CA1039229A - Process for hydrodimerizing olefinic compounds - Google Patents

Abstract

PROCESS FOR HYDRODIMERIZING OLEFINIC COMPOUNDS

ABSTRACT OF THE DISCLOSURE
In a process for hydrodimerizing an olefinic nitrile, amide or ester by electrolyzing an aqueous solution of the olefinic compound, an alkali metal salt and quarternary ammonium cations, the selectivity with which the hydrodimer is produced is sur-prisingly high when the solution contains less than about 5%
by weight of the olefinic compound, more than 5% by weight of the alkali metal salt and/or alkali metal cations constituting more than hair of the total weight of all cations in the solution and the solution is electrolyzed in contact with a cathode consisting essentially of cadmium. Even in a cell in which the anode is in contact with the aqueous solution, fouling of such a cathode proceeds very slowly and the hydrodimer selectivity remains high for an exceptionally long time when the cathodic surface has a centerline average not greater than about 90 microinches.

Description

~3922~

Production of paraffinic dinitriles, dicarboxamides or dicarboxylates by electrolytic hydrodimerization of an alpha, beta-olefinic nitrile, carboxamide or carboxylate is well known, e.g. from U.S. Patent Nos. 3,193,481 through 3,193/483 which issued to Manuel M. Baizer on July 6, 1965. Although the process has ~een sufficiently attractive that it has been in comm rcial use for over seven years, efforts to develop improvemen~`s thereon have been continued with particular emphasis on lower-ing electric power costs and mitigating electrode corrosion and fou~ing tendencies because of which it has been heretofore com-mercially preferable to carry out the process with a cell-dividing membrane. With the objectives of maintaining high ¦ electrolyte conductivity while employing a relatively low porpor-tion of organic salts in the electrolysis medium, one approach to improvement of the process has been to carry out the elec~roly-sis in an aqueous solution of a mixture of quaternary ammonium ~ and alkali metal salts together with the olefinic compound to ¦ be hydrodimerized.
An example of a process utilizing such an approach is described in Netherlands Patent Application 66,10378 which was laid open for public inspection on January 2~, 1967. As des-cribed in that application, adiponitrile is produced by electrolyzing a neutral aqueous solution of acrylonitrile, an alkali metal salt of a polyvalent acid such as phosphoric, boric or sulfuric and a small quantity of a quaternary ammonium salt.
According to the examples of that application, good selectivities can be achieved when such a process is carried out in an undivided (membraneless) cell having a graphite cathode. As is known in the art, ho~ever, commercial-scale use of graphite cathodes in a process of the type discussed herein is not very attractive, primarily because graphite is quite brittle and, at the desirably

- 2 - 7~ ' lQ39Z29 elevated hydrodimerization temperatures and generally optimum-electrolyte flow rates of at least several feet per second, sufficiently subject to erosion and/or fouling that it soon becomes roughened and the selectivity of the reaction (which takes place at the cathode) drops sharply.
Superficially, it might have seemed that various other materials having high hydrogen overvoltages could be satisfactorily substituted for graphite as the cathode in electrolytic hydrodimeriZation (EHD) processes similar to ~ 10 that of Canadian Patent 813,877 issued May 27, 1969, entitled METHOD OF PREPARING ADIPONITRILE to A. P. Tomilov et al and, in fact, the suitability of a variety of such other materials for use in certain EHD processes has been suggested in the aforecited U.S. Patent Nos. 3,193,481-483, in U.S. Patent No.

3,511,765 which issued to Fritz Beck et al on May 12, 1970 and U.S. Patent No. 3,595,764 which issued to Maomi Seko et al on July 27, 1971. However, and notwithstanding those suggestions, it has long been recognized in the art that particularly when , an olefinic compound E~ID medium contains significant amounts of alkali metal salts, the selectivity with which the desired hydrodimer is produced is highly dependent on the specific .i cathode material employed. To illustrate, in British Patent ¦ No. 1,014,428 which issued to Ivan L. Knounjants et al on ~ December 22, 1965, tha patentees demonstrated that the hydrodimer selectivity in electrolytic hydrodimerization of an olefinic compound such as acrylonitrile is quite high (70-80%~ when a graphite cathode is employ~d with a low-temperature (below 0C.) , aqueous electrolyte containing alkali metal ions in substantial concentration (0.7 to 1.2N) but that with the same electrolyte, an iron cathode yielded o~ly about 20% of the dinitrile ~based on the converted monomer) and a cadmium cathode pxovi.ded ' . ~
: - 3 -. ' ~39~
practically no reaction product other than the saturated monomer (propionitrile). The high ratios of propionitrile to adipo-nitrile obtained when various cathode materials other than graphite are employed with an electrolyte containing alkali ~- metal ions are also demonstrated and an explanation is provided by Baizer in Journal of the Electrochemical Society, Vol. 111, No. 2, at pages 215-22 (1964).
For reasons including those set forth hereinbefore, a process by which an olefinic nitrile, carboxamide or carboxylate can be electrolytically hydrodimerized with high selectivity while using an the electrolysis medium an aqueous solution con-taining an alkali metal salt in significant amount and in which the cathode is dimensionally stable and resistant to corrosion for long periods of time is highly attractive for commercial use. Accordingly, the provision of such a process is a primary objective of the invention described herein. Another object of this invention is to provide such a process which can be satis-factorily carried out in an electrolytic cell in which the anode is in contact with the electrolysis medium and despite the anode being subject to corrosion under those circumstances. Further ob~ectives of the invention will be apparent from the following ~I description and Examples in which all percentages are by weight except where otherwise noted.
It has now been discovered that an olefinic compound ' having the formula R2C=CR-X wherein -Xis-CN, -CONR2 or -COOR', Rishydrogen or R' and R' is Cl-C4 alkyl can be hyarodimerized to prepare a hydrodimer having the formula X-CHR-CR2-CR2-CHR X
wherein X and R have the aforesaid significance with a high molar selectivity ~at least about 75~ and in many cases at least about 80%) based on the converted olefinic compound by electrolyzing an aqueous solution of the olefinic compound, quaternary ammonium ~L03~2Z9 cations and an alkali metal salt in contact with a cathodic sur-face consisting essentially of cadmium. In one embodiment of the invention, the aqueous solution has dissolved therein at least about 0.1% of the olefinic compound, quaternary ammonium cations in a concentration of at least about 10 5 gram mol per liter and at least about 0.1~ of alkali metal salt sufficient to provide alkali metal cations constituting more than half of the total weight of all cations in the solution. In another embodiment of the invention, the aqueous solution has dissolved therein at least about 0.1~ of the alkali metal salt, quaternary ammonium cations in a concentration of at least about 10 5 gram mol per liter and at least about 0.1~ but less than about 5%
of the olefinic compound. In still another embodiment of the invention, the aqueous solution has dissolved therein at least about 0.1% of the olefinic compound, quaternary ammonium cations in a concentration of at least about 10 5 gram mol per liter and at least about 5% of the alkali metal salt. Even when the process is carried out in an electrolytic cell in which the anode is in contact with the aqueous solution, fouling of the cathode proceeds very slowly and the hydrodimer selectivity remains high for an exceptionally long time when the cathodic surface has a centerline average not greater than about 90 micro inches. Each of the embodiments of the invention is particularly t useful in the preparation of adiponitrile, a nylon 66 intermediate, by the hydrodimerization of acrylonitrile.
Olefinic compounds that can be hydrodimerized by the process of this invention include those having the structural formula R2C=CR-X wherein -X is -CN, -CONR2 or -COOR', R is hydrogen or R' and R' is Cl-C4 alkyl (i.e., methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl or tertbutyl). Compounds having that formula are known as having alpha, beta mono-:
- ~)392Z9 unsaturation and in each such compound, at least one R may be :, R' while at least one other R is hydrogen and at least one R', if present, may be an alkyl group containing a given number of carbon atoms while at least one other R', if present, is an alkyl group containing a different number of carbon atoms.
Such compounds include olefinic nitriles such as, for example, ; acrylonitrile, methacrylonitrile, crotononitrile, 2-methylene-; butyronitrile, 2-pentenenitrile, ~-methylenevaleronitrile, 2-methylenehexamenitrile, tiglonitrile or 2-ethylidenehexanenitrile;
olefinic carboxylates such as, for example, methyl acrylate, ethyl acrylate or ethyl crotonate; and olefinic carboxamides such as, for example, acrylamide, methacrylamide, N,N-diethylacrylamide or N,N-diethylcrotonamide. Products of hydrodimerization of such compounds have the structural formula X-CMR-CR2-CR2-CHR-X wherein X and R have the aforesaid significance, i.e., paraffinic dini-triles such as, for example, adiponitrile and 2,5-dimethyladi-ponitrile; paraffinic dicarboxylates such as, for example, dimethyladipate and diethyl-3,4-dimethyladipate; and paraffinic dicarbo~amides such as, for example, adipamide, dimethyladipamide ` 20 and N,N'-dimethyl-2,5-dimethyladipamide. All of such hydrodimers are useful in the manufacture of high molecular weight conden-I sation polymers, e.g. by reaction with dihydroxy or dicarboxylic '~ compounds, and in the case of the dinitriles, as intermediates which can be hydrogenated by known processes to prepare paraffinic diamines that are similarly useful in the manufacture of high ~
molecular weight condensation polymers. Other examples of the various olefinic compounds that can be hydrodimerized by the ~, process of this invention and the hydrodimers thereby produced ! are identified in the aforecited U.S. Patent Nos. 3,193,~81-483.

The invention is herein described in terms of electro-lyzing anaqueous solution having dissolved therein certain ~ _ 1~39~229 proportions of the olefinic compound to be hydrodimerized, quaternary ammonium cations and an alkali metal salt. The process of ~his invention can be quite satis~actorily carried out with the recited aqueous solution containing anywhere from a very small to a very substantial proportion of an undissolved organic phase during electrolysis of the solution. ~lence in some embodiments of the invention there may be suitably electrolyzed an aqueous solution containing essentially no undissolved organic phase, by which is meant that the solution ~.
may contain either no measurable amount of undissolved organic phase or a minute proportion of undissolved organic phase such as might remain entrained in the aqueous solution despite the latter being permitted to stand without agitation after electro-lysis and cooling and/or addition of more of the olefinic starting material to facilitate-separation of a product-containing organic phase, but the presence of which has no significant effect on the olefinic compound converslon per pass or hydrodimer selectivity achieved when the separated aqueous phase is recycled for further electrolysis in accor-dance with the process of this invention. Such a minute proportion, if present, would be typically less than 5% of the combined weight of the aqueous solution and the undissolved organic phase contained therein. In other embodiments, the invention can be carried out by electrolyzing an aqueous solution of the type described hereinbefore but having dispersed therein an undissolved organic phase in a larger proportion (e.g. from about 5% up to 15%, 20% or even about 25% or more of the combined weight of the aqueous solution and the undissolved organic phase contained therein~ which may or may not signiflcantly affect the con~ersion per pass or hydrodimer selectivity depending on other conditions of the process. In continuous ~39~g process embodiments involving recycle of unconverted olefinic compound and whether present in a minute or larger proportion, such an organic phase would be normally made up mainly of the olefinic compound to be hydrodimerized and the hydrodimer product with some small amounts of organic hydrodimerization by-products, quaternary ammonium cations, etc. possibly also ~ `
present. In any event, however, the concentrations of the constituents dissolved in the aqueous solution to be electrolyzed, as set forth in this specification and the appended claims, are with reference to the recited aqueous solution alone and not the combined contents of said aqueous solution and an undis-solved organic phase which, as aforesaid, may be present but need not be present in the aqueous solution as the process o ., ~
this invention is carried out. On the other hand, the weight ; percentages of undissolved organic phase in the aqueous solu-tions described in this disclosure (including the Examples) and the appended claims are based on the combined weight of the aqueous solution and the undissolved organic phase contained therein.
Referring now to the constituents of the aqueous phase, the olefinic compound to be hydrodimerized will be present in ~ at least such a proportion that electrolysis of the solution, -i~ as described herein, will result in a substantial amount of the ' ~
desired hydrodimer being produced. That proportion is generally at least about 0.1% of the aqueous solution, more typically at least about 0.5% of the aqueous solution and, in some embodi-ments of the invention, preferably at least about 1% of the i aqueous solution. Inclusion of one or more additional consti-tuents which increase the solubility of the olefinic compound in the solution may permit the carrying out of the process with the solution containing relatively high proportions of the 1039Z~g .

olefinic compound, e.g. at least about 5% or even 10% or more, but in many embodiments of the invention, the aqueous solution contains less than about 5% (e.g. not more than 4.5~) of the olefinic compound and, in most of those embodiments, preferably not more than about 1.8% of the olefinic compound.
The minimum required proportion of quaternary ammonium cations is very small. In general, there need be only an amount sufficient to provide the desired hydrodimer selectivity (e.g.
at least about 75%) although much higher proportions can be present if desired or convenient. In most cases, the quaternary ammonium cations are present in a concentration of at least about 10 gram mol per liter of the aqueous solution. Even more typically their concentration is at least about 10 4 gram mol ! per liter of the solution, and, in many embodiments, preferably l at least about 10 3 gram mol per liter. Although higher propor-j tions may be present in some cases, as aforesaid, the quaternary - ammonium cations are generally present in the aqueous solution . in a concentration ].ower than about 0.5 gram mol per liter and even more usually, in a concentration not higher than about 0.1 gram mol per liter. In some preferred embodiments, the concen-tration of quaternary ammonium cations in the solution is at Z least about-Z x 10 3 gram mol per liter but not more than about ~ 5 x 10 2 and, in many cases, not more than about 2 x 10 2 gram '~! mol per liter.
The quaternary ammonium cations that are present in such concentrations are those positively-charged ions in which a nitrogen atom has a valance of five and is directly linked to Z other atoms ~e.g. carbon) satisfying four fifths o~ that valence.
Such cations may be cyclic, as in the case of the piperidiniums, pyrrolidiniums and morpholiniums, but they are generally of the type in which the nitrogen atom is directly linked to a total _ 9 _ 1039~
o~ four monovalent organic groups Erom the group consisting of alkyl or aryl radicals or combinations:thereof. The aryl groups contain typically from six to twelve carbon atoms and preferably only one aromatic ring as in, for example, a phenyl or benzyl radical. The alkyl groups can be straight-chain, branched or cyclic and each typically contains from one to twelve carbon ' atoms. Although quaternary ammonium cations containing a com-bination of such alkyl and aryl groups (e.g. benzyltriethyl-ammonium ions) can be used, many embodiments of the invention are preferably carried out with tetraalkylammonium ions and superior .:
results are generally obtained with the use of those containing at least three C2-C6 alkyl groups and a total of from 8 to 24 carbon atoms in the four alkyl groups, e.g. tetraethyl-, ethyl-tripropyl-, ethyltributyl-, ethyltriamyl-, ethyltrihexyl-, octyl-triethyl-, tetrapropyl-, methyltripropyl-, decyltripropyl-, meth-yltributyl-, tetrabutyl-, amyltributyl-, tetraamyl-, tetrahexyl-, i ethyltrihexyl-, diethyldioctylammonium and many others such as the bis quaternary compounds - e.g. N-trimethyl-Ni-trimethylene-diammonium di-p-toluenesulfonate referred to in the aforecited U.S. Patent Nos. 3,193,481-483 as well as other references such as U.S. Patent 3,689,382 issued September 5, 1972 to Fox et al.
Most practical from the economic standpoint are generally those tetraalkylammonium ions in which each alkyl group contains two to five carbon atoms, e.g. diethyldi~myl-, tetrapropyl-, tetra-butyl-, amyltripropyl-, tetraamylammonium, etc. Such cations can be incorporated into the aqueous solution to be electrolyzed in any convenient manner, e.g. by dissclving the quaternary ammonium hydroxide or a salt thereof in the solution in the ' amount required to provide the desired quaternary ammonium cation concentration.

1.(~39Z~ :
The alkali metal salts whic~ can be employed in the invention are those of sodium, potassium, lithium, cesium and rubidium. Generally preferred for economic reasons are those of lithium and especially sodium and potassium. They may be salts of a monovalent acid, e.g. a perchlorate, a nitrate or a halide such as a chloride or bromide. In some cases, e.g.
where corrosion control is more of a factor, it may be desir-able to use an alkali metal salt of a polyvalent acid, e.g. an orthophosphate, borate, carbonate or sulfate, and particularly an incompletely-substituted salt of that type, i.e. a salt in which the anion has at least one valence thereof satisfied by hydrogen and at least one other valence thereof satisfied by an alkali metal. Examples of such salts include disodium phosphate (Na2HPO4), potassium acid phosphate (KH2PO4), sodium bicar-bonate (NaHCO3), dipotassium borate (K2HBO3), and sodium acid sulfate (NaHSO4). Also useful are the alkali metal salts of ; condensed acids such as pyrophosphoric, metaphosphoric, meta-' boric, pyroboric and the like (e.g. sodium pyrophosphate, potas-sium metaborate, etc.). Depending on the acidity of the aqueous solution to be electrolyzed, the stoichiometric proportions of I such anions and alkali metal cations in the solution may cor-f respond to a mixture of two or more of such salts, e.g. a mixture of sodium acid phosphate and disodium phosphate, and accordingly, such mixture of salts (as well as mixtures of salts of different alkali metals and/or different acids, e.g. phosphoric and boric) are intended to be within the scope of the expressions "alkali , metal salt" and "alkali metal phosphate, borate, perchlorate, carbonate or sulfate" as used in this specification and the appended claims. Any of the alkali metal salts may be dissolved in the a~ueous solution as such or otherwiseJ e.g. as the alkali metal hydroxide and the acid necessary to neutralize the hydroxide to the extent of the desired acidity of the aqueous solution.

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The concentration of alkali metal salt in the solution should be at least sufficient to substantially increase the electrical conductivity of the solution above its conductivity without such a salt being present. In general, there is also enough alkali metal salt dissolved in the solution to provide alkali metal cations constituting more than half of the total ~-weight of all cations in the solution. In most cases, the solution has dissolved therein at least about 0.1% of the alkali I metal salt. More advantageous conductivity levels are achieved ! lo when the solution has dissolved therein at leask about 1~ o~
alkali metal salt or, more pre~erably, at least about 2% of such a salt. In many cases, optimum process conditions include the solution having dissolved therein more than 5% (typically at least 5.5%) of alkali metal salt. The maximum amount of alkali metal salt in the solution is limited only by its solubility therein, which varies with the particular salt employed. With salts such as sodium or potassium phosphates, it is generally ~`
most convenient when the solution contains between about 8% and , about 13~ of such a salt or mixture thereof.
i 20 The acidity of the solution is preferably such that a neutral or alkaline condition prevails at the cathode. Since there is normally an acidity gradient across the cell, pH at the anode can be lower than seven, if desired. In most cases, however, pH o~ the overall solution should be at least about two, is preferably at least about five and when the solution is in contact with certain metals subject to corrosion, is most conveniently at least about seven. Also in most cases, the overall solution pH is not higher than about twelve, typically ¦ not higher than about eleven and, with the use of sodium and/or potassium phosphates, generally not higher than about ten.

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The temperature of the solution may be at any level com-patible with existence as such of the solution itseIf, i.e., above its freezing point but below its boiling point under the pressure employed. Good results can be achieved between about 5 and about 75C. or at even higher temperatures if pressures substantially above one atmosphere are employed. The optimum temperature range will vary with the specific olefinic compound and hydrodimer, among other factors, but in hydrodimerization of acrylonitrile to adiponitrile, an electrolysis temperature between about 25 and about 65C. is usually preferred.
1 Although not necessary, a liquid-impermeable cathode is ; usually preferred. With the use of such a cathode, the aqueous solution to be electrolyzed is generally passed along the sur-face thereof at a linear velocity with reference to the adjacent , cathodic surface of at least about 0.305 meter per second, preferably at least about 0.61 meter per second and even more I preferably between about 0.915 and about 2.44 meters per second ;l although, if desired, a solution velocity up to 6.1 meters per second or higher can be employed, if desired. The gap between the anode and cathode can be very narrow, e.g. about 1.0 milli-meter or less, or as wide as 1.27 centimeters or even wider, but is generally of a width between about 1.52 and about 6.35 milli-meters.
As is well known, electrolytic hydrodimerization of an olefinic compound having a formula as set forth hereinbefore must be carried out in contact with a cathodic surface having a cathode potential sufficient for hydrodimerization of that com-pound. In general, there is no minimum current density with which the process can be carried out at such a cathodic surface but in most cases, a current density of at least about 0.01 amp per square centimeter of the cathodic surface is used and a ~L03~Z9 current density of at least about 0.05 amp per square centimeter of the cathodic surface is usually preferred. Although higher current densities may be practical in some instances, those -; generally employed in the present process are not higher thanabout 1.5 amps per square centimeter ancl ev~n more typically not higher than about 0.75 amp per square centimeter of the afore-described cathodic surface. Depending on other process variables, current densities not higher than about 0.5 amp per square centimeter may be preferred in some embodiments of the invention.
As aforesaid, the process of this invention is carried out with a cathodic surface consisting essentially of cadmium, , meaning that the cathodic surface contains a very high percentage of cadmium (generally at least about 90%, more typically at least about 95% and preferably at least about 98~) but that it may contain a small amount of one or more other constituents -~ that do not alter the nature of the cadmium cathode so as to prevent it from providing the advantages of the present invention, ~ particularly as described herein. Such other constituents, if ;I present, are desirably other materials having relatively high hydrogen overvoltages, e.g. thallium, mercury, manganese, lead, zinc, tin, graphite, etc., but preferably not such materials of relatively low hydrogen overvoltage as copper or nickel in any concentration higher than about 0.05% or, even more desirably, about 0.02% based on the cadmium in the cathodic surface. When such other materials are present in a relatively high concentra-tion such as, for example, from about 0.5% up to about 5% or higher, they are preferably lead and/or mercury. However, best results are generally obtained when the cathodic surface has a cadmium content of at least about 99.5%, even more typically at least about 99.8% and most desirably at least about 99.9% as in ASTM Designation B440-66T (issued 1966). Such proportions i - 14 -~)3~Z91 are expressed, of course, without reference to any constituents of the aqueous solution to be eLectrolyzed although, in operation of the process, certain of those constituents may become asso-ciated with the cathodic surface, either transiently or other-wise, so as to act as a part of the cathodic surface in the sense of having the potential difference between the solution and cathode re~uired for hydrodimerization of the olefinic starting material.
Cathodes employed in this invention can be prepared by any of various techniques such as, for example, electroplating of cadmium on any suitably-shaped substrate of some other mater-ial, e.g. a metal having greater structural rigidity, or by chemically, thermally and/or mechanically bonding a layer of cadmium or an alloy thereof containing one or more of the afore-mentioned other optionally-present cathode constituents to a similar substrate. Alternatively, a plate, sheet, rod or any other suitable configuration consisting essentially of cadmium may be used without such a substrate, if desired.
As aforesaid and contrary to expectations based on the disclosure of British Patent No. 1,014,428, use of the pro-cess embodiments described herein including a cathodic surface consisting essentially of cadmium provides the desired hydrodimer with a high molar selectivity, based on the converted olefinic starting material, and for clearly long enough periods of time for attractive commercial practice of the process. The hydro-dimer selectivity of the present invention, as contrasted with essentially zero in the British Patent No. 1,014,42~ process embodiments using a cadmium cathode, is normally at least about 75~, i.e., at least about 75% of the mols of converted olefinic starting material are converted to the desired dinitrile, dicar-boxylate or dicarboxamide. In many cases, the molar selectivity ~L039~2~
of the present process is at least about 80~ and, in some in-; stances, including certain embodiments employed in hydrodimeriza-tion of acrylonitrile to adiponitrile, as high as 85% or aven higher.
The process of this invention can be satisfactorily carried out in a divided cell having a cation-permeable membrane, diaphragm or the like separating the anode and cathode compart-ments of the cell in such a way that the aqueous solution under- ~-going electrolysis is not in contact with the anode of the cell and products of anode corrosion, if any, are substantially pre-vented from migrating to the cathode of the cell. The process can also be carried out in a cell that is not divided in that manner, i.e., in an electrolytic cell in which the aforedescribed aqueous solution is in contact with the anode of the cell while it is in contact with the cathode of the same cell, and in which the anode is composed of a material not corroded by the solution at a substantial rate (e.g. at least about 10 3 inch per year) such as, for example, one of the materials conventionally regard-ed as corrosion-proof (e.g. platinum, various alloys of platinum, other precious metals and alloys thereof, lead dioxide, carbon, etc.~. In both of such embodiments, anode corrosion products normally do not reach the cathode of the cell in a quantity large enough to plate out on or foul the cathode to a degree sufficient to greatly lower the hydrodimer selectivity of the process and it has been found that the surface smoothness of the cathode is generally not of critical importance to long-term maintenance of high selectivities when that is the case.
In another embodiment, the process of this invention can be carried out in an undivided cell in which the anode is in contact with the aqueous solution~ as aforesaid, and the anode is composed of a material which, depending on process ~onditions ~ 3~2Z9 such as the particular alkali metal salt employed, the solution temperature, etc., may or may not be corroded by the solution ~` at a substantial rate under the electrolysis conditions. Such less corrosion-resistant anode materials include the ferrous metals such as iron and steel, magnetite, nickeI, nickel sili-cide and, in fact, any metal or alloy capable of being passi-vated, particularly if the solution undergoing electrolysis is alkaline or at least not strongly acidic (i.e., pH not substan-; tially below seven). When the process is carried out with an anode comprising such a less corrosion-resistant material in contact with the solution undergoing electrolysis and the anode is substantially corroded under the conditions o~ the process, e.g. such that products of corrosion of the anode become dis-persed in the electrolysis medium and subsequently tend to plate out on and/or foul the cathodic surface to a degree which -would otherwise substantially lower the hydrodimerization , selectivity, it is generally most advantageous for long-term , ¦ maintenance of high hydrodimer selectivities to inhibit such plating out and/or fouling by employing a cathodic surface having a degree of smoothness corresponding to a centerline , average not greater than ~out 90 microinches (2.29 microns) as determined in accordance with the definition of centerline average set forth in American Standard ASA B46.1-1962 (Surface Texture) published by The American Society of Mechanical Engineers, 345 East 47th Street, New York, N.Y. In most cases, the centerline average of the cathodic surface employed in this ~ embodiment of the present process is desirably less than about 70 YI microinches ~1.78 microns), preferably less than about 50 micro-inches (1.27 microns) and, for superior results in many cases, less than about 30 microinches, (1.06 microns) all determined in accordance with the definition in the aforecited ASA

~ ' ' : ~E1139~;2Z9~
-publication. Centerline average, as the term i5 used herein, can be measured by various procedures and typesof apparatus, exemplary of which are the Rank Taylor Hobson Talysurf 4 and ~` the procedures described in the Talysurf 4 Operator's Handbook distributed by Rank Precision Industries Ltd., Metrology Division, P. O. Box 36, Leicester House, Lee Circle, Leicester LEl 9JB, England and in the U.S.A. by Engis Equipment Company, 8035 Austin Avenue, Morton Grove, Illinois 60053. In some embodiments in which anode corrosion may otherwise proceed at a relatively high rate, it may be desirable to also include in the electrolysis medium a small amount (generally between about 0.02~ and about 3%) of an inhibitor of corrosion of the anode material employed (e.g. an alkali metal salt of a boric or ! condensed phosphoric acid when the anode material comprises a ferrous metal) and/or a similarly small amount of a chelating agent for the anode metal (e.g. an alkali metal or ammonium 3 salt of a nitrilocarboxylic acid, such as tetrasodium ;~ ethylenediaminetetraacetate or propionate, trisodium nitrilo-triacetate or the like).
The following specific examples of the process of this invention are included for purposes of illustration only ~ and do not imply any limitations on the scope of the invention.

4 Example I
In a continuous process, an aqeous solution having dissolved therein approximately 1.6% acrylonitrile, 1.2% adiponi-trile, 0.2% acrylonitrile EHD byproducts, 5.8 x 10 gram mol per liter of ethyltributylammonium cations, 10% of a mixture of incompletely-substituted sodium orthophosphates corresponding to the solution pH of 9 (approximately Nal gHl lPO~), 0.1% of a ferrous metal corrosion inhibitor (tetrasodium pyrophosphate) and 0.05% of tetrasodium ethylenediaminetetraacetate was ' ~39~
circulated at 55C. and a velocity between 1.22 and 1.37 meters .~ per second through an undivided electro:Lytic cell having a car-bon steel anode separated by a gap of 2.72 millimeters from a .~ cathodic surface composed of a rolled sheet of cadmium conform-ing to ASTM Designation B440-66T issued 1966 (at least 99.9% Cd) and having a centerline average of about lO microinches (0.25 micron) measured in accordance with the definition set forth in American Standard ASA s46.1-1962. The solution, which also had entrained therein approximately 1% by weight of an organic phase ' lO containing about 5~% adiponitrile, 29~ acrylonitrile, 9% acrylo-~ nitrile EHD byproducts and 8~ water, was electrolyzed as it '~ passed through the cell with a voltage drop across the cell of l 4.7 volts and a current density of 0.27 amp per square centimeter of cathodic surface and then fed into a decanter for equilibra-~¦ tion with an accumulated upper layer having approximately the composition of the aforedescribed organic phase and withdrawal of equilibrated lower (aqueous) layer for recycle through the cell. After 776 hours of electrolysis during which acrylonitrile and water were continuously added to the circulating aqueous '` 20 solution and equivalent amount of product was removed from the .l~ decanter upper layer, it was found that acrylonitrile in thei solution had been converted to adiponitrile with an average molar selectivity of 86.1% and the cathodic surface had cor-roded at the average rate of only 0.076 millimeter per year.
¦ 'Example II . ~:
3 In a continuous process, an aqueous solution having 3 dissolved therein approximately 1.6~ acrylonitrile,1.2% adiponi-'I trile, 0.2% acrylonitrile EHD byproducts, ethyltributylammonium cations in a concentration varying between 9 and 25 x 10 3 gram mol per liter, 9% of a mixture of incompletely-substituted sodium orthophosphates corresponding to the solution pH of 9 (approximately Nal gHl lPO4~, 0.1~ of a ferrous metal corrosion 1 q _ 3139~Z~
inhibitor ~tetrasodium pyrophosphate) and 0.05~ of tetrasodium ethylenediaminetetraacetate was circulated at a temperature between 50 and 55C. and a velocity between 0.914 and 1.22 meters per second through an undivided electrolytic cell having a carbon steel anode separated by a gap of 3.175 millimeters from a cathodic surface composed of a roller sheet of cadmium essentially the same in composition and centerline average as - that employed in Example I. The solution, which also had entrained therein approximately 4~ by weight of an or~anic phase containing about 5~% adiponitrile, 29% acrylonitrile, 9~ ;
acrylonitrile E~ID byproducts and 8% water, was electrolyzed as it passed through the cell with a voltage drop across the cell of 4.5 volts and a current density of 0.23 amp per square cen~
timeter of cathodic surface and then fed into a decanter for equilibration with an accumulated upper layer having approxi-mately the composition of the aforedescribed organic phase and then withdrawal of equilibrated lower (aqueous) layer for re-cycle through the cell. After 325 hours of electrolysis during which acrylonitrile and water were continuously added to the circulating aqueous solution and an equivalent amount of product was removed from the decanter upper layer, it was found that :;
acrylonitrile in the solution had been converted to adiponitrile with an average molar selectivity of 86.1% and the cathodic surface had corroded at the average rate of only 0.051 milli-meter per year.
, ~Example III
In a continuous process, an aqueous solution having dissolved therein approximately 0.8% acrylonitrile, 1.1% adiponi-trile, 0.15~ acrylonitrile EHD byproducts, 8 x 10 3 gram mol per liter of tetrabutylammonium cations, 13~ of a mlxture of incom pletely-substituted sodium orthophosphates corresponding to the Z2~
solution pH of 8 (approximately Nal 7H1 3PO4) and 0.05-0.1% of a ferrous metal corrosion inhibitor (tetrasodium pyrophosphate) was circulated at 50C. and a velocity of 1.22 meters per second through an undivided electrolytic cell having a carbon steel anode separated by a gap of 2.39 millimeters from a cathodic surface composed of a rollea sheet of cadmium essentially the same in composition and centerline average as that employed ; in Examples I and II. The solution, which also had entrained ~;
therein approximately 4% by weight of an organic phase contain-ing about 64% adiponitrile, 17% acrylonitrile, 11% acrylonitrile EHD byproducts and 8% water, was electrolyzed as it passed , through the cell with a voltage drop across the cell of 4.35 ~i volts and a current density of 0.25 amp per square centimeter ~! 0~ cathodic surface and then fed into a decanter for equilibra-tion with an accumulated upper layer having approximately the composition of the aforedescribed organic phase and then with-drawal of equilibrated lower (aqueous) layer for recycle through the cell. After 28 hours of electrolysis during which acrylo-, ~ nitrile and water were continuously added to the circulating aqueous solution and an equivalent amount of product was removed from the decanter upper layer, it was found that acrylonitrile in the solution had been converted to adiponitrile with an ;~ a~erage molar selectivity of 85.8% and corrosion o~ the cathodic ,~
surface had been negligible, i.e., less than 0.025 millimeter per year.
Example IV
In a continuous process, an aqueous solution having dissolved therein approximately 1.7% acrylonitrile, 1.2% adiponi-trile, 0.2% acrylonitrile EHD byproducts, between 2 and 4.8 x 10 3 gram mol per liter of ethyltributylammonium cations, 10%
i of a mixture of incompletely-su~stituted sodium orthophosphates `

