FR2798380A1 - PROCESS FOR PREPARING CHLORIDES OF ACIDS AND BENZENIC ALDEHYDES - Google Patents

Abstract

The invention concerns a semi-continuous method for preparing acid chlorides and benzene aldehydes which consists in: producing in a reactor a starter comprising for the major part a dichloromethylated benzene compound; simultaneously and continuously introducing simultaneously in the reactor, a carboxylic acid or its anhydride, a dichloromethylated benzene compound (2) and at least a Friedel-Crafts catalyst; and in causing them to react, under stirring, under a pressure P1 not higher than atmospheric pressure and at a temperature ranging between 60 DEG C and 180 DEG C; continuously extracting chloride acid (3) from the reaction medium and optionally formed HCI, by distillation under pressure P1 and at reaction temperature, then in ceasing to introduce reagents when the working volume of the reactor containing for the major part benzene aldehyde is reached; and in performing total or partial fractionated distillation of the reaction medium, consisting for the major part of benzene aldehyde, under pressure P2 < P1 and at a temperature not higher than 180 DEG C.

Description

 The invention relates to a process for the preparation of acid chlorides and to the preparation of acid chlorides. benzene aldehydes. Acid chlorides are important synthetic intermediates in the chemical industry. They are very widely used for the synthesis of various pharmaceutical products (antiviral agents, anti-inflammatory) or phytosanitary (herbicides, insecticides). They are also used for the synthesis of peroxides which are especially used as initiators for radical polymerizations.

The main routes of access to acid chlorides include processes that react with conventional reagents such as phosgene, sulfonyl chloride, phosphorus tri- or pentachlorides, and thionyl chloride.

However, all these processes represent complex technologies in view of the reagents involved and the need to perform expensive treatments of the products obtained and effluents, unacceptable for industrial production.

Thus, for example in the method described by Butlerow (Justus Liebiegs Ann Chem, p 373, 1874) which consists of reacting pivalic acid with phosphorus pentachloride according to the reaction.

    (CH3) 3 <SEP> C <SEP> COOH <SEP> + <SEP> PC15 <SEP>> <SEP> <B> (CHI </ B> <SEP> C <SEP> COCI <SEP> + <SEP > POC13 <SEP> + <SEP> HCI The POC13 and pivaloyl chloride obtained have temperatures so close (104-106 ° C) that it is almost impossible to separate them.

It has been proposed to use phosphorus trichloride which reacts with a carboxylic acid according to the reaction

PC13 <SEP> + <SEP> RCOOH <SEP><B> - 1 </ B><SEP> CKIN <SEP> + <SEP> H3P03 <SEP> + <SEP> HCI Although it is generally possible to obtain high yields, it is very difficult to eliminate the last traces of phosphorous acid, which are unacceptable for the use of acid chlorides in certain syntheses. One of the most frequently mentioned acid chloride synthesis processes in the literature is that employing thionyl chloride according to the reaction

    RCOOH <SEP> + <SEP> SOC12 <SEP> <B> --- 1 </ B> <SEP> CKIN <SEP> + <SEP> S02 <SEP> + <SEP> HCI In general, the The reaction is carried out in the presence of a molar excess of 20% to 50% SOC12.

Under these conditions, for example, molar yields of chlorides of distilled acids which are close to 90% are obtained. The addition of catalysts such as DMF, pyridine or N-methylacetamide makes it possible to increase the kinetics of the reaction and to improve the selectivity (lowering of the percentage of secondary products such as anhydride).

However the use of SOC12 has the disadvantage of leading to acid chlorides that may contain sulfur. In addition, in the event that a catalyst is used, its recycling is difficult.

Acid chlorides can also be obtained from phosgene according to the reaction

    RCOOH <SEP> + <SEP> COC12 <SEP> <B> - 1 </ B> <SEP> RONCI <SEP> + <SEP> HCI <SEP> + <SEP> C02 However, these processes have the disadvantage to use phosgene which is a highly toxic reagent and difficult to handle. In addition, in order to have acceptable yields greater than 90%, it is necessary to use nitrogenous catalysts such as tertiary amines, imidazoles, imides, lactams.

