US3560354A - Electrolytic chemical process - Google Patents

Electrolytic chemical process Download PDF

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US3560354A
US3560354A US675534A US3560354DA US3560354A US 3560354 A US3560354 A US 3560354A US 675534 A US675534 A US 675534A US 3560354D A US3560354D A US 3560354DA US 3560354 A US3560354 A US 3560354A
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Donald C Young
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    • 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

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  • the invention comprises the use of a diaphragmless, alternating current electrolytic cell for the conducting of irreversible chemical reductions or oxidationsv
  • the electrolytic cell is used to generate an intermediate that is reactive with the reactant to form a chemical product.
  • the reaction is performed in the electrochemical cell under irreversible conditions.
  • the reaction is applied to the oxidation of olefins using an electrolyte containing a Group VIII noble metal and sufficient dissolved salts for providing the desired conductivity between the electrodes.
  • the reaction can be performed in aqueous acids, organic carboxylic acids, alcoholic electrolytes, etc., and the product of the oxidation depends upon the choice of this medium.
  • Use of aqueous electrolytes results in the formation of unsaturated carboxylates; and use of alcoholic reaction media results in the formation of acetals and unsaturated ethers. Examples of specific use are the oxidations of ethylene to acetaldehyde and/ or vinyl acetate; or dimethyl acetal.
  • the cell is operated at relatively mild conditions of temperatures from 30350 C. and pressures from atmospheric to about 1000 atmospheres, the higher pressures being employed for gaseous reactants.
  • the chemical reaction is irreversible while the companion electrochemical reaction is made irreversible by application of a potential which exceeds the over voltage of the particular electrochemical reaction. In this manner it is possible to operate the cell without a diaphragm and to achieve elficient utilization of the electrical energy input to the electrolytic cell.
  • the electrolyte is agitated during the reaction and a high concentration of the chemically reacting species is maintained to insure this reaction favorably competes with the undesired, competing electrolytic reaction.
  • the invention relates to the electrolytic processing of organic compounds and comprises the application of a diaphragmless electrolytic cell having an input electrical alternating current potential.
  • the electrolytic cell is applied to an irreversible oxidation or reduction of a chemical reactant to produce a useful product involving the electrolytic generation of an intermediate needed for the reaction.
  • the companion oxidation or reduction reaction which occurs in the cell is maintained irreversible by the application of a sufficient potential that exceeds the over voltage of the particular reaction.
  • Diaphragms in electrolytic cells also have a high maintenance requirement.
  • the diaphragms generaly are structurally weak and only very moderate pressure differentials can be maintained across the diaphragm. This often precludes the use of high pressures in the chamber containing the chemically reactive species despite the obvious advantage that the application of superatmospheric pressures would have on the reaction.
  • the method of my invention is applied to a reaction wherein a reaction intermediate can be electrolytically generated.
  • the intermediate can be an oxidized intermediate such as a peroxide, hydroperoxide or an olefin complexing metal cation.
  • Typical of such olefin complexing metals are the Group VIII noble metals, mercury, thallium, silver, etc. These metals exhibit the ability to form pi-complexes with olefins and these pi-complexes are decomposable in the presence of a suitable reactive 7 species to produce a substituted olefin with resultant reducting species, e.g., a soluble salt, can also be present.
  • the reduced form of the pi-complexing metal is electrolyticaly oxidized in the cell, and chemical reduction by reaction with the olefinic compound rather than electrochemical reduction of the pi-complexing metal by the reverse potential is insured by maintaining an environment in the electrolyte that is highly concentrated with the olefinic compound.
  • the companion electrochemical reduction which occurs with the oxidation of the olefinic compound is generally the reduction of protons to hydrogen. To insure that this electrolytical reduction is irreversible the potential applied to the electrodes exceeds the over potential of the hydrogen at the electrodes so that the hydrogen formed is evolved as hydrogen gas from the eletcrolytic cell.
  • the electrolyte is maintained under moderate to severe agitation to insure mobility of the reduced species of the pi-complexing metal and to insure thorough contacting of the olefinic compound with the high valency state of the pi-complexing metal.
  • the efficiency of the electrochemical cell is influenced considerably by its size and design. Significant factors in the design of the electrolytic cellwhich are interrelated are the spacings between the electrodes, the degree of agitation applied to the electrolyte, the conductivity of the cell and the mobility of the ions and pi-complexing metal in the solution. The latter characteristic is affected by the state of the pi-complexing metal, e.g., metallic form, or ionic as well as the solutions viscosity, tempera- 3 maximum. This optimum alternating current frequency can be readily determined by operation of the cell throughout a range of frequencies while observing the yield of product at each frequency setting.
  • the figure illustrates a typical efiiciency-frequency relationship in an electrochemical cell of my invention.
  • the efiiciency is plotted on the ordinate and is the quotient of the gram equivalent weight of product obtained during a time period divided by the Faradays of electrical input over that time period.
  • the relationship is shown as two curves, a-b and bc which intersect as shown.
  • Curve ab will intercept the ordinate at cycles per hour (direct current condition) while curve b-c approaches the abscissa at the maximum frequency.
  • At the ordinate intercept infinite time is available to permit difiusion and equilibrium of the cell.
  • Some product is obtained and the resultant efficiency can be referred to as the saturation efiiciency and reflects the rate of the following reaction:
  • Y is a chemical reactant
  • M is charged intermediate with x being the valency of the intermediate.
  • F Faradays of electrical energy
  • the value of the saturation efficiency and position of curve a-b depends on variables which influence the rate of reactions 1 and 2. Increasing the concentration of Y, e.g., by use of superatmospheric pressures in the event that Y is a gaseous reactant or by changing other reaction conditions such as temperature, agitation of the liquid, etc., will provide efliciencies following related curves a'b and a"b" shown in dashed lines.
  • the efliciency of the cell increases, as shown, with reversal of the applied EMF whenever a finite amount of species M is maintained in the liquid.
