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
  • 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
  • C25B3/01—Products
  • C25B3/11—Halogen containing compounds

Definitions

• Monochloroacetic acid and its derivatives are important intermediates in industrial organic synthesis. They are used for the production of adhesives, pesticides or pharmaceutical products.
• the production of monochloroacetic acid by chlorinating acetic acid is always associated with the formation of di- and trichloroacetic acid.
• electrochemical dehalogenation is also available for removing di- and trichloroacetic acid from the product mixture (EP-B 0 241 685).
• the latter dehalogenation is carried out using graphite cathodes in the presence of small amounts of metal salts with a hydrogen overvoltage of at least 0.4 V (at a current density of 4000 A / m 2 ), preferably in water-containing, acidic electrolytes.
• This process has a high selectivity because the thermodynamically favored reduction of protons to hydrogen takes place at the cathode at low concentrations of the partially dehalogenated di- and trichloroacetic acid. In this way, undesired dehalogenation of the monochloroacetic acid is avoided, but the di- and trichloroacetic acid are also dehalogenated only with poor current efficiency.
• This method is not suitable for dehalogenation down to a very low concentration level of di- and trichloroacetic acid, since an increasing proportion of the electrical charge is used for the reduction of protons to hydrogen.
• An economical implementation of dehalogenation to monochloroacetic acid at a low concentration of di- and trichloroacetic acid has therefore only been insufficient to date (comparative example).
• the task was therefore to selectively dehalogenate di- and trichloroacetic acid with very extensive conversion to monochloroacetic acid, that is to say not completely.
• Nekrasov et al. investigated the dehalogenation of trichloroacetic acid and monochloroacetic acid in the presence of tetramethylammonium or tetraethylammonium salt in a non-protic electrolyte (Nekrasov et al., Elektrokhimiya 1988, 24, 560-563). The effects they observed in no way suggest that ammonium salts in an aqueous electrolyte could inhibit the above-mentioned undesired reduction of protons to hydrogen.
• di- and trichloroacetic acid can be dehalogenated continuously or discontinuously to form monochloroacetic acid with very extensive conversion in divided electrolysis cells if electrolysis is carried out in aqueous solutions in which, in addition to metal salts, a hydrogen overvoltage of at least 0.4 V (at a Current density of 4000 A / m 2 ) quaternary ammonium and / or phosphonium salts are still dissolved.
• Another object is an electrolysis solution for the partial dehalogenation of tri- and / or dichloroacetic acid, which contains at least one of these two acids, one or more metal salts with a hydrogen overvoltage of at least 0.4 V (at a current density of at least 4000 A / m 2 ) contains at least one compound selected from the group of compounds of the formula I to V.
• the compounds of the formulas I to V are used in concentrations of 1 to 5000 ppm, preferably 10 to 1000 ppm, but in particular 50 to 500 ppm.
• the metal salts with a hydrogen overvoltage of at least 0.4 V are generally the soluble salts of Cu, Zn, Cd, Hg, Sn, Pb, Ti, Bi, V, Ta and / or Ni, preferably the soluble salts of Cu, Zn, Cd, Sn, Hg and Pb.
• CI-, Br-, SO 4 2- , NO 3 - or CH 3 COO- are preferably used as anions, the anion being chosen so that a soluble metal salt is formed (for example PbN0 3 ).
• the salts can be added directly to the electrolysis solution or, e.g. by adding oxides or carbonates - or by adding the metals themselves, such as Zn, Cd, Sn, Pb, Ni - in the solution.
• the salt concentration in the catholyte is expediently set to about 0.1 to 5000 ppm, preferably to about 10 to 1000 ppm.
• the starting material for the process is di- and / or trichloroacetic acid or mixtures thereof with monochloroacetic acid which are inevitably formed in the acetic acid chlorination.
• the proportion by weight of di- and trichloroacetic acid in the total amount of chlorinated acetic acids is less than 10% by weight. This proportion by weight can easily be less than 5% by weight, or even less than 2% by weight, which was particularly surprising.
• the catholyte can also contain mineral acids (eg HCl, H 2 S0 4 etc.).
• the anolyte is preferably an aqueous mineral acid, in particular an aqueous hydrochloric acid or sulfuric acid.
• the same material as that for the cathode can generally be used as the anode material.
• other customary electrode materials which, however, must be inert under the electrolysis conditions, for example titanium, coated with titanium dioxide and doped with a noble metal oxide, such as e.g. Ruthenium dioxide.
• Cation exchange membranes made of perfluorinated polymers with carboxyl and / or sulfonic acid groups are generally used to divide the cells into the anode and cathode compartments. It is also generally possible to use anion exchange membranes which are stable in the electrolyte, diaphragms made of polymers or inorganic materials.
• the electrolysis temperature should generally be below 100 ° C, preferably between 10 and 90 ° C.
• the electrolysis can be carried out either continuously or batchwise.
• a continuous process is preferred, especially at a low concentration of di- and trichloroacetic acid.
• chloride is constantly consumed due to the anodic chlorine evolution. In general, the chloride consumption is then compensated for by continuously introducing gaseous HCl or aqueous hydrochloric acid.
• the electrolysis product is worked up in a known manner, e.g. by distillation.
• the metal salts and the quaternary ammonium and phosphonium compounds remain in the residue and can be returned to the process.
• the invention is illustrated by the following examples. Examples 1-9 are followed by a comparative example.
• the comparative example shows that under the electrolysis conditions of EP-B 0 241 685, when a dichloroacetic acid concentration of 31% (based on the total amount of dissolved acetic acids) is reached, the major part of the electrical charge is used for the reduction of protons to hydrogen .

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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)

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• 1990
  • 1990-05-18 DE DE4016063A patent/DE4016063A1/de not_active Withdrawn
• 1991
  • 1991-05-16 DE DE59103750T patent/DE59103750D1/de not_active Expired - Fee Related
  • 1991-05-16 JP JP3111938A patent/JPH0593290A/ja not_active Withdrawn
  • 1991-05-16 EP EP91107944A patent/EP0457320B1/de not_active Expired - Lifetime
  • 1991-05-16 FI FI912381A patent/FI912381A7/fi unknown
  • 1991-05-17 BR BR919102050A patent/BR9102050A/pt not_active Application Discontinuation
  • 1991-05-17 CA CA002042862A patent/CA2042862A1/en not_active Abandoned
• 1993
  • 1993-10-19 US US08/139,337 patent/US5362367A/en not_active Expired - Fee Related

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