but without further significant advantage. According to the process of the invention, the oxidation is carried out in an aqueous medium containing an alkaline agent in solution. In this regard, sodium or potassium hydroxide is generally used as the alkaline agent. The proportion of inorganic base to be used is between 0.5 and 3 mol of sodium hydroxide) potassium with respect to hydroxymethyl 2-hydroxy-benzoic acid. The concentration of the 2-hydroxybenzoic acid hydroxyl side in the aqueous solution of the alkaline agent, it should preferably be such that any precipitation is avoided and a homogeneous solution is preserved. The concentration by weight of 2-hydroxy-benzoic hydroxymethylated acid in the aqueous medium is usually between 1 Z and 60 Z, preferably between 2 Z and 30 Z. One way of carrying out the process in practice is in contacting with molecular oxygen or a gas containing it, for example air, the aqueous solution containing the hydroxymethyl 2-hydroxy-benzoic acid to be oxidized, the alkaline agent, the platinum-based or palladium-based catalyst and, optionally, , the co-catalyst based on a bismuth derivative, according to the proportions shown above. The process is carried out at atmospheric pressure but it is also possible, if appropriate, to carry out the process under pressure between 1 and 20 bars. The mixture is then stirred at the desired temperature, until an amount of oxygen corresponding to that necessary to convert the alcohol functional group to an aldehyde functional group has been consumed. The progress of the reaction is therefore verified periodically by measuring the amount of oxygen absorbed. The temperature of the reaction to be adopted varies according to the thermal stability of the products to be prepared. The reaction is generally carried out in a temperature range from 50 ° C to 100 ° C, preferably from 60 ° C to 80 ° C. At the end of the reaction, which preferably lasts between 30 minutes and 2 hours, the acid -hydrobenzoic acid which is formylated in the 5-position is recovered, and which is substituted at least in the 3-position by an alkoxy group. , and which preferably corresponds to formula (IV). The catalyst, after cooling, if this takes place, is then separated from the reaction mixture, for example by filtration. In the last step of the process of the invention, a decarboxylation reaction is carried out. To do this, the resulting liquid is acidified by the addition of a protonated acid of inorganic origin, preferably hydrochloric acid or sulfuric acid, until a pH of less than or equal to 3, preferably between 0 and 3, is obtained. The reaction mixture it is heated to a temperature which varies, for example, between 120 ° C and 350 ° C, and preferably between 150 ° C and 220 ° C. The process is preferably carried out under the autogenous pressure of the reagents. At the end of the reaction, the reaction mixture is cooled to between 20 ° C and 80 ° C. A two-phase mixture is obtained, which is composed, on the one hand, of an organic phase which co-learns the 4-hydroxybenzaldehyde substituted in at least the 3-position by an alkoxy group, and which preferably corresponds to the formula (V ), and optionally the initial substrate of the formula (I) and, on the other hand, of an aqueous salt phase. The organic and aqueous phases are separated and the 4-hydroxybenzaldehyde is recovered from the organic phase according to conventional separation techniques, preferably by distillation. As mentioned above, the process of the invention is particularly well suited for the preparation of vanillin and of et il-vanillin lina. Examples of the implementation of the invention are given below. These examples are given by way of illustration and without implied limitation.