The aliphatic and aromatic acid chlorides can be obtained simultaneously by reaction of an aromatic compound containing at least one residue -CC 13 linked to an aromatic carbon with an aliphatic carboxylic acid in the presence of catalysts such as H 2 SO 4 (US 4,163,753) 1-13 PO 4 , HC104 (US 1,965,556) FeCl3 or ZnCl2 (FR 2,686,601).

Benzene aldehydes and especially benzaldehyde are used in perfumery and as intermediates for the synthesis of various chemical products (dyes, antibiotics). Routes of access to benzene aldehydes, especially benzaldehyde, include processes which make up the hydrolysis of the corresponding dichloromethylated benzene compounds.

Thus, benzaldehyde is obtained industrially by hydrolysis, acid or alkaline, of benzylidene chloride according to the reaction.

    C6H5CHCl2 <SEP> + <SEP> H2O <SEP> <B> <SEP> C6H5CH0 <SEP> + <SEP> 2HC1 Acidic hydrolysis of benzylidene chloride catalysed by metal salts at yields benzaldehyde (> 90%). The acids used are in particular H3PO4, mentioned in the patent application (FR 216,374), HCl (DE 2,756,612) and HC02H (EP 41,672).

Sulfuric acid has also been used but has the disadvantage of leading to discharges which consist of dilute solutions of H2SO4.

However, H2SO4 has been used for the hydrolysis of certain substituted benzylidene chlorides such as 2,4- and 2,6-dichloro-1- (dichloromethyl) benzenes.

Benzaldehyde can also be obtained by partial oxidation of toluene. Thus, the international application WO 95/20560 describes a process which consists in partially oxidizing the toluene in the liquid phase at temperatures of between 10 ° C. and 200 ° C. under pressures ranging from 2 to 50 bars in the presence of Co and Mn catalysts. .

The simultaneous industrial production of acid chlorides and benzene aldehydes is poorly described in the literature.

Only a few tests at the laboratory stage have been carried out. Thus, in DE 11 494 (1879) it is mentioned that one mole of C6H, CHCl2 can react with one mole of acetic acid in the presence of ZnCl2, SbCl3 or CUCl2 to yield benzaldehyde, acetyl chloride and hydrogen chloride according to the reaction.

    C6 <B> 1-1 </ B>, CHC12 <SEP> + <SEP> CH3C02H <SEP> <B> --- 1 </ B> <SEP> C6 <B> 1-1 </ B> 5CH0 <SEP> + <SEP> CH3COC1 <SEP> + <SEP> HCI In US Pat. No. 3,691,217, Example 16 is described the preparation of benzaldehyde and propionyl chloride by reacting, with stirring, at 100 ° C. for 1 hour 30 minutes. , 5 moles of benzylidene chloride and 0.5 moles of propionic acid in the presence of 0.005 moles of SnCl4.

No yield is mentioned.

The major disadvantage of this process is to use a volatile catalyst such as SnCl4 (Eb = 114.1 C), which is likely to be entrained with the acid chlorides during their distillation. This is unacceptable for the purity of said acid chlorides and for a continuous or semi-continuous industrial process.

The applicant has made batch tests to reproduce the methods of the prior art described above. It has obtained conversions and low yields and has found the presence of significant amounts of by-products, which in particular contain cinnamic acid derivatives in the case of the reaction with acetic acid (or its anhydride) and so In general, with the other acids, aromatic diesters such as benzylidene dicarboxylates. Without the applicant being held responsible for any explanation on the formation of these diesters, she thinks that they can be obtained from the products formed according to the scheme.

