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
• • 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
  • C25B11/00—Electrodes; Manufacture thereof not otherwise provided for
• • 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
  • C25B11/00—Electrodes; Manufacture thereof not otherwise provided for
  • C25B11/04—Electrodes; Manufacture thereof not otherwise provided for characterised by the material
  • C25B11/051—Electrodes formed of electrocatalysts on a substrate or carrier

Definitions

• the present invention relates to a method for the electrochemical reduction of organic compounds.
• a disadvantage of these established manufacturing processes is that, after the catalytically active layer has been inactivated, the electrodes frequently have to be removed from the electrolysis apparatus and fed to an external regeneration, so that short catalyst service lives preclude economic use of the electrochemical synthesis system.
• Another disadvantage is the complex production of the catalytically active layer as such and the difficulties in achieving a sufficient connection with the carrier electrode.
• the development effort for a classic electrode coating process is economically justified only for larger technical processes, such as chlor-alkali electrolysis or the cathodic dimerization of acrylonitrile.
• the use of commercially available heterogeneous catalysts is often forbidden because a thermal change in thermal coating processes or a covering of the active areas in cold adhesive processes cannot be ruled out.
• a catalytically active electrode which flows through a filter layer consisting of a suspension of finely dispersed catalyst material on a porous body is used according to EP-B 0 479 052 in a process for the separation of metal ions from process and waste water.
• the object of the invention is to provide a process for reducing organic compounds which, on the one hand, delivers high space-time yields, enables high selectivity for compounds which can be reduced several times, and which avoids the formation of hydrogen during the reduction and is applicable on an industrial scale.
• This object is achieved according to the invention by means of a method for the electrochemical reduction of an organic compound by bringing the organic compound into contact with a cathode, the cathode comprising a carrier made of a conductive material and an electrically conductive, cathodically polarized layer formed thereon by precoating .
• the catalytically active electrode is stabilized in the operating state by the pressure loss at the electrically conductive, cathodically polarized layer formed by precoating.
• the catalytically active electrode can be suspended again by reversing the flow and removed, for example, by filtration or suction.
• the reduction of organic compounds is thus carried out on a system which is suitable for forming and dismantling a catalytically active electrode in the process, only interventions being necessary which are already established in the operational practice of a chemical operation, such as switching pumps and actuators.
• Electrically conductive materials are used as carriers for the electrically conductive, cathodically polarized layer.
• materials such as stainless steel, steel, nickel, nickel alloys, tantalum, platinum-coated tantalum, titanium, platinum-coated titanium, graphite, electrode carbon and similar materials and their mixtures are to be mentioned.
• the supports are in the form of permeable porous material, i.e. the carrier has pores.
• these can be woven in the form of commercially available filter fabrics made of metal wires or carbon fibers.
• Filter fabric according to the type of linen weave, twill weave, twill braid weave, braid weave and satin weave.
• perforated metal foils, metal felts, graphite felts, edge filters, sieves or porous sintered bodies can also be used as large-area supports in the form of plates or candles.
• the pore size of the support is generally 5 to 300 microns, preferably 50 to 200 microns.
• the supports which can be used well in the context of the present method preferably have at least approximately 30%, more preferably at least approximately 20% and in particular approximately 50% free area, the free area being a maximum of approximately 70%.
• All electrically conductive materials can be used as the electrically conductive material for the electrically conductive, cathodically polarized layer, as long as it is possible to form a layer from these by floating onto the carrier defined above.
• the cathodically polarized layer preferably contains a metal, a conductive metal oxide or a carbon-like material, such as coal, in particular Activated carbon, carbon black or graphite, or a mixture of two or more thereof.
• All classic hydrogenation metals in particular the metals of subgroups I, II and VIII of the Periodic Table, in particular Co, Ni, Fe, Ru, Rh, Re, Pd, Pt, Os, Ir, Ag, Cu, Zn, are preferably used as metals , Pb and Cd.
