Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B3/00—Electrolytic production of organic compounds
  • C25B3/20—Processes
  • C25B3/25—Reduction

Definitions

• the invention relates to a process for the electrochemical synthesis of an aldehyde by electrolysis in a cell provided with electrodes of an organic halide and of an N, N-disubstituted formamide, then hydrolysis of the reaction medium.
• Aldehydes are compounds commonly used in many fields of the chemical industry, notably in perfumery, agrochemicals and pharmacy.
• aldehydes There are many methods of synthesizing aldehydes. Among these, mention may be made of those for which the aldehyde is obtained by electrolysis, in a cell provided with electrodes, an organic halide and an N, N-disubstituted formamide, then hydrolysis of the reaction medium.
• CASARDO and GALLARDO in Electrochimica Acta, Vol. 32, n ° 8, pp. 1145-1147, (1987) describe the synthesis of traces of benzaldehyde during the electrolysis of bromo or iodobenzene solutions in dimethylformamide (DMF).
• the cell has 2 separate compartments, anodic and cathodic.
• the cathode is made of mercury and the inert anode is made of graphite.
• VIEIRA and PETERS in J. Org. Chem., Vol. 51, n ° 8, pp. 1231-1239, (1986) describe the synthesis of pivalic aldehyde during the electrolysis of a solution of tert-butyl bromide in DMF. The yields are very low, less than 14%.
• the cell has 2 separate compartments, anodic and cathodic.
• the cathode is made of mercury and the inert anode is made of carbon.
• the method according to the invention compared with the closest aforementioned state of the art, has, in addition to a considerable improvement in yield and a widening of the field of application, a certain number of other advantages, the main ones of which are: a simpler implementation since the process is carried out in an electrolysis cell comprising only one compartment, without diaphragm or sintered, which is very important at the industrial stage, - a very much higher halide concentration, - a higher current intensity, of the order of several amperes per dm2, - the possibility of using a very low support electrolyte concentration, of the order of 10 ⁇ 2M, - the use of solid electrodes limiting the risks of pollution by heavy metals such as mercury.
• the electrolysis cell is a cell comprising only one compartment, that is to say for which there is no comparison separate anode and cathode tents. This possibility of using such a cell is an important advantage, as has already been mentioned.
• the anode is consumable, that is to say it is consumed during the electrochemical reaction of which it is the seat. This is the reason why such processes are sometimes called "soluble anode".
• the anode is made of a metal chosen from the group consisting of reducing metals and their alloys, that is to say any alloy containing at least one reducing metal.
• the anode is made of a reducing metal chosen from the group consisting of magnesium, aluminum, zinc and their alloys, that is to say any alloy containing at least one of the three metals mentioned above, namely zinc, aluminum and magnesium.
• This anode can have any shape and in particular all the classic forms of metal electrodes such as twisted wire, flat bar, cylindrical bar, renewable bed, balls, fabric, grid.
• a cylindrical bar of diameter adapted to the dimensions of the cell is used.
• the cathode is any metal such as stainless steel, gold, nickel, platinum, copper, aluminum, iron or carbon such as, for example, vitreous carbon or graphite. It is preferably formed by a grid or a cylindrical plate arranged concentrically around the anode.
• the Applicant has discovered that, unexpectedly, the efficiency is considerably improved when the cathode is covered with an electrolytic deposit of a metal M chosen from the group consisting of zinc, cadmium, lead and tin.
• the electrodeposition of the metal M on the cathode, prior to the electrosynthesis of the aldehyde, can be carried out according to various methods, in particular those described in Examples 14 to 38.
• the electrodes are supplied with direct current via a stabilized power supply.
• the aldehyde corresponds to the general formula RCHO in which R represents an organic radical
• the organic halide corresponds to the general formula RX in which R has the abovementioned meaning and X represents an atom of halogen, preferably chlorine or bromine
• the N, N-disubstituted formamide corresponds to the general formula in which R1 and R2, identical or different, represent an aliphatic or aromatic chain, substituted or unsubstituted, preferably either an alkyl chain containing 1 to 8 carbon atoms, or a substituted or unsubstituted phenyl ring, or alternatively R1 and R2 form a cycle.
• R represents an aliphatic, arylaliphatic, aromatic, alkylaromatic or heterocyclic organic radical, substituted or unsubstituted, preferably an alkyl radical or a phenyl group, substituted or unsubstituted.
• R carries various substituents, these must be more difficult to reduce than the R-X bond.
• the formamide is DMF.
• other formamides mention may be made of N, N-dialkylformamides and N-phenyl N-methylformamide (N-methylformanilide).
• the hydrolysis of the reaction medium is for example carried out with an acidic aqueous solution.
• the formamide N, N-disubstituted in addition to its role as reagent, also plays the role of solvent. This is particularly the case when using DMF. It is then not necessary to use another solvent. Electrolysis can however be carried out in the presence of a co-solvent chosen from aprotic solvents with low electrophilicity, such as, for example, tetramethylurea (TMU) and tetrahydrofuran (THF).
