FR2566434A1 - PROCESS FOR ELECTROSYNTHESIS OF CARBOXYLIC ACIDS - Google Patents

Abstract

PROCESS FOR ELECTROSYNTHESIS OF CARBOXYLIC ACIDS BY ELECTROCHEMICAL REDUCTION OF ORGANIC HALOGENIDES IN THE PRESENCE OF CARBON GAS IN AN ORGANIC SOLVENT MEDIUM CONTAINING AN ELECTROLYTE SUPPORT CHARACTERIZED BY THE USE OF A MAGNESIUM ANODE. THIS PROCESS WITHOUT CATALYST IS VERY EASY TO IMPLEMENT AND ALLOWS THE USE OF A CELL WITH A SINGLE COMPARTMENT. IT IS APPLICABLE TO THE ELECTROSYNTHESIS OF A VERY NUMBER OF CARBOXYLIC ACIDS WITH HIGH YIELDS. THE ABOVE ACIDS ARE COMMONLY USED IN THE CHEMICAL INDUSTRY, IN PARTICULAR AS SYNTHETIC INTERMEDIARIES OR AS PHYTOSANITARY OR ANTI-INFLAMMATORY COMPOUNDS.

Description

Electrosynthesis process for carboxylic acids

  The invention relates to a process for the electrosynthesis of carboxylic acid

  by electrochemical reduction of organic halides in the presence of carbon dioxide, process carried out in an electrolysis cell in a solvent-organic medium containing an indifferent electrolyte Carboxylic acids are compounds commonly used in the chemical industry, especially as intermediates of synthesis,

  as phytosanitary or anti-inflammatory compounds, as precursors

  penicillin synthesis.

  Several processes for the electrosynthesis of carboxylic acids by electrochemical reduction of organic halides in the presence of carbon dioxide are known: BAIZER (J.Org.Chem., Vol. 37, No. 12, 1972 pages 1951-1960) performs the electrochemical reduction with potential controlled control of benzyl and allyl halides in the presence of carbon dioxide, in a two-compartment electrolysis cell, in dimethylformamide (DMF) medium containing tetraethylammonium chloride as indifferent electrolyte. The cathode is mercury and the anode is platinum. he

  obtain the corresponding esters. -

  WAWZONEK and SHRADEL (Journal Electrochemical Society, March 1979, vol. 126, No. 3, pages 401-403) realize the electrochemical reduction

  at controlled potential and at room temperature of phenyl dichlo-

  romethane in the presence of carbon dioxide, in a cell with

  in a DMF medium containing tetrabutyl bromide

  ammonium at 0,2 M concentration as indifferent electrolyte. The cathode is mercury and the anode is platinum. The concentration of phenyldichloromethane in DMF is 0.13 M. The maximum yield is

  the mandelic acid obtained is 9.8%.

  MATSUE, KITAHARA and OSA (Denki Kagaku, 1982, vol 50, no.

  732-735), perform electrochemical reduction with potential

  10 μl of phenyl halides in the presence of carbon dioxide, in a cell with separate compartments, in DI-F medium containing tetraethylammonium perchlorate at the 0.1 M concentration as indifferent electrolyte. The cathode is mercury and the anode is platinum. The concentration of phenyl halide ranges from 10 to 50 m according to the examples. The conversion rates of the phenyl halides vary according to the examples from 49 to 87%. Corresponding acid yields are obtained ranging from 0 to 40% depending on the halogen. This document also teaches that under these conditions

  no acid is obtained from the n-butyl bromide.

  TROUPEL, ROLLIN, PERICHON and FAUVARQUE (New Journal of Chemistry,

  vol.5, no. 12, 1981 pages 621-625) perform the electrosynthesis of

  aromatics by electrochemical reduction of aromatic halides

  at room temperature in the presence of carbon dioxide and a nickel-based catalyst in a 2-compartment cell in tetrahydrofuran (THF) / hexamethylphosphoric triamide (HMPT) containing an indifferent electrolyte (LiClO4, NBu4C104). The anode is in platinum and the cathode in mercury or graphite. The electrochemical reduction of NiX2L2 nickel complexes (L = PPh3 and X = Cl or Br) in the presence of aromatic halides (ArX) and an excess of L provides ArNiXL2 stable complexes. In the presence of CO 2, such complexes are electro-reducible and give the arylcarboxylates

  ArCOO with yields of 40 to 90% depending on the nature of Ar.

