US 3361653 A
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Description (OCR text may contain errors)
Jan. 2, 1968 G. T. MILLER 3,361,553
ORGANIC ELECTROLYTIC REACTIONS Filed Nov. 4, 1963 2 sheets-sheet 2 A P I HI 1" f United States Patent Ofiice 3,361,653 Patented Jan. 2, 1968 tion of New York Filed Nov. 4, 1963, Ser. No. 321,240 9 Claims. (Cl. 204-74) This invention relates to electrolytic reactions. More particularly, it relates to an efiicient mass transfer of a reactant material that has low electrical conductivity and is substantially insoluble in an electrolyte, to an electrode where electrolysis takes place and the material is reacted with a product of electrolysis.
The inability of a reactant material, that has low con ductivity and is substantially insoluble in an electrolyte, to be readily and efficiently transferred to an area of an electrode where oxidation or reduction may take place has posed a difiicult problem in electrochemistry. It is known in the art that to effect a transfer of such a reactant material to an electrode often requires vigorous agitation or the addition of a solvent. Thus, such transfer of the reactant material requires special equipment and extra materials, i.e., stirrers, solvents, which add to the cost and complexity of the system. Still another problem in electrochemistry, which in many instances leads one instead to utilization of chemical means to oxidize, reduce or otherwise change a reactant, is due to the materials lack of conductivity, A low current density is generally encountered on the electrode making it necessary to have an unduly large apparatus constructed to compensate for this low current density.
It has been found that mass transfer of a reactant material, having low conductivity and substantial insolubility in an electrolyte may be carried out in the absence of agitation and without the necessity for employment of solvents, while maintaining a high current density on the electrode in contact with the reactant material, so as to promote a chemical reaction. In accordance with this invention a reactant material having low electrical conductivity and substantial insolubility in an electrolyte may be electrolyzed by adding the reactant material to an electrolytic cell having electrodes and an electrolyte therein so that the body of reactant material contacts a minor proportion of an electrode in the cell, and passing an electric current through said electrolytic cell whereby the material is maintained as a thin film on the surface of said electrode in contact with the reactant material.
The aspects of the invention will be readily apparent from the following description, taken with the drawings illustrative of embodiments of the invention, in which drawings FIG. 1 is a vertical sectional view of an apparatus utilizing a diaphragm, in which this invention is practiced; and
FIG. 2 is a vertical sectional view of a similar apparatus wherein the diaphragm is absent.
In FIG. 1 cell vessel 10 contains anode compartment 12, anode 14, cathode compartment 16, and cathode 18. A porous or permeable diaphragm 2i) separates the anode and cathode compartments and separates the electrolyte into anolyte section 17 and catholyte section 19. In the cathode compartment 16 is a reactant material 24. Ports 26 and 28 permit the addition and removal of anolyte to and from the anode section 12. Ports 30 and 31 permit the addition and removal of catholyte to and from the cathode section 16. Port 32 permits the addition of the reactant material 24. Port 34 permits the removal of the reactant material from cathode section 16 after it has been subjected to electrolysis. Sufiicient reactant material 24 is added to the cathode compartment 16 so that the pool or body of the reactant material contacts a minor proportion of cathode 18. Anolyte gas discharge port 36 is provided in the top of the anode section to remove anolyte gas, if any, from the electrolytic cell. Catholyte gas discharge port 38 is provided on the top of the cathode section 16 to remove catholyte gas, if any. Liquid-gas interfaces are indicated at 15. Electrolyzing current to the electrodes is transmitted by anode electrical connector 40 and cathode electrical connector 42, joining the anode and cathode to the positive and negative poles, respectively, of a source 44 of direct current. If desired, a heating or cooling means, such as a constant temperature bath, not shown, may be employed to maintain the cell at or near a desired temperature.
The numerals in FIG. 2 correspond to those of FIG. 1. However, FIG. 2 illustrates the anode 14 in cell 10 out of contact with the reactant material 24 and the cell contains no diaphragm 20. The inlet and outlet ports 26 and 28 allow electrolyte to be charged into and removed from the cell and ports 36 and 38 allow gases evolved in the process, if any, to exit from the cell. These figures illustrate the utilization of the vertical cathode where a reduction type of reaction may take place. However, the cells may be readily modified so that the anode 14 may be in contact with the reactant material 24 to cause oxidation or other analogous reaction.
