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
  • C25B3/29—Coupling reactions

Definitions

• diesters of dicarboxylic acids can be prepared by electrochemical condensation (Kolbe synthesis) of monoesters of lower dicarboxylic acids. This is carried out in aqueous solution or preferably in solution in methanol. The monoester is partly neutralized. for example with sodium methylate. to increase conductivity. Platinum anodes are generally used in the electrolysis.
• Suitable starting materials include the monoesters of dicarboxylic acids of four to ten carbon atoms such as glutaric. adipic. pimelic. suberic axelaic and sebacic acids with primary or secondary linear or branched alcohols of four to twelve carbon atoms and preferably from six to ten carbon atoms.
• Specific examples are the monobutyl. monoisobutyl. mono-Z-butyl. monopentyl. monohexyl. monocyclohexyl. monooctyl. mono-2- methylhexyl-(S). mono-Z-ethylhexyl. monodecyl or monododecyl esters of the said acids.
• Monoesters of adipic acid and particularly the Z-ethylhexanol monoester are of great industrial interest.
• the monoesters of dicarboxylic acids are used according to this new process in from 20 to 60 percent and preferably in from 30 to 50 percent by weight solution in methanol.
• the acid solutions are partly neutralized to achieve adequate conductivity.
• Basic compounds such as sodium carbonate. sodium methylate. sodium hydroxide or amines are used for this purpose.
• methanol electrolyte which consists for example of a solution in methanol of the monoester which has been partly neutralized with sodium methylate.
• concentration of water may however be set up particularly advantageously by carrying out the neutralization with the calculated amount of aqueous caustic soda solution or aqueous sodium carbonate solution.
• neutralization with sodium or potassium hydroxide or with sodium carbonate.
• the neutralization and control of the water content in a single stage by adding caustic soda solution is particularly suitable for continuous operation.
• the degree of neutralization i.e. the molar percentage of ester which is neutralized. is from 1 to 30 and preferably 2 to 15 mole7c.
• the electrolyte may also contain other organic solvents such as ethers, ketones. acetic acid or formic acid. In this case the water content of from 0.01 to 5 percent by weight is based on the electrolyte.
• Electrochemical dimerization is carried out for example at a current density of from 5 to 50 amps/dm and preferably of from 10 to 30 amps/dm". Depending on the conditions the potential thus set up is from 5 to 30 volts but usually from 6 to volts.
• the reaction temperature is generally kept at from to 65C and preferably from to C.
• Smooth platinum anodes are particularly suitable. but other anode materials which contain platinum as an alloy component such as Pt-Rh, Pt-Ru. Pt-lr. Pt-Au or platinized metals such as Ti or Ta may also be used.
• the cathodes may consist of the materials conventionally used in the Kolbe synthesis such as alloy steel. nickel. titanium or platinum.
• Cells of various types are suitable as the electrolytic cells.
• the cells described in Belgian Patent Specification No. 723.694 and having vibrating pairs of electrodes which are permeable to liquid may be used and also those cells which vibrate and have an electrode which is permeable to liquid or cells which have two liquid-permeable electrodes and do not vibrate.
• Capillary-slit cells such as described in Chem. lng. Techn. 41 (1969 page 945. are also suitable. It is particularly advantageous to carry out the reaction in an electrolytic cell such as is described in German Printed Application DOS 2.039.590.
• the electrolyte in this case is circulated from a buffer vessel through an undivided electrolytic cell with bipolar electrode plates of similar construction to a filter press and through a cooler and gas separator.
• the reacted electrolyte is discharged through an overflow and fresh electrolyte is fed in at the rate of reaction which is determined by titration or by measurement of the pH.
• acetic acid or formic acid in the advantageous novel process: periodic shortcircuiting of the electrodes is also not necessary. Platinum erosion is however clearly less even in the presence of these additives and when periodically shortcircuiting the electrodes.
• the ratio of working periods to rest periods may conveniently be from one to thrity minutes to from two to sixty seconds. preferably from two to twenty minutes to from live to fifteen seconds.
• EXAMPLE I A solution of 40 parts of mono-Z-ethylhexyl adipate in 60 parts of methanol is adjusted to a degree of neutralization of with sodium hydroxide. Then 0.5 part of water is added to the solution. The solution obtained is pumped at a flow rateof 50 cm/second at 50 to 55C through a cell having bipolar electrodes arranged in the manner of a filter press.