  From benzyl chloride, only bibenzyl is obtained but

  no phenylacetic acid. From ArX + RX mixtures (halogenated

  aliphatic res), ArCOO and ArCOOR esters are obtained but not RCOO.

  These last tests clearly show the limits of the field of application

  cation of this technique. French Patent No. 2,530,266 describes a process for the preparation of arylacetic and arylpropionic acids from the corresponding halides. An electrochemical reduction, under a carbon dioxide atmosphere, of said halides in the presence of a catalyst comprising at least one metal halide ligand of

  MY2L formula, M being palladium or nickel, Y being a halogen

  ne, L a ligand of formula PR2- (CH2) -PR in which P denotes PR-C2n 2 phosphorus and R a radical chosen from the group formed by the phenyl radical and the aliphatic radicals, n being a number

integer less than or equal to 3.

  The cell comprises 2 separate compartments, the cathode is in

  mercury and the lithium anode. The yields of carboxylic acids

  They vary from 19 to 51% depending on the tests.

  Therefore, to the best of the applicant's knowledge, there is no

  simple process of electrosynthesis of carboxylic acids by reduction

  electrochemical formation of organic halides in the presence of

  carbon dioxide in an electrolysis cell in an organic solvent medium

  that contains an indifferent electrolyte, having a very high efficiency

  high and generally applicable, that is to say applicable for the electro-

  synthesis of most of the usual carboxylic acids.

  The present invention relates to such a method.

  The process of electrosynthesis of carboxylic acids by reduction

  electrochemical organic halides in the presence of carbon dioxide

  in an electrolysis cell equipped with electrodes, in

  organic solvent containing an indifferent electrolyte according to

  The invention is characterized in that a magnesium anode is used.

  As can be seen from the description that follows,

  totally unexpected way, we thus obtain very high yields with little or no by-products whereas 1) this method is very simple to implement; it can on the one hand and contrary to all the processes described in the state of the art be implemented in an electrolysis cell to a

  only compartment without diaphragm or sintered, which is very important

  so much, especially at the industrial level, and secondly be implemented without resorting to one or catalysts;

  (2) this process is general in scope and applies to electro-

  synthesis of many carboxylic acids.

  The cell is a classic cell well known to the horme of

  business, with only one compartment.

  This possibility of using a single compartment cell is

  a major advantage as has already been mentioned.

  According to a particular embodiment of the invention, the halo

  organic creatures are mono or dihalogenated and respond to the

  wherein X is a halogen atom selected from the group consisting of chlorine, bromine and iodine; X 'present or not is, when present, a halogen atom, identical to or different from X, selected from the group consisting of chlorine, bromine and iodine; A is:

  an R 1 alkyl or cycloalkyl chain, substituted or unsubstituted,

  with or without 1 to 21 carbon atoms,

  an aryl group R2 optionally substituted with one or more

  R1 or by one or more non-electro-functional functional groups

R3,

  an aromatic heterocyclic group.

  Non-electroreducible functional groups are defined as

  non-electroreducible groups under the conditions of electro-

  synthesis. Preferably, when X 'is present, X and X' are borne by the same carbon atom, or by carbon atoms in position

o, or -Y.

  Preferably, when A is an aromatic heterocyclic group, A is selected from the group consisting of thiophene,

furan and pyridine.

  Also preferably, when the R chain is substituted, R is substituted with one or more aromatic groups or with one or more R3o non-electro-functional functional groups.

  R3 non-electro-functional functional groups are preferably

  selected from the group consisting of groups

  carbonyl, cyano, ether, sulfide, ester, tertiary amine, fluorine.

  According to another particular embodiment of the invention, the process is carried out by electrochemical reduction of a mixture

  different organic halides.