• Ni, Co, Ag and Fe are preferably used as Raney-Ni, Raney-Co, Raney-Ag and Raney-Fe, which may be caused by foreign metals such as Mo, Cr, Au, Mn, Hg, Sn or other elements of the periodic table. in particular S, Se, Te, Ge, Ga, P, Pb, As, Bi and Sb can be used.
• the metals used according to the invention are preferably in finely divided and / or activated form.
• conductive metal oxides e.g. Magnetite.
• the cathodically polarized layer can also be formed by simply floating the carbon-like material defined above.
• the cathode can be built up in situ in that the abovementioned metals and conductive oxides are washed onto the support in each case on carbon-like materials, in particular activated carbon.
• the present invention thus also relates to a method of the type in question here, the cathodically polarized layer containing a metal or a conductive metal oxide or a mixture of two or more thereof, each applied to activated carbon.
• layers which contain Pd / C, Pt / C, Ag / C, Ru / C, Re / C, Rh / C, Ir / C, Os / C and Cu / C should be mentioned, these in turn by Foreign metals or other elements of the periodic table, preferably S, Se, Te, Ge, Ga, P, Pb, As, Bi and Sb can be doped.
• the above-mentioned metals can be in the form of nanoclusters, the production of which e.g. in DE-A-44 08 512, on surfaces such as e.g. Metals and carbonaceous materials that are washed onto the carrier.
• the cathodically polarized layer can contain an electrically conductive auxiliary material which improves the adhesion of the above-defined metals, metal oxides or nanoclusters to the support or increases the surface of the cathode, with electrically conductive oxides such as magnetites and carbon, in particular activated carbon, carbon black, carbon fiber and graphite are to be mentioned.
• a cathode is used, which is obtained by first washing the electrically conductive auxiliary material onto the support and then this auxiliary material in situ by reducing salts of metals of I., II. And / or VIII Subgroup is doped with these metals on the coated electrode.
• salts of the above Metals are preferably metal halides, phosphates, sulfates, chlorides, carbonates, nitrates and the metal salts of organic acids, preferably formates, acetates, propionates and benzoates, particularly preferably acetates.
• the cathode used according to the invention is built up in situ by the fact that the above-mentioned metals or metal oxides are applied directly or after application of the electrically conductive auxiliary material are washed onto the carrier.
• the average particle size of the particles forming the layer defined above and the thickness of the layer is always chosen so that an optimal ratio of filter pressure loss and hydraulic throughput is guaranteed and an optimal mass transfer is possible.
• the average particle size is about 1 to about 400 ⁇ m, preferably about 30 to about 150 ⁇ m
• the thickness of the layer is generally about 0.05 mm to about 20 mm, preferably about 0.1 to about 5 mm.
• the pore size of the support generally exceeds the average diameter of the particles forming the layer, so that two or more particles form bridges over the interspaces during the formation of the layer on the support, which has the advantage that the formation of the layer on the support results in no appreciable flow obstruction for the solution containing the organic compound to be reduced.
• the pore size of the support is about two to about four times the average particle size of the particles forming the layer.
• supports with pore sizes which are smaller than the average particle size of the particles forming the layer can also be used in the context of the present invention, but attention must then be paid very precisely to the flow obstruction emanating from the layer which forms.
• the cathode used according to the invention is formed in situ by floating the constituents forming the layer onto the electrically conductive support, the constituents forming the layer Particle-containing solution flows through the carrier until the entire solids content of this solution is suspended or held.
• the catalytically active layer After the reduction has ended or when the catalytically active layer has been used up, it can be separated from the support by simply switching the flow direction and disposed of or regenerated independently of the reduction. After the used layer has been completely removed from the system, it is then possible again to coat the support again with the particles forming the layer and, after these particles have been completely suspended, continue to reduce the organic compound.
• the current densities within the process according to the invention are generally about 100 to about 10,000 A / m 2 , preferably about 1,000 to about 4,000 A / m 2 .
• the throughput of the solution containing the organic compounds to be reduced is generally about 1 to about 4,000 m 3 / (m 2 xh), preferably about 50 to about 1,000 m 3 / (m 2 xh).
