US3088885A - Manufacture of lead organometallic compounds - Google Patents

Description

United States Patent Virginia No Drawing. Filed Dec. 24, 1959, Ser. No. 861,777 4 Claims. (Cl. 204-59) This invention relates to the manufacture of lead organometallio compounds and more particularly to the manufacture and recovery of lead tetrahydrocarbon compound. Illustratively, the invention is ideally suited for the preparation of valuable lead tetraalkyl compounds, especially tetraethyllead, finding wide usage as components for antiknock compositions.

For an extended period, the rtetrahydrocarbon compounds of lead, of which tetraethyllead is a most specific .illustrative and important example, have been manufactured by a reaction of an alkyl halide with a reactive form of lead, such as an alloy of lead with an electropositive metal such as sodium. Illustrative of such a process is the reaction of 4 moles of ethyl chloride with 4 moles of monosodium alloy, which produces, with 100 percent reaction efliciency, 1 mole of tetraethyllead and 3 atoms of lead. It is apparent that this prior process converts only, at the very best, one-fourth of the available lead to the desired lead tetrahydrocarbon product of the reaction. Hence, extensive lead recovery operations, and complex operations for the separation of the tetrahydrocarbon lead from the reaction product mixtures, have heretofore been necessary.

It has recently been discovered that the electrolysis of certain anhydrous organometallic compositions provides a highly effective technique for the synthesis of tetrahydrocarbon lead compound directly from lead metal. In such an operation, an electrolyte is employed comp-rising one or more components which are complex organometallic compounds containing a plurality of metals. The electrolyte is electrolyzed in the presence of a lead anode, resulting in the direct formation of the desired lead organometallic product. Illustrative of such a process is the electrolysis of an electrolyte comprising a mixture of, for example, sodium aluminum tetramethyl and sodium aluminum tetraethyl, which electrolysis results in the formation of tetraethyllead. The operation also inevitably results in the electrolytic release of a corresponding quantity of an organometallic component derived from the electrolyte itself, viz., in the illustrative example above, aluminum triethyl. In most instances, the co-released organometallic component is completely miscible with the lead tetr-ahydrocarbon product formed adjacent or at the anode, hence a significant separation problem has existed. It is difficult, and relatively expensive, to separate the tetraorganolead product and a second organometallic component derived from the electrolyte. Distillation is sometimes employed, but in many instances the physical properties are not sufficiently dissimilar to admit of a sharp and efiective separation.

A need thus exists for an electrolytic process coupled with or in conjunction with a highly practical and effective separation step which will readily and economically allow the resolution of the products or components resulting from an electrolysis, into a desired lead tetrahydrocarbon product and another component which is recoverable or reutilizable in the process or for other purposes.

A principal object of the present invention, then, is to provide a new and improved process comprising, in combination, an electrolysis of an 'organometallic electrolyte resembling a fused salt electrolyte, in the presence of a lead anode, in conjunction with an efiicient and economical recovery operation. More particularly, a specific ice object of the present invention is to provide a process whereby a lead tetrahydrocarbon product is formed electrolytically, employing any anhydrous electrolyte, and concurrently an organometallic compound derived from the electrolyte is released in a mixture therewith, and said mixture is further treated to allow ready separation of a lead tetrahydrocarbon product of a high degree of purity. An additional object of the present invention, or particularly of the most highly effective embodiments, is to provide, in combination, an electrolysis, a lead tetrahydrocarbon separation step, and a regeneration of the organometallic component separated from the lead tetrahydrocarbon product component. Other objects will appear hereinafter.

In its most general form, the present invention comprises the electrolysis of an organometallic electrolyte in the presence of a lead anode, resulting in the formation of a mixture of a desired lead tetrahydrocarbon compound and an organometallic compound released by the electrolysis. The step indicated is followed by the treatment of the mixture so formed, within or without the confines of the electrolysis zone, with a complexing agent which selectively reacts or complexes with the non-lead organometallic component of the mixture. This complex treatment is further utilizable in several ways, viz., the so formed complex is readily separable as such as a separate phase, or is a complex miscible with the lead compound as a single phase which admits of separation of the lead tetrahyclrocarbon compound by purely physical means, or, last, is particularly susceptible to a chemical treatment involving a selective reaction with the complex. Thus, in all forms of the invention, the anodic product of the electrolysis step is further treated with a complexing material capable of complexing with the nonlead compound present, and this complexing step can be carried out within the general confines of the electrolysis zone, or, preferably, the lead tetrahydrocarbon compositions can be withdrawn and the complexing step conducted in a separate zone. The necessary treatment with a complexing agent is carried out under such conditions that the lead tetrahydrocarbon product is not appreciably attacked by the complexing agent.