  • M is a metal, often a precious metal, and the amount used in a cell is limited.
  • a high concentration of M is initially formed at the electrode wherein the active intermediate M is generated.
  • the M ions are rapidly reacted at the interface with reactant Y so the cell has a high initial efliciency.
  • Some ions M however, will escape into the solution and be decomposed at the opposite electrode.
  • the available source of M is depleted by this electrolytic decomposition of M to M at the opposite electrode. As this depletion occurs the concentration of M about the generating electrode decreases relative to the concentration of M in the solution and the rate of reaction (1) relative to reaction (2) also decreases so that the cell becomes less eflicient.
  • Curve bc represents the limit to the direct relationship of efiiciency and frequency shown in curve a-b.
  • This curve is the diffusion limit curve and reflects internal cycling of the MSM reaction within the envel p about the electrodes. As the frequency of EMF reversal increases it approaches a value Where the generated M ions do not reach the interface between the electrode envelope and the solution and therefore can not react with Y during the generating half cycle. In the succeeding half cycle these M ions are decomposed to M with a resultant loss in efiiciency which increases with increasing frequency.
  • the curve bc illustrates this relationship.
  • a series of related curves b'-c' and b"-c" with progressively increasing mobility of the ions M and/or decreasing thickness of the envelope is shown by the dashed lines superimposed on curve bc.
  • efficiency of the cell can also be maximized by decreasing the thickness of the envelope surrounding the electrodes, e.g., by decreasing the solution viscosity, increasing its temperature, etc., or by increasing the mobility of the M species, e.g., by avoiding bulky ligands or other components that may complex with M ions and retard their movement.
  • Olefins that can be reacted in accordance with my invention in general comprise any olefin having the following structure:
  • R R and R are selected from the class consisting of hydrogen, alkyl, cycloalkyl, aryl, alkaryl, aralkyl, alkanyl alkyl, alkanyl aryl, halo, halo alkyl, halo aryl, carboxyl, carboxyl alkyl, carboxyl aryl, acyloxy, nitroaryl and alkylene wherein two of said R R and R groups comprises a common alkylene group.
  • olefins examples include: the aliphatic hydrocarbon olefins such as ethylene, propylene, butene-l, butene-2, pentene-2, Z-methylbutene-l, hexene-l, octene-3,
  • olefins include: vinylcyclohexane, allylcyclohexane, styrene, p-methylstyrene, 0c methylstyrene, fl-methylstyrene, p-vinylcumene, 1 vinylnaphthalene, 1,2-diphenylethylene, allylbenzene, 6-phenylhexene l, 1,3-diphenylbutene-l, 3-benzylheptene-2, o-vinyl p-xylene, a-chlorostyrene, p-chlorostyrene, m-nitrostyrene, divinylbenzene, l-allyl,4-vinylbenzene, 1,5-heptadiene, 2,5-decadiene, vinyl chloride, vinylidene dichloride, vinyl fluoride, trichloroethylene, trifluoroethylene, di(chloromethyl)ethylene, propen
  • cycloalkenes are also reactive.
  • alkylene cycloalkanes including: cyclobutene, cyclopentene, cyclohexene, methylcyclohexene, amylcyclopentene, cycloheptene, cyclooctene, cyclodecene, methylenecyclohexane, ethylidene cyclohexane, propylidene cyclohexane, etc.
  • olefin complexing metals examples include the Group VIII noble metals comprising the platinum subgroup of platinum, osmium and iridium as well as the palladium subgroup of palladium, ruthenium and rhodium.
  • Other complexing compounds include rhenium, mercury, thallium, etc.
  • suitable salts include the halides, nitrates, sulfates or carboxylates of lower molecular weight (C C carboxylic acids, etc.
  • Suitable chelating agents include acetylacetonate, citric acid, alkylene diamines, alkylene diamine tetracarboxylic acids and salts thereof, complexes of cyclopentadienyl, cyclobutadienyl and the lower alkyl and phenyl derivatives thereof such as tetraphenyl cyclobutadienyl, etc.
  • the metals can also be added to the reaction medium as the oxide.
  • Suitable salts or oxides include platinum chloride, palladium bromide, osmium fluoride, iridium bromide, ruthenium oxide, rhenium oxide, mercuric sulfate, palladium acetate, platinum propionate, iridium benzoate, osmium caproate, ammonium perrhenate, etc.
  • the complexing metal is employed as an electron transferring reactant, relatively minor quantities of the metal can be employed.
  • the electrolytic cell therefore is operative with electrolytes containing as little as 0.001 weight percent of the complexing metal.
  • Higher quantities of the complexing metal can of course be employed up to and exceeding the solubility of the particular salt of the complexing metal in the electrolyte. Generally, concentrations up to about 25 percent can be employed; however, I prefer to use concentrations of the complexing metal expressed as the metal from about 0.5 to about weight percent.
  • the electrolyte can also contain other dissolved salts to increase its electrical conductivity.
  • suitable dissolved salts include the alkali metal, alkaline earth metal, and multivalent transition metal soluble salts including the halides, sulfates, nitrates, C -C carboxylates etc.
  • such salts include potassium chloride, sodium acetate, lithium nitrate, calcium chloride, barium nitrate, cupric chloride, ferric chloride, vanadyl sulfate, chromium nitrate, etc.
  • the amount of the additional salt employed for conductivity through the electrolyte can vary from about 1 to about 50 weight percent, preferably from about 1 to about weight percent.
  • the reactants that can be employed besides or instead of the aforementioned olefins include carboxylic acids and soluble salts thereof, alcohols, alkylamines, water, etc.
  • the particular reactant depends upon the desired conversion, e.g., olefins can be oxidized in the presence of aqueous mineral acids of pH values from 0 to 7 to produce carbonyl products; in the presence of organic carboxylic acids to produce unsaturated carboxylates; and in the presence of anhydrous alkanols to produce alkoxy derivatives.
