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
  • 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
• • 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
  • C25B3/03—Acyclic or carbocyclic hydrocarbons
• • 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

Definitions

• Cyclohexadiene carboxylic acids are suitable for the production of cyclic polycarboxylic acids, e.g., by reaction with maleic acid, which are excellent plasticizers, e.g., for polyvinyl chloride.
• the present invention relates to a process for the production of cyclohexadiene dicarboxylic acids, more particularly to the use of certain cathodes in the electrochemical production of said carboxylic acids from the corresponding phthalic acids.
• 3,S-cyclohexadiene-1,2-dicarboxylic acid can be prepared by electrochemically hydrogenating o-phthalic acid with dilute sulfuric acid as the catholyte above 60 C.
• the reaction is carried out on specially prepared, very pure lead cathodes in 15% sulfuric acid.
• patent specifications 2,477,579 and 2,477,580 the disadvantages of the lead cathodes are described and the use of mercury cathodes in 5% sulfuric acid recommended.
• apparatus is described in US.
• 3,5-cyclohexadiene-1,2-dicarboxylic acid or 2,5-cycloheXadiene-1,4-dicarboxylic acid may be obtained by the electrochemical hydrogenation of ophthalic acid or terephthalic acid in dilute aqueous sulfuric acid at temperatures above C. and with a current density of 1 to 40 amps per sq.
• decimeter if desired using lead or mercury cathodes, without the difliculties usually encountered with lead and mercury cathodes, when the cathode used is amalgamated lead, cadmium, tin, thallium or bismuth, or alloys, which may also be amalgamated, of at least two of the metals lead, mercury, silver, cadmium, tin, thallium and bismuth or pure cadmium, tin or bismuth.
• amalgamation we mean the coating of metals or alloys with a mercury alloy by applying small amounts of mercury to the metal or alloy.
• the amalgamated cathodes which may be used are of lead coated with an alloy of lead and mercury, cadmium coated with an alloy of cadmium and mercury, tin coated with an alloy of tin and mercury, thallium coated with an alloy of thallium and mercury or bismuth coated with an alloy of bismuth and mercury.
• the binary, ternary or higher alloys which may be used are alloys of lead and mercury; lead and silver; lead and cadmium; lead and tin; lead and bismuth; lead and thallium; mercury and silver; mercury and cadmium; mercury and tin; mercury and bismuth; mercury and thallium; cadmium and tin; cadmium and bismuth; cadmium and thallium; tin and bismuth; tin and thallium; bismuth and thallium; lead, mercury and silver; lead, mercury and cadmium; lead, mercury and tin; lead, mercury and bismuth; lead, mercury and thallium; lead, silver and cadmium; lead, silver and tin; lead, silver and bismuth; lead, silver and thallium; lead, cadmium and tin; lead, silver and bismuth; lead, silver and thallium; lead, cadmium and tin; lead, silver and bis
• the relative proportions of the individual metals may vary within a wide range, the limits being determined by the mechanical processability of the resulting alloy. In the case of cadmium, tin and bismuth pure, i.e. 100%, metals may be used. When mercury is used as amalgam or in an alloy, the content of mercury should be chosen in such a way that the mercury alloy or the amalgamated metal remains solid at the reaction temperature. The limits with leadzmercury are, therefore, from 30:70 to 99.5:0.5 or 0.1 to 2 g.
• Lead or platinum metal is usually used for the anode.
• Electrolysis is carried out in conventional electrolytic cells, in which the anode and cathode are separated by a diaphragm, for example of porous clay.
• the anode and cathode are arranged in conventional manner, for example a double-Walled tube may be used which may be heated or cooled and in which the cylindrical cathode is arranged on the inner wall of the tubular cell or is the inner wall of the tube and surrounds the likewise cylindrical diaphragm.
• the anode is for example, a water-cooled lead pipe.
• throughlike cells with electrodes in the form of plates and with suitable cooling elements may be used equally Well.