which can react on the acid present according

où R représente un radical alkyle, linéaire ou ramifié, ayant un nombre d'atomes de carbone allant de 1 à 12 et, de préférence, allant de 1 à 8, éventuellement substitué par 1 ou plusieurs atomes d'halogène tel que CI, Br, F ; un radical alcényle ayant un nombre d'atomes de carbone allant de 2 à 8, éventuellement substitué par 1 ou plusieurs atomes d'halogène tels que CI, F ; un radical phényle éventuellement substitué par un ou plusieurs atomes de CI, Br ou F, par un reste alkyle linéaire ou ramifié, ayant un nombre d'atomes de carbone allant de 1 à 4, ledit reste pouvant contenir 1 ou plusieurs atomes d'halogène tel que CI, Br, F ; (131)R, désigne que le noyau benzénique peut avoir un ou plusieurs substituants, identiques ou différents, choisis dans le groupe constitué par un atome de CI, un atome de Br, un atome de F, un radical alkyle, linéaire ou ramifié, ayant un nombre d'atomes de carbone allant de 1 à 4, -CF3 et -CH2C1 ; m = 0 ou un nombre entier allant de 1 à 3 ; n = 1 out; ledit procédé étant caractérisé en ce qu'il consiste a) à réaliser dans un réacteur un pied de cuve comprenant majoritairement le composé benzénique dichlorométhylé (2), b) à effectuer, simultanément et en continu b') d'une part, l'introduction simultanée dans le réacteur, de l'acide carboxylique (1) ou son anhydride (la), du composé benzénique dichlorométhylé (2) et d'au moins un catalyseur de type Friedel et Crafts, et à les faire réagir, sous agitation, sous une pression P1 inférieure ou au plus égale à la pression atmosphérique et, de préférence, sous une pression allant de 100 mbar à 500 mbar et à une température allant de 60 C à 180 C et, de préférence, allant de 80 C à 150 C ; b2) d'autre part, l'extraction en continu du chlorure d'acide (3) du milieu réactionnel et éventuellement de l'HCI formé, par distillation sous une pression P1 et à la température de réaction, puis c) à arrêter l'introduction des réactifs quant au plus le volume utile du réacteur contenant majoritairement l'aldéhyde benzénique est atteint ; et d) à entreprendre la distillation fractionnée, totale ou partielle du milieu réactionnel, constitué en majorité par de l'aldéhyde benzénique, sous une pression P2 < P1 et à une température au plus égale à 180<B>OC.</B> La distillation fractionnée totale ou partielle du milieu réactionnel peut être effectuée séparément dans une installation de distillation fractionnée. Dans cette éventualité, le contenu du réacteur où la réaction a été effectuée est transféré, en totalité ou en partie, dans ladite installation de distillation. Dans le cas d'un transfert partiel, la partie non transférée sert de pied de cuve pour une opération ultérieure. C6H5CHClO (O) R <SEP> + <SEP> RCOOH <SEP><B> - 1 </ B><SEP> C6H, CH [OC (O) R] 2 <SEP> + <SEP> HCI now found a process for preparing acid chloride (3) and benzene aldehyde (4) by reacting a carboxylic acid (1) or its anhydride (Ia) with a dichloromethyl benzene compound (2), in the presence of at least one catalyst of Friedel and Crafts type, according to reactions (I) 6 (II)