EXAMPLES Example 1 l - Carboxylation of potassium guayacolate under pressure of_C02 224 g (1.81 mol) of guaiacol are charged to a 500 ml Burton Corbelin reactor, made of nickel-iron-mol ibdeno B2 alloy and equipped with a turbine mixer. 31.5 g (228 mmol) of potassium carbonate are added. The reactor is purged with a current of CO ». A slight exotherm takes place. The reaction mixture is heated at 170 ° C for 7 hours, while maintaining the pressure of C02 at 20 bars. After cooling the reactor to room temperature, 200 ml of water are added. A solution of hydrochloric acid is added 5N until a pH of about 7.0 is obtained. Phase separation occurs. The organic phase, composed essentially of guaiacol, is separated by settlement. The aqueous phase is acidified to pH 1 with hydrochloric acid. The precipitation of orthovain-11 ico acid has 1 ugar. The separation is carried out by filtration. The product obtained is washed with water and dried at 40 ° C under a reduced pressure of 20 mm of mercury. 38 g of ortho-vainic acid are recovered, assaying at 96 Z by weight. The yield is 96 Z with respect to potassium carbonate. 1 _ Condensation of ortho-vainylic acid / paraformal-dehyde 14.66 g of a 30 Z aqueous solution of sodium hydroxide (0.11 mole) are added, with stirring and while heating, to a suspension of 16.8 g (0.1 mole) of tovain acid 11 ico in 16.72 g of water. When the mixture is homogeneous and is at a temperature of 70 ° C, 3 g of paraforraal-dehyde (0.1 mol) are added. After stirring for 6 hours at 70 ° C, the purple solution obtained is determined quantitatively by high performance liquid chromatography. The results obtained are as follows: - DC (acid o-va iní 11 ico) ™ no. of moles of converted o-vanillic acid / no. of moles of o-vanillic acid used • 42.5 Z-RY 3-methoxy-5-hydroxymethylsalicylic acid) not of moles of 3-methoxy-5-hydroxymethyl-isalic acid formed / no. of moles of used o-vanillic acid - 29.95 Z - CY - no. of moles of 3-methoxy-5-hydroxy-methylsilic acid formed / no. of moles of converted o-vanillic acid - 70.5 Z.

To the previous solution, 1.63 g of 2.5 Z of platinum on mineral coal (0.2 Z mol) and then 140 mg of bismuth sulfate (0.2 Z mol) are added. The temperature is adjusted to 65 ° C and the pH to 12. The latter will be kept at this value during the reaction by the addition of 30 Z sodium hydroxide. Oxygen is transported to the reactor with strong stirring at a flow rate of 1.5 liter / hour. After 3 hours, 0.815 g of platinum is added to the mineral coal and the reaction is continued for an additional 3 hours. At this time, the quantitative determination of the reaction mixture by high-performance liquid chromatography gives: - DC acid (3-methoxy-5-hydroxymethyl isic) "No. of moles of 3-methoxy-5-hydroxymethylsalicylic acid converted / not molar of 3-methoxy-5-hydroxymethyl-isaliclic acid used • 100 Z-RY (5-carboxy-vinillin) -not of moles of 5-carboxy vanillin ina / moles of acid 3 -methoxy-5-hydroxymethylsalicylic acid used - 59 Z. 4 - . 4 - Decarboxylation The reaction mixture resulting from the oxidation is diluted with 100 ml of water and then charged to a Burton Corbelin reactor made of nickel-iron-mol ibdeno B_ alloy. A solution of 2N sulfuric acid is added until a pH of about 1.9 is obtained. The reactor is purged under a current of pyrogen and the heating is then carried out for 30 minutes at 200 ° C. Cooling is carried out rapidly by a stream of cold water. The reaction mixture is diluted with acetonitrile and then determined quantitatively by high performance liquid chromatography. The results obtained are as follows: DC (5-car boxi vainil 1 ina) »no. of moles of 5- car box i vain i 11 ina converted / no. of moles of 5- carbox i vaini 11 ina used «100 Z. CY (vanillin) * no. of moles of vanillin formed / not. of moles of 5-car boxi vaini 1 converted lina - 99.4 Z - RY (vanillin / o-vamylic acid) - no. of moles of vanillin formed / not. of moles of o-vanillic acid used = 27.4% Examples 2 to 4 A series of decarboxylation tests are carried out on 3-carboxy-4-hydroxy-5-methoxyben-zaldehyde. The following materials are charged to a Burton Corbelin reactor made of nickel-iron-mol ibdeno B alloy, and equipped with a turbine mixer: 0.246 g (1.26 mols) of 5-car box and 1 lina vaini and 20 ml of a mixture of acetic acid and water (50/50 by volume) in Example 2, 20 ml of water in Example 3 and 20 ml of sulfuric acid solution (5 mmol / l) in the emp eld Example. The reactor is purged under a stream of nitrogen. The heating is carried out for 20 minutes, at 160 ° C in Examples 2 and 3, and at 200 ° C in Example 4. The reaction mixture is determined quantitatively by high-performance liquid chromatography after dilution with acetonitrile: Lichro column Cart RP of 18 - 5 microns - 250/4 ram, marketed by Merck; eluent: 800 ml of water / 200 ml of CHYN / 3.5 ml of phosphoric acid; flow rate: 1 ml / minute; UV detection: 240 microns; room temperature . The results are recorded in the following Table (I): Table (I) Nature No. Tempe- Duration DC CY Example of solvent (hours) 5-carbox? - (vanillin) (ßC) vanillin) (Z) 2 CH3COOH / H20 160 7 h 05 89.6 95.1 3 H20 160 6 h 35 96.5 91.1 4 H2S04 200 0 h 20 98.9 98.4