.1 ~,, 103~?;~9 having an average formula of approximately Nal 8H1 2PO4, about 0.6~ (17.0 millimols per liter) of tetrasodium ethylenediamine-- tetraacetate and the mixture of sodium borates produced by :. neutralizing orthoboric acid in an amount corresponding to 1.8~
of the solution (0.32 gram atom of boron per liter of the solu-. tion) to the solutlon pH of 8.5 was circulated at a temperature . of 55C. and a velocity of four feet per second through an undi-vided electrolytic cell having an AISI 1020 carbon steel anode separated by a gap of 70 mils from a cathode composed of cad-mium conforming to ASTM Designation B440-66T (at least 99.9% Cd) and having a centerline average of 10-15 microinches measured .~ according to American Standard ASA B~6.1-1962. The solution, which also had dispersed therein approximately 1~.6% by weight of an organic phase containing about 52~ adiponitrile, 31%
" .
' J acrylonitrile, 9~ acrylonitrile EHD byproducts and 8~ water, ,. f , was electrolyzed as it passed through the cell with a voltage ; drop across the cell of 3.95 volts and a current density of ~ 0.185 amp per square centimeter of cathodic surface and then fed into a decanter for equilibration with an accumulated upper 20 layer having the composition of the aforedescribed organic phase and then withdrawal o:E lower (aqueous) layer from the decanter for recycle through the cell as ~ust described.
¦ Throughout the operation of the process and for each Faraday of ., current passed through the cell, 12 grams of lower layer from i the decanter were purged from the system and 0.15 grams of .- tetrasodium ethylenediaminetetraacetate and the mixture of sodium borates produced by neutralizing 0.3 grams of orthoboric acid to the solution pH of 8.5 were added to the system. After 69 hours of electrolysis during which acrylonitrile and water 30 were continuously added to the system and an equivalent amount , ~, 10392;~9 of product was continuously removed from the decanter upper ~ layer, it was found that acrylonitrile in the system had been : converted to adiponitrile with a molar selectivity of 87.8% and . the cathodic surface had corroded at the average rate of only 0.003 inches per year.

'~'.

~3 ':~

Claims (25)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A process for hydrodimerizing an olefinic compound having the formula R2C=CR-X wherein -X is -CN, -CONR2 or -COOR', R is hydrogen or R' and R' is C1-C4 alkyl to prepare a hydro-dimer having the formula X-CHR-CR2-CR2-CHR-X wherein X and R
have the aforesaid significance with a molar selectivity of at least about 75%, which process comprises electrolyzing, at a temperature of 5-75°C, an aqueous solution having dissolved therein about 0.1%-5% by weight of said olefinic compound, quaternary ammonium cations in a concentration of at least about 10-5 gram mol per liter and at least about 0.1% by weight of alkali metal salt and sufficient to provide alkali metal cations constituting more than half of the total weight of all cations in the solution in contact with a cathodic surface having a cathode potential sufficient for hydrodimerization of said ole-finic compound and consisting essentially of cadmium, said electrolysis being carried out with an electric current at a current density of at least about 0.01 amp per square centi-meter of the surface of the anode in contact with the solution.

2. The process of Claim 1, said solution having dissolved therein at least about 2% by weight of alkali metal salt.

3. The process of Claim 1, wherein the olefinic compound is acrylonitrile, said solution having dissolved therein at least about 0.5% by weight of said olefinic compound, at least about 10-4 gram mol per liter of C8-C24 tetraalkylammonium ions containing at least three C2-C6 alkyl groups and at least about 1% by weight of alkali metal phosphate, borate, perchlorate, carbonate or sulfate.

4. The process of Claim 1 or 3, said solution having dis-solved therein not more than about 1.8% by weight of said ole-finic compound.

5. The process of Claim 3, said solution having dissolved therein at least about 2% by weight of alkali metal salt.

6. The process of Claim 3, said solution having dis-solved therein more than 5% by weight of alkali metal salt.

7. A process for hydrodimerizing an olefinic compound having the formula R2C=CR-X wherein -X is -CN, -CONR2 or -COOR', R is hydrogen or R' and R' is C1-C4 alkyl to prepare a hydro-dimer having the formula X-CHR-CR2-CR2-CHR-X wherein X and R
have the aforesaid significance with a molar selectivity of at least about 75%, which process comprises electrolyzing, at a temperature of 5-75°C, an aqueous solution having dissolved therein at least about 0.1% but less than about 5% by weight of said olefinic compound, at least about 0.1% by weight of alkali metal salt and quaternary ammonium cations in a concentration of at least about 10-5 gram mol per liter in contact with a cath-odic surface having a cathode potential sufficient for hydrodi-merization of said olefinic compound and consisting essentially of cadmium, said electrolysis being carried out with an electric current at a current density of at least about 0.01 amp per square centimeter of the surface of the anode in contact with the solution.