In the practice of this invention it is desirable to utilize those reactants that have low conductivity and are also insoluble in the electrolyte utilized in the electrolytic cell. Organic materials, sometimes referred to as depolarizers, and some inorganic materials containing the elements in Groups Ila, IIIa IVa and VIa of the Periodic Table having low electrical conductivity and being substantially insoluble in an electrolyte may be employed in the practice of this invention. By a material having low conductivity is meant those reactants having a conductivity of from about 10 to 10- reciprocal ohms per centimeter (mhos per centimeter).
Examples of such reactant materials are compounds of silica, sulfur, selenium, tellurium, bromine and other elements of the recited periodic groups.
Organic compounds which may be reactants include, for examples, acetal, o-ethoxyacetanilide, N-tolyacetarnide, acetoacetanilide, acetonaphthol(l,2), acetophenone, diacetyl disulfide, acetylsalol, acetylene dibromide, acetylene dichloride, aldehydan, allyl acetate, allyl acetone, allyl acetonitrile, allyl isoamyl ether, allyl anoline, allyl benzoate, allyl bromide, allyl isocyanide, allyl formate, allyl iodide, allyl chloride, allyl iso-thiocyanate, allyl thiocyanate, amino-acetophenone, o-amino beuzaldehyde, o-amino benzonitrile, amino camphor, p-amino diethylaniline, o-dirnethyl aniline, rn-dimethyl aniline, allyl acetic acid, aniline, anisaldehyde, anisole, azobenzene, benzaldehyde, benzene, benzil, benzophenone, benzyl alcohol, benzyl chloride, anthranil, arsenic diethyl, arsenic triphenyl, bromobenzene, dimethylazobenzene, azoxybenzene, benzyl formate, butyl acetate, bromoform, bromotoluene, caproic acid, carbon tetrachloride, o-chloroaniline, chlorobenzaldehyde, chlorobenzene, chloroform, cyclohexane, cyclohexanol, cyclohexene, cymene, dibenzyl, dibromoethane, ethylacetate, ethyl acrylate, ethyl acrylic acid, furfural, furfural acetone, furan, furfuryl acetate, geramyl formate, germanium tetraethyl, glucose pentabutyrate, glucose pentapropionate, glycerol iso-amyl ether, glycerol n-butyl ether, acrylonitrile, oleic acid, octyl alcohol, octyl acetate, phenol, nitropropane, nitrophenetole, nitrocresol, chloronitrobenzene, nitrobenzene, octylene, octane, toluiene, ammonium iodate, beryllium stearate, carbon disulfide, carbon selenosulfide, germanium chloroform, dibasic sodium phosphate, silicone oils and related compounds. It will be seen that most of these are of 1 to 40 carbon atoms, preferably of about 1 to 20 carbon atoms per molecule.
Utilizing these reactants in accordance with the invented processes, products may be formed, as illustrated below.
Reactant: Products formed Toluene with mineral acid electrolyte Benzaldehyde. Benzene in HCl electrolyte Monochlorobenzene. Nitrobenzene Aniline, p-amino phenol,
Bromobenzene Benzene. Acrylonitrile Adiponitrile. Carbontetrachloride chloroform. Monochlorobenzene Benzene.
These are only a few illustrations of the various reactions which may be effected. During the reaction the reactant material preferentially wets the electrode and reacts there, usually either to be reduced or oxidized depending on the charge of the electrode. Thus, alcohols may be oxidized to aldehydes and acids, aldehydes may be reduced, nitro groups may be converted to amino radicals, chlorohydrocarbons may be reduced to hydrocarbons, and so forth, generally, as will be clear to one from this specification.
Cell vessel It) may be constructed of a material capable of resisting corrosion by the electrolyte and other materials employed in the electrolytic cell. Typical examples of suitable materials of construction of cell vessel include glass, glazed ceramic, tantalum, titanium, hard rubber, polyethylene, polyurethanes, polyester polyurethenes (particularly those made from chlorendic acid), coated phenol formaldehyde resins, and the like.
Diaphragm which separates the anode section 12 from the cathode section 16, may be semi-permeable or permeable material, resistant to the cell contents, and capable of maintaining any anode and cathode gases separate. Typical examples of suitable materials for use as diaphragms include: porous alundum, porous porcelain, resin impregnated wool felt, porous glass, porous polyethylene, other permiselective membranes, woven fabrics, and various other separators of the types which may be normally employed.
Solid materials preferably having a hydrogen overvoltage (as normally measured in the absence of the reactant material) exceeding the hydrogen over-voltage of smooth platinum may be employed as the cathode. Typical cathodic materials include lead, amalgamated lead, cadmium, tin, aluminum, nickel, alloys of nickel, such as Munetal (an alloy containing 77.2 percent nickel, 4.8 percent copper, 1.5 percent chromium, and 14.9 percent iron), Monel, copper, silver, bismuth, and alloys thereof. For example, lead-tin, lead-bismuth, and leadbismuth alloys may be employed. Various shapes of cathodes may be employed. The cathode may be a solid plate illustrated, or may be cylindrical or of other shape. Mats of metallic wool and porous metallic sheaths may also be employed, if desired. Suitable anode materials include lead, platinum, lead peroxide, graphite, and other materials of construction capable of conducting current and resisting corrosion under the conditions of electrolysis employed. Essentially, the reactant wets a large proportion of the anode or cathode, depending upon the predominant reaction desired, i.e., oxidation or reduction by covering the electrode surface thinly. It does this even though only a small proportion of the electrode surface is below the surface of or in a body of reactant material. One may better visualize this action by comparing it to wicking or capillary action. However, in this instance the reactant material covers or coats the surface of the electrode from a pool of material and the wetting occurs as the electrical current is passed through the electrolyte and appears to be promoted rather than adversely affected by the passage of the current.
The electrolyte may be an aqueous solution or an organic or inorganic liquid, in which the reactant material utilized is substantially non-soluble. Typical examples of suitable aqueous solutions which may be employed as the electrolyte include solutions of hydrochloric acid, sodium chloride, lithium chloride, potassium chloride, sodium sulfate, potassium sulfate, mono-sodium phosphate, bi-sodium phosphate, acetic acid, ammonium hydroxide, phosphoric acid, sulfuric acid, and mixtures thereof.
Examples of non-aqueous inorganic electrolytes are ammonia, sulfur dioxide, potassium chloride, anhydrous hydrogen fluoride, hydrogen cyanide and so forth.
Examples of organic electrolytes are methyl alcohol, acetic acid and the like. Although ideally insoluble in the electrolyte, in many cases the reactant material may be soluble therein to the extent of about 0 to 10 percent but usually the solubility is between 0 and about 3 percent and preferably between 0 and about 1.0 percent.
Improved results may be obtained when metallic ions are present in the electrolyte in small proportions. For example, suitable concentrations of metal ions may be between about 0.01 percent and 5 percent by weight of electrolyte, however, between about 0.02 percent and 3 percent by weight of electrolyte may also be utilized. Preferably though, between about 0.02 percent and 0.5 percent by weight of electrolyte is present. Examples of metallic ions which may be used are antimony, bismuth, and lead, tin, cadmium, mercury, silver, zinc, cobalt, calcium, barium, and mixtures thereof. The metal ions may be placed in the electrolyte by employing a consumable anode of the desired metal or metals, such as a lead anode, whereby the metal ions are formed in the electrolyte and transferred to the area adjacent to the cathode. Salts or other compounds of the metals such as chlorides, phosphates, acetates, and the like also may be dissolved in the electrolyte if desired.
In a cell utilized for electrolysis of the reactant material the temperature of the cell is usually above the melting point of the reactant material and below the boiling point of the electrolyte. Temperatures between about 0 degree centigrade and degrees centigrade are generally satisfactory, but optimum yields may be obtained at temperatures between about twenty-five degrees centigrade and seventy degrees centigrade when utilizing an aqueous electrolyte. When utilizing a non-aqueous electrolyte temperatures of from 60 degrees centigrade to 800 degrees centigrade may be utilized, depending on the system employed.
It has been found that when electric current is passed through a cell with a vertical electrode touching the reactant material and the electrolyte, the reactant material will wet or wick up substantially the full surface of the electrode. It has also been found that should the material be of lower density than the electrolyte, the material will wet down the vertical electrode it is in contact with and undergo a reaction, such as an oxidation or reduction, along the entire length of the electrode. The amount of material consumed by the oxidation or reduction is replenished by the continuous flow of the reactant from the source thereof along the surface of the electrode.
