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  • 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
  • C25B3/01—Products
  • C25B3/09—Nitrogen containing compounds
• • 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
  • C25B11/02—Electrodes; Manufacture thereof not otherwise provided for characterised by shape or form
  • C25B11/03—Electrodes; Manufacture thereof not otherwise provided for characterised by shape or form perforated or foraminous
  • C25B11/031—Porous electrodes
• • 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
  • C25B11/042—Electrodes formed of a single material
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  • 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
  • C25B11/052—Electrodes comprising one or more electrocatalytic coatings on a substrate
• • 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
  • C25B11/055—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the substrate or carrier material
  • C25B11/057—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the substrate or carrier material consisting of a single element or compound
  • C25B11/061—Metal or alloy
  • C25B11/063—Valve metal, e.g. titanium
• • 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
  • C25B11/073—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material
  • C25B11/075—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material consisting of a single catalytic element or catalytic compound
  • C25B11/081—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material consisting of a single catalytic element or catalytic compound the element being a noble metal
• • 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
  • C25B3/01—Products
  • C25B3/07—Oxygen containing compounds
• • 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
  • C25B9/00—Cells or assemblies of cells; Constructional parts of cells; Assemblies of constructional parts, e.g. electrode-diaphragm assemblies; Process-related cell features
  • C25B9/17—Cells comprising dimensionally-stable non-movable electrodes; Assemblies of constructional parts thereof
  • C25B9/19—Cells comprising dimensionally-stable non-movable electrodes; Assemblies of constructional parts thereof with diaphragms

Definitions

• the present invention relates to a process for the electrochemical hydrogenation of organic compounds.
• the protons required for the hydrogenation/reduction of organic compounds on the cathode side are preferably generated from water on the anode side, i.e., the reaction preferably takes place in aqueous solution.
• Navarro et al. (Tetrahedron Letters 44 (2003), 4725 - 4727 ) describes the electrocatalytic hydrogenation of organic compounds in an undivided cell using water-methanol mixtures and ammonium acetate or ammonium chloride as the electrolyte.
• These electrolytes have the disadvantage that the preparation of the materials and the resulting purification steps for the electrolyte use are very complex.
• the use of chloride-containing electrolytes releases chlorine as a byproduct of the electrochemical process, which must be removed and treated separately.
• CN 116497375 A discloses a process for the electrochemical hydrogenation of benzaldehyde to benzyl alcohol in a ternary electrolyte/water/solvent mixture, which is carried out in an undivided cell.
• Various salts particularly imidazolium salts and tetraalkylammonium salts, can be used as electrolytes. These have the disadvantage that the preparation of the materials and the purification steps resulting from the use of the electrolyte are very complex.
• RU 2 198 158 C2 discloses the electrochemical hydrogenation of aldehydes and ketones in a split cell with a platinum anode and a copper cathode activated by a nickel skeleton catalyst.
• Aqueous solutions of non-oxidizing salts or aqueous solutions of alkali metal hydroxides are used as the electrolyte.
• Benzene is also used as a solvent.
• organic solvents such as benzene increases the necessary downstream processing effort and reduces economic viability.
• regular renewal of the nickel skeleton catalyst is necessary, and the products become contaminated with nickel-containing material. This leads to higher production costs and increased purification effort.
• Pintauro et al. J. Appl. Electrochem. 21 (1991), 799-804 ) discloses the electrocatalytic hydrogenation of benzene, aniline, and nitrobenzene in a split cell in the presence of a solvent mixture consisting of water and t-butanol, containing a hydrotrophic salt (a toluenesulfonate or tetraalkylammonium salt) as the electrolyte.
• a hydrotrophic salt a toluenesulfonate or tetraalkylammonium salt
• Raney nickel and fractal nickel electrodes have the disadvantage that the electrodes must be catalytically activated prior to use by pressing on nanoparticulate nickel (referred to as “activation” or “modification”). These electrodes are disadvantageous because they are sensitive to abrasion and are oxidation-labile.
• US 2021/0348283 A1 discloses a process for the hydrogenation of nitriles using a basic buffer solution containing a chelating agent and a tetraalkylamine.
• a split cell is used in the examples.
• Anodes disclosed include those made of (Raney) nickel, carbon steel, a Pt-Ir dimensionally stable anode material, and palladium.
• Cathode materials include metals, carbon, and combinations thereof.