  • aqueous mineral acids including aqueous sulfuric, nitric hydrohalic acids such as hydrochloric, hydrobromic, hydrofluoric and hydriodic acid to produce carbonyls such as acetaldehyde, acetone, methylethyl ketone, etc. from respectively, ethylene, proplene, butene- 1, etc.
  • carboxylic acids as the reaction medium such as acetic, propionic, isobutyric, butyric, valeric, pivalic, caproic, caprylic, decanoic, benzoic, phthalic, naphthoic, toluic, etc. results in the production of an unsaturated ester of the carboxylic acid.
  • the products are the vinylcarboxylates when the olefin is ethylene, e.g., vinyl acetate from ethylene and acetic acid; allyl and propenyl products are obtained by the oxidation of propylene; etc.
  • the olefins can be oxidized to alkoxy derivatives, e.g., acetals are obtained from the reaction of olefins and alcohols such as dimethyl acetal, diethyl acetal, dibutyl acetal, from the reaction of ethylene and alcohols such as methanol, ethanol and n-butanol.
  • suitable alcohols include the alkanols such as methyl, ethyl, propyl, isopropyl, butyl, amyl alcohols, heptanol, octanol, decanol, etc.
  • the carbonylation of amines to prepare substituted ureas can also be practiced in the electrolytic cell.
  • a primary or secondary amine can be carbonylated by contacting the amine with carbon monoxide in the presence of the mercuric ions to produce a substituted urea with the resultant production of mercury and protons.
  • the mercury is regenerated in the electrolyic cell and the protons are reduced to hydrogen and evolved from the cell.
  • This reaction can be employed on any primary or secondary alkyl, alkaryl, aryl amine such as methyl, ethyl, isopropyl, butyl, isoamyl, hexyl, isoheptyl, octyl, nonyl, isodecyl amine, aniline, p-methyl aniline, o-ethyl aniline, m-butyl aniline, p-hexyl aniline, 2,5-xylidine, dimethylamine, dipropylamine, N.N-rnethylethylamine, N,N-ethylbutylamine, dihexylamine, N-methyl aniline, N-butyl aniline, N-hexyl aniline, N-ethyl 2,5-xylidine, dipenylamine, di-p-tolylamine, di-otolylamine, pyrroline, piperidine, pyrizole, pyrrolidine, etc
  • the reaction can also be applied to the oxidative carbonylation of olefins, a reaction which is initiated by complexing of the olefin with any of the aforementioned Group VIII noble metals, particularly with the palladium salts, oxide or chelates.
  • This reaction is practiced by the simultaneous introduction of carbon monoxide and the olefin into the electrolytic cell which can contain a carboxylic acid or alcoholic electrolyte.
  • the carbonylation of the olefin results in the production of a mixture of alpha, beta-ethylenically unsaturated carboxylic acids having one more carbon atom than the olefin and betaacyloxy substituted acids thereof wherein the carboxylic acid solvent adds across the ethylenically unsaturated bond.
  • the resultant product is the ester of the aforementioned alpha, beta-ethylenically unsaturated bond.
  • suitable conversions with olefins include the production of acrylic and beta-acetoxy propionic acid by the reaction of ethylene with an acetic acid reaction medium containing the Group VIII noble metal salt.
  • Other examples include the production of methacrylic and crotonic acids by the reaction of propylene as well as the production of the beta acyloxy derivatives thereof.
  • the reaction is performed in an alcohol such as ethanol, the resultant acids are esterified to produce, e.g., ethyl acrylate, beta-ethoxy ethyl propionate, isopropyl methacrylate, etc.
  • the reactions are performed at temperatures from about 30300 0, preferably from about -250 C.
  • the pressure in the electrolytic cell can be from atmospheric to superatmospheric, up to about 1500 atmospheres; preferably from about 10 to about 150 atmospheres. The higher pressures are preferred when a gaseous reactant is employed such as ethylene, propylene, carbon monoxide, etc.
  • the absence of a diaphragm simplifies the cell design and permits use of the cell at the aforementioned high pressures.
  • the voltage applied to the electrodes of the electrolytic cell can be varied over a wide range; however, care should be taken not to exceed the over voltage of undesired electrolytic reactions. In general, the oxidations that produce the desired chemical products require the accompanying reduction of hydrogen in the cell.
  • the applied voltage under such circumstances should exceed the over voltage for the evolution of hydrogen from the cell.
  • voltages from about 1 to about volts, preferably from about 2 to about 10 volts, can be employed.
  • the electrodes are positioned in the electrolytic cell with a sufficient spacing to permit the necessary conductivity in the cell and to provide a reaction zone between the electrodes for the reacting species.
  • the particular frequency that achieves maximum cell efiiciency varies considerably depending on the cell design and ion mobility in the manner previously described.
  • the cells usually will be most efficient when operated over a frequency of from 0.5 to 200,000 cycles per hour.
  • EXAMPLE The electrolytic oxidation of ethylene to acetaldehyde was performed in a diaphragmless cell using a low frequency alternating current.
  • the electrolytic cell comprised a glass flask containing an electrolyte and two parallel carbon plates approximately 7 x inches that were s aced one inch apart. Provision was made to stir the electrolyte in the electrolytic cell which comprised a. 2 percent solution of sulfuric acid containing 1 weight percent palladium chloride. Provision was made for the introduction of ethylene between the carbon plates and the exit connection from the flask was passed through a reflux condenser and two product traps including an acetone-dry ice trap for the condensation of the acetaldehyde product.
  • the cell washeated to raise the contents to reflux temperature and ethylene was introduced into the cell while stirring the electrolyte.
  • An alternating current of amps. was passed through the cell at varied frequencies of the applied voltage from /2 cycle per hour to 60 cycles per second while the stirring rate, temperature and other variables 'were maintained constant.
  • reaction efficiencies expressed as mols of product per equivalent mols of electrical input were obtained:
  • substantially the same results can be achieved by the use of other metals such as aforedescribed in the electrolyte or the use of any of the other aforementioned olefins or reactants.
