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
  • C25B3/295—Coupling reactions hydrodimerisation

Definitions

• the present invention relates to the electrolytic hydrodimerisation of O B-ethylenic monomers, more particularly acrylonitrile.
• a diaphragm a porous body or ion exchange membrane
• diaphragms are not without disadvantages.
• their presence in the electrolysis medium increases the resistance of the cell and leads to an additional consumption of energy.
• the present invention provides a process for the hydrodimerisation of a,5-ethylenic compounds by electrolysis in a cell without a diaphragm, by which it is possible to obtain simultaneously excellent chemical and electrical efiiciencies, in relation to the hydrodimerisation product.
• This process consists in subjecting to electrolysis, in a single compartment cell, a homogeneous aqueous solution of an a,,B-ethylenic compound and an electrolyte consisting of a quaternary ammonium salt of an oxidised mineral acid, which cannot be oxidised or reduced under the electrolysis conditions into a product capable of harming the reaction, the concentration of the a,fi-ethylenic compound in the reaction medium being below 10.5% by weight, and preferably below 5% by weight.
• the electrolyte employed in the new process is a quaternary ammonium salt of the formula:
• A represents the anion of an oxidised mineral acid as hereinafter defined and R R R and R represent identical or different hydrocarbon radicals each comprising 1 to 20 carbon atoms in their chain.
• the anion A is chosen from thos which are not oxidised at the anode or reduced at the cathode under the reaction conditions, or which do not give harmful products when anodically oxidized.
• the non-oxidisable or reducible anions derived from oxidised mineral acids it is preferred to use the sulphate, borate, phosphate and carbonate anions. It is also possible to use anions oxidisable at the anode without the formation of corrosive products; thus, the bisulphite anion, oxidised at the anode into the sulphate ion, can be used, although there is not particular advantage in so doing.
• R R R and R can be linear or branched alkyl radicals, such as methyl, ethyl, propyl, butyl, isopropyl, pentyl, hexyl, heptyl, octyl, dodecyl, and 2-ethylhexyl; cycloalkyl or alkyl-cycloalkyl radicals, such as cyclohexyl; or aryl radicals such as phenyl.
• cations are tetrabutyl-ammonium, triethyl- (n-octyl) ammonium, triethyl (n-dodecyl)-ammonium, tetra-(n-pentyl)-ammonium, tetraethyl-arnmonium, tetra- (n-propyl)-ammonium, methyl-triethyl-ammonium, triethylbutyl-ammonium, triethylhexyl-ammonium, and triethyl- (2-ethylhexyl)-ammonium.
• Suitable quaternary ammonium salts which are particularly well suited for carrying out the process of the invention, are the sulphates, borates, phosphates and carbonates of tetra- (n-butyl -amrnonium, tetran-pentyl -ammoniurn, triethyl-(n-dodecyl) ammonium, triethyl-(n-octyD- ammonium, triethylhexyl-ammoniurn and triethyl-(Z- ethylhexyl)-ammonium.
• the concentration of the electrolyte in the electrolysis bath should be at least and preferably should be between 10 and by weight, related to the total mixture.
• inert solvents such as dimethylformamide, dimethylacetamide, dimethylsulphoxide, dioxane, diethylene glycol, ethanol, hexamethylphosphotriamide and acetonitrile.
• the pH of the electrolysis medium is between 5 and 10.
• the anion of the quaternary ammonium salt used as electrolyte is derived from a weak acid, and particularly when using acid salts of which the pK is between 5 and 11, the pH of the aqueous solution is generally higher than 10. It is appropriate in this case for the solution to have added thereto an acid in a quantity sufficient to bring the pH of the solution within the preferred limits.
• an acid of which the anion cannot be oxidised at the anode it is preferred to use an acid of which the anion cannot be oxidised at the anode.
• the use of acids corresponding to the anions of the quaternary ammonium salts being used is particularly suitable.
