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
• • 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

Definitions

• the present invention relates to a process for the selective dimerization of conjugated diolefins by electrochemical means.
• the conjugated diolefins will exclusively give dimers with a cyclohexene structure.
• 1,3-butadiene will lead only to vinyl-4-cyclohexene and isoprene to a mixture of isomers with a cyclohexene structure: limonenes (methyl-isopropenylcyclohexenes) and dimethylvinylcyclohexenes.
• French patent n ° 1.502.141 teaches the use of a catalyst composed of a dinitrosylfer halide, a reducing agent (organo-magnesian, organo-aluminum) and a third component (arsine, stibine, phosphine, ether, sulfide, nitrogen derivative).
• US Patents 3,655,793 and 3,767,593 describe as catalyst the dinitrosylfer halide / reducer couple (organo-aluminum, borohydride, aluminum hydride).
• French Patent No. 2,225,401 describes the use of the dinitrosylfer halide / metal - carbonyl catalytic couple.
• the reaction is carried out in the presence of an adequate solvent and optionally of a conductive salt and, if one operates on a concentrated solution of diolefin to be dimerized, the reaction mixture is separated into two phases, the upper phase not containing practically than the dimer sought.
• the present invention also relates to a process for the selective dimerization of conjugated diolefins into dimers having a cyclohexene structure, characterized in that one operates electrochemically by bringing together in an electrochemical cell, comprising an anode, a cathode and an electrode of reference: an appropriate solvent, the diolefin to be dimerized, and a compound chosen between dinitrosylfer chloride and the mixture of iron chloride and nitrogen monoxide NO, then carrying the cathode, relative to the reference electrode, at a potential corresponding to the last reduction wave of said compound and by keeping this potential constant throughout the duration of the reaction.
• the potential is kept constant by means of a potentiostat which automatically supplies the voltage and the current between anode and cathode.
• a conductive salt can be used, if desired. (electrolyte) which allows to work, initially, with a lower voltage between anode and cathode.
• the electrochemical cell therefore has 3 electrodes: a cathode, an anode and a reference electrode.
• the cathode is made of a material inert with respect to the reaction medium; a platinum cathode is preferably used and better still the cathode is a grid of intertwined platinum wires.
• the cathode can also be made of glassy carbon or iron.
• the anode is made of oxidizable metal; aluminum was preferably chosen in the case of the use of dinitrosylfer chloride, and preferably iron in the case of the use of the iron chloride + NO mixture.
• the anode is a hollow aluminum or iron cylinder and the cathode a cylindrical grid made of platinum wires external and concentric with the anode. We have noticed that it was useless to separate anode and cathode by compartmentalization.
• the reference electrode can be chosen from known electrodes such as Ag / AgCl, Ag / Ag + , Hg / Hg 2 C1 2 (calomel) electrodes. It will preferably be placed near the cathode.
• the electrochemical solvent must be inert both with respect to the reactants present and under the operating conditions adopted. It is preferable that it has a sufficiently high dielectric constant. Preference is given to propylene carbonate.
• a conductive salt electrophilicity-sensitive organic compound
• it must be soluble in the solvent used. It can be a lithium salt or a quaternary ammonium salt. Tetrabutylammonium perchlorate is ideal.
• the Applicant has found that equally high yields can be obtained, in the case where the reaction medium does not contain conductive salt, by adding (except in the case of the calomel electrode) or not conductive salt in the liquid of junction of the reference electrode.
• the general formula of the diolefin to be dimerized is: the radicals R, R 1 , R 2 , R 3 , R 4 and R 5 being all hydrogen or else partially hydrogen and partially alkyl radicals.
• R, R 1 , R 2 , R 3 , R 4 and R 5 being all hydrogen or else partially hydrogen and partially alkyl radicals.
• 1,3-butadiene, isoprene and piperylene are used. These products are pure or well included in a petrochemical fraction; for example butadiene-1,3 may be contained in a fraction called "C4 cut" from the steam cracking of naphtha. This C4 cut can be subjected as such to dimerization according to the method of the invention.