  The process which is the subject of the invention is characterized in that the anode is magnesium. This anode can have any shape and in particular all the conventional forms of metal electrodes well known to those skilled in the art (twisted wire, flat bar, cylindrical bar, renewable bed, balls, canvas, grid, etc.). Preferably, a cylindrical bar of diameter adapted to the dimensions of the cell is used. For example, for a cell whose total volume is 45 cm3, the diameter of the bar is of the order of 1 cm.

  Before use it is best to clean the surface of the anode

  chemically (by dilute HCl for example) or mechanically (lime, Emeri cloth for example) so as to remove the oxide of

  magnesium often present on the surface of the metal. The purity of the magnet

  sium is not an important parameter and the industrial qualities are suitable. To the knowledge of the Applicant, no other metal than magnesium can obtain all the results presented in the context of this invention. In particular, tests were carried out with an anode either lithium, aluminum or zinc, all other conditions identical to those used when the anode is magnesium. These tests have shown that in many cases, the yield of carboxylic acid is lower than that obtained with the magnesium anode (see Examples 43).

at 45).

  The cathode is any metal such as stainless steel, nickel, platinum, gold, copper, or graphite. She is

  preferably constituted by a grid or a cylindrical plate

  drique arranged concentrically around the anode. For reasons

  In economic terms, stainless steel is preferably used.

  The electrodes are fed with direct current through

  of a stabilized power supply.

  Organic solvents used in the context of this invention

  are all the little protic solvents usually used in electricity.

  organic trochemistry. For example, hexamethylphosphonate

  phorotriamide (HMPT), tetrahydrofuran (THF), THF

  HMPT, N-methylpyrrolidone (NMP), tetramethylurea (TMU),

  dimethylformamide (DMF), acetonitrile, acetone.

  The indifferent electrolytes used may be the usual ones

  used in organic electrochemistry. For example,

  tetrabutylammonium tetrafluoroborate (BF4 NBu4), the

  lithium chlorate (LiClO4), tetrabutylammonium chloride

  (ClNBu4), tetraethylammonium chloride (ClNEt4) and perchloride

  tetrabutylammonium spleen (C104NBu4).

  Preferably, the concentration of indifferent electrolyte in the organic solvent is between 10-2M and 2 10-1M. Also preferably, the concentration of organic halide (s) in the organic solvent is between 10 M and 1 M. This concentration can therefore be relatively high, which is quite unusual in electrosynthesis. This finding is of course very

  interesting on the economic level.

  The electrolysis is conducted: 1) at a temperature generally between 0 C and 60 C, preferably at room temperature (about 20 C) for reasons of convenience; 2) under a current density on the magnesium anode which can vary from 10-1 to 100 mA / cm 2, generally between 5 and mA / cm 2. In general, the operation is carried out at constant intensity, but it is also possible to operate at constant voltage, at controlled voltage or with variable intensity and potential; 3) under a CO 2 atmosphere, the carbon dioxide pressure in the cell being between 10 1 and 50 bar, preferably atmospheric pressure, for simplicity. In this case, we realize by

  bubbling through a pipe plunging into the water.

  lution. 4) with stirring of the solution, for example via

  of a magnetized bar. After passing a quantity of current -

  corresponding to 2 Faraday (2 x 96,500 C) per mole of monohalide derivatives

  logenés (2n Faraday per mole of halogenated derivatives) we have:

  1. Assayed by gas chromatography (GC), the halogenated

  residual organic matter to deduce its conversion rate, 2. assayed the carboxylate formed by pH metric to deduce the

  yield of product formed in relation to the initial quantity of ha-

  3. Isolates the carboxylic acid formed for characterization and

  calculation of the yield of isolated product.

  The yields obtained in carboxylate formed are high, very

  wind over 99%. Isolated carboxylic acid yields

  vary from 70 to 90% of the yield of carboxylate formed.

  In the very particular case of chlorinated aromatic derivatives, the chlorine atom of which is directly linked to the aromatic ring of the XAX type: where X represents chlorine, X ', present or not, represents, when present, chlorine,

  A represents an aryl group R2 as defined above.

  (eg chlorobenzene), better yields have been found when the current density is low, the temperature is

  is less than 20 C (5 C for example) and the solvent DM4F.

  The single figure very schematically represents an electricity cell.

  trolysis usable for the implementation of the invention.