where R represents a linear or branched alkyl radical having a number of carbon atoms ranging from 1 to 12 and, preferably, ranging from 1 to 8, optionally substituted by 1 or more halogen atoms such as CI, Br , F; an alkenyl radical having a number of carbon atoms ranging from 2 to 8, optionally substituted with 1 or more halogen atoms such as CI, F; a phenyl radical optionally substituted with one or more Cl, Br or F atoms, with a linear or branched alkyl radical, having a number of carbon atoms ranging from 1 to 4, said radical may contain 1 or more halogen atoms; such as CI, Br, F; (131) R, denotes that the benzene ring may have one or more substituents, identical or different, selected from the group consisting of a CI atom, a Br atom, an F atom, a linear or branched alkyl radical, having a number of carbon atoms ranging from 1 to 4, -CF3 and -CH2Cl; m = 0 or an integer from 1 to 3; n = 1 out; said method being characterized in that it consists of a) producing in a reactor a stock comprising predominantly the benzene dichloromethyl compound (2), b) to be carried out simultaneously and continuously b ') on the one hand, the simultaneous introduction into the reactor of the carboxylic acid (1) or its anhydride (1a), the dichloromethylated benzene compound (2) and at least one Friedel-Crafts type catalyst, and reacting them with stirring, at a pressure P1 less than or at most equal to the atmospheric pressure and, preferably, at a pressure ranging from 100 mbar to 500 mbar and at a temperature ranging from 60 ° C. to 180 ° C., and preferably ranging from 80 ° C. to 150 ° C. C; b2) on the other hand, the continuous extraction of the acid chloride (3) from the reaction medium and optionally the HCl formed, by distillation under a pressure P1 and at the reaction temperature, and then c) to stop the reaction. introduction of the reagents as to the most useful volume of the reactor containing predominantly benzene aldehyde is achieved; and d) starting the fractional distillation, total or partial reaction medium, consisting predominantly of benzene aldehyde, under a pressure P2 <P1 and at a temperature at most equal to 180 <B> OC. </ B> Total or partial fractional distillation of the reaction medium may be carried out separately in a fractional distillation plant. In this event, the contents of the reactor where the reaction has been carried out is transferred, wholly or in part, to said distillation plant. In the case of a partial transfer, the non-transferred part serves as a stock for a subsequent operation.

According to the present invention, the base stock comprises in majority dichloromethyl benzene compound (2) and a defined proportion of catalyst.

It may also comprise, in small amounts, acid chloride and / or benzene aldehyde from a previous operation, in particular fractional distillation intermediate cuts of the reaction medium.

According to the present invention, the bottom of the tank represents at most 30% by volume of the reactor used for carrying out the process. According to the present invention, the benzene dichloromethyl compound (2) and the carboxylic acid (1) or its anhydride (1 a) will be used in a molar ratio (2) / (1) or (2) I (1 a) ranging from from 1 / n to 1.2 / n and preferably from 1 / n to 1.05 / n.

By Friedel-Crafts type catalyst is currently meant a Lewis acid or Brönsted acid.

By way of illustration of Lewis acid that may be used according to the invention, mention may be made of FeCl 3, ZnCl 2, SbCl 4, COCl 2, BiCl 3 and ZrCl 4.

Preferably ZnCl2 or FeCl3 will be used.

Illustrative Brønsted acid used in the present invention include sulfuric acid, phosphoric acid.

These Friedel and Crafts type catalysts can be introduced into the reaction zone as such or in the form of aqueous solutions or in solution in one of the reagents.

According to the present invention, a molar amount of pure Lewis acid of between 0.01% and 2% and preferably between 0.05% and 0.5% relative to the amount of the dichloromethyl compound will be used ( 2) cover.

According to the present invention, a molar amount of pure Bronsted acid of between 0.1% and 5% and preferably between 0.5% and 2%, based on the amount of the dichloromethyl compound (2 ) covered. The present invention is particularly applicable to carboxylic acids (1) or their anhydrides (la) having the carbon at a CO (carbonyl) most substituted possible. By way of illustration of such acids, mention may be made of isobutyric, pivalic, 2-chloropropionic, trifluoroacetic and trichloroacetic acids. The invention is equally applicable to benzoic acid or its substituted derivatives.

By way of illustration of dichloromethylated benzene compounds (2) which can be used according to the present invention, mention may be made of (dichloromethyl) benzene or benzylidene chloride, 2-chloro, 3-chloro and 4-chloro-1- (dichloromethyl) benzenes, 4-fluoro-1- (dichloromethyl) benzene, 4-trifluoromethyl-1- (dichloromethyl) benzene, 1,2- and 1,4-bis (dichloromethyl) benzenes.

The process of the invention is particularly applicable to the preparation of acid chlorides having the carbon at a maximum of the most substituted CO and benzaldehyde from the benzylidene chloride and the carboxylic acids (or their anhydrides) mentioned above. above.