• a buffer system is then formed in the aqueous electrolysis solution, e.g. the system quaternary ammonium borate/boric acid, quaternary ammonium carbonate/bicarbonate, and quaternary ammonium monobasic phosphate/dibasic phosphate, which enables the pH to be maintained between the preferred values throughout the entire reaction.
• the buffering effect is at its maximum when the basic form and the acid form are in equal concentrations.
• One convenient method for obtaining the aqueous buffer systems consists in adding to an aqueous solution of a quaternary ammonium hydroxide of selected concentration an acid such as boric, phosphoric or carbonic acid, until the pH of the solution is close to the pK of the buffer pair.
• the temperature of the reaction medium can vary between 0 and the reflux temperature of the medium. Generally, a temperature between 20 and 45 C. is used.
• the electrodes can be made of any metal or alloy generally employed in connection with electrolysis and suitable in view of the chemical nature of the compound subjected to the electrolysis.
• the cathode should be formed of a material which does not permit water to be reduced at the voltage used for the reduction of the 04,3- ethylene compound.
• Mercury, graphite, lead, lead/mercury and lead/ antimony alloys, Darcet alloy, tin and zinc are among the materials which fulfil this condition.
• Mercury, lead and graphite are particularly suitable.
• the anode should be made of a metal or metal alloy which provides a slight oxygen over-voltage in the electrolysis of water, such as, for example, lead, which may or may not be covered with oxide, nickel, which may or may not be surface-oxidised, platinum, gold, and stainless steel, which is preferably passivated. It is preferred to use insoluble anodes which have an oxygen over-voltage smaller than that of gold.
• the voltage applied to the terminals of the electrolysis cell can vary within wide limits. It is generally unnecessary to make use of high voltages and voltages between 3 and 8 volts are generally quite suitable. To minimise the ohmic voltage drop and correlatively the energy loss due to the Joule effect in the electrolyte, it is possible to reduce the distance of the electrodes. This distance or spacing is not critical, but in order to ensure a good circulation of the liquid between the electrodes, it can with advantage be between 1 and 15 millimetres and preferably between 1 and 3 millimetres.
• the current density is not critical and can consequently vary within very wide limits. In general, the productivity of the installation is higher as the current density is higher. It is possible to work at current densities which are from 1 to 50 amperes/dmF, and preferably 1 to 10 amperes/ dm. Although the speed of circulation of the electrolysis bath can assume extremely different values, it is preferable to have high circulation speeds. Speeds which are between 5 cm./sec. and 2 m./sec., and preferably between 10 and cm./sec., are very suitable.
• the process according to the invention can be applied to any a,fi-ethylenic compound, such as nitriles (e. g. acrylonitrile and methacrylonitrile), aldehydes (e.g. acrolein and methacrolein), acrylates and methacrylates, and acrylamides and methacrylamides.
• nitriles e. g. acrylonitrile and methacrylonitrile
• aldehydes e.g. acrolein and methacrolein
• acrylates and methacrylates acrylamides and methacrylamides.
• the product of the electrolysis is a homogeneous aqueous solution.
• the products formed during the reaction can be isolated, e.g., by distillation and solvent extraction.
• One particularly convenient separation method consists in lowering the temperature of the reaction mass to a smallest possible value at which it remains liquid in order to cause a lowering of the solubility of the organic compounds in the saline aqueous phase.
• An organic phase then generally forms comprising the major part of the reaction products.
• the aqueous phase containing the major part of the untransformed monomer can be used again as electrolysis bath after addition of monomer until the desired concentration is obtained.
• the process which forms the subject of the present invention is very suitable for being carried out continuously.
• the apparatus employed is formed by an electrolysis cell connected by a glass pipe, on the one hand, to an expansion chamber and, on the other hand, to a circulating pump which is itself connected to the expansion chamber.
• the electrolysis cell is formed by two square metal plates, each with an area of 1 dm. and a thickness of 1 mm., separated on their periphery by a silicone resin joint with a thickness of 3.5 mm. Each metal plate is covered externally by a plate of plastic material. The tightness of the assembly is ensured by clamping with bolts.
• One of the metal plates consists of hard lead (lead/antimony alloy with of antimony).
• the other plate consists of pure lead.
• the two electrodes are connected to a direct current source.
• the hard lead plate serves as anode and the pure lead plate as cathode.
• Each plate contains an orifice, one of which serves for the entry of the electrolytic solution into the space between the electrodes and the other for the discharge of the said solution.
• the outlet orifice of the electrolysis bath is connected to the expansion chamber formed by a container comprising a double jacket, in which cold water is circulating.
• This container has arranged above it a cold water condenser, above which is a condenser with a mixture of acetone/ solid carbon dioxide.
• a graduated burette opens into the expansion chamber. The solution leaving the expansion chamber is returned by the pump into the cell.
• the hard lead anode Prior to the electrolysis, the hard lead anode is formed by filling the cell with 5 N-sulphuric acid and causing a current of amperes to flow for 15 minutes. The cell is then emptied and rinsed with distilled water.
• the quantity of electricity used during the reaction is 113,500 coulombs (i.e. 31.5 ampere-hours).
• the extract thus treated, is dried over anhydrous sodium sulphate, filtered, and distilled in vacuo. 1.4 g. of a fraction distilling between and C./ 0 .1 mm. Hg are collected in this way. The distillation residue is 0.3 .g.
• EXAMPLE 2 The experiment is carried out in the apparatus used in Example 1 and with an electrolytic solution obtained in the same manner, but in which the concentration by weight of acrylonitrile is 4.3%. This concentration is kept substantially constant throughout the operation.
• the current density is 7.8 amperes and the applied voltage is 9.5 volts.
• the operation is continued until 31.5 ampere-hours have passed through the cell.
• the rate of circulation is 600 litres/hour.
• the quantity of acrylonitrile used is 79.9 g.
• the reaction mass is treated as in Example 1.
• the balance of the reaction is as follows:
• Ratio by weight of adiponitrile to propionitrile 40.7 :1.
• EXAMPLE 3 An electrolytic solution is prepared by causing a stream of carbon dioxide gas to pass into 400 g. of a 15% by weight aqueous solution of triethyl-(n-octyl)-ammonium hydroxide until a pH of 9 is obtained. Using the apparatus described in Example 1, electrolysis is carried out under the following conditions:
• EXAMPLE 4 The experiment is carried out in the apparatus described in Example 1, but with an electrolyte solution obtained by passing carbon dioxide gas into 400 g. of a 15% by weight aqueous solution of tetra-(n-butyl)- ammonium hydroxide until a pH equal to 9 is obtained.
• the electrolysis is carried out under the following conditions:
• ADN PN HT adiponitrile
• PN propiouitrile
• HT hydrotrimer
• Example 4 the same electrolytic solution as in Example 4 (350 g.) of an aqueous solution of the tetra-(n-butyl)- ammonium carbonate/bicarbonate system at pH 9 was used, but of which the concentration of acrylonitrile was brought to 17.1% by addition of 72.3 g. of acrylonitrile. This concentration is maintained throughout the operation by addition of 2 cc. of acrylonitrile every 2910 coulombs. The current density is 5 .6 amperes at 5 .6 volts. The reaction is continued until 31.5 ampere-hours have passed through the cell. The total quantity of acrylonitrile used is 133.3 g.
• the chemical yields are respectively 69.7%, 0% and 12.1% and the electrical yields are 89%, 0% and 10%.
• EXAMPLE 9 As electrolyte, 417 g. of an aqueous solution of triethyl- (n-octyl)-arnmonium monobasic phosphate/dibasic phosphate at pH 7, obtained by adding phosphoric acid to 400 g. of a 15% solution of triethyl-(n-octyl)-ammonium hydroxide, are used.
• 16 cc. of acrylonitrile (a concentration of 3%) are introduced into this solution.
• the electrolysis is carried out as in Example 1, with a current density of 5.65 amps/dm. at 5.4 volts.