• a system pressure of generally approximately 1 ⁇ 10 4 Pa (absolute) to approximately 4 ⁇ 10 6 Pa, preferably approximately 4 ⁇ 10 4 Pa to approximately 1 ⁇ 10 6 Pa the pressure loss in the layer is approximately 1 at the flow rates used according to the invention x 10 4 Pa to about 2 x 10 5 Pa, preferably about 2.5 x 10 4 Pa to about 7.5 x 10 4 Pa.
• the process according to the invention is generally carried out at temperatures between approximately -10 ° C. to the boiling point of the solvent or solvent mixture, but temperatures between approximately 20 ° C. and approximately 50 ° C., in particular in the vicinity of room temperature, are preferred.
• the process according to the invention can be carried out in acid, i.e. at a pH below 7, preferably -2 to 5, more preferably 0 to 3, in neutral, i.e. at a pH of about 7, and in basic, i.e. medium is carried out at a pH which is above 7, preferably from 9 to 14 and in particular from 12 to 14.
• the reaction is particularly preferably carried out at normal pressure and at room temperature.
• the type of cell type used, the shape and the arrangement of the electrodes have no decisive influence, so that in principle all cell types customary in electrochemistry can be used.
• Perforated materials such as nets, expanded metal sheets, lamellae, profile webs, grids and smooth sheets can generally be used as electrode materials.
• this takes place in the form of flat surfaces, in the embodiment with candle-shaped electrodes in the form of a cylindrical arrangement.
• anode material or its coating depends on the solvent of the anolyte.
• graphite electrodes are preferably used in organic systems, while materials or coatings with a low oxygen overvoltage are preferably used in aqueous systems.
• acidic anolytes are titanium or tantalum carriers with electrically conductive intermediate layers on which electrically conductive mixed oxides of IV. To VI. Subgroup are applied, which are doped with metals or metal oxides of the platinum group to name.
• iron or nickel anodes are preferably used.
• protic solvents i.e. Solvents that contain or release protons and / or can form hydrogen bonds
• aprotic polar solvents e.g. THF
• lower alcohols e.g. Methanol, ethanol, 1-propanol, isopropanol, 1-butanol, sec-butanol or tert-butanol
• ether such as e.g. Diethyl ether, 1,2-dimethoxyethane, furan, tetrahydrofuran and dimethylformamide are used.
• Water is further preferred, optionally as a mixture with one or more of the above.
• Alcohols, ethers and DMF are used, a mixture of water with methanol, THF or DMF being particularly preferred.
• the corresponding acids or amines can also be used.
• reaction When using higher alcohols or higher carboxylic acids or higher amines, it should be noted that the reaction must then be carried out at relatively high temperatures in order to keep the viscosity of the solutions obtained within a range tolerable for carrying out the reaction.
• the reduction according to the invention is carried out in the presence of an auxiliary electrolyte.
• the addition of the same serves to adjust the conductivity of the electrolysis solution and / or to control the selectivity of the reaction.
• the content of the electrolyte is usually at a concentration of approximately 0.1 to approximately 10, preferably approximately 1 to approximately 5% by weight, based in each case on the reaction mixture.
• Protonic acids such as, for example, organic acids, where methanesulfonic acid, benzenesulfonic acid or toluenesulfonic acid can be mentioned, and mineral acids, such as, for example, sulfuric acid and phosphoric acid, are suitable as the auxiliary electrolyte.
• Neutral salts can also be used as auxiliary electrolytes.
• fluoride such as, for example, methanesulfonate, benzenesulfonate, toluenesulfonate
• sulfates such as, for example, sulfate, methylsulfate, ethylsulfate, phosphates, such as, for example, methylphosphate, ethylphosphate, dimethylphosphate, diphenylphosphate, such as methylafluorophosphate, hexafluorophosphate, such as hexafluorophosphate Phenylphosphonate methyl ester.