Claims

1. A process for the preparation of a substituted 4-hydroxybenzaldehyde, substituted at least in the 3-position by an alkoxy group, characterized in that it comprises holding a substituted phenol compound, substituted at least in the 2-position by an alkoxy group and in which positions 4 and 6 are free, to a first stage of carboxylation at position 6, then to a hydroxymethyl phase at position 4, followed by an oxidation step of the hydroxymethyl group to a formyl group, and finally to a final stage of decarboxilation.

2. The process according to claim 1, characterized in that the substituted phenol compound corresponds to the general formula (I): in the formula (I): _ -7 represents a linear or branched alkoxy radical having from 1 to 12 carbon atoms, preferably from 1 to 4 carbon atoms, such as the radicals raetoxy, ethoxy, propoxy, isopropoxy, butoxy , isobutoxy, sec-butoxy and tert-butoxy, -Z2 and Z-, which are identical or different, represent a hydrogen atom or one of the following groups: a linear or branched alkyl radical having from 1 to 2 carbon atoms; carbon, preferably 1 to 4 carbon atoms, such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl or tert-butyl, a linear or branched alkepyl radical having from 2 to 12 carbon atoms, preferably from 2 to 4 carbon atoms, such as vinyl or allyl, a linear or branched alkoxy radical having from one to 12 carbon atoms, preferably from 1 to 4 carbon atoms, such as methoxy, ethoxy, propoxy, isopropoxy, butoxy , isobutoxy, sec-butoxy and tert-butoxy,. a radical, phenyl, a halogen atom preferably a fluorine, chlorine or bromine atom.

3. The process according to any of claims 1 and 2, characterized in that the substituted phenol compound corresponds to the formula (I) in which Z. represents a linear or branched alkoxy radical having from 1 to 6 carbon atoms, preferably of 1 to 4 carbon atoms, Z2 and Z ~ represent a hydrogen atom.

4. The process according to any of claims 1 to 3, characterized in that the substituted phenol compound is guaiacol or 2-ethoxy-phenol.

5. The process according to any of claims 1 to 4, characterized in that, in a first step, a substituted phenol compound according to formula (I) is carboxylated by the reaction of said compound in the salified form, with carbon dioxide.

6. The process according to claim 5, characterized in that the substituted phenol compound is in the salified form, preferably in the form of salts of metal elements of the periodic classification group, preferably in the form of sodium salts. or potassium.

7. The process according to any of claims 5 and 6, characterized in that the substituted phenol coapuesto in the salified form is prepared by the reaction of said compound with a base, preferably sodium or potassium hydroxide, or a quaternary ammonium hydroxide. , and then by removing the water formed during the salification reaction or adding an anhydrous alkali carbonate, preferably potassium carbonate.

8. The process according to any of claims 5 to 7, characterized in that the temperature at which the carboxylation takes place is between 150 ° C and 250 ° C, preferably between 160 ° C and 200 ° C.

9. The process according to any of claims 5 to 8, characterized in that the pressure of the carbon dioxide varies between the atmospheric pressure and approximately 100 bar, preferably between 1 and 20.

10. The process according to any of claims 5 to 5, characterized in that the first step of the process of the invention comprises the use of substituted phenol and the base, the elimination of water, if necessary, by distillation, and then the introduction of carbon dioxide.

11. 2-Hydrobenzoic acid hydroxymethyl in position 5 and substituted at least in the position by an alkoxy group.