• RU 2 218 325 C2 discloses a process for the electrocatalytic hydrogenation of, among other things, nitriles, in which the reaction takes place in a divided cell at a cathode activated with a nickel catalyst and a magnetite or platinum anode.
• Basic aqueous solutions containing non-oxidizing metal salts are optionally used as catholytes.
• a disadvantage is that regular renewal of the nickel catalyst is required.
• An activated electrode is required, and the products are contaminated by nickel-containing material. This leads to increased production and purification costs.
• the alkaline electrolyte has the disadvantage that, in the presence of ketones/enones with enolizable protons, e.g., isophorone, byproducts from base-catalyzed reactions, including aldol reactions, can be formed. This reduces the selectivity of the process. Furthermore, the reaction solution must be neutralized during workup, which leads to increased effort and the formation of salt-containing waste streams.
• ketones/enones with enolizable protons e.g., isophorone
• Raney nickel and similar catalytically active electrodes require a complex process, such as pressing or coating them onto suitable support materials. This increases the manufacturing effort and results in lower physical and chemical stability of the electrodes.
• the use of graphite granules as fixed/fluidized bed electrodes requires greater technical effort to stabilize the bed around the main conductor, e.g., platinum wire, and thus has limited economic viability.
• electrolysis requires the use of a reference electrode (Ag/AgCl) by applying a defined voltage (also known as “potentiostatic"). This increases the technical complexity of the process.
• Miller et al., J. Org. Chem., Vol. 43, No. 10, 1978, 2059-2061 discloses a process for the electrochemical hydrogenation of phenols, in which the hydrogenation takes place in a divided cell in sulfuric acid solution.
• the anode consists of platinum and the cathode of carbon electroplated with catalyst metal or platinized platinum.
• the cathodes used have the disadvantage that They are not stable over the long term, especially under large-scale industrial conditions. They therefore require re-electroplating. They also require a complex activation process before they can be used.
• the present process is a process for the electrochemical hydrogenation of an organic compound selected from the group consisting of ketones, enones, aromatics, and nitriles. If a ketone is used as the starting material, the corresponding hydroxyl-containing compound is formed by hydrogenation. If an enone is used as the starting material, the corresponding unsaturated hydroxyl-containing compound, the corresponding saturated carbonyl-containing compound (i.e. ketone or aldehyde), or the corresponding saturated hydroxyl-containing compound can be produced by hydrogenation.
• the process according to the invention is particularly suitable for the hydrogenation of enones to the corresponding saturated hydroxyl-containing compounds.
• the corresponding optionally partially unsaturated cyclic hydrocarbon compound is formed by hydrogenation.
• the process according to the invention is particularly suitable for the hydrogenation of aromatics to the corresponding saturated cyclic hydrocarbon compounds.
• the organic compounds used selected from the group consisting of ketones, enones, aromatics, and nitriles, cannot exclusively be organic compounds containing the functionalities mentioned.
• the term "organic compound selected from the group consisting of ketones, enones, aromatics, and nitriles” therefore includes, here and below, organic compounds which, in addition to the functionalities mentioned, also contain other, non-electrochemically hydrogenatable functionalities or Substituents.
• the organic compounds mentioned may also be organic compounds that contain additional oxygen and/or nitrogen and/or other heteroatoms in addition to the oxygen and nitrogen atoms present in the keto, enone, and nitrile functionalities.
• the process according to the invention is particularly suitable for the electrochemical hydrogenation of organic compounds which contain exclusively carbon and hydrogen and optionally also nitrogen and/or oxygen.
• the process according to the invention is particularly suitable for the hydrogenation of isophorone, isophoronenitrile, a mixture of 2,2,4- and 2,4,4-trimethylhexanedinitrile, 4,4'-methylenedianiline and naphthalene.
• the process according to the invention is also particularly suitable for the electrochemical hydrogenation of ketones. Even more preferably, the process according to the invention is a process for the electrochemical hydrogenation of ketones containing exclusively carbon, hydrogen, and oxygen.
• the process according to the invention is particularly suitable for the hydrogenation of isophorone to 3,3,5-trimethylcyclohexanol.
• the concentration of the organic compound is preferably 0.01 - 1 mol/l, preferably 0.048 - 0.1 mol/l, since the organic compound can then be dissolved particularly well.
• the process is carried out in a split cell.
• split cells the two half-cells are separated by a separator.
• Split cells have the advantage of preventing the formation of oxidized byproducts through anodic side reactions, thus improving the selectivity of the overall process.