The electrolyte for the electrolysis step includes at least one, and usually two, compounds or components which are bimetallic organometallic complexes, the metals thereof being a strongly electro-positive metal such as an alkali metal, and a metal of Group III of the periodic system, particularly an aluminum sub-group metal, such as aluminum, gallium, indim or thallim. The organo radicals of at least one of the electrolyte components include a plurality of hydrocarbon radicals which correspond to the radicals desired on the lead tetrahydrocarbon product. Illustrative components of the electrolyte are sodium aluminum tetraethyl or sodium aluminum tetra-isopropyl,'although numerous other components can be used as is shown hereinafter.

The lead tetrahydrocarbon compounds suitable for production by the present invention include the lead tetraalkyls wherein the alkyl groups contain up to, for example, 16 carbon atoms. Those compounds having lower alkyl substituents, of up to four carbon atoms are the preferred products, including, for example lead tetra ethyl, lead teramethyl, lead tetra-isopropyl, lead tetraisobutyl, as well as those members ofthe group having mixed alkyl substituents, such as lead dimethyl diethyl, and lead diethyl diisopropyl. The process contemplates production of lead products having cycloalkyl, a-ryl, aralkyl or alkaryl substituents. However, the aryl or substituted aryl, substitu-ent, lead compounds are high melting. Hence, ordinarily only one or two aryl radicals on the molecule are preferred. Thus, in preparing tetraethyllead, a plurality of ethyl groups, is present as organo radicals on an electrolyte component. The mixture released by the electrolysis is, most frequently, a liquid 'phase including the lead tetrahydrocarbon product plus a group III-A metal trihydrocarbon product.

The complexing agents of the invention, viz., those compounds with which the mixture released in the electrolysis is treated, include, in the most effective operations, the hydrides of the alkali metals, but the invention is not thus rigorously limited. In certain instances, hydrides of alkaline earth metals can be employed, and in other cases,

certain alkali metal halides are suitable.

After formation of the complex, the treated system is further processed in one of the modes already indicated, all of these several modes being directed to separating the lead tetrahydrocarbon product as such.

The techniques of the invention and the mode of ob- :taining its benefits will be clear from the following examples, wherein concentrations are given in weight per cent, unless otherwise specified.

Example I In this operation, a closed cell was provided with an annular steel cathode and an axially positioned lead anode. An electrolyte was provided in this cell comprising equimolar proportions of sodium aluminum tetramethyl and sodium aluminum tetraethyl. The cell was heated to a temperature of about 100 C. and a potential of 3.6 volts was applied across the electrodes, resulting, during opera- 7 tion in a current density of 250 milliamps per square cent-imeter. Tetraethyllead was produced at the anode and separated as a liquid insoluble in the electrolyte mixture. In addition to the tetraethyllead, a substantial quantity of aluminum trialkyl, principally triethylaluminum, was coreleased and dissolved in or with the tetraethyllead. The lead tetraethyl and aluminum alkyls, predominantly triethyl aluminum, consisted of roughly about 40- percent tetraethyllead and 60 percent aluminum alkyl. The liquid mixture is Withdrawn from the electrolyte zone, and is treated, at a temperature of about 50 C., with solid sodium hydride, in the proportions of at least about 6.2 parts-perlOO parts of the mixture, this corresponding to at least one-half mole of sodium hydride per mole of the trialkyl aluminum component. The sodium hydride promptly dissolves in the mixture and reacts with the aluminum alkylcomponent, forming a separate homogeneous, liquid phase. This complex is removed by straightforward mechanical manipulation, i.e., decanting, leaving the tetraethyllead as a substantially pure product. The 1 thus separated complex is available for other purposes, or

for regeneration and recycle.