• the anodes are of platinum and the anode and cathode surfaces each amount to 1.9 dm": the distance between electrodes is 0.5 mm.
• the electrolysis proceeds at a cell potential of from 1 l to 12 volts and a current density of amps/dm'-'. After twenty minutes the current is interrupted by a relay for fifteen seconds. Fresh electrolyte is fed in at such a rate that the degree of reaction is 80 percent. The reacted electrolyte is discharged continuously.
• the discharge is worked up by evaporating the solvent and washing the residue first with 2.5 percent caustic soda solution and then three times with water.
• the crude di-Z-ethylhexyl sebacate is purified from byproducts by steam distillation at 150C and mm Hg. The purity of the ester which remains is determined by gas chromatography.
• di-Z-ethylhexyl sebacate is obtained in a material yield of 80% and a current yield of 60%.
• the energy consumption is 2.6 kwh/kg of ester.
• Unreacted monoester can be precipitated from the caustic soda solution by acidification with sulfuric acid and-reused after it has been washed with water.
• a loss of platinum of 15 'y/amperehour (3.3 mg/kg of ester) is determined by weighing the anodes before and after the experiment. Without the addition of water the loss of platinum is 56 'y/amperehour 12.1 mg/kg of ester).
• EXAMPLE 2 A solution of 30 parts of mono-2-ethylhexyl adipate in 30 parts of methanol is adjusted with sodium methylate to a degree of neutralization of 10 percent and 1 part of water is added. Electrolysis is carried out in the cell described in Example 1 at a degree of conversion of 90 percent. The electrolytic current is interrupted for ten seconds every ten minutes.
• the discharge is processed as in Example 1.
• Di-2- ethylhexyl sebacate is obtained in a material yield of 78 percent and a current yield of57 percent.
• the loss of platinum is 18 y/amperehour (3.9 mg/kg of di-2- ethylhexyl sebacate).
• the platinum loss at the anodes is 86 y/amperehour.
• Electrolysis is carried out batchwise in a bipolar cell at to C. 14 to 15 volts and a current density of 25 amps/dm" to a degree of conversion of 97 percent. The current is interrupted for 15 seconds every 15 minutes. After the electrolyte has been reacted for two hours it is processed as described in Example 1. Di-Z-ethylhexyl suberate is obtained in a material yield of percent and a current yield of 49 percent. Loss of platinum after the experiment has proceeded for two hours is 38 'y/amperehour (8.4 mg/kg of di-Z-ethylhexyl suberate). Without adding water and with shortcircuiting of the electrodes the loss of platinum is 66 y/amperehour 19.9 mg/kg of di-Z-ethylhexyl suberate).
• EXAMPLE 4 A solution of 40 parts of mono-2-ethylhexyl glutarate in 60 parts of methanol is neutralized to the extent of 10 percent with the calculated amount of caustic soda solution. Electrolysis of the solution which contains 1 part of water is carried out continuously ina bipolar plate cell at 50 to 55C. a current density of 20 ampercs/dm and at 12 volts. The degree of conversion is 80%. Current is interrupted for 15 seconds every 15 minutes. After the experiment has been carried on for 60 hours di-2-ethylhexyl suberate is obtained in a material yield of 64 percent and a current yield of 51 percent. Loss of platinum is 27.2 y/amperehour (7.9 mg of platinum per kg of di-Z-ethylhexyl suberate).
• a process for the production of dicsters of dicarboxylic acids of six to 18 carbon atoms and alcohols of four to twelve carbon atoms wherein a monoester of a dicarboxylic acidof four to ten carbon atoms and an alcohol of four to twelve carbon atoms is electrochemically condensed at a current density of from 5 to 50 amps/dm and a temperature of from 20 to 65C in a 20 to 60% by weight solution in methanol which contains from 0.2 to 2 percent by weight of water in the presence of such an amount ofa basic compound that the degree of neutralization is from 1 to 30mole percent.

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• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Electrolytic Production Of Non-Metals, Compounds, Apparatuses Therefor (AREA)
• Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)

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Citations (4)

• 1972
  • 1972-10-04 DE DE19722248562 patent/DE2248562A1/de active Pending
• 1973
  • 1973-09-10 NL NL7312464A patent/NL7312464A/xx unknown
  • 1973-09-19 IT IT29130/73A patent/IT998637B/it active
  • 1973-09-25 BE BE135987A patent/BE805251A/xx unknown
  • 1973-10-02 FR FR7335135A patent/FR2202059B1/fr not_active Expired
  • 1973-10-02 CA CA182,490A patent/CA1029329A/en not_active Expired
  • 1973-10-03 JP JP48110606A patent/JPS4975518A/ja active Pending
  • 1973-10-03 GB GB4620173A patent/GB1438335A/en not_active Expired
  • 1973-10-04 US US403614A patent/US3879271A/en not_active Expired - Lifetime

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