According to the present invention, in the case where a carboxylic acid (1) is used, the hydrogen chloride formed can be backwashed with the dichloromethylated benzene compound (2) in order to recover any entrained acid chlorides. . The recovered HCl is conveniently absorbed into water in a slaughter column to yield very pure commercial aqueous HCI solutions.

The organic washing solution can be reused for synthesis. The process has the advantage of leading to acid chlorides and benzene aldehydes of high purity and consistent quality with high yields and selectivities.

This method also has the advantage of generating little or no by-products, no gaseous effluents in the case where an acid anhydride is used as reagent or generates valuable HCI in the form of commercial solutions. when a carboxylic acid is used.

In addition, this method also has the advantage of not using volatile catalysts which would be driven substantially continuously during the extraction of the products, which would generate a pollution of the products and a loss of activity during the reaction step.

The following examples illustrate the invention. EXAMPLE 1 (not in accordance with the invention) The reaction is carried out batchwise in a 500 ml glass reactor surmounted by a water cooler and equipped with a stirring anchor, a temperature sensor and an inerting system. The refrigerant outlet is connected to a dry ice trap (to trap any volatile organic matter) followed by a water scrubber to absorb HCI.

After purging the entire assembly with nitrogen, 1 mol of pivalic acid (103 g to about 99% purity) is introduced successively into the reactor at room temperature. 1 mol of benzylidene chloride (162.6 g to approximately 99% purity) and 2 mmol of FeCl, anhydrous (165 mg). The mixture, with stirring, is gradually heated to 105 ° C. in 30 minutes and then maintained at this temperature for 2 hours 30 minutes (until the release of HCI).

 The HCI absorbed continuously during the reaction corresponds to 80 of the theoretical amount.

GPC analysis of the crude reaction product then reveals a conversion of benzylidene chloride of 66% and a conversion of pivalic acid of 60% for a crude molar yield of pivaloyl chloride (relative to the initial pivalic acid) of only 33% and a crude molar yield of benzaldehyde (relative to the initial benzylidene chloride) of only 47%.

The poor selectivity to pivaloyl chloride (55%) corresponds to the formation of benzylidene pivalate C6H, CH [OC (O) C (CH3) 212 identified by CPG / MS coupling.

EXAMPLE 2 (in accordance with the invention) The reaction is carried out semi-continuously in a 500 ml glass flask surmounted by an Oldershaw type distillation column of 10 theoretical plates. The column head equipped with a reflux timer is connected to two dual circulation refrigerants to condense and recover the organic in a first recipe. The refrigerant outlet is connected to a vent line with a dry ice trap (second recipe) followed by a water scrubber to absorb the HCI.

After purging the entire assembly with nitrogen, 0.68 moles of benzylidene chloride B (1 g / 12 g at 98% purity) and 180 mg of anhydrous ZnCl 2 were introduced into the reactor ( about 1.3 mmol). This base of the tank is brought to a temperature of 150 ° C., with stirring and at atmospheric pressure. While maintaining the temperature at 150 ° C., 258 g (2.5 mol) of pivalic acid, 300 g (1.82 mol) of benzylidene chloride and 490 mg (3.6 mmol) of ZnCl 2 are then continuously introduced. in 6 h 30. In order to facilitate the implementation, the reactants have been premixed to obtain a stock solution (maintained at a temperature below 25 ° C.) which can then be introduced into the reactor using a single dosing pump. at a flow rate of 80 ml / h.

The start of the evolution of HCl is observed from the beginning of the introduction of the reagents and this evolution continues at a flow rate of between 0.3 and 0.4 mol / h.

The pivaloyl chloride begins to condense at the top of the column after about 1 h 30 of introduction, it is then withdrawn continuously with an average flow rate of the order of 25 g / h.

At the end of the introduction of the reagents, the total amount of HCI absorbed corresponds to 102.5% of the theoretical amount. The mass of pivaloyl chloride extracted is 134.6 g (of which 118.1 g in the first recipe and 16.5 g in the second recipe) with a purity of 97.6%, which represents a yield of 43.6 g. , 6%.