The structure of the electrodes utilized in the practice of this invention may vary, depending on the reactant material utilized, it being preferred, however, to employ electrodes such as those illustrated in my copending ap plication, S.N. 262,497, filed Mar. 4, 1963. As the reactant material is consumed on the surface of the elec trode to yield the oxidized or reduced product, additional reactant materials are supplied to the electrode surface from the source which is usually in contact with a minor portion of the electrode (although when the reactant wicks downwardly into the electrolyte it may be in contact with the height of the body of reactant). Electrode current density may be set by the operator and is de pendent upon which density gives the best results for the cell design, reactant material and the construction of the electrode. Generally, the current density to be utilized in carrying out the process of this invention will depend on the product desired. Thus, a current density of from 0.1 ampere per square foot to about 500 amperes per square foot may be utilized. A preferable range being from about amperes per square foot to about 300 amperes per square foot. However, other current densities consistent with the economic production of the product desired may also be utilized to transfer reactant material to, and wet an electrode in contact with electrolyte.
The following examples are presented to illustrate the invention. They are not to be considered limiting. All parts and percentages are by weight and all temperatures are in degrees centigrade, unless otherwise specified.
Example 1 Twenty percentsulfuric acid (200 milliliters) was charged equally to the anolyte and catholyte compartments of an electrolytic cell like that illustrated in FIG. 1. This cell had an amalgamated lead plate as a cathode and two platinum electrodes as anodes. The cathode and anode were separated by a ceramic diaphragm. A temperature of from to degrees centigrade was maintained by a water bath. Nitrobenzene (5 grams) was then added to the catholyte section, below the electrolyte and an average current of 25 amperes per square foot was impressed and maintained on the electrolytic cell for a period of approximately 4.2 hours, so as to maintain a potential difference of 0.9 volt between the cathode and a standard calomel electrode inserted in the cell for measuring purposes only.
The electrolyte was then removed from the electrolytic cell and neutralized to a pH of 6, utilizing a percent sodium hydroxide solution. The resultant mixture was then ether extracted. The ether layer was removed and evaporated to near dryness. The residue was thereafter dissolved in choroform, which was extracted with water. The water was separated and combined with the water solution separated from the ether layer. The chloroform solution was then evaporated to approximately 10 cc.
The aqueous solution was analyzed by ultraviolet spectroscopic methods and the chloroform solution was analyzed by infrared means. These analytical procedures showed the presence of nitrobenzene, azoxybenzene, aniline and p-aminophenol. Table I, which follows after Example 2, shows the amounts of nitrobenzene unreacted, ampere hours and current density utilized.
Example 2 The procedures of Example 1 were repeated, utilizing the same cell equipment but with a 1.4 ampere-hour current passage. The results, upon analysis, were as indicated in Table I. It was further observed in Example 1 and this example, by polarographic traces, that essentially 100 percent reversible reactions took place at the cathode, indicative of a high eificiency for the reduction of nitrobenzene.
Measured utilizing 0.9 volt between the cathode and a standard calomel electrode.
Example 3 An electrolytic cell was utilized similar to FIGURE 2, in which the anode is in contact with, and the cathode is maintained out of contact with the reactant material. A 10 percent HCl solution (200 milliliters) was utilized as the electrolyte. Both the anode and cathode were made of lead having V-shaped grooved surfaces one-eighth of an inch peak to peak and one-eighth of an inch deep. The lower proportion of the anode was immersed in monochlorobenzene (1O milliliters). A current density of amperes per square foot was impressed on this system. The organic material was observed to wet the entire surface of the anode. A polarographic trace showed essentially a completely reversible reaction. There was no evidence of gas evolution. After about 15 minutes, a yellow haze was evident in the vicinity of the anode. The haze increased with further electrolysis. These observations indicate a high efficiency of oxidation of the monochlorobenzene.
Example 4 The electrolytic cell of Example 3 was again utilized. The cathode was now placed in contact with, and the anode remained out of contact with, the monochlorobenzene. A wetting of the cathode by the monochlorobenzene was visible on impressing a direct current of about 70 amperes per square foot on the system. Hydrogen gas evolution from the cathode was terminated as the organic monochlorobenzene wetted or covered the cathode surface. Polarographic traces showed a reversible reaction evidencing high efiiciency of the reduction of monochlorobenzene. From the above illustration, it is seen that the wetting of a solid cathode by a depolarizer or reactant material, either at the anode or cathode, causes creation of an eflicient mass transfer of a depolarizer or reactant material.