• Basic compounds such as e.g. Alkali or alkaline earth metal hydroxides, carbonates, bicarbonates and alcoholates can be used, methylate, ethylate, butylate and isopropylate being preferably used as alcoholate anions.
• the process according to the invention can be carried out not only using a homogeneous solution of the organic compound to be reduced in a suitable solvent, but also in a two-phase system consisting of a phase comprising at least one organic solvent as defined above and the organic compound to be reduced, and a second, water-containing phase.
• the electrochemical reduction according to the invention can be carried out either continuously or batchwise.
• the cathode is first produced in situ by forming a catalytically active layer on the support by precoating.
• the carrier is left in suspension of the finely divided metal and / or the conductive metal oxide and / or the nanocluster and / or the carbonaceous material, that is, the material that is to be washed up, until essentially all of the material contained in the suspension is on the support. Whether this is the case can be visually recognized, for example, by the fact that the suspension, which is cloudy at the start of the precoat, becomes clear.
• an intermediate layer it is also possible to flow through the carrier provided with an intermediate layer with a solution or a suspension of a metal salt of a metal with which the carrier layer is to be doped, and by applying a suitable voltage to the cell in it To reduce the solution or suspension of existing metal cations in situ at the cathode.
• the organic compound to be reduced is then fed into the system and reduced by introducing a precisely defined amount of current into the system.
• a precisely defined amount of current By precisely controlling the amount of electricity supplied, it is possible within the scope of the method according to the invention to isolate even partially reduced connections.
• the selectivities are at least 70%, in general over 80% and with particularly smooth reductions at greater than 95%.
• any used catalyst can be replaced by reversing the direction of flow in the electrolysis cell, as a result of which the washed-on layer loses contact with the support and the catalyst e.g. can be removed by suction or filtration of the suspension containing them.
• the layer can then be built up again as described above and new feed can then be added and reacted.
• the steps of conversion (reduction), renewal of the catalyst and renewed conversion (reduction) can also be carried out alternately, by first producing the cathode in situ as described above, then adding the organic compound to be reduced and converting it, after completion of the implementation, the flow direction within the electrolysis cell is changed and the used catalyst, for example is removed by filtering, then the cathode is again built up with fresh material forming the cathodically polarized layer and is then further reduced.
• the electrolysis unit consisting of at least one cathode with a common catholyte circuit, is operated stationary as a homogeneously continuous reactor. This means that after the catalyst has been washed once, a defined concentration level of starting materials and products is maintained.
• the reaction solution is continuously pumped in a circuit via the electrochemically active cathode and educt is continuously fed to the circuit, product being continuously removed from this circuit so that the reactor content remains constant over time.
• At least two electrolysis units are connected in series, the starting material being fed to the first unit and the product being removed from the last unit. This procedure ensures that the concentration in the first electrolysis unit (s) is significantly lower than that in the last unit (s). This means that, on average, higher space-time yields are achieved across all electrolysis units compared to a reaction procedure in which the electrolysis units are operated in parallel.
• This cascade connection of the electrolysis units is particularly advantageous when the required production capacity requires the installation of several electrolysis units.
• all organic compounds with reducible groups can be used as starting materials as organic compounds in the process according to the invention.
• both partially reduced compounds and completely reduced compounds can be obtained as products.
• the corresponding alkene can be obtained as well as the corresponding fully hydrogenated or reduced alkane.
• Organic compounds which have at least one of the following reducible groups or bonds are preferably reduced: CC double bonds, CC triple bonds, aromatic CC linkages, carbonyl groups, thiocarbonyl groups, carboxyl groups, ester groups, CN triple bonds, CN double bonds, aromatic CN linkages , Nitro groups, nitroso groups, C-halogen single bonds, further preferably reducing an organic compound selected from a group comprising: nitriles, dinitriles, nitro, dinitro compounds, saturated and unsaturated ketones, aminocarboxylic acids.