12. The acid according to claim 11, characterized in that it corresponds to the general formula (III): (III) in the formula (III): - Z. represents a linear or branched alkoxy radical having from 1 to 12 carbon atoms, preferably from 1 to 4 carbon atoms, such as methoxy, ethoxy, propoxy, isopropoxy, butoxy, isobutoxy, sec-butoxy and tert-butoxy, -Z "and Z ,, which are identical or different, represent a hydrogen atom or one of the following groups: a linear or branched alkyl radical having from 1 to 2 carbon atoms; carbon, preferably 1 to 4 carbon atoms, such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, 9β-t-butyl or tert-butyl, a linear or branched alkenyl radical having from 2 to 12 carbon atoms, preferably from 2 to 4 carbon atoms, such as vinyl or allyl, a linear or branched alkoxy radical having from one to 12 carbon atoms, preferably from 1 to 4 carbon atoms, such as methoxy, ethoxy, propoxy, isopropoxy, butoxy , isobutoxy, sec-butoxy and tert-butoxy,. a phenyl radical, a halogen atom, preferably a fluorine, chlorine or bromine atom. - M represents a hydrogen atom and / or a metal cation of group (la).

13. The acid according to any of claims 11 and 12, characterized in that it corresponds to the general formula (III) in which 2. represents a linear or branched alkoxy radical having from 1 to 6 carbon atoms, preferably from The carbon atoms, and more preferably still a methoxy or ethoxy radical, Z "and Z_ represent a hydrogen atom.

14. The process for the preparation of 5-hydroxy-benzoic acid which is hydroxymethylated in the 5-position, which is substituted at least in the 3-position by an alkoxy group described in any of claims 11 to 13, characterized in that it comprises the reaction of a 2-hydrox ibenzoic or substituted acid, substituted at least in the 3-position by an alkoxy group, with formaldehyde or a formaldehyde generator, optionally in the presence of a base.

15. The process according to claim 14, characterized in that the substituted 2-hydroxybenzoic acid, substituted at least in the portion 3 by an alkoxy group, corresponds to the general formula (II): in the formula (II): -Z. , Z ~. Z "and M have the meanings given in claims 12 and 13.

16. The process according to any of claims 14 and 15, characterized in that the formaldehyde generator is trioxane or paraformaldehyde, used in the form of linear polymorphisms in which the degree of polymerization is not important, preferably having a number of units (CH20) of between 8 and 100 units.

17. The process according to any of claims 14 to 16, characterized in that the molar ratio of ormaldehyde / hydroxybenzoic acid salt is between 0.5 and 3.0.

18. The process according to any of claims 14 to 17, characterized in that the temperature of the reaction varies from 50 ° C to 100 ° C and preferably from 60 ° C to 80 ° C.

19. The process for the preparation of a 2-h id r ox i benzoic acid which is formylated in the 5-position, and which is substituted at least in the 3-position by an alkoxy group, characterized the process because it comprises the oxidation of the 2-hydroxy-benzoic acid which is hydroxymethylated in the 5-position, and which is substituted at least in the 3-position by an alkoxy group, in the liquid phase, using molecular oxygen or a gas containing it, the oxidation in an aqueous medium containing an alkaline agent, in the presence of a catalyst based on platinum or palladium, optionally in the presence of a cocatalyst based on a bismuth derivative.

20. The process according to claim 19, characterized in that the 2-hydroxy-benzoic acid, which is hydroxymethyl in the 5-position and which is substituted at least in the 3-position by an alkoxy group, corresponds to the general formula (III ) described in any of claims 12 v 13.

21. The product according to any of claims 19 and 20, characterized in that the catalyst is chosen from: platinum black, palladium black, platinum oxide, palladium oxide or the noble metal itself deposited on various supports such as black of carbon, calcium carbonate, aluminas and activated silicas, or equivalent materials.

22. The process according to any of claims 19 to 21, characterized in that the amount of this catalyst to be used, expressed as COBO, weight of platinum or palladium with respect to that of hydroxymethoxylated 2-hydroxybenzoic acid, can vary from 0.01 to 4 Z and preferably from 0.04 to 2 Z.

23. The process according to any of the rei indications 19 to 22, characterized in that it is used, as co-catalyst of an inorganic or organic bisauto derivative, in which the bismuth atom has an oxidation number greater than zero, for example equal to 2, 3, 4 or 5.