  It includes a single compartment. The upper part 5 is made of glass and is equipped with 5 pipes allowing the arrival and the exit of the

  carbon dioxide, electric passages and samples

  solution during electrolysis (tubing 4). The lower part 6 is constituted by a plug provided with a seal 3 and screwed on

the glass part 5.

  The anode 1 is a magnesium cylindrical bar and the cathode 2 is a cylindrical stainless steel cloth arranged concentrically

around the anode 1.

  Arrows A and B respectively signify entry and exit

carbon dioxide.

  The invention is illustrated by the following nonlimiting examples,

provided for information only.

Example 1

  The cell is of the type described above and very schematically represented in the single figure. The total volume of the

  cell is 45 cm3. The anode is a cylindrical bar of magneto-

  sium with a diameter of 1 cm. It is introduced into the cell through the central tubing and dips into the solution on a

  length of 2.5 cm. The initial working surface of this elec-

trode is 8 cm2.

  35 ml of anhydrous NMP are introduced into the cell, 17.4 millimoles

  benzyl chloride (C6H5CH2Cl), 1.75 millimoles of tetrafluoro-

  tetrabutylammonium borate (BF4NBu4). CO2 is bubbled through

  the solution using a tubing dipping into this solution.

  The CO2 pressure is the atmospheric pressure.

  The solution is stirred by means of a magnetized bar and

  maintains the ambient temperature (about 20 C).

  The electrodes are fed with direct current through

  of a stabilized diet and then

  constant current of 400 mA, a current density of 50 mA / cm2

on the magnesium anode.

  After passing 2 Faradays per mole of benzyl chloride, the latter is completely converted to phenylacetate (C6H5CH2C2)

(6H52CH20) '

  as indicated by GC (assay of C 6 H 5 CH 2 Cl) and the dosage of

  carboxylate which is carried out in the following manner: 2 ml of

  are treated with 1M NaOH and then with diethyl ether. The aqueous phase is separated and acidified with 1 M H 2 SO 4 and finally extracted with ether twice. The ethereal phase is added

  of water, basified and assayed pH-metric by H2SO4.

  Over the entire solution, the same treatment stopped after extraction with ether in an acid medium and then evaporation of the ether makes it possible to recover the pure phenylacetic acid (identified by its melting point of 76 C for a value 77 C and its NMR and IR spectra with a yield of 90% compared to

C6 H5CH2Cl initial.

Examples 2 to 7

  The following experiments were conducted under conditions identical to those of Example 1 but with different current densities on the magnesium anode. Example n Current Density Conversion Rate Anode Yield (mA / cm2) (%) of C6H CH2C1 to C6H5CH2CO2

6 5 2 6 5 2 2

2 Faraday / mole (%)

2 6,25> 99> 99

3 12.5> 99> 99

4 25> 99> 99

31.25> 99> 99

6 37.5> 99> 99

7,125 90,80

  The yields of C6H5CH2CO are those resulting from the acid-

6 5 2 2

  based. It should be noted for Example 7 that 7% of C 6 H 5 CH 2 CH 2 C 6 H 5 and 3% of C 6 H 5 CH 3 were formed. Examples 8 to 13 The following experiments were carried out under conditions similar to those described in Example 1. but on the one hand with different concentrations of the BF4NBu4 electrolyte and, on the other hand, with other electrolytes. Current density on anode

  magnesium was set at 31.25 mA / cm 2.

  Example n Nature of the electrolyte Conversion rate Yield and concentration (mole / l) (%) of C6H 5CH2Cl to C6H5CH2CO2 2 Faraday / mole (%) 8 BF4NBu4 0.02> 99> 99 9 BF4NBu4 0.2> 99> 99 ClNBu 0.05> 99> 99 ClNEt4 0.05 90- 70 12 LiClO4 0.05 95 92 For Examples II and 12, toluene is obtained as another product

  reduction. This is due to the use of hydrated salts.

  Examples 13 to 17 The following experiments were conducted under conditions similar to those of Example 1, but with solvents other than NMP and variable current densities specified for each

example.