• the separator material can be any material resistant to the sulfuric acid used. Separators made of microporous plastics and nonwovens made of polyethylene or fiberglass have proven particularly suitable. Separators made of microporous plastics can also be reinforced to achieve better strength and tear resistance. Cation exchange membranes can also be used with preference. These are also more preferably reinforced to achieve better strength and tear resistance. Most preferably, the separator comprises a perfluorosulfonic acid-polytetrafluoroethylene copolymer. This is also more preferably reinforced to achieve better strength and tear resistance. Suitable separators can be selected from the NAFION® membranes from The Chemours Company FC, LLC. Most preferably, the NAFION® 424 membrane or similar types can be used.
• a further solvent is present, it is preferably present in mass fractions of 0.01:1 to 10:1 and particularly preferably in mass fractions of 0.5:1 to 2:1, based on the mass of the water present. Further preference is given to using a mixture of water and methanol. Very particular preference is given to using a mixture of methanol and water in which the mass fraction of methanol used is 0.8:1 to 1.2:1, even more preferably 1:1, based on the mass of water present.
• the electrochemical hydrogenation process is carried out in the presence of sulfuric acid (H 2 SO 4 ) in the anolyte and catholyte.
• Sulfuric acid is preferably the only electrolyte present.
• one or more additional electrolytes can also be used. If additional electrolytes are added, they can preferably be selected from the group consisting of boric acid, sodium sulfate, and alkylammonium salts. If additional electrolytes are added, they are preferably used in proportions of 0.01-30 mol%, more preferably 0.01-10 mol%, and most preferably 0.01-5 mol%, based on the total amount of electrolytes.
• the cathode is particularly preferably a nickel foam electrode, as this leads to particularly high yields.
• the anode used in the process according to the invention is an electrode selected from solid and supported electrodes with an active material selected from platinum, graphite, boron-doped diamond, ruthenium oxide, platinum oxide and/or iridium oxide.
• the corresponding anodes are solid-body electrodes or supported electrodes, in which the respective active material is the aforementioned electrode material.
• the aforementioned anodes are solid-body or supported electrodes with an active material selected from platinum, graphite, boron-doped diamond, ruthenium oxide, platinum oxide, and/or iridium oxide. If a support is used, this is preferably a material selected from graphite, tantalum, titanium, iron, and silicon. Electrodes with a support selected from titanium, iron, and silicon with a coating selected from ruthenium oxide, platinum oxide, and/or iridium oxide are also commercially available as DSA electrodes (dimensionally stable anodes).
• the anode used is particularly preferably a platinum electrode.
• the platinum is preferably pressed, welded, or coated onto a carrier material.
• carrier materials that are stable to the electrolyte are used, preferably tantalum.
• the aforementioned cathodes and anodes have the advantage of particularly long service lives under the reaction conditions. This makes them particularly suitable for large-scale use.
• the hydrogenation is preferably carried out between 10-30 °C and 950-1050 mbar.
• the reaction is particularly preferably carried out under SATP conditions (25 °C, 1013 mbar).
• the process according to the invention enables hydrogenation in batch and continuous processes.
• the process according to the invention can be carried out both potentiostatically, i.e., at a constant voltage and varying current, and galvanostatically, i.e., at a varying voltage and constant current.
• the process according to the invention is particularly preferably carried out galvanostatically.
• the galvanostatic reaction procedure eliminates the need for an additional third electrode as a reference electrode. This offers an economic advantage and allows for a simpler design.
• the process according to the invention is particularly suitable for galvanostatic use at high current densities.
• the present invention thus provides a hydrogenation process that can be carried out at current densities of 15–250 mA/ cm2 and has the advantage of leading to particularly high yields.
• the comparatively high current intensity for organic electrochemical reactions enables the use of smaller electrode surfaces to achieve a sufficient charge. This enables a reduction in investment costs for electrochemical processes on an industrial scale.
• the process according to the invention can most preferably be carried out at current densities of 25–35 mA/ cm2 .
• Galvanostatic electrolysis was carried out at room temperature and ambient pressure with a constant current density of 35 mA/cm 2 for a period of 2.1 h (185 °C, 8 °F).
• GC analysis against an internal standard showed 91% conversion of isophorone to 3,3,5-trimethylcyclohexanol.

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• 2024
  • 2024-03-20 EP EP24164798.1A patent/EP4621103A1/fr active Pending
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