• a co-solvent chosen from aprotic solvents with low electrophilicity, such as, for example, tetramethylurea (TMU) and tetrahydrofuran (THF).
• the concentration of the reactants is preferably chosen so as to ensure a very large molar excess of formamide, since the latter also preferably plays the role of solvent.
• the concentration of the organic halide in the reaction medium is generally between 0.05 and 2 mol / l.
• the reaction medium is made conductive by a slightly reducible support electrolyte.
• a slightly reducible support electrolyte Mention may be made, for example, of salts whose anion is a halide, a carboxylate, a fluoroborate, a perchlo spleen or a hexafluorophosphate and the cation a quaternary ammonium, aluminum, zinc, sodium, potassium, calcium, lithium, a tetraalkylphosphonium, as well as mixtures of these salts. Tetramethylammonium fluoroborate or tetrabutylammonium bromide is preferably used.
• the solution is oxygenated by bubbling an inert gas, nitrogen or argon for example.
• the reaction temperature is preferably between 0 and 80 ° C, for example room temperature.
• the solution is stirred, maintained under an inert atmosphere, of nitrogen or argon for example, and cooled if necessary to maintain its temperature between 0 and 80 ° C. preferably.
• the current density on the cathode is preferably chosen between 0.2 and 20 A / dm2.
• the duration of the electrolysis is preferably chosen so that the amount of current involved corresponds approximately to 2 Faraday (193 103C) per mole of organic halide.
• reaction medium After electrolysis, the reaction medium is hydrolyzed with an acidic aqueous solution, for example dilute hydrochloric acid, then extraction is carried out with an organic solvent. After drying and evaporation of the extraction solvent, the aldehyde is obtained which is identified and assayed according to conventional methods of analysis, after optional purification by passage over a column of silica for example.
• acidic aqueous solution for example dilute hydrochloric acid
• organic solvent After drying and evaporation of the extraction solvent, the aldehyde is obtained which is identified and assayed according to conventional methods of analysis, after optional purification by passage over a column of silica for example.
• a cathode covered with an electrolytic deposit of a metal M as defined above it is possible, when M represents cadmium, lead or tin, to directly introduce the metal M to be deposited on the cathode in the form of salt, cadmium bromide, lead acetate or tin chloride for example, in the organic halide and N, N-disubstituted formamide mixture.
• the metal M is deposited on the cathode.
• the yield is improved by adding the organic halide gradually into the reaction medium during electrolysis.
• a conventional electrolysis cell comprising only one compartment.
• the upper part of the cell is made of glass and is equipped with 5 tubes, including a central one, allowing the arrival and the exit of argon used as inert gas, the possible samples of solution during electrolysis, the addition of reagents, electrical passages.
• the lower part consists of a stopper fitted with a seal, screwed onto the upper glass part.
• the total volume of the cell is close to 45 cm3 and its volume uti the neighbor of 35 cm3.
• the anode is a cylindrical bar with a diameter close to 1 cm, made of zinc, magnesium or aluminum according to the tests. It is introduced into the cell through the central tube and is thus located approximately in axial position relative to the cell.
• the cathode consists of a metallic cylindrical grid arranged concentrically around the anode.
• the working surface of the cathode is around 20 cm2.
• the cell is immersed in a thermostatic bath set to the chosen temperature.
• reaction medium is stirred, for example by means of a magnetic bar.
• the solution to be electrolyzed consisting of: - organic halide, - the formamide N, N-disubstituted or the mixture of formamides N, N-disubstituted, - possibly the co-solvent, the support electrolyte, tetramethylammonium fluoroborate at a concentration of 5 ⁇ 10 -2 M except for Example 7 for which the support electrolyte is tetrabutylammonium bromide at the concentration of 10 ⁇ 2M.
• This mixture is degassed by bubbling argon, then it is maintained under an argon atmosphere.
• reaction medium After constant intensity electrolysis for a corresponding period dant at 3 Faraday (290 103C) per mole of organic halide, the reaction medium is hydrolyzed with a 1N aqueous hydrochloric acid solution and then extracted with diethyl ether.
• the organic phase is then separated and washed with water.
• the aldehyde obtained is purified by chromatography on a silica column and then identified according to conventional methods of analysis, in particular by infrared (IR), mass (SM) and nuclear magnetic resonance (NMR) spectrometries. ).
• the organic halide concentration is 0.5 M for Examples 1, 3 to 9, 12 and 0.125 M for Example 2.
• CF3Br being a gas
• it is introduced by bubbling into the reaction medium under a pressure of 105Pa (1 bar).
• the cathode is made of nickel for examples 10 and 11, of stainless steel for examples 1 to 6, 8, 9 to 12, of lead for example 7.
• the anode is made of zinc for example 10, of aluminum for examples 1 to 4, 6 to 9 and 12.
• the volume of formamide, or mixture of formamides, is 36cm3. This volume includes the co-solvent when it is present.
• the formamide is DMF for examples 1 to 5 and 7 to 12, a 1/1 mixture by volume of DMF / N-methylformanilide for example 6.
• Examples 2 and 4 are carried out in the presence of a co-solvent.
• the co-solvent is THF and the volume ratio DMF / THF is 2/1 respectively.
• the co-solvent is TMU and the volume ratio DMF / TMU is respectively 1/1.
• the current density on the cathode is 2A / dm2 for examples 1, 2, 7 to 11, 1.5 A / dm2 for example 12, 1 A / dm2 for examples 3 and 4 and 0.5 A / dm2 for examples 5 and 6.
• the reaction temperature is 25 ° C for Examples 1 to 9 and 0 ° C for Examples 10 to 12.
• the trifluoroacetaldehyde is isolated in the form of a hydrate and the yield indicated in Table 1 is a faradaic yield calculated from the amount of electricity used.
• the experimental conditions for this example are the same as those of Example 1 but the initial concentration of benzyl chloride is 0.125 M. After electrolysis corresponding to the passage of 2 Faraday (193 103C) per mole of benzyl chloride, we add an amount of benzyl chloride equal to that present at the start. Electrolysis is then continued until the total duration thereof corresponds to 3 Faraday (290 103C) per mole of benzyl chloride used. The yield of isolated pure aldehyde is 50%.
• the cathode made of stainless steel or nickel, is covered with an electrolytic deposit of a metal M.
• MBr2 is added at a concentration of the order of 5 10 ⁇ 2M to 10-1M.
• the cell is equipped with a metal anode M and a current of 0.1 to 0.2 A is imposed for 0.5 to 1 hour, which makes it possible to transport M from the anode to the cathode.
• the anode M is then replaced by a magnesium bar and the electrolysis is continued at constant intensity for the time necessary for the almost complete exhaustion of the M2+ ions present in the solution.
• the organic halide is then added to this solution.
• MBr2 is added at a concentration of the order of 5 10 ⁇ 2M to 10 ⁇ 1M.
• the cell is equipped with a magnesium anode and a current of 0.1 to 0.2 A is imposed for the time necessary for the electrodeposition of the M2+ ions on the cathode.
• the organic halide is then added.
• M is cadmium, lead or tin
• DMF containing tetrabutylammonium bromide as support electrolyte at the concentration of 10 ⁇ 2M, CdBr2, Pb (CH3CO2) 2 or SnCl2 are added, at a concentration of the order of 5 10 52 to 10 ⁇ 1M, as well as organic halide.
• the cell is equipped with a magnesium anode and a constant intensity current is imposed.
• the cathode coated according to one of the aforementioned methods A, B or C then having served for the electrosynthesis of an aldehyde according to the invention is reused without modification in a new electrosynthesis of aldehyde with a magnesium anode, in DMF medium containing tetrabutylammonium bromide at a concentration of 10 ⁇ 2M as a support electrolyte.
• electrosynthesis is carried out at ambient temperature, by imposing a current of constant intensity such that the current density on the cathode is 1 A / dm2.
• the duration of the electrolysis is chosen so as to employ 2.1 Faraday (203 103 C) per mole of organic halide.
• reaction medium Before electrolysis, the reaction medium is degassed for barbota argon, then the medium is maintained under an argon atmosphere.
• the medium is hydrolyzed, then the aldehyde formed is isolated, purified, identified and assayed according to the method described for Examples 1 to 14.
• the aldehyde is recovered in the form of a hydrate.
• the following table 2 specifies for each example the nature and the concentration in DMF of the organic halide, the nature of the cathode as well as the method used for electrodepositing the metal M.
• Table 3 specifies for each example the conversion rate of the organic halide as well as the nature and the yield with respect to the starting organic halide, of the aldehyde formed. For certain examples, the yield of isolated pure aldehyde is also indicated in brackets.
• the operation is carried out according to the general conditions relating to examples 14 to 38 but: -
• the current density on the cathode is 0.1 A / dm2.
• the reaction medium is a 75/25 mixture by volume of N-methylformanilide and TMU respectively, containing tetrabutylammonium bromide as support electrolyte at the concentration of 10 ⁇ 2M and pCF3C6H4Cl as organic halide at the concentration of 0.50 mol / l.

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• Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
• Engineering & Computer Science (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Electrolytic Production Of Non-Metals, Compounds, Apparatuses Therefor (AREA)
• Compounds Of Unknown Constitution (AREA)
• Electrodes For Compound Or Non-Metal Manufacture (AREA)
• Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)

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• 1988
  • 1988-11-23 FR FR8815235A patent/FR2639364B1/fr not_active Expired - Lifetime
• 1989
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