In many cases, the electrolyte employed in the electrolytic step of the process includes a plurality of alkali metals, as in the following example.

Example I] In this operation, the electrolyte was substantially the same as in the preceding example except that the corresponding potassium compounds are substituted for a total of A, on a mole basis, of the electrolyte complex components. Upon electrolysis, at a temperature of about 80 C., a good deposition of tetraethyllead, accompanied by aluminum triethyl or other trialkyl aluminum components, was realized, the current etficiency being again of the order of about 80 percent.

The liquid phase including the tetraethyllead in the aluminum trialkyl is withdrawn from the electrolyte compartment, and is treated, at only moderate temperatures of 40 60 C., with a mixture of sodium hydride and potassium hydride, the treating components corresponding in molar ratio, of sodium to potassium, to the sodium and potassium ratio of the alkali metal deposition at the cathode of the electrolytic step.

Again, the alkali metal hydride treating agent rapidly dissolves in and reacts with the aluminum triethyl comco-release of substantial quantities of aluminum tri-iso- .from the lead tetraisopropyl. On the other hand, when Example III In this operation the electrolyte consists of a mixture of potassium aluminum tetramethyl and potassium aluminum tetraisopropyl, in the proportions of, respectively, 8:1 on a molal basis. Upon electrolysis by passage of direct current therethrough, at a temperature of the orderyof about C., a good conversion of the lead anode to lead tetraisopropyl is achieved, accompanied by propyl. The lead tetraisopropyl and aluminum tri-isopropyl mixture is withdrawn as a single liquid phase from the electrolyte compartment, and treated with sodium hydride, lithium hydride, or cesium hydride, in the proportions of from at least about /2 mole of the alkali metal hydride up to about 1 mole of the alkali metal hydride. When the alkali metal hydride is provided at or near the lower limit of the above described range, the complex formed is a liquid which is readily separable the proportion of the alkali metal hydride is increased to about a range of about one mole per mole of aluminum tri-isopropyl, usually a solid complex is precipitated out.

-In both cases, the tetraisopropyllead is readily separated therefrom.

Example IV In this operation the electrolyte comprises a mixture of rubidium aluminum tetramethyl and sodium aluminum tetramethyl, in the molal proportions of 1:6, respectively.

-The electrolyte also contains some concentration of a .liquid or low melting hydrocarbon, such as methylated naphthalenes.

Electrolysis is conducted at a temperature. of about C., with a relatively low current den- .sity of the order'of about 15 milliamps per square centimeter. Lead tetramethyl and aluminum trimethyl are jointly released, the cathode product being predominantly metallic sodium, which is liquid at the temperature of operation. The lead tetraorgano containing liquid product alsocontains a certain amount of the aromatic dissolved therein. The liquid solution is withdrawn and 7 treated with sodium hydride, in the proportions of at least about /2 mole per mole of the aluminum trimethyl. Again a separate phase complex is readily formed which is easily separable from the lead tetramethyl.

Example V Inthis operation, the electrolyte corresponds to the electrolyte of Example I, plus a small amount of addi tional calcium aluminum tetraethyl. On carrying out the electrolysis as before, again a mixture of tetraethylleadand aluminum triethyl is formed adjacent the anode and is separately withdrawable from the system. Calcium hydride is employed, or alternatively, a mixture of calcium hydride and sodium hydride, in the molal proportions corresponding to the mixture of sodium and calcium which is released at the cathode in the electrolysis .step. A complex, varying in properties from being an immiscible liquid to an insoluble solid, dependent upon the ratio of the electropositive metal hydride to the aluminum trialkyl, is separated from the tetraethyllead product, and separation can be achieved by decanting or filtration.

The following example illustrates the present process tively stable aromatic organic liquids. this component assures high fluidity of the electrolyte at component.