8. The process of Claim 7, said solution having dissolved therein not more than about 1.8% by weight of said olefinic compound.

9. The process of Claim 8, said solution having dissolved therein more than 5% by weight of alkali metal salt.

10. The process of Claim 7, wherein the olefinic compound is acrylonitrile, said solution having dissolved therein at least about 0.5% by weight of said olefinic compound, at least about 10-4 gram mol per liter of C8-C24 tetraalkylammonium ions containing at least three C2-C6 alkyl groups and at least about 1% by weight of alkali metal phosphate, borate, perchlorate, carbonate or sulfate.

11. The process of Claim 10, said solution having dissolved therein not more than about 1.8% by weight of said olefinic compound.

12. The process of Claim 11, said solution having dissolved therein more than 5% by weight of alkali metal salt.

13. A process for hydrodimerizing an olefinic compound having the formula R2C=CR-X wherein -X is -CN, -CONR2 or -COOR', R is hydrogen or R' and R' is C1-C4 alkyl to prepare a hydrodimer having the formula X-CHR-CR2-CR2-CHR-X wherein X and R have the aforesaid significance with a molar selectivity of at least about 75%, which process comprises electrolyzing, at a temperature of 5-75°C, an aqueous solution having dissolved therein about 0.1%-5% by weight of said olefinic compound, more than 5% by weight of alkali metal salt and quaternary ammonium cations in a concentra-tion of at least about 10-5 gram mol per liter in contact with a cathodic surface having a cathode potential sufficient for hydro-dimerization of said olefinic compound and consisting essentially of cadmium, said electrolysis being carried out with an electric current at a current density of at least about 0.01 amp per square centimeter of the surface of the anode in contact with the solution.

14. The process of Claim 8, wherein the olefinic compound is acrylonitrile and the alkali metal salt is a phosphate, borate, perchlorate, carbonate or sulfate, said solution having dissolved therein at least about 0.5% by weight of said ole-finic compound and at least about 10-4 gram mol per liter of C8-C24 tetraalkylammonium ions containing at least three C2-C6 alkyl groups.

15. A process for hydrodimerizing an olefinic compound having the formula R2C=CR-X wherein -X is -CN, -CONR2 or -COOR', R is hydrogen or R' and R' is C1-C4 alkyl to prepare a hydrodimer having the formula X-CHR-CR2-CR2-CHR-X wherein X and R have the aforesaid significance with a molar selectivity of at least about 75%, which process comprises electrolyzing, at a tempera-ture of 5-75°C, an aqueous solution having dissolved therein about 0.1%-5% by weight of said olefinic compound, at least about 0.1% by weight of alkali metal salt and quaternary ammonium cations in a concentration of at least about 10-5 gram mol per liter in contact with a cathodic surface having a cathode poten-tial sufficient for hydrodimerization of said olefinic compound and consisting essentially of cadmium, said process being carried out in an electrolytic cell in which the anode is in contact with and corroded by said solution and said cathodic surface has a centerline average smoothness not greater than about 90 micro-inches (2.29 microns), said electrolysis being carried out with an electric current at a current desntiy of at least about 0.01 amp per square centimeter of the surface of the anode in contact with the solution.

16. The process of Claim 15 wherein the anode comprises a ferrous metal and the centerline average smoothness of the cathodic surface is less than about 50 microinches (1.27 microns).

17. The process of Claim 15, wherein the olefinic compound is acrylonitrile, said solution having dissolved therein at least about 0.5% by weight of said olefinic compound, at least about 10-4 gram mol per liter of C8-C24 tetraalkylammonium ions containing at least three C2-C6 alkyl groups and at least about 1% by weight of alkali metal phosphate, borate, perchlorate carbonate or sulfate.

18. The process of Claim 17, wherein the anode comprises a ferrous metal and the centerline average of the cathodic surface is less than about 50 microinches (1.27 microns).

19. A process for hydrodimerizing acrylonitrile to prepare adiponitrile with a molar selectivity of at least about 80%, which comprises electrolyzing an aqueous solution having dis-solved therein from about 0.5 to about 1.8% by weight of acry-lonitrile, at least about 1% by weight of sodium or potassium phosphate and tetra(C2-C5 alkyl)-ammonium ions in a concentra-tion of at least about 10-4 mol per liter in contact with a cathodic surface having a cathode potential sufficient for hy-drodimerization of said olefinic compound and consisting essentially of cadmium with a current density between about 0.01 and about 0.75 amp per square centimeter of said cathodic surface while passing the solution along said cathodic surface at a velocity of at least about 0.61 meter per second, said solution having a pH of at least about 7 and a temperature between about 5° and about 75°C.

20. The process of Claim 19, wherein sodium or potassium ions in the solution constitute more than half of the total weight of all cations in the solution.

21. The process of Claim 20, said solution having dissolved therein at least about 2% by weight of alkali metal salt.

22. The process of Claim 19, said solution having dis-solved therein more than 5% by weight of alkali metal salt.

23. The process of Claim 19, carried out in an electro-lytic cell wherein the anode is in contact with said solution and said cathodic surface has a centerline average smoothness not greater than about 90 microinches (1.27 microns).

24. The process of Claim 19, wherein the anode comprises a ferrous metal and the centerline average smoothness of the cathodic surface is less than about 50 microinches (1.27 microns).

25. The process of Claim 19, said solution having dissolved therein between about 10-3 and 10-1 gram mol per liter of tetra-(C2-C5 alkyl)ammonium ions.