  • substantially the same operation of the cell can be applied to the oxidative carbonylation of olefins by the simultaneous introduction of carbon monoxide into the electrolytic cell.
  • Higher molecular weight olefins than ethylene can be reacted by charging them to the electrolytic cell, e.g., by substituting propylene for the ethylene introduction or by adding to the electrolyte a higher boiling olefin such as octene, decene, etc.
  • Substitution of the electrolyte with an electrolyte comprising an amine containing mercuric oxide can be used in combination with the introduction of carbon monoxide for the production of substituted ureas.
  • the method for conducting an oxidation reaction in an electrolytic cell comprising an electrolytic chamber, an electrolyte containing a soluble oxidized reaction intermediate selected from the group consisting of a per- 8 oxide, a hydroperoxide and ions of platinum, osium, iridium, palladium, ruthenium, rhodium, rhenium, mercury and thallium maintained therein, and at least two electrodes within a common chamber of said electrolytic cell which comprises contacting said electrolyte with a chemical reactant capable of reducing said oxidized reaction intermediate in the electrolytic cell at a temperature from about 30 to 300 C.
  • said oxidized reaction intermediate comprises ions of a Group VIII noble metal
  • said reactant comprises an olefin
  • said electrolyte comprises a substituent tobe incorporated on said olefinic reactant.
  • said olefin is ethylene
  • said Group VIII noble metal is palladium
  • said electrolyte comprises an aqueous mineral acid selected from the group consisting of sulfuric, nitric, hydrochloric, hydrobromic, hydrofluoric and hydriodic acid.
  • olefin introducing said olefin into said chamber and into contact with an aqueous electrolyte containing ions of platinum, osmium, iridium, palladium, ruthenium, rhodium, rhenium, mercury or thallium;
  • said electrolyte also contains from 1 to weight percent of a soluble salt of an alkali metal or an alkaline earth metal.
  • said electrolyte comprises an aqueous mineral acid selected from the group consisting of sulfuric, nitric, hydrochloric, hydrobromic, hydrofluoric and hydriodic acid.

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Abstract

THE INVENTION COMPRISES THE USE OF A DIAPHRAGMLESS, ALTERNATING CURRENT ELECTRILYTIC CELL FOR THE CONDUCTING OF IRREVERSIBLE CHEMICAL REDUCTIONS OR OXIDATIONS. THE ELECTROLYTIC CELL IS USED TO GENERATE AN INTERMEDIATE THAT IS REACTIVE WITH THE REACTANT TO FORM A CHEMICAL PRODUCT. THE REACTION IS PREFORMED IN THE ELECTROCHEMICAL CELL UNDER IRREVERSIBLE CONDITIONS. IN A SPECIFIC EMBODIMENT THE REACTION IS APPLIED TO THE OXIDATION OF OLEFINS USING AN ELECTROLYTE CONTAINING A GROUP VIII NOBLE METAL AND SUFFICIENT DISSOLVED SALTS FOR PROVIDING THE DESIRED CONDUCTIVITY BETWEEN THE ELECTRODES. THE REACTION CAN BE PREFORMED IN AQUEOUS ACIDS, ORGANIC CARBOXYLIC ACIDS, ALCOHOLIC ELECTROLYTES, ETC., AND THE PRODUCT OF THE OXIDATION DEPENDS UPON THE CHOICE OF THIS MEDIUM. USE OF AQUEOUS ELECTROLYTES RESULTS IN THE FORMATION OF UNSATURATED CARBOXYLATES; AND USE OF ALCOHOLIC REACTION MEDIA RESULT IN THE FORMATION OF ACETALS AND UNSATURATED ETHER. EXAMPLES OF SPECIFIC USE ARE THE OXIDATIONS OF ETHYLENE OT ACETALDEHYDE AND/OR VINYL ACETATE; OR DIMETHYL ACETAL.

Description

D. C. YOUNG Filed Oct. 16, 1967 ELECTROLYTIC CHEMICAL PROCESS Feb. 2,- 1971 u m b we v u. w C o r r W l W 1 a I r M N \MQMYMRQN INVENTOR. DOA 4L0 6'. YOU BY V g? FREQVE/VCY-(AOMI/IHM/C 5:445)
fiauaa United States Patent 3,560,354 ELECTROLYTIC CHEMICAL PROCESS Donald C. Young, Fullerton, Calif., assignor to Union Oil Company of California, Los Angeles, Calif., a corporation of California Filed Oct. 16, 1967, Ser. No. 675,534 Int. Cl. C07b 3/00 US. Cl. 204-80 10 Claims ABSTRACT OF THE DISCLOSURE The invention comprises the use of a diaphragmless, alternating current electrolytic cell for the conducting of irreversible chemical reductions or oxidationsv The electrolytic cell is used to generate an intermediate that is reactive with the reactant to form a chemical product. The reaction is performed in the electrochemical cell under irreversible conditions. In a specific embodiment the reaction is applied to the oxidation of olefins using an electrolyte containing a Group VIII noble metal and sufficient dissolved salts for providing the desired conductivity between the electrodes. The reaction can be performed in aqueous acids, organic carboxylic acids, alcoholic electrolytes, etc., and the product of the oxidation depends upon the choice of this medium. Use of aqueous electrolytes results in the formation of unsaturated carboxylates; and use of alcoholic reaction media results in the formation of acetals and unsaturated ethers. Examples of specific use are the oxidations of ethylene to acetaldehyde and/ or vinyl acetate; or dimethyl acetal.
The cell is operated at relatively mild conditions of temperatures from 30350 C. and pressures from atmospheric to about 1000 atmospheres, the higher pressures being employed for gaseous reactants. The chemical reaction is irreversible while the companion electrochemical reaction is made irreversible by application of a potential which exceeds the over voltage of the particular electrochemical reaction. In this manner it is possible to operate the cell without a diaphragm and to achieve elficient utilization of the electrical energy input to the electrolytic cell. The electrolyte is agitated during the reaction and a high concentration of the chemically reacting species is maintained to insure this reaction favorably competes with the undesired, competing electrolytic reaction.