24. The process according to claim 23, characterized in that the bismuth derivative is taken from the group consisting of: bismuth oxides, bismuth hydroxides, bismuth or bismuthyl salts of inorganic hydrocides, preferably chloride, bromide, iodide, sulfide, selenide and telluride, bisautyl bisautyl salts of inorganic oxyacids, preferably sulfite, sulfate, nitrite, nitrate, phosphite, phosphate, polyphosphate, carbonate, perchlorate, antimonlate, arsenate, selenite and selenite, bisautyl or bismutyl salts of organic aliphatic acids or Atoates, preferably acetate, propionate, salicylate, benzoate, oxalate, tartrate, lactate and citrate, or bismuth or bismuthyl phenoxides, preferably gallate and pyrogalate.

25. The process according to claim 24, characterized in that the bismuth derivative is removed from the group consisting of: bismuth oxides Bi-O »T Bl2 ^ '• bismuth nidroxide Bi (0H) 3, bisauto chloride BlCl', broauro of bismuth BiBr », bismuth iodide Bil», neutral bismuth sulphate BiYSOY », neutral bismuth nitrate Bi (O- .5H20, bismuth nitrate BiO (N03), bismutyl carbonate (BiO) 2C03 -0.5 H, 0, bismuth acetate Bi (C2H302) 3 ° bismutyl salicylate C6H4C0? Bi 0) 0H.

26. The process according to any of claims 23 to 25, characterized in that the amount of cocatalyst used is chosen so that it is introduced into the mixture: on the one hand, at least 0.1 Z by weight of metallic bismuth with respect to the weight of the noble metal used and, on the other hand, from 10 to 800 ppm by weight of the metallic bismuth, with respect to the 2-idrox ibenzoic hydroxymethylated acid.

27. The process according to any of claims 19 to 26, characterized in that the oxidation reaction is carried out in an aqueous medium containing from 0.5 to 3 mol of sodium or potassium hydroxide, with respect to 2-hydroxy acid -benzoic hydroxymeth side.

28. The process according to any of claims 19 to 27, characterized in that the oxidation reaction is carried out at a temperature in the range of 50 ° C to 100 ° C, preferably in the range of 60 ° C to 80 ° C.

The process according to any of claims 19 to 28, characterized in that the reaction mixture is cooled, and because the catalyst is separated.

30. The process according to any of claims 19 to 29, characterized in that the hydroxybenzoic acid that is formylated in the 5-position, and which is substituted at least in the 3-position by at least one alkoxy group, is decarboxylated.

31. The process according to claim 30, characterized in that the 2-hydroxy-benzoic acid which is formylated in the 5-position, and which is substituted at least in the 3-position by an alkoxy group. corresponds to the general formula (IV): in the formula (IV): Zi, Z2, Z- and M have the meanings given in accordance with claims 12 and 13.

32. The process according to any of claims 30 and 31, characterized in that the acid is desired to be boxylated by the addition of a protonated acid of inorganic origin, preferably hydrochloric acid or sulfuric acid, until a pH of less than or equal to 3 is obtained. , preferably between 0 r 3.

33. The process according to any of claims 30 to 32, characterized in that the reaction mixture is heated to a temperature ranging between 120 ° C and 350 ° C and preferably between 150 ° C and 220 ° C and, after cooling , because the 4-hydroxyl substituted ibenzaldehyde is removed, substituted at least in the 3-position by an alkoxy group, which corresponds preferably to the formula (V): in the formula (V): - Z., Z2 > Z3 and M have the meanings given in in claims 12 and 13, EXTRACT The object of the present invention is a process for the preparation of a 4-hydroxybenzaldehyde having at least one substituent in the ortho position to the OH group. This relates more particularly to the preparation of 3-methoxy-4-hydroxybenzaldehyde and 3-ethoxy-4-hydroxy-benzaldehyde. The process for the preparation of a substituted 4-hydroxy-benzaldehyde, substituted at least in the 3-position with an alkoxy group, is characterized in that it comprises a substituting a substituted phenol compound, substituted at least in the 2-position by an alkoxy group and in which positions 4 and 6 are free, to a first stage of carboxylation in position 6, then to a hydroxymethylation stage in position 4, followed by an oxidation step of the hydroimage group to a formyl group, and finally to a final stage of decarboxylation.