  Solvent Example Neck Density Conversion Rate Yield on anode (%) C6H5CH2Cl in Mg (mA / cm2) 2 Faraday / mole C6H CH2C0 (%) 13 Dimethyl-Formamide Tetrahydrofuran 37.5> 99> 99 tetrahydrofuran 6,25> 99> 99 drofuran

(75% vol.) -

hexamethylphosphoric

phosphora-

  mide (25% vol.) 16 Acetone 31.25> 99 * 80 17 Acetonitrile 27.5> 99 **> 99 For Example 14, note the low solubility of the carboxylate

  formed which is deposited in part on the magnesium anode.

  For example 16, the electrolyses can not be conducted under these conditions, to their end (2 Faraday / C6H5CH2Cl), because of a

  increase in the viscosity of the solutions, which are

  Gel electrolysis was stopped after consumption of 75 ml of 7.5 mmoles of C6H5CH2Cl, 43% of the initial amount (17.4 mmol). ** For example 17, the electrolysis was stopped after passage of

  1 Faraday per mole of C6H5CH2Cl. The yield indicated in C6H5CH2COO-

has been calculated accordingly.

  Examples 18 to 20 The following experiments were carried out under conditions similar to those of Example 1, but in the presence of varying amounts of benzyl chloride and with a current density of

mA / cm 2 on the magnesium anode.

TABLE 4

  Example n C6H5CH2Cl initial C6H5CH2Cl trans-Yield in (millimoles) formed (millimoles) C H CH CO

6 5 2 2

(%)

18 8.7 8.7> 99

19 34.8 25> 99

73.9 30 95

  In practice, under these experimental conditions, one can not exceed concentrations of C6H5CH2CO2 formed of about 0.7 M. Beyond, the

  solutions obtained become too viscous.

  For Examples 19 to 20, the electrolysis was stopped after use

  1.4 and 0.8 Faraday per mole of initial C 6 H 5 CH 2 Cl respectively. Examples 21 to 41 The following examples were conducted under the same conditions

  than those described in the various examples 1 to 20.

  The halogenated derivatives listed in the following Tables I and II

  were used in place of C6H 5CH2Cl.

  TABLE I - Operating conditions -

  NO o Example n Organic halide Solvent Current density at the anode Temperature u% Cl.____________.____.__._._.__._.of Mg (mA / cm2) 21 p. Bromofluorobenzene THF-HMPT 12.5 Ambient

22 "NMP 25 40 C

23 "DMF 25 40 C

24 "DMF 31.25 5 C

  2-Chlorothiophene THF-HMPT 6.25 ambient 26 3-Bromofuran U 6.25 27 V Bromostyrene (mixture of 6.25 cis and trans isomers) 28 p. Bromoacetophenone "6.25 1-Bromodecane 6.25 1-Chloroethylbenzene (Phenyl chloride-6.25), 31 3-Chloro-1-phenyl-propene" t 6.25 32 Bromobenzene THF 15 33 Ethyl Chloroacetate THF 6.25 34 Bromobenzene DMF 37.5 TABLE I (continued) Example n Organic halide Solvent Current density at anode Temperature of Mg (mA / cm 2) δ *. Dichloromethane THF 6.25 Ambient 36 1-Bromododecane (12.3 mmol) DMF 18.75 Ambient 37 1-Bromooctadecane (6 mmol) THF-HMPT 6.25 Ambient 38 mono-chloroacetone DMF 31.25 5 C (12.4 mmol) 39 1,3 dichloroacetone DMF 3755 5 C (9.5 mmol) 1,2 dichloroethane DMF 37.5 50 C n (12.6 mmol) 41 chlorobenzene (19 mmol) DMF 12.5 50C

TABLE II - Results -

  Example Halide% Halide Yield Yield Melting Point of a-

  organic cm converted to carboxylate carboxylic acid isolated at C 2 Faraday / mole (%) isolated (as Result of carboxy-experimental Thore late formed) 21 p.Bromofluoro-> 99> 99 85 184 185 benzene