DESCRIPTION OF THE INVENTION The invention relates to the electrolytic processing of organic compounds and comprises the application of a diaphragmless electrolytic cell having an input electrical alternating curent potential. The electrolytic cell is applied to an irreversible oxidation or reduction of a chemical reactant to produce a useful product involving the electrolytic generation of an intermediate needed for the reaction. The companion oxidation or reduction reaction which occurs in the cell is maintained irreversible by the application of a sufficient potential that exceeds the over voltage of the particular reaction.
Chemical processing in eletcrolytic cells separated into two chambers with a diaphragm has been applied to a number of chemical reactions. The cathode and anode are placed in the separate chambers which are filled with their respective electrolyte solutions and electrical conductivity is maintained between the chambers by use of a salt bridge or through a diaphragm which is permeable to an ionic species in the electrolyte, typically permeable to protons. The diaphragms are used to insure that the desired reaction occurs by preventing diffusion of other ions between the electrodes. One of the disadvantages of the separated electrode cell is the relatively high potential drop across the diaphragm which results in a large power requirement for the reaction. Diaphragms in electrolytic cells also have a high maintenance requirement. The diaphragms generaly are structurally weak and only very moderate pressure differentials can be maintained across the diaphragm. This often precludes the use of high pressures in the chamber containing the chemically reactive species despite the obvious advantage that the application of superatmospheric pressures would have on the reaction.
I have now found that the objectionable diaphragm in electrolytic cells where a reaction intermediate is electrolyticaly generated can be eliminated by the use of an alternating current potential which is applied to the electrodes provided that the reactions which occur in the electrolytic cell are irreversible. Generally the desired electrochemical reaction that produces a useful product is irreversible. The companion electrolytic reaction is made irreversible by the application of a potential which exceeds the over potential of the particular electrochemical reaction. In this manner reversibility is eliminated and the application of an alternating current potential to the cell is feasible and can result in an efiicient eletcrolytic cell operation.
The method of my invention is applied to a reaction wherein a reaction intermediate can be electrolytically generated. The intermediate can be an oxidized intermediate such as a peroxide, hydroperoxide or an olefin complexing metal cation. Typical of such olefin complexing metals are the Group VIII noble metals, mercury, thallium, silver, etc. These metals exhibit the ability to form pi-complexes with olefins and these pi-complexes are decomposable in the presence of a suitable reactive 7 species to produce a substituted olefin with resultant reducting species, e.g., a soluble salt, can also be present.
The reduced form of the pi-complexing metal is electrolyticaly oxidized in the cell, and chemical reduction by reaction with the olefinic compound rather than electrochemical reduction of the pi-complexing metal by the reverse potential is insured by maintaining an environment in the electrolyte that is highly concentrated with the olefinic compound. The companion electrochemical reduction which occurs with the oxidation of the olefinic compound is generally the reduction of protons to hydrogen. To insure that this electrolytical reduction is irreversible the potential applied to the electrodes exceeds the over potential of the hydrogen at the electrodes so that the hydrogen formed is evolved as hydrogen gas from the eletcrolytic cell.
Preferably, the electrolyte is maintained under moderate to severe agitation to insure mobility of the reduced species of the pi-complexing metal and to insure thorough contacting of the olefinic compound with the high valency state of the pi-complexing metal.
The efficiency of the electrochemical cell is influenced considerably by its size and design. Significant factors in the design of the electrolytic cellwhich are interrelated are the spacings between the electrodes, the degree of agitation applied to the electrolyte, the conductivity of the cell and the mobility of the ions and pi-complexing metal in the solution. The latter characteristic is affected by the state of the pi-complexing metal, e.g., metallic form, or ionic as well as the solutions viscosity, tempera- 3 maximum. This optimum alternating current frequency can be readily determined by operation of the cell throughout a range of frequencies while observing the yield of product at each frequency setting.
When a potential is applied between electrodes immersed in a conducting liquid there is an envelope of the solution in close proximity about each electrode Where the current carrying species, typically dissolved or solvated ions, freely transfer their charges to the electrodes. Diffusion of ions between these envelopes and the bulk of the solution depends on the mobility of the various ions in the liquid.
The figure illustrates a typical efiiciency-frequency relationship in an electrochemical cell of my invention. The efiiciency is plotted on the ordinate and is the quotient of the gram equivalent weight of product obtained during a time period divided by the Faradays of electrical input over that time period. The relationship is shown as two curves, a-b and bc which intersect as shown. Curve ab will intercept the ordinate at cycles per hour (direct current condition) while curve b-c approaches the abscissa at the maximum frequency. At the ordinate intercept, infinite time is available to permit difiusion and equilibrium of the cell. Some product is obtained and the resultant efficiency can be referred to as the saturation efiiciency and reflects the rate of the following reaction:
(1) wherein:
Y is a chemical reactant;
M is charged intermediate with x being the valency of the intermediate.
The competing electrolytic reaction, however, occurs as follows:
wherein:
F represents Faradays of electrical energy.
The value of the saturation efficiency and position of curve a-b depends on variables which influence the rate of reactions 1 and 2. Increasing the concentration of Y, e.g., by use of superatmospheric pressures in the event that Y is a gaseous reactant or by changing other reaction conditions such as temperature, agitation of the liquid, etc., will provide efliciencies following related curves a'b and a"b" shown in dashed lines.
The efliciency of the cell increases, as shown, with reversal of the applied EMF whenever a finite amount of species M is maintained in the liquid. Typically, M is a metal, often a precious metal, and the amount used in a cell is limited. At the electrode wherein the active intermediate M is generated, a high concentration of M is initially formed. At the initial high level of M in the envelope about the generating electrodes, the M ions are rapidly reacted at the interface with reactant Y so the cell has a high initial efliciency. Some ions M however, will escape into the solution and be decomposed at the opposite electrode. The available source of M is depleted by this electrolytic decomposition of M to M at the opposite electrode. As this depletion occurs the concentration of M about the generating electrode decreases relative to the concentration of M in the solution and the rate of reaction (1) relative to reaction (2) also decreases so that the cell becomes less eflicient.