• C4 cut can be subjected as such to dimerization according to the method of the invention.
• butadiene will be dimerized, the other constituents remaining intact and being able to be separated at the end of the reaction, from vinylcyclohexene formed, for example by distill
• Dinitrosylfer chloride is prepared by any known means, in particular according to the reaction: or by reaction of NO with the Fe + FeCl 3 mixture in tetrahydrofuran.
• the product obtained can, if desired, be purified by a second sublimation.
• the iron chloride is either ferrous chloride FeCl 2 or ferric chloride FeCl 3 ; if necessary, these products are dried before use.
• NO nitrogen monoxide is preferably used in the gaseous state, obtained from liquefied gas commercially delivered in bottles. The Applicant has found that it is preferable to operate with reports between 2 and 12, the yields being improved in this case.
• the potential of the cathode, relative to the reference must be from -100 to -400 mV; with an Ag / Ag reference electrode it must be from -1500 to -1800 mV and with a calomel reference electrode it must be from -700 to -1000 mV, always with Fe (NO) 2 Cl.
• the potential of the cathode relative to said reference electrode will be between -600 and -1600 mV.
• a potentiostat is used which, in a manner known per se, delivers a working voltage and current, between anode and cathode, functions of the chosen reference potential. and functions of the characteristics of the medium (dielectric constant of the solvent, resistivity of the reaction mixture).
• the potentiostat generates, after the reference potential has been set, a current, between anode and cathode, which has been found to be a function of the concentration of iron compound.
• a current between anode and cathode, which has been found to be a function of the concentration of iron compound.
• dinitrosylfer chloride it is between 40 and 100 milliamps for concentrations of Fe (NO) 2 Cl between 5 and 40 millimoles per liter, under a voltage which has been found to be an inverse function of the concentration in conductive salt and close to 2 to 5 volts for tetrabutylammonium perchlorate concentrations close to 0.16 to 0.12 mol per liter of reaction mixture.
• These intensity and voltage values correspond to a spacing between anode and cathode of approximately 1 cm.
• the values of the intensity and of the working voltage decrease as a function of time, reaching in a few hours the respective values of a few hundred microamperes and a few millivolts, in the case of tests in the presence of salt. conductor, and a few milliamps and a few volts in the absence of conductive salt, the reference potential always being at its value imposed at the start.
• the process is preferably carried out at room temperature and under the pressure corresponding to the vapor pressure of the reaction medium at the temperature considered. This pressure does not generally exceed 1 bar.
• reaction medium must be constantly agitated so as to accelerate the diffusion phenomena.
• the agitation can be produced mechanically, in a manner known per se. It is also possible to renew the liquid layer in contact with the working electrodes using a rotating anode and cathode.
• the process is carried out in a glass electrochemical cell capable of working under a maximum pressure of 1 bar and which includes inlet and outlet pipes for the products, magnetic stirring, a hollow cylindrical anode with a diameter of approximately 2 cm and of height approximately 6cm, a cathode concentric with the anode of the same height and 4 cm in diameter, a reference electrode placed as close as possible to the cathode.
• the raw material is cooled to -10 ° C before introducing it into the electrochemical cell.
• the temperature of the reaction medium is then allowed to rise to ambient (about 20 ° C).
• potentiostat Using the potentiostat, a potential of -100 mV is applied to the cathode, relative to the reference electrode.
• the potentiostat automatically generates a voltage of 4 V and a current of 40 mA between anode and cathode. These values become, after 20 minutes: 2 V and 25 mA and after 3 hours a few tenths of a volt and 1 mA.
• the electrochemical cell (Ag / Ag + reference electrode) is put in place:
• a potential of -1500 mV is applied to the cathode relative to the reference electrode.
• the potentiostat automatically maintains this constant potential throughout the duration of the test.
• the working voltage is 2 V and the intensity of 40 mA.
• the reaction is stopped after 5 hours.
• the reaction medium forms two phases. Chromatographic analysis of the upper phase shows that it contains 17.3% by weight of butadiene and 82.7% by weight of vinylcyclohexene.
• the lower phase contains, in addition to propylene carbonate and the conductive salt: 5.5% by weight of butadiene and 5.7% by weight of vinylcyclohexene.
• the conversion rate of butadiene into vinylcyclohexene is 75%.
• the reactor is cooled to -10 ° C, withdraw the upper phase, distill the butadiene and rectify the vinylcyclohexene formed. 36 g of chromatographically pure vinyl-4-cyclohexene are thus collected.
• a potential of -750 mV is applied to the cathode relative to the reference electrode.
• the potentiostat automatically generates, at time zero, a voltage between anode and cathode, of 2 V and a current of 80 mA.
• the voltage has become negligible (the potential of the cathode relative to the reference electrode is always equal to -750 mV) and the current is approximately 2 mA.
• a potential of -100 mV is applied to the cathode relative to the reference electrode.
• the potentiostat generates between initial cathode and anode an initial current of approximately 100 mA under a voltage of approximately 5 V.
• the reaction medium occurs in two phases.
• the chromatographic analysis of these two phases shows that the isoprene is selectively transformed into its dimers with cyclohexenic structure (the product formed contains 88% of the two dimethylvinylcyclohexenes and 12% of the two limonenes) with a conversion rate of 50%.
• the upper phase contains 15% isoprene and 85% dimers which can be purified by distillation and rectification.
• Example 4 The conditions of Example 4 are repeated using 33.3 g (0.49 mole) of isoprene.
• the working voltage is initially 3 V and the current 70 mA.
• the conditions of example 4 are repeated, but by applying to the cathode a potential of +200 mV relative to the reference electrode Ag / AgCl.
• This value corresponds to the first reduction wave that can be determined voltammetrically on the propylene carbonate + tetrabutylammonium perchlorate + Fe (NO) 2 Cl (reference electrode Ag / AgCl) mixture.
• a potential of -100 mV relative to the reference electrode is imposed on the cathode, using the potentiostat.
• the potentiostat generates an initial voltage and current of 35 V and 90 mA.
• Example 7 The conditions of Example 7 are repeated without introducing tetrabutylammonium perchlorate into the reference electrode and using 144.7 mg (0.96 millimole) of Fe (NO) 2 Cl.
• the voltage and current between anode and cathode are 30 V and 68 mA respectively.
• the potentiostat After a potential of -100 mV relative to the reference electrode has been imposed on the cathode, the potentiostat generates an initial current between anode and cathode of 135 mA at an initial voltage of 34 V.
• a potential of -100 mV is applied to the cathode relative to the reference electrode, using the potentiostat which automatically generates an initial current between anode and cathode of 44 mA at a voltage of 20 V.
• the reaction is stopped after 3 h and the two liquid phases are separated.
• the upper phase contains 92% by weight of vinyl-4-cyclohexene and 8% by weight of butadiene.
• the lower phase contains, in addition to propylene carbonate, 12% of vinyl-4-cyclohexene and 3% butadiene.
• the conversion rate of 1,3-butadiene to vinyl-4-cyclohexene is 90%.
• the selectivity of this transformation is, as in all the other examples, 100%.
• the solution of FeCl 3 in propylene carbonate was prepared in advance. This solution is put in place in the electrochemical cell, the diene (or the petrochemical cut containing it) is added; optionally, the electrolyte; the medium is purged with nitrogen then the nitrogen monoxide is introduced and the potentiostat is adjusted. We operate at room temperature.
• the reaction is stopped after a time appearing in the table, time after which the corresponding degree of conversion into dimer is obtained (the selectivity is always 100%, which means that higher rates of conversion could be obtained in increasing the reaction time).

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• 1979
  • 1979-05-04 EP EP79400285A patent/EP0005406B1/de not_active Expired
  • 1979-05-04 DE DE7979400285T patent/DE2961120D1/de not_active Expired
  • 1979-05-09 US US06/037,549 patent/US4238301A/en not_active Expired - Lifetime

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