22 "98 50 80 184 185

23 78 67 80 184 185

24 '> 99 91 80 184 185

  2-Chlorothiophene> 99> 99 80 126 129 26 3-Bromofuran> 99 95 78 121 122-123 27 p -Bromostyrene> 99> 99 80 106 trans: 135 (mixture of isocis: 42-56 cis and trans mothers) 28 p.Bromoacetophene> 99) 99 82 206 210 none 29 1-Bromodecane> 99> 99 75 28 28.6

  1-Chloroethylben-> 99> 99 80 unmeasured

  zen (phenyl chloride) 31 3-chloro 1 phenyl> 99> 99 85 85 87 propene 32 Bromobenzene> 99 90 85 122 122.4 TABLE II (continued) Example n Halide% Halide Yield in a-Point of the organic acid converted to the carboxylate carboxylic acid isolated in C 2 Faraday / mole (in%) as isolated (as Result of the carboxy-experimenta Thorie late formed) eprmn

  33 Chloroacetate> 99 90 not determined -

  of ethyl 34 Bromobenzene> 99 81 85 122 122.4

  Dichloromethane not determined Not determined - -

including nodé

  ClCH2CO27 CH2 (CO022, non-metered r 36 1-Bromododecane> 9960 (12.3 mmol)

37 1-Bromooctadecane> 99 50 "-

  (6 mmol) 38 mono-chloroaceton> 99> 99 (12.4 mmol) 39 1.3 dichloroacetate> 99> 99 tone (9.5 mmol) after passing 4 F / mole) 1,2 dichloroethane> 99> 99 (12.6 mmol) after passing 4 F / mol) 41 chlorobenzene 78 66 (19 mmol) (+ 12% benzene) In Examples 33, 35 to 41, the acids were not isolated. In all cases, the yields are obtained by acid-base

  carboxylate formed. Isolated acid yields are, for example,

  21 to 32 and 34 between 70 and 90% of the quantity determined

  born by carboxylate assay. Isolated acids have been identified

  by their NMR and IR spectra as well as by their melting point.

Example 42

  The following experiment was carried out under the same general conditions as those described in Example 1, except that the electrolysis of a mixture CH 5 Cl and p.BrC6H4F was mixed. 2 6 4 in dimethylformamide under a current density at the anode of

31.25 mA / cm 2 at 5 C.

  Number of Faraday C6H5CHC1 resebrc 6H4F res- C6H5CH2CO2 per mole of both (mmol) and (mmol) + mixture p.FC6H4CO2 formed (mmol)

O 9 9 O

1 4 4,5 not dosed

2 0 0.5 16.7 (+ 1.3

from C6H5F) 6 5)

Example 43

  The following experiment was conducted under conditions identical to those described in Example 1, with a current density of 31.25 mA / cm 2, replacing the magnesium anode with an anode of

  zinc of identical shape and diameter.

  After passing 2 Faradays per mole of C6H5CH2Cl, only 60% of it is converted into a mixture of C6H5CH3 (90%) and traces

of bibenzyl and C6H5CH2CO.

6 5 2 2-

Example 44

  The following experiment was carried out under identical general conditions to those described in Example 1, in DMF-LiClO4 -2 medium.

  5.10 M at 5 C under a current density of 31.25 mA / cm 2,

* placing the magnesium anode through a lithium anode of shape and

identical diameter.

  After passing 2 Faradays per mole of C6H5CH2Cl, 40% of it was

  has been converted to bibenzyl (> 99%).

Example 45

  The following experiment was carried out under identical general conditions to those described in Example 34, but in DMF-NBu medium BF 4.10 M at 5 ° C., under a current density of 20 mA / cm 2.

  and replacing the anode with magnesium by an aluminum anode.

  After passing 2 Faradays per mole of C6H5Br, 50% of it was converted into several products including benzene and benzoic acid, the latter compound being the majority and representing

% of products formed. -

Example 46

  An electrolyser having an anode consisting of a

  magnesium bar centered on the axis of a stainless steel tube

  dable serving as a cathode. The solution to be electrolyzed, contained in a thermostated reactor, is circulated between these two electrodes by means of a pump. This solution consists of 150 g of DMF containing 1 g of NBU4BF4 and 4 g of 1 (6 methoxy).

2 naphthyl) -1 chloroethane.