• the process may be used for the partial hydrogenation of both o-phthalic acid, which may also be in the form of phthalic anhydride, and terephthalic acid.
• the particular phthalic acid may be dispersed in a concentration of 2 to 8%, preferably 3 to 6%, by weight, in dilute aqueous sulfuric acid which generally contains more than 2% but not more than 50%, preferably 3 to 20%, by weight of sulfuric acid.
• a sufiiciently large amount of the particular phthalic acid goes into solution for the partial hydrogenation to proceed smoothly. It is advisable to exploit the maximum solubility of the phthalic acid at the particular reaction temperature and with the given sulfuric acid content.
• the values can be easily determined by simple experiments, e.g., 4.95 g. of o-phthalic acid dissolves in 100 g. of 5% sulfuric acid at 85 C. In general it is not necessary to use temperatures above 100 C. It is preferably to carry out the process at temperatures between and 98 C. Dilute sulfuric acid is advantageously used as the anolyte as wellin approximately the same concentration as in the case of the catholyte. The concentration may, however, be slightly higher.
• Electrolysis may be carried out with a current density of 140, preferably 3-20, amps/sq. decimeter (cathode current).
• the catholyte is fed to the cathode chamber of the electrolytic cell by means of a metering pump, the mixture of phthalic acid and sulfuric acid being allowed to flow from the bottom to the top of the cell.
• the hydrogen formed provides additional convection.
• the reaction mixture is cooled, preferably to below 15 C.
• the cyclohexadiene dicarboxylic acid which has been formed then crystallizes out. It is separated in conventional manner and the mother liquor, after phthalic acid has been added to it, can be returned to the electrolytic cell.
• the cyclohexadiene dicarboxylic acids prepared in this way are obtained in extremely pure form. Since the cyclohexadiene dicarboxylic acids are very reactive on account of their double bonds, it is recommendable to work them up at relatively low temperatures, preferably below 20 C.
• the hydrogenation cell consists of a double-walled glass tube provided with a cylindrical amalgamated lead cathode, a cylindrical clay diaphragm and a water-cooled lead tube as anode.
• the catholyte is introduced at the bottom of the cell by means of a metering pump and withdrawn at the top.
• EXAMPLE 27 120 cc. of a suspension of very finely ground terep hthalic acid (10 g.) in 5% sulfuric acid is hydrogenated at a temperature of to C. in a cylindrical glass electrolytic vessel containing a trough-like clay diaphgram surrounded by a cylindrical cathode of an amalgamated lead/mercury allow (90% Pb+10% Hg). 15% sulfuric acid is used as the anolyte. The anode is of platinum and the current density is 5 amps per sq. decimeter. The reaction is stopped after one hour, the suspension is cooled to 15 C. and the precipitate is filtered and dried. NMR analysis shows a yield of 89% of the theory of 2,5-cyclohexadiene-1,4-dicarboxylic acid with reference to the reacted terephthalic acid.
• a process for the production of 3,5-cyclohexeadiene-1,2-dicarboxylic acid or 2,5-cyclohexadiene-1,4-dicarboxylic acid which comprises electrochemical hydrogenation of o-phthalic acid or terephthalic acid in aqueous sulfuric acid at temperatures of from 70 to C. and with a current density of 1 to 40 amps per sq.
• decimeter on a cathode consisting of cadmium, tin, bismuth, amalgamated lead, amalgamated cadmium, amalgamated tin, amalgamated thallium, amalgamated bismuth or an alloy of at least two of the metals lead, mercury, silver, cadmium, tin, thallium and bismuth or an amalgamated alloy of the said metals.

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• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
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• Metallurgy (AREA)
• Electrolytic Production Of Non-Metals, Compounds, Apparatuses Therefor (AREA)
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Citations (3)

• 1967
  • 1967-03-20 US US624129A patent/US3471381A/en not_active Expired - Lifetime
  • 1967-03-20 NL NL6704132A patent/NL6704132A/xx unknown
  • 1967-03-23 BE BE695978D patent/BE695978A/xx unknown
  • 1967-03-23 GB GB03721/67A patent/GB1176036A/en not_active Expired

Patent Citations (3)

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