The reaction crude remaining in the flask is then distilled under reduced pressure (from 500 to 50 mbar) and a complementary fraction of 82.8 g of pivaloyl chloride with a purity of 99.1% is obtained. recyclable intermediate of 7.8 g containing 26.8% of pivaloyl chloride and 66.7% of benzaldehyde, a fraction of 248.5 g rich in benzaldehyde (88.5%) but containing 10% of pivalic anhydride, then 73 g of distillation residues containing 2.7% of benzaldehyde, 20.8% of pivalic anhydride and 0.7% of residual benzylidene chloride.

At the end of the operation, the conversions of benzylidene chloride and pivalic acid are respectively 99.8% and 97.7% with an overall yield of pivaloyl chloride of 71.6% and a yield of crude benzaldehyde of 85.6%.

EXAMPLE 3 (in accordance with the invention) The reaction is carried out in an assembly similar to that of Example 2, but the synthesis step is carried out under reduced pressure and with a molar excess of sodium chloride. benzylidene of 5.6% with respect to pivalic acid.

The vacuum is provided by a diaphragm pump (all Teflon) connected to the line of vents at the outlet of the dry ice trap and whose output is connected to the water scrubber to absorb the HCI.

After having purged the entire assembly with nitrogen, 2 g (0.68 mol) of benzylidene chloride are introduced into the reactor <B> 11, and 192 mg (# 1.4 mmol) of benzylidene chloride are added to the reactor. Anhydrous ZnCl2.

This base of the tank is brought to a temperature of 120 ° C., with stirring and under a pressure of 180 mbar. While maintaining the temperature at 120 ° C., 206 g (2 mol) of pivalic acid, 236.4 g (1.432 mol) of benzylidene chloride and 391 mg (2.9 mmol) of ZnCl 2 are introduced continuously by gravity. in 5 hours, the rate of introduction of the mixture, adjusted using a micrometer valve, is 80 ml / hour.

The onset of HCl evolution is observed from the beginning of the introduction of the reagents and this evolution continues at an average flow rate of 0.4 mol / h.

The pivaloyl chloride begins to condense at the top of the column after about 30 minutes of introduction, it is then withdrawn continuously with an average flow rate of the order of 45 g / h.

At the end of the introduction of the reagents, the total amount of HCI absorbed corresponds to <B> 97.5% of the theoretical amount. The mass of pivaloyl chloride extracted is 224.7 g (of which 161.8 g in the first recipe and 62.9 g in the second recipe) with a purity of 99.2%, which represents a yield of 92%. , 4%.

The reaction crude remaining in the flask is then distilled under reduced pressure (at 150 mbar) and a complementary fraction of 11 g of pivaloyl chloride with a purity of 98% is obtained. A recyclable intermediate cut of 11.6 is obtained. g containing 27.8% pivaloyl chloride and 64.9% benzaldehyde, a fraction of 200.4 g of benzaldehyde with a purity of 98%, then 16.1 g of distillation residues containing 38% of benzaldehyde and 14% residual benzylidene chloride.

At the end of the operation, the conversions of benzylidene chloride and pivalic acid are respectively 99.1% and 99.9% with an overall yield of distilled pivaloyl chloride (purity greater than 99%) of 97% relative to the pivalic acid used and a yield of benzaldehyde distilled 92.5%.

<B> EXAMPLES 4-7 </ B> The reaction is carried out according to a process analogous to that of Example 3 but by reaction of benzylidene chloride with isobutyric acid (Example 4), isobutyric anhydride (Examples 5). and 6) and 2-chloropropionic acid (Example 7). The purity of the benzylidene chloride used is between 97% and 99%. In all cases the catalyst used is ZnCl 2 with a molar ratio of 0.2 relative to the benzylidene chloride, except in Example 4 where the molar ratio is only 0.1%.

Table No. 1 indicates the reaction conditions.

Table 2 shows the respective conversions of the reagents, the yields of acid chloride extracted simultaneously with the feed of said reagents, the overall molar yields of acid chloride and the yields of benzaldehyde obtained after distillation under reduced pressure of the reaction base. .