When the applied EMF is frequently reversed the amount of time of the low efiiciency (low M concentration) operation will be reduced and the average efiiciency during the particular half cycle will increase. The increase of this efiiciency with increasing frequency of the EMF reversal is shown as the positive slope of curve a-b. This curve a-b is the chemical reactivity curve.
Curve bc represents the limit to the direct relationship of efiiciency and frequency shown in curve a-b. This curve is the diffusion limit curve and reflects internal cycling of the MSM reaction within the envel p about the electrodes. As the frequency of EMF reversal increases it approaches a value Where the generated M ions do not reach the interface between the electrode envelope and the solution and therefore can not react with Y during the generating half cycle. In the succeeding half cycle these M ions are decomposed to M with a resultant loss in efiiciency which increases with increasing frequency. The curve bc illustrates this relationship. A series of related curves b'-c' and b"-c" with progressively increasing mobility of the ions M and/or decreasing thickness of the envelope is shown by the dashed lines superimposed on curve bc.
From the preceding discussion, it is apparent that efficiency of the cell can also be maximized by decreasing the thickness of the envelope surrounding the electrodes, e.g., by decreasing the solution viscosity, increasing its temperature, etc., or by increasing the mobility of the M species, e.g., by avoiding bulky ligands or other components that may complex with M ions and retard their movement.
Olefins that can be reacted in accordance with my invention in general comprise any olefin having the following structure:
R R C:CHR wherein:
R R and R are selected from the class consisting of hydrogen, alkyl, cycloalkyl, aryl, alkaryl, aralkyl, alkanyl alkyl, alkanyl aryl, halo, halo alkyl, halo aryl, carboxyl, carboxyl alkyl, carboxyl aryl, acyloxy, nitroaryl and alkylene wherein two of said R R and R groups comprises a common alkylene group.
Examples of useful olefins are: the aliphatic hydrocarbon olefins such as ethylene, propylene, butene-l, butene-2, pentene-2, Z-methylbutene-l, hexene-l, octene-3,
r 2-propylhexene-1, decene-2, 4,4'-dimethylnonene-1, dodecene-l, 6-propyldecene-l, tetradecene-4, 7-amyldecene-3, hexadecene-l, 4-ethyltridecene-2, octadecene-l, 5,5-dipropyldodecene-3, eicosene-7, etc. Of these the aliphatic hydrocarbon olefins having from 2 to about 6 carbons are preferred.
Other olefins include: vinylcyclohexane, allylcyclohexane, styrene, p-methylstyrene, 0c methylstyrene, fl-methylstyrene, p-vinylcumene, 1 vinylnaphthalene, 1,2-diphenylethylene, allylbenzene, 6-phenylhexene l, 1,3-diphenylbutene-l, 3-benzylheptene-2, o-vinyl p-xylene, a-chlorostyrene, p-chlorostyrene, m-nitrostyrene, divinylbenzene, l-allyl,4-vinylbenzene, 1,5-heptadiene, 2,5-decadiene, vinyl chloride, vinylidene dichloride, vinyl fluoride, trichloroethylene, trifluoroethylene, di(chloromethyl)ethylene, propenyl chloride, acrylic acid, crotonic acid, maleic acid, p-vinylbenzoic acid, p-allylphenylacetic acid, vinyl acetate, vinyl propionate, propenyl acetate, butenyl caproate, ethylidene diacetate, etc.
Also reactive are the cycloalkenes, their substituted derivatives and alkylene cycloalkanes including: cyclobutene, cyclopentene, cyclohexene, methylcyclohexene, amylcyclopentene, cycloheptene, cyclooctene, cyclodecene, methylenecyclohexane, ethylidene cyclohexane, propylidene cyclohexane, etc.
Examples of suitable olefin complexing metals that can be employed in the electrolyte include the Group VIII noble metals comprising the platinum subgroup of platinum, osmium and iridium as well as the palladium subgroup of palladium, ruthenium and rhodium. Other complexing compounds include rhenium, mercury, thallium, etc. These metals can be added to the electrolyte as the metal, as a dissolved salt or as a soluble complex. Examples of suitable salts include the halides, nitrates, sulfates or carboxylates of lower molecular weight (C C carboxylic acids, etc. Examples of suitable chelating agents that can be used include acetylacetonate, citric acid, alkylene diamines, alkylene diamine tetracarboxylic acids and salts thereof, complexes of cyclopentadienyl, cyclobutadienyl and the lower alkyl and phenyl derivatives thereof such as tetraphenyl cyclobutadienyl, etc. The metals can also be added to the reaction medium as the oxide. Examples of suitable salts or oxides as aforedescribed include platinum chloride, palladium bromide, osmium fluoride, iridium bromide, ruthenium oxide, rhenium oxide, mercuric sulfate, palladium acetate, platinum propionate, iridium benzoate, osmium caproate, ammonium perrhenate, etc.
Since the complexing metal is employed as an electron transferring reactant, relatively minor quantities of the metal can be employed. The electrolytic cell therefore is operative with electrolytes containing as little as 0.001 weight percent of the complexing metal. Higher quantities of the complexing metal can of course be employed up to and exceeding the solubility of the particular salt of the complexing metal in the electrolyte. Generally, concentrations up to about 25 percent can be employed; however, I prefer to use concentrations of the complexing metal expressed as the metal from about 0.5 to about weight percent.
The electrolyte can also contain other dissolved salts to increase its electrical conductivity. Examples of suitable dissolved salts include the alkali metal, alkaline earth metal, and multivalent transition metal soluble salts including the halides, sulfates, nitrates, C -C carboxylates etc. Examples of such salts include potassium chloride, sodium acetate, lithium nitrate, calcium chloride, barium nitrate, cupric chloride, ferric chloride, vanadyl sulfate, chromium nitrate, etc. The amount of the additional salt employed for conductivity through the electrolyte can vary from about 1 to about 50 weight percent, preferably from about 1 to about weight percent.
In the electrolytic cell the reactants that can be employed besides or instead of the aforementioned olefins include carboxylic acids and soluble salts thereof, alcohols, alkylamines, water, etc. The particular reactant depends upon the desired conversion, e.g., olefins can be oxidized in the presence of aqueous mineral acids of pH values from 0 to 7 to produce carbonyl products; in the presence of organic carboxylic acids to produce unsaturated carboxylates; and in the presence of anhydrous alkanols to produce alkoxy derivatives. With an olefin as the reactant and a Group VIII noble metal salt in the electrolyte, the following electrolytes can be employed to produce the indicated products: aqueous mineral acids including aqueous sulfuric, nitric hydrohalic acids such as hydrochloric, hydrobromic, hydrofluoric and hydriodic acid to produce carbonyls such as acetaldehyde, acetone, methylethyl ketone, etc. from respectively, ethylene, proplene, butene- 1, etc. The use of carboxylic acids as the reaction medium such as acetic, propionic, isobutyric, butyric, valeric, pivalic, caproic, caprylic, decanoic, benzoic, phthalic, naphthoic, toluic, etc. results in the production of an unsaturated ester of the carboxylic acid. The products are the vinylcarboxylates when the olefin is ethylene, e.g., vinyl acetate from ethylene and acetic acid; allyl and propenyl products are obtained by the oxidation of propylene; etc. When the reaction medium comprises an anhydrous alcohol, the olefins can be oxidized to alkoxy derivatives, e.g., acetals are obtained from the reaction of olefins and alcohols such as dimethyl acetal, diethyl acetal, dibutyl acetal, from the reaction of ethylene and alcohols such as methanol, ethanol and n-butanol. Examples of suitable alcohols that can be used for the reaction include the alkanols such as methyl, ethyl, propyl, isopropyl, butyl, amyl alcohols, heptanol, octanol, decanol, etc.
Other reactions that can be performed, particularl in the presence of mercury salts and mercuric oxide in the reaction medium comprise the carbonylation of alcohols to produce alkyl carbonates, resulting in the stoichiometric reduction of the mercuric salt or oxide to the free metal. The resultant metal is reoxidized to mercuric compound or oxide by the electrolytic cell.
The carbonylation of amines to prepare substituted ureas can also be practiced in the electrolytic cell. In this reaction a primary or secondary amine can be carbonylated by contacting the amine with carbon monoxide in the presence of the mercuric ions to produce a substituted urea with the resultant production of mercury and protons. The mercury is regenerated in the electrolyic cell and the protons are reduced to hydrogen and evolved from the cell. This reaction can be employed on any primary or secondary alkyl, alkaryl, aryl amine such as methyl, ethyl, isopropyl, butyl, isoamyl, hexyl, isoheptyl, octyl, nonyl, isodecyl amine, aniline, p-methyl aniline, o-ethyl aniline, m-butyl aniline, p-hexyl aniline, 2,5-xylidine, dimethylamine, dipropylamine, N.N-rnethylethylamine, N,N-ethylbutylamine, dihexylamine, N-methyl aniline, N-butyl aniline, N-hexyl aniline, N-ethyl 2,5-xylidine, dipenylamine, di-p-tolylamine, di-otolylamine, pyrroline, piperidine, pyrizole, pyrrolidine, etc. It is of course apparent that non-symmetrical substituted ureas can also be obtained by the use of mixtures of any of the aforementioned amines.
The reaction can also be applied to the oxidative carbonylation of olefins, a reaction which is initiated by complexing of the olefin with any of the aforementioned Group VIII noble metals, particularly with the palladium salts, oxide or chelates. This reaction is practiced by the simultaneous introduction of carbon monoxide and the olefin into the electrolytic cell which can contain a carboxylic acid or alcoholic electrolyte. When the reaction medium comprises the carboxylic acid, the carbonylation of the olefin results in the production of a mixture of alpha, beta-ethylenically unsaturated carboxylic acids having one more carbon atom than the olefin and betaacyloxy substituted acids thereof wherein the carboxylic acid solvent adds across the ethylenically unsaturated bond. When this reaction is performed in an alcoholic medium, the resultant product is the ester of the aforementioned alpha, beta-ethylenically unsaturated bond. Examples of suitable conversions with olefins include the production of acrylic and beta-acetoxy propionic acid by the reaction of ethylene with an acetic acid reaction medium containing the Group VIII noble metal salt. Other examples include the production of methacrylic and crotonic acids by the reaction of propylene as well as the production of the beta acyloxy derivatives thereof. When the reaction is performed in an alcohol such as ethanol, the resultant acids are esterified to produce, e.g., ethyl acrylate, beta-ethoxy ethyl propionate, isopropyl methacrylate, etc.
The reactions are performed at temperatures from about 30300 0, preferably from about -250 C. The pressure in the electrolytic cell can be from atmospheric to superatmospheric, up to about 1500 atmospheres; preferably from about 10 to about 150 atmospheres. The higher pressures are preferred when a gaseous reactant is employed such as ethylene, propylene, carbon monoxide, etc. The absence of a diaphragm simplifies the cell design and permits use of the cell at the aforementioned high pressures. The voltage applied to the electrodes of the electrolytic cell can be varied over a wide range; however, care should be taken not to exceed the over voltage of undesired electrolytic reactions. In general, the oxidations that produce the desired chemical products require the accompanying reduction of hydrogen in the cell. To insure irreversibility of this reaction, the applied voltage under such circumstances should exceed the over voltage for the evolution of hydrogen from the cell. Generally, voltages from about 1 to about volts, preferably from about 2 to about 10 volts, can be employed. The electrodes are positioned in the electrolytic cell with a sufficient spacing to permit the necessary conductivity in the cell and to provide a reaction zone between the electrodes for the reacting species.
The particular frequency that achieves maximum cell efiiciency varies considerably depending on the cell design and ion mobility in the manner previously described. The cells usually will be most efficient when operated over a frequency of from 0.5 to 200,000 cycles per hour. The
lower frequencies will most probably be most efficient and I prefer to use frequencies from about 2 to 1000 cycles per hour.
The invention will now be described by reference to the following example:
EXAMPLE The electrolytic oxidation of ethylene to acetaldehyde was performed in a diaphragmless cell using a low frequency alternating current. The electrolytic cell comprised a glass flask containing an electrolyte and two parallel carbon plates approximately 7 x inches that were s aced one inch apart. Provision was made to stir the electrolyte in the electrolytic cell which comprised a. 2 percent solution of sulfuric acid containing 1 weight percent palladium chloride. Provision was made for the introduction of ethylene between the carbon plates and the exit connection from the flask was passed through a reflux condenser and two product traps including an acetone-dry ice trap for the condensation of the acetaldehyde product. The cell washeated to raise the contents to reflux temperature and ethylene was introduced into the cell while stirring the electrolyte. An alternating current of amps. was passed through the cell at varied frequencies of the applied voltage from /2 cycle per hour to 60 cycles per second while the stirring rate, temperature and other variables 'were maintained constant. At these conditions the following reaction efficiencies, expressed as mols of product per equivalent mols of electrical input were obtained:
Cycles per hour Reaction efllciency The preceding data demonstrate that an optimum cycle of frequency for the alternating current exists and that for the particular cell under investigation this optimum cycle was at about 10 cycles per hour. Simultaneous with the production of the acetaldehyde was the reduction of protons at the electrode and production of hydrogen which was removed in the mixed gas stream containing the acetaldehyde.
Substantially the same results can be achieved by the use of other metals such as aforedescribed in the electrolyte or the use of any of the other aforementioned olefins or reactants. Similarly, substantially the same operation of the cell can be applied to the oxidative carbonylation of olefins by the simultaneous introduction of carbon monoxide into the electrolytic cell. Higher molecular weight olefins than ethylene can be reacted by charging them to the electrolytic cell, e.g., by substituting propylene for the ethylene introduction or by adding to the electrolyte a higher boiling olefin such as octene, decene, etc. Substitution of the electrolyte with an electrolyte comprising an amine containing mercuric oxide can be used in combination with the introduction of carbon monoxide for the production of substituted ureas.
The preceding illustration of the invention is not intended to be unduly limiting of the invention but rather it is intended that the invention be defined by the steps and reagents and their obvious equivalents set forth in the following claims.
I claim:
1. The method for conducting an oxidation reaction in an electrolytic cell comprising an electrolytic chamber, an electrolyte containing a soluble oxidized reaction intermediate selected from the group consisting of a per- 8 oxide, a hydroperoxide and ions of platinum, osium, iridium, palladium, ruthenium, rhodium, rhenium, mercury and thallium maintained therein, and at least two electrodes within a common chamber of said electrolytic cell which comprises contacting said electrolyte with a chemical reactant capable of reducing said oxidized reaction intermediate in the electrolytic cell at a temperature from about 30 to 300 C. and at a pressure from about 1 to 1500 atmospheres to reduce said intermediate and form an oxidized product from said reactant and regenerating the reduced reaction intermediate to the oxidized intermediate by applying to said electrodes an alternating cur rent potential having a frequency between about 0.5 and 200,000 cycles per hour and suflicient voltage to exceed the over voltage of hydrogen.
2. The method of claim 1 wherein said oxidized reaction intermediate comprises ions of a Group VIII noble metal, said reactant comprises an olefin and said electrolyte comprises a substituent tobe incorporated on said olefinic reactant.
3. The method of claim 2 wherein said olefin is ethylene, said Group VIII noble metal is palladium and said electrolyte comprises an aqueous mineral acid selected from the group consisting of sulfuric, nitric, hydrochloric, hydrobromic, hydrofluoric and hydriodic acid.
4. The method of claim 3 wherein said olefin is ethylene, said complexing metal is palladium, said electrolyte comprises a substantially anhydrous carboxylic acid and said product is a vinyl ester.
5. The method of claim 3 wherein said olefin is methylene, said complexing metal is palladium, said electrolyte comprises a substantially anhydrous alkanol and the product of said reaction is a dialkyl acetal.
6. The method for oxidizing an olefin in an electro lytic cell having at least two electrodes inserted with a common chamber thereof which comprises:
introducing said olefin into said chamber and into contact with an aqueous electrolyte containing ions of platinum, osmium, iridium, palladium, ruthenium, rhodium, rhenium, mercury or thallium;
maintaining the temperature of said chamber at about 30 to 300 C. and the pressure within said chamber from 1 to about 1500 atmospheres; and
simultaneously applying a continuous alternating potential across said electrodes at a frequency of between about 0.5 and 200,000 cycles per hour and at a sufiicient voltage to exceed the over voltage of hydrogen and to maintain said metal in said electrolyte as ions.
7. The method of claim 6 wherein said electrolyte also contains from 1 to weight percent of a soluble salt of an alkali metal or an alkaline earth metal.
8. The method of claim 6 wherein said electrolyte comprises an aqueous mineral acid selected from the group consisting of sulfuric, nitric, hydrochloric, hydrobromic, hydrofluoric and hydriodic acid.
9. The method of claim 6 wherein said electrolyte contains palladium ions and wherein said olefin is an aliphatic hydrocarbon olefin having from about 2 to about 6 carbons.
10. The method of claim *8 wherein said mineral acid is sulfuric acid.
References Cited UNITED STATES PATENTS 3,147,203 9/1964 Klass 204 JOHN H. MACK, Primary Examiner R. L. ANDREWS, Assistant Examiner US. Cl. XJR. 204--72
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