Example 5 An electrolytic cell similar to that of FIG. 2, was charged with water grams), phenol (5 grams) and sodium acetate (5 grams) which formed an electrolyte solution. In this electrolytic cell, a graphite rod was utilized as a cathode and a lead sponge anode, such as is conventional in storage batteries, was employed. Approximately 10 milliliters of benzene were added to this solution and floated on top of the electrolyte. The lead sponge anode was inserted through the benzene layer into the aqueous layer, leaving a portion in contact with the body of the benzene. It was observed that the benzene wetted the lead anode. A current density of 20 amperes per square foot was then applied. Gas bubbles came from the cathode (hydrogen) and none from the anode. A sodium sulfate test demonstrated that the lead anode was not oxidized. These observations and analysis evidence oxidation of the benzene to phenol. Continued electrolysis evidenced that the benzene was wicking down the electrode. In this example both the anode and cathode were in contact with the reactant material.
This invention has been described with respect to illustrations and preferred embodiments thereof, but is not so limited. It is evident that variations may be made and equivalents may be substituted therein without departing from the scope of the invention, as claimed.
What is claimed is:
1. A process for electrolyzing an organic reactant material having low conductivity and substantial insolubility in an electrolyte comprising adding a sufiicient amount of the material to an electrolytic cell having electrodes and having said electrolyte that said organic reactant material contacts a least portion of one of said electrodes in the cell, said organic material forming a substantially horizontal interface with said electrolyte, and said contactingelectrode extending through said horizontal interface into said electrolyte, and passing an electric current through the electrolyte, said passing of said electric current being sufiicient that the material is maintained as a thin film on the surface of said electrode.
2. A process of electrolysis comprising adding a sufficient amount of an organic reactant material having low conductivity and substantial insolubility in an electrolyte to an electrolytic cell having electrodes and having said electrolyte in said electrolytic cell that said organic reactant material contacts a minor proportion of one of said electrodes in the cell, said organic material forming a substantially horizontal interface with said electrolyte, and said contacting-electrode extending through said horizontal interface into said electrolyte, and passing an electric current through said electrolytic cell said passing of said electric current being sufiicient that the material wets and is maintained as a thin film on the surface of the electrode in contact With and surrounded by the body of electrolyte.
3. A process in accordance with claim 1 wherein the reactant material has a conductivity of from about 10'" to 10 reciprocal ohms per centimeter and a solubility of to percent in the electrolyte.
4. A process of reacting nitrobenzene electrolytically which comprises adding a sufiicient amount of nitrobenzene, to an electrolytic cell containing electrodes and containing a nonsolvent electrolyte, that the body of nitrobenzene is in contact with a proportion of one of said electrodes, said nitrobenzene forming a substantially horizontal interface with said electrolyte, and said contacting-electrode extending through said horizontal interface into said electrolyte, and passing a suificient amount of an electric current through the electrolyte, that the nitrobenzene wets the electrode in contact therewith and forms a reaction product.
5. A process in accordance with claim 4 wherein the electrode at which the reaction product is formed is a cathode and the reaction product comprises aniline.
6. A process in accordance with claim 1 wherein the reaction electrode is an anode and the reaction product is an oxidized form of the reactant.
7. A process in accordance with claim 1 in which the reaction electrode is a cathode and the reaction product is a reduced form of the reactant.
8. A process of reacting monochlorobenzene electrolytically which comprises adding a suflicient amount of monochlorobenzene, to an electrolytic cell containing electrodes and containing a non-solvent electrolyte, that the monochlorobenzene is in contact with a proportion of one of said electrodes, said benzene forming a substantially horizontal interface with said electrolyte, and said contacting-electrode extending through said horizontal interface into said electrolyte, and passing a sufficient amount of an electric current through the electrolyte, that the monochlorobenzene wets the electrode in contact therewith and forms a reaction product, said monochlorobenzene being substantially free of a solvent.
9. A process of reacting benzene electrolytically which comprises adding a sufficient amount of benzene, to an electrolytic cell containing electrodes and a non-solvent electrolyte, that the benzene is in contact with a minor proportion of one of said electrodes, said benzene forming a substantially horizontal interface with said electrolyte, and said contacting-electrode extending through said horizontal interface into said electrolyte, and passing a sufficient amount of an electric current through the electrolyte, that the benzene wets the electrode in contact therewith and forms a reaction product, said benzene being substantially free of a solvent.
References Cited OTHER REFERENCES Allen, M. 1.: Organic Electrode Processes, Chapman and Hall Ltd., London, 1958, pages 125, 148, and 149.
ROBERT K. MIHALEK, Primary Examiner.
JOHN H. MACK, Examiner.
H. M. FLOURNOY, Assistant Examiner.