Claims (1)

<B> CLAIMS </ B> <B> 7. </ B> Process for preparing acid chloride (3) and benzene aldehyde (4) by reacting a carboxylic acid (1) or its anhydride (la) on a dichloromethylated benzene compound (2), in the presence of at least one Friedel-Crafts type catalyst, according to reactions (I) or (II)

    where R represents a radical, linear or branched, having a number of carbon atoms ranging from 1 to 12 and, preferably, ranging from 2 to 8, optionally substituted with 1 or more halogen atoms such as CI, Br, F; an alkenyl radical having a number of carbon atoms ranging from 2 to 8 optionally substituted with 1 or more halogen atoms such as CI, F; a phenyl radical optionally substituted with one or more atoms of Cl, Br or F, with a linear or branched alkyl radical having a number of carbon atoms ranging from 1 to 4, said radical possibly containing 1 or more atoms of halogen such as CI, Br, F; (R ') R denotes that the benzene ring may have one or more substituents, identical or different, selected from the group consisting of a CI atom, a Br atom, an F atom, a linear or branched alkyl radical; having a number of carbon atoms ranging from 1 to 4, -CF3 and -CH2Cl; m = 0 or an integer from 1 to 3; n = 1 out; said method being characterized in that it consists of a) producing in a reactor a stock comprising predominantly the benzene dichloromethyl compound (2), b) to be carried out simultaneously and continuously b ') on the one hand, the simultaneous introduction into the reactor of the carboxylic acid (1) or its anhydride (1a), the dichloromethylated benzene compound (2) and at least one Friedel-Crafts type catalyst, and reacting them with stirring, under a pressure P1 less than or at most equal to the atmospheric pressure and at a temperature ranging from 60 C to 180 C; b2) on the other hand, the continuous extraction of the acid chloride (3) from the reaction medium and optionally the HCl formed, by distillation under a pressure P1 and at the reaction temperature, and then c) to stop the reaction. introduction of the reagents as to the most useful volume of the reactor containing predominantly benzene aldehyde is achieved; and d) to undertake the fractional distillation, total or partial of the reaction medium, consisting predominantly of benzene aldehyde, under a pressure P2 <P1 and at a temperature at most equal to 180 C. <B> 2. </ B> Process according to claim 1, characterized in that one operates in step b) under a pressure P1 ranging from 100 mbar to 500 mbar and at a temperature ranging from 80 C to 150 C. 3. Process according to claim 1 or 2, characterized in that the bottom of the tank represents at most 30% by volume of the reactor. <B> 4. </ B> Process according to any one of claims 1 to 3, characterized in that the benzene compound dichloromethyl (2) and the carboxylic acid <B> (1), </ B> or its anhydride (1 a) in a molar ratio (2) I (1) or (2) / (1 a) ranging from 1 / n to 1.2 / n. 5. Method according to claim 4, characterized in that the molar ratio (2) / (1) or (2) I (1 a) ranges from 1 / n to 1.05 / n. <B> 6. </ B> Process according to any one of claims 1 to 5, characterized in that the Friedel-Crafts type catalyst is a Lewis acid. 7. Process according to claim 6, characterized in that the Lewis acid is ZnCl2 or FeCl3. <B> 8. </ B> Process according to one of Claims 6 or 7, characterized in that a molar amount of Lewis acid of between 0.01% and 2% is used, and preferably , between 0.05% and 0.5 %% relative to the amount of dichloromethyl compound used. <B> 9. </ B> Process according to any one of claims 1 to 8, characterized in that the dichloromethyl compound (2) is benzylidene chloride. <B> 10. </ B> Process according to any one of claims 1 to 8, characterized in that the carboxylic acid (1) or its anhydride (1a) have the carbon at a CO as much substituted as possible. 11. Process according to claim 10, characterized in that the carboxylic acid (1) is pivalic acid, 2-chloropropionic acid, isobutyric acid, trifluoroacetic acid or trichloroacetic acid. <B> 12. </ B> Process according to claim 10, characterized in that the anhydride (Ia) is isobutyric anhydride.