• the rate of flow of liquid circulating in the bath is 450 litres/hour.
• the concentration of acrylonitrile is kept in the region of its initial value, as in the preceding examples.
• the reaction is stopped when the quantity of electricity which has passed through the cell is 31.5 ampere-hours.
• the quantity of acrylonitrile employed is 73.8 g.
• EXAMPLES 10 TO 12 The electrolyte used is obtained by adding boric acid to a 15% by weight aqueous solution of tetra-(n-butyl)-ammonium hydroxide until a pH of 9 is obtained.
• ADN PN HT ADN PN HT ADN adiponitrile; PN propiom'trile; HT hydrotimer.
• EXAMPLE 13 An electrolyte solution is prepared by causing a current of carbon dioxide to pass into a 15 aqueous solution of triethyl-(n-dodecyl)-ammonium hydroxide until the pH is 9. Electrolysis is carried out in the apparatus of Example 1, under the following conditions:
• EXAMPLE 14 An electrolyte, a solution obtained by passing carbon dioxide into a 15% aqueous solution of tributyl-(n-dodecyl)-ammonium hydroxide until a pH equal to 9 is obtained, is used.
• the electrolysis conditions are those of Example 13 except as follows:
• the concentration of acrylonitrile is 2.3%.
• the current density is 4.35 amps/dmP.
• the voltage is 6.6 volts.
• the circulation rate is 450 litres/hour.
• the quantity of acrylonitrile employed is 50.3 g.
• the quantity of electricity is 21.8 ampere-hours.
• EXAMPLE 15 The electrolyte solution is obtained by adding boric acid to a 15% aqueous solution of tetra-(n-pentyl)-ammonium hydroxide until a pH equal to 9 is obtained.
• the electrolysis is carried out as in Example 14, but at a current density of 5.3 arnps/dm. (voltage of 7.8 volts).
• the quantity of electricity used is 31.5 amperehours and the quantity of acrylonitrile employed is 70.1 g., for a concentration kept between 2.9 and 2.4%.
• Example 418 g. of the solution prepared in Example 1 and to which has been added 16 cc. of acrylonitrile (a concentration of 3%) are used. This concentration is maintained during the reaction by addition of acryonitrile.
• the reaction conditions are those of Example 1. Altogether, 90.2 g. of acrylonitrile and 40 ampere-hours of electricity are employed.
• composition of the different phases is given in the following table:
• Process for the electrolytic hydrodimerisation of an alpha,beta-ethylenic compound which comprises subjecting to electrolysis in a single compartment cell a homogeneous aqueous solution of a pH 5 to 10 of said com- 12 pound and a quaternary ammonium salt of an oxygen containing inorganic acid having a pK in water of 5 to 11, the concentration of said quaternary ammonium salt being from 5 to 30% and the concentration of said alpha, beta-ethylenic compound :being 2.3 to 4.6% both by weight of solution.

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• 1967
  • 1967-06-01 FR FR108793A patent/FR1548304A/fr not_active Expired
• 1968
  • 1968-05-24 NL NL686807382A patent/NL139520B/xx unknown
  • 1968-05-30 BE BE715915D patent/BE715915A/xx unknown
  • 1968-05-31 AT AT524568A patent/AT280983B/de not_active IP Right Cessation
  • 1968-05-31 US US733306A patent/US3630861A/en not_active Expired - Lifetime
  • 1968-05-31 CH CH806368A patent/CH491063A/fr not_active IP Right Cessation
  • 1968-05-31 SU SU1260395A patent/SU461490A3/ru active
  • 1968-05-31 LU LU56179D patent/LU56179A1/xx unknown
  • 1968-05-31 GB GB26278/68A patent/GB1184754A/en not_active Expired
  • 1968-05-31 DE DE19681768584 patent/DE1768584A1/de active Pending
  • 1968-06-01 CS CS4065A patent/CS174762B2/cs unknown
  • 1968-06-01 ES ES354605A patent/ES354605A1/es not_active Expired

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