  After passing 1.2 times the amount of theoretical current (electrolysis at a constant intensity of 500 mA), evaporation of the solvent, neutralization of the medium and extraction, it is isolated

  the corresponding acid (Naproxen) with a yield of 80%.

  The product has been identified by R.M.N. and mass.

Example 47

  The experiment was conducted in the same electrolyser as the one

  used in the previous example 46 but the solution is

  100 g of DMF containing 2 g of NBu4BF4 and 7 g of metaphenoxyphenyl chloride. After passage of 2 times the amount of theoretical current is 4 Faraday per mole of chloride (electrolysis at constant intensity of 1A), 80% of the corresponding acid (fenoprofen) identified by spectrometers is obtained.

  Mass and R.M.N. and 18% of unprocessed starting material.

Claims (14)

claims   1. Electrosynthesis process of carboxylic acids by reduction   electrochemical character of organic halides in the presence of carbon dioxide   in an electrolysis cell provided with electrodes, in an organic solvent medium containing an indifferent electrolyte, characterized   in that a magnesium anode is used.   2. A process for the electrosynthesis of carboxylic acids, according to the   1 wherein the organic halides are mono or halogenated and correspond to the formula XAX 'wherein: X is a halogen atom selected from the group consisting of chlorine, bromine and iodine, X' present or not is, when present, a halogen atom, identical to or different from X, selected from the group consisting of chlorine, bromine and iodine A is:   an R 1 alkyl or cycloalkyl chain, substituted or unsubstituted,   with or without 1 to 21 carbon atoms,   an aryl group R2 optionally substituted with one or more   R1 or by one or more non-electroreduction functional groups R3,   an aromatic heterocyclic group.   3. A process for the electrosynthesis of carboxylic acids according to the   wherein X and X 'are borne by the same carbon atom, or by carbon atoms in position a, or 4. Electrosynthesis process of carboxylic acids according to one   any of claims 2 and 3 characterized in that A is a   aromatic heterocyclic group selected from the group consisting of   thiophene, furan and pyridine.   5. Electrosynthesis process of carboxylic acids according to one   any of claims 2 and 3 characterized in that the   R1 chain is substituted by one or more aromatic groups or   by one or more non-electro-functional functional groups R3.   6. Electrosynthetic process of carboxylic acids according to one   any of claims 2, 3, 4 and 5, characterized in that the   R3 non-electroreducible functional groups are chosen from the group consisting of carbonyl, cyano, ether, sulphide, ester, tertiary amine and fluorine groups. 7. Electrosynthesis process of carboxylic acids according to one   any of the preceding claims, characterized in that   is implemented by electrochemical reduction of a mixture of halogenated different organic lesions.   8. Electrosynthesis process of carboxylic acids according to one   any of the preceding claims characterized in that one   uses an organic solvent selected from the group consisting of hexamethylphosphorotriamide (HMPT), tetrahydrofuran (THF)   HMPT-THF mixtures, acetone, acetonitrile, N-methylpyrrolidine   rolidone (NMP), dimethylformamide (Dr4F) and tetramethylurea (TMU).   9. Electrosynthesis process for carboxylic acids according to one   any of the preceding claims characterized in that   the indifferent electrolyte is chosen from the group constituted by the   tetrabutylammonium tetrafluoroborate, tetrabut perchlorate   tylammonium and lithium perchlorate.   10. Electrosynthesis process of carboxylic acids according to one   any of the preceding claims characterized in that the   organic halide concentration is between 10 M and 1 M in the organic solvent and the indifferent electrolyte concentration is between 10 2M and 2.10 1M in the organic solvent. 11. Electrosynthesis process of carboxylic acids according to one   any of the preceding claims characterized in that the   electrochemical reduction of organic halides occurs at approximately ron 20 C.   12. Process for the electrosynthesis of carboxylic acids according to one   any of the preceding claims characterized in that the   Carbon dioxide pressure is the atmospheric pressure.   13. Electrosynthesis process for carboxylic acids according to one   any of the preceding claims characterized in that   performs the electrochemical reduction at constant intensity.   14. Electrosynthetic process of carboxylic acids according to one   any of the preceding claims characterized in that   uses a stainless steel cathode.