• the above definition includes all organic compounds which have at least one C UNEC double bond, such as, for example, unsaturated carboxylic acids, aromatic compounds which are substituted by one or more alkenyl groups, and compounds of the general formula (A) wherein R 1 , R 2 , R 3 and R 4 are each independently hydrogen, an alkyl group, an aryl group, an aralkyl group, an alkylaryl group, an alkoxyalkyl group, an alkoxy group or an acyl group.
• R 1 , R 2 , R 3 and R 4 are each independently hydrogen, an alkyl group, an aryl group, an aralkyl group, an alkylaryl group, an alkoxyalkyl group, an alkoxy group or an acyl group.
• the above definition includes all organic compounds which have at least one C ⁇ C triple bond, such as, for example, the compounds of the general formula (B), R 1 - ⁇ -R 2 (B) where R 1 and R 2 are as defined above.
• the above definition encompasses all organic compounds which have at least one heterocyclic ring, such as, for example, 5-, 6- or higher-membered, unsaturated heterocycles which contain 1 to 3 nitrogen atoms and / or an oxygen atom. or contain sulfur atom, for example compounds of the general formula (D) where Y, X 1 and R 1 are as defined above.
• the above definition includes all organic compounds which have at least one carbon-heteroatom double bond, such as aldehydes, ketones and the corresponding thio compounds and imines, which can be represented by the following general formula (E) where X, R 1 and R 2 are as defined above and also aliphatic or aromatic, saturated or unsaturated carboxylic acid derivatives, which then have the structure R 1 COOR 2 , where R 1 and R 2 are again as defined above.
• the above definition encompasses all organic compounds which have at least one C ⁇ N triple bond, such as dinitriles and mononitriles, the latter being represented by the following general formula (F) R 1 - C ⁇ N (F) where R 1 is as defined above.
• connection classes or connections can be implemented:
• a filter plate was covered with a 50 ⁇ m twill weave made of stainless steel material no. 1.4571 installed as cathode.
• the filtrate can be removed from a cavity under the filter fabric via a separate filtrate line.
• a titanium anode coated with Ta / Ir mixed oxide for oxygen development was used as the anode.
• a Nafion 324 cation exchange membrane (commercial product from Du Pont) served as the separation medium. The divided cell was installed in a two-circuit electrolysis apparatus with pump circuits.
• the catholyte was prepared by adding 5 g of vinclozolin [(RS) -3- (3,5-dichlorophenyl) -5-methyl-5-vinyl-oxazoline-2,4-dione] in a mixture consisting of 500 g of water, 375 g of methanol, 375 g of isobutanol and 65 g of acetic acid were dissolved. 1200 g of the catholyte batch were filled into the cathode circuit.
• the catholyte preparation is free of chloride before the reaction.
• the catholyte consisted of a mixture of 693 g of methanol, 330 g of H 2 O, 22 g of NaOH, 55 g of adiponitrile (0.509 mol) and 7.5 g of Raney nickel (BASF H 1 -50).
• the implementation was carried out as follows: First, the two cell compartments were filled and then the Raney nickel was washed to the above cathode within 10 minutes.
• the electrolysis was then carried out at a temperature between 30 and 40 ° C. with a current density of 1000 A / m 2 at normal pressure. The electrolysis was stopped after 8.5 F / mol ADN. After the NaOH had been separated off by electrolysis, the product was isolated by distillation. 56 g (95% based on the amount of ADN used) of hexamethylene diamine were obtained.
• This example was carried out in the same apparatus as Example 2. 1100 g of 1% sulfuric acid were used as the anolyte.
• the catholyte consisted of a mixture of 418 g of methanol, 318 g of dist. Water, 297 g of sodium methyl sulfate solution 7.4% in methanol, 55 g of cyclohexanone oxime (0.487 mol) and 8 g of copper powder.
• the implementation was carried out as follows: First, the cell compartments were filled and then the copper powder washes onto the above cathode within 10 minutes. Thereafter, the electrolysis was carried out at a temperature between 30 and 50 ° C with a current density of 1000 A / m 2 under normal pressure. A charge of 12 F / mol based on the oxime used was applied.
• the catholyte was adjusted to a pH of 13 with sodium hydroxide solution, the copper powder was filtered off, the filtrate was concentrated to 639 g and extracted five times with 100 g each of MTBE. After drying and removing the solvent, the crude product was distilled. 35.2 g of cyclohexylamine (73% based on the oxime used) could be isolated as the reaction product.
• Example 2 This example was carried out in the same apparatus as Example 2. 1100 g of 1% sulfuric acid were used as the anolyte.
• the catholyte consisted of a mixture of 418 g of methanol, 330 g of dist. Water, 297 g sodium methyl sulfate solution, 7.4% in methanol, 55 g 2-butyne-1,4-diol (0.64 mol) and 15 g Raney nickel (BASF H1-50).
• This example was carried out in the same apparatus as Example 2. 1100 g of 1% sulfuric acid were used as the anolyte.
• the catholyte consisted of a mixture of 704 g of methanol, 330 g of dist. Water, 11 g sulfuric acid, 55 g nitrobenzene (0.447 mol) and 8 g copper powder.
• the catholyte was adjusted to a pH of 13 with sodium hydroxide solution, the copper powder was filtered off, the filtrate was concentrated to 597 g and extracted five times with 100 g each of MTBE. After drying and removing the solvent, the crude product was distilled. 26.2 g of aniline could be isolated as the reaction product.
• This example was carried out in the same apparatus as example 2, in a modification an edge filter (pore size 100 ⁇ m) made of stainless steel was used as the cathode. 1100 g of 1% sulfuric acid were used as the anolyte.
• the catholyte consisted of a mixture of 806 g of methanol, 377 g of dist. Water, 52 g sodium hydroxide, 48 g 2-thienylacetonitrile (0.391 mol) and 30 g Raney nickel (BASF H1-50).
• the reaction was carried out at 21 ° C and a current density of 1000 A / m 2 .
• the starting material was added in 14 portions.
• a charge of 6.45 F / mol based on the substrate was applied.
• the nickel powder was filtered off, the catholyte was neutralized with sulfuric acid and the methanol was removed by distillation. After adjusting the pH to 13, extraction was carried out with MTBE. After drying and removing the solvent, the crude product was distilled. 37 g of thienylethylamine could be isolated as the reaction product.
• This example was carried out in the same apparatus as Example 2, in a modification an edge filter (pore size 100 ⁇ m) made of platinized titanium was used as the cathode. 1200 g of 1% sulfuric acid were used as the anolyte.
• the catholyte consisted of a mixture of 651 g of ethylene glycol dimethyl ether, 651 g, dist. Water, 28 g sodium hydroxide, 70 g 2-thienylacetonitrile (0.569 mol) and 50 g Raney nickel (BASF H1-50).
• the reaction was carried out at 23 ° C. and a current density of 1000 A / m 2 .
• a charge of 5.5 F / mol based on the substrate was applied.
• the nickel powder was filtered off, the filtrate was mixed with 4% sodium hydroxide and saturated with NaCl. After the phases had been separated, the mixture was distilled. 45 g of thienylethylamine could be isolated as the reaction product.
• This example was carried out in the same apparatus as Example 2, in a modification an edge filter (pore size 100 ⁇ m) made of platinized titanium was used as the cathode. 1200 g of 1% sulfuric acid were used as the anolyte.
• the catholyte consisted of a mixture of 882 g of methanol, 420 g of dist. Water, 28 g sodium hydroxide, 70 g veratryl cyanide (0.395 mol) and 50 g Raney nickel (BASF H1-50).
• the reaction was carried out at 21 ° C. and a current density of 1000 A / m 2 .
• a charge of 4 F / mol based on the substrate was applied.
• the nickel powder was filtered off, the methanol was removed from the filtrate by distillation and the remaining crude aqueous solution was extracted with 5 ⁇ 100 g of MTBE. After drying and removing the solvent, the crude product was distilled. 54.5 g of homoveratrylamine could be isolated as the reaction product.

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• 1996
  • 1996-05-23 DE DE19620861A patent/DE19620861A1/de not_active Withdrawn
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