Example VI In this example, the electrolyte includes sodium boron I tetraphenyl and sodium aluminum tetraethyl, in approximately molal proportions of 2 to 3. The electrolyte is electrolyzed at a temperature of about 110 C., with a lead anode, as in preceding examples. An anode product comprising a lead tetrahydrocarbon liquid, with phenyl and ethyl radicals, is produced. About 1 percent naphthalene is provided to the anodic product to minimize thermal decomposition. The lead tetrahydrocarbon product is accompanied or admixed with about four moles of a mixture of boron triphenyl and aluminum triethyl.

The above anodic product mixture is withdrawn from the electrolysis Zone and sodium hydride is added, in the proportions of about 2 moles per 4 moles of the boron tri-phenyl and aluminum triethyl. A separation of the system into two liquid phases occurs, the lead tetrahydrocarbon liquid phase being readily withdrawable.

In addition to the aryl substituted lead products, the process is adaptable to the production of substituted aliphatics, as in the following example.

Example VII In this operation, the electrolyte comprises sodium aluminum tetrabenzyl and potassium aluminum tetrabenzyl, in varying proportions. In addition, the electrolyte includes approximately weight percent of an aromatic which can be selected from the group, for example, of biphenyl, naphthalene, toluene, and various other rela- The presence of relatively low temperatures. Electrolysis is carried out with a moderate current density and results in release at the anode of a mixture of lead tetrabenzyl and aluminum tribenzyl. These components being relatively high melting, a stream of selective solvent can be provided adjacent the anode to dissolve the anodic product and allow its discharge from the electrolysis zone. Care should be taken in such cases to minimize interfacial contact with the electrolyte, to minimize. mixing of the solvent with the electrolyte.

In the foregoing example, the complexed phase, produced to facilitate recovery of the lead tetrabenzyl product, is not readily regeneratable to form the electrolyte The example following, however,,describes an embodiment particularly susceptible to an integrated operation including recovery of the non-lead components and reconversion to the necessary electrolyte components.

Example VIII In this operation, the electrolyte comprises an equimolal mixture of sodium aluminum tetra beta phenylethyl and potassium aluminum tetra-beta phenyl ethyl. On

electrolysis, in the presence of a lead anode, an anode sulting in formation of a separate phase of the lead prod not and a liquid complex phase. The latter, after separation from the lead compound, is reacted with additional sodium and potassium hydride, and is thereafter or concurrently reacted with styrene, regenerating the electrolyte component. The hydrides employed in this operation are obtained by pressure hydrogenations of the cathode product, potassium-sodium alloy, of the electrolysis operation. 1

Example IX The operation of Example I is repeated, except that the electrolyte is a mixture of sodium aluminum tetracyclohexyl and potassium aluminum tetracyclohexyl. Comparable results are achieved, viz., deposition of lead tetracyclohexyl plus aluminum tricyclohexyl, and the latter is readily complexed with an alkali or alkaline earth metal hydride and is separated from the lead containing component.

The eletcrolyte of the electrolytic step is not necessarily a mixture of simple components, but can be a relatively low melting tetraalkyl complex material, wherein the alkyl groups are different, as in Example X below.

Example X The operation of the preceding examples is repeated, except that the electrolyte is a homogeneous material comprising sodium aluminum dimethyl diethyl. It is found that electrolysis of this system results in release of lead tetraethyl and triethylaluminum, with only minor or insignificant quantities of methylated lead compounds present in the anodic product.

The anode liquid product is treated, either immediately as formed within the cell confines, or after withdrawal and in a separate vessel, with sodium hydride in the proportions of about per mole of the triethyl aluminum.

Aluminum, by virtue of its low price and ready availability, is the most common component, or group III-A metal component, of the electrolyte system, the principles of the invention are adaptable when other members of this group of metals in the periodic arrangement of the elements are employed as in the example below.

Example XI The operations of the preceding examples are repeated, except that a gallium, indium, or thallium component are substituted corresponding to the aluminum complex component specifically illustrated. Similar results are achieved.

As a further illustration of the applicability of the process to difierent lead tetraalkyl products, the following example is illustrative.

Example XII The electrolyte here employed is an equimolar mixture of sodium aluminum tetraisobutyl and potassium aluminum tetraisobutyl. The mixture is again electrolyzed, generally as in preceding examples, and the anodic product is a liquid mixture of lead tetraisobutyl and triisobutyl aluminum. Treatment of this mixture with lithium hydride, potassium hydride, sodium hydride, cesium hydride, or mixtures thereof, results in formation of a readily separable material from the mixture with the lead tetraisobutyl.

As clear from the preceding examples, the alkali metal hydrides are the preferred reagents for treating the anodic product of the electrolysis step. This step is not solimited however and other reagents can be employed when desired. Certain metal halides, particularly the alkalimetal fluorides, can be used for this purpose, as in the example below.

Example XIII Electrolysis is conducted as in Example I, providing an anodic product having the approximate composition of one mole of lead tetraethyl to four moles of aluminum triethyl. This liquid is treated with sodium fluoride at about 60 C., in the proportion of about 19 parts of sodium fluoride to parts of the triethyl aluminum. A liquid phase is rapidly formed by reaction of the sodium fluoride with the aluminum triethyl, this liquid promptly stratifying from the lead tetraethyl.

Example XIV In this instance, the electrolyte includes the complex and solvent separation.

sodium aluminum triethyl ethoxide, which, when elec ablew into separable phases comprising the lead tetraalkyl and the aluminum component by treating with sodium hydride in the proportions of at least /2 mole per mole 'of the aluminum component of the mixture.

As previously mentioned, the benefits of the invention are of particular importance in those operations wherein a working installation of such an embodiment wherein the recovery step is followed by appropriate regeneration and reuse of the aluminum component.

Example XV In this process installation, a variety of individual reactions or steps are performed, viz. electrolysis, separation of the lead alkyl and aluminum trialkyl components, secondary complexing, addition of ethylene to complex Proportions given below are relative to final production of one mole of tetraethyllead, viz. 323 pounds. A parallel group of operations is required, namely the treatment of sodium metal obtained as a cathodic product to form sodium hydride.

In the electrolysis operation, an electrolyte corresponding to that employed in Example I, viz, an equimolal mixture of sodium aluminum tetramethyl and sodium aluminum tetraethyl is provided. The electrolyte is subjected to electrolysis at a temperature of about 100 C., and an anodic product consisting of lead tetraethyl and aluminum triethyl is formed and is withdrawn from the electrolyte zone, in proportions of about 775 parts, in

which the tetraethyylead is present in a concentration of about 40 percent. Concurrently with the withdrawal of the said anodic product, a stream of liquid sodium corresponding to about 90 parts is continuously withdrawn. (The anode product is passed to an initial complexing step, in which approximately 48 pounds of sub-divided sodium hydride is added. The sodium hydride promptly enters into solution, at only moderate temperatures, re-

, sulting in the formation of a separate liquid phase containing substantially all the aluminum complex, and leaving the tetraethyllead as a relative high purity bottom percent solution in the aromatic hydrocarbon, is passed to an ethylene addition step. In this operation, gaseous ethylene is charged to react with the hydride bonds existent therein, forming sodium aluminum tetraethyl in good yield, this complex remaining in solution as approximately a 67 percent solution. Said solution is then passed to an evaporator, in which substantially all the solvent is distilled away, and the sodium aluminum tetraethyl is available for feeding to the electrolysis as a make-up to the electrolyte.

Concurrently with the foregoing operation, the sodium metal withdrawn from the electrolysis zone as a cathodic product is charged to a hydriding operation. In this operation, molecular hydrogen is reacted with the elemental sodium, preferably at elevated pressure and in the presence of minor quantities of certain dispersing agents to form sodium hydride. Approximately one-half of ide, and the like.

8 this sodium hydrideis fed to the complexing-stratifying step heretofore described, and the other half is fed to the secondary complexing and solvation operation already described.

It will be readily apparent to those skilled in the art that all of the foregoing operations can be conducted in a continuous manner. On the other hand, if desired, the individual steps can be operated cyclically when such operation is more efiicient. It will be further understood that depending upon the efiiciency of reaction and recovery in each of the discrete steps of the process, various 'make-up components will be required to maintain the process in balance. Normally, however, a high conversion of the lead supplied to the process as the anode material of the order of 70 to percent is realized. Similar effectiveness is encountered with respect to the other basic feed components, viz. hydrogen and ethylene.

From the preceding description and examples, it will be seen that the embodiments of the present invention which are greatly preferred involve a separation operation followed by separate treatments to regenerate a desired electrolyte component. Considerable variation is possible, however, supplementing the complexing treatment of the lead tetrahydrocarbon-Group III-A metal organometallic mixture. For example, the complexing agent can be added in such proportions that it forms a normally solid phase. This phase can be separated by, for example, filtration, and then regenerated. Thus, in the mixture of lead tetraethyl and aluminum triethyl, an alkali metal hydride can be added in equimolal proportions to the mixture, forming a normally solid complex, sodium aluminum triethyl hydride. This material can then be removed by filtration, dissolved in hot toluene, and reacted with ethylene gas to provide sodium aluminum tetraethyl. Another variation, with the same system, involves concurrently introducing sodium hydride and ethylene gas to the anodic product mixture, resulting in formation of sodium aluminum tetraethyl and its precipitation.

In addition to the metal hydrides, and certain metal halides illustrated by the foregoing examples, numerous other complexing agents can be used. Illustrative materials thus qualified are the organometallic compounds of the alkali and alkaline earth metals, such as sodium ethyl, lithium ethyl, potassium ethyl, magnesium diethyl, magnesium ethyl chloride, sodium phenyl, sodium acetyl- Certain pseudo halides, such as the cyanides, amides, or thiocyam'des of sodium, lithium, magnesium or calcium, can be successfully employed instead of an alkali metal hydride.

While the lead tetraalkyl compounds, in which the alkyl groups are lower 'alkyls of 1 to 4 carbon atoms, are the most commercially significant products of the process, it is not thus limited. Other lead tetrahydrocarbon compounds, in addition to those illustrated by the examples above, are lead tetrahexyl, lead tetraoctyl, etc.

The electrolysis step of the present process can be carried out with considerable latitude in operating conditions. Generally, it is desired to carry out the electrolysis at as low a temperature as is feasible, but the operation is fully feasible at temperatures ranging from about as low as 0 up to about 200 C. The upper temperature of this portion of the process is usually limited by the decomposition temperature of the lead tetraorgano product obtained, although this is not a rigorous limitation owing to availability of an improvement in the decomposition characteristics with the use of certain thermal stabilizers. However, with tetraethyllead, for example, and with no thermal stabilizer, it is preferred to operate below C., and preferably not over C. Another limiting factor under certain circumstances, at least with respect to the preferred embodiments of the process, is the melting point of the metal cathodic product coreleased in the process. Thus, if the electrolyte components contain only sodium as the electropositive metal (in addition to the group III-A portion) then the temperature should be above or about 100 C., to provide the sodium in the liquid phase thereby allowing its ready withdrawal. On the other hand, mixtures of the alkali metals, formed as low melting alloys, which can be liquid at temperatures below room temperature. In cases in which the cathodic metal product jointly released is a solid, the process is still quite operable, but is complicated by the necessity of removal from the electrolysis zone of these solid materials.

The pressure of operation of the electrolysis zone is usually at or about atmospheric pressure. The salt-like components of the electrolyte, as such, have very low vapor pressures or substantially no vapor pressure, hence pressure to preserve the electrolyte components in the liquid phase is unnecessary. On the other hand, the lead tetraorgano products, particularly when the organo radicals are lower alkyl groups, have very significant vapor pressures, but maintaining a closed electrolysis zone prevents loss by vaporizing.

Various apparatus configurations are quite suitable for the electrolysis step as such. Generally, it is highly desirable to provide the lead anode in a shape having a relatively high surface-mass proportion. In other words, inasmuch as the lead tetraorgano product is formed electrolytically at the surface of the anode, a high surface shape is desirable, such as thin cylinders, plates, or the like. Since the load anode is, in effect, a reactant in the process, in the most preferred operations, provision is made for rapid addition of new or fresh anodes, or for continuous feeding of an anode shape. For example, the lead anode may be fed to the electrolysis zone by unwinding a coil of thin strip, the portion of the strip within the zone forming the actual electrolyte anode.

With respect to the current density employed in the electrolysis, and the voltage of current applied, these variables are also subject to considerable variation. It will be understood that the current density is a function of the conductivity of the electrolyte system and of the voltage impressed and of the length of the electrolyte pass. Voltages of the order of 4 to about 20 volts are frequently used, and current densities from as low as 5 up to 300 milliamps per square centimeter can be employed.

Frequently, it is highly desirable to provide a small amount of a thermal stabilizer to be admixed or dissolved in the tetraethyllead or other lead tetraorgano product substantially immediately upon its formation and collection for withdrawal from the electrolysis zone. A large number of effective stabilizers are disclosed in United States Patents 2,660,591 through 2,660,596, inelusive. A representative group of thermal stabilizers which can be used in accordance with this invention are butadiene, di-amylene, di-pentene, heptene, trimethylethylene, styrene, divinylbenzene, cyclohexene, dicyclopentadiene, azobenzene, 2,2'-azonaphthalene, anthracene, chrysene, naphthalene, alpha-methyl naphthalene, tetrahydronaphthalene, indene, di-isobutylene, tetramethylene, semi-carbazide, stilbene, methyl styrene, oethylstyrene, and lepidine. These stabilizers are normally used in amounts varying from 0.0 1 to about 5 percent by weight of the tetraorganolead compound and greatly increase the stability of the lead compound at more elevated temperatures. When a thermal stabilizer is used and particularly when the stabilizer consists of an aromatic hydrocarbon type compound, it is preferably introduced at the point at which the tetrahydrocarbon lead product is accumulated in the zone. In most cases a collection sump or receptacle is provided to accumulate the tetrahydrocarbon lead product for removal as a discrete stream to another operation of the process. By employing this technique, solution of the thermal stabilizer in the electrolyte composition, as such, is avoided. Anhydrous solvent materials are frequently desirable or and especially sodium and potassium, can be necessary for the most effective operation of the process, either in the electrolysis, or in the subsequent steps.

Certain precautions in the use of solvents are necessary, controlled by the following principles. Solvents should not be used in the electrolysis, unless necessary to accomplish a melting point reduction, because hydrocarbon solvents reduce the conductivity of the electro lyte. In addition, frequently, the anodic product mixture is also soluble in such a solvent, so particular care must be taken so that the solvent does not solubilize the lead tetraorgano product in the electrolyte bath. By appropriate adjustment of the selection and proportions of the solvent, the anode products can be withdrawn quite efficiently. Generally, the lead tetrahydrocarbon compounds and the concurring metal organic, are somewhat more soluble in aliphatics than the complex components of the electrolyte bath. Hence, it is frequently feasible to dissolve or dilute the anode products on a more-orless selective basis. In the majority of installations of the process, viz., when manufacturing a lead tetraethyl with up to four carbon atoms in the alkyl groups, solvents are not required.

This application is a continuation-in-part of my prior application Serial No. 827,444, filed July 16, 1959.

I claim:

1. A process for the manufacture and recovery of a lead tetraalkyl compound, the alkyl radicals thereof having at least two carbon atoms, comprising (a) electrolyzing in the presence of a lead anode a bimetallic organometallic complex consisting of an alkali metal, aluminum, and organo radicals selected from the group consisting of alkyl and alkoxide, and having at least three alkyl groups including at least one alkyl corresponding to the alkyl groups of the desired lead tetraalkyllead compound, forming thereby as the cathode product the alkali metal and an anode product consisting essentially of the lead tetraalkyl compound having in admixture therewith an aluminum triorgano compound selected from the group consisting of trialkyl aluminum and dialkyl aluminum alkoxide,

(b) hydriding the alkali metal cathode product from (a) and forming thereby the corresponding alkali metal hydride,

(0) adding to the anode product from (a), the alkali metal hydride from (b) and reacting with the aluminum triorgano component in the anode product and forming thereby a separate phase alkali metal aluminum triorganohydride complex insoluble in the lead tetraalkyl compound,

(d) separating the lead tetraalkyl and the alkali metal aluminum triorganohydride complex, and

(e) reacting the alkali metal aluminum triorganohydride complex from (d) with an olefin corre sponding to the alkyl of the lead tetraalkyl product, and converting thereby the said complex to the bimetallic organ-ometallic complex electrolyzed, and returning to the electrolysis zone.

2. A process for the manufacture and recovery of a lead tetraalkyl compound, the alkyl radicals thereof having at least two carbon atoms, said process comprising (a) electrolyzing in the presence of a lead anode an alkali metal aluminum tetraalkyl electrolyte, wherein at least one of the alkyl groups of the electrolyte has at least two carbon atoms, forming as the cathode product the alkali metal and an anode product consisting essentially of the lead tetraalkyl having trialkyl aluminum dissolved therein,

(b) hydriding the alkali metal from (a) and forming thereby the corresponding alkali metal hydride,

(0) adding to the anode product from (a) the alkali metal hydride from (b), and reacting with the trialkyl aluminum in the anode product and forming a separate phase alkali metal trialkyl aluminum hy- 'dride complex insoluble in' the lead tetraalkyl compound,

(d) separating the lead tetraalkyl and the alkali metal trialkyl aluminum hydride complex, and

(e) reacting the alkali metal aluminum trialkyl hydride complex from (d) with an olefin corresponding to the alkyl of the tetraaalkyllead product and converting thereby the said complex to alkali metal aluminum tetraalkyl, and returning said alkali metal aluminum tetraalkyl to the electrolysis zone.

3. 'The process of claim 2 wherein the lead tetraalkyl is lead tetraethyl, the alkali metal aluminum tetraaalkyl v electrolyte is sodium aluminum tetraalkyl, the alkyl groups thereof being methyl and ethyl groups.

' 4. The process of claim 2 wherein the lead tetraalkyl is lead 'tetraethyl, and the electrolyte alkali metal alu- 2,786,860 Ziegler et a1. Mar. 26, 1957 2,985,568 Ziegler et al. May 23, 1961 3,028,325 Pinkerton Apr. 3, 196Q FOREIGN PATENTS 797,093 Great Britain June 25, 1958 OTHER REFERENCES Chemical Reviews, vol. 54 (October 1954), pages 844- 845.

Claims (1)

1. A PROCESS FOR THE MANUFACTURE AND RECOVERY OF A LEAD TETRAALKYL COMPOUND, THE ALKYL RADICALS THEREOF HAVING AT LEAST TWO CARBON ATOMS, COMPROSING (A) ELECTROLYZING IN THE PRESENCE OF A LEAD ANODE A BIMETALLIC ORGANOMETALLIC COMPLEX CONSISTING OF AN ALKALI METAL, ALUMINUM, AND ORGANO RADICALS SELECTED FROM THE GROUP CONSISTING OF ALKYL AND ALKOXIDE, AND HAVING AT LEAST THREE ALKYL GROUPS INCLUDING AT LEAST ONE ALKYL CORRESPONDING TO THE ALKYL GROUPS OF THE DESIRED LEAD TETRALKYLED COMPOUND, FORMING THEREBY AS THE CATHODE PRODUCT THE ALKALI METAL AND AND ANODE PRODUCT CONSISTING ESSENTIALLY OF THE LEAD TETRAALKYL COMPOUND HAVING IN ADMIXTURE THEREWITH AN ALUMINUM TRIORGANO COMPOUND SELECTED FROM THE GROUP CONSISTING OF TRIALKYL ALUMINUM AND DIALKYL ALUMINUM ALKOXIDE, (B) HYDRIDING THE ALKALI METAL CATHODE PRODUCT FROM (A) AND FORMING THEREBY THE CORRESPONDING ALKALI METAL HYDRIDE, (C) ADDING TO THE ANODE PRODUCT FROM (A), THE ALKALI METAL HYDRIDE FROM (B) AND REACTING WITH THE ALUMINUM TRIOGANO COMPONENT IN THE ANODE PRODUCT AND FORMING THEREBY A SEPARATE PHASE ALKALI METAL ALUMINUM TRIOGRANOHYDRIDE COMPLEX INSOLUBLE IN THE LEAD TETRAALKYL COMPOUND, (D) SEPARATING THE LEAD TETRAALKYL AND THE ALKALI METAL ALUMINUM TRIORGANOHYDRIDE COMPLEX, AND (E) REACTING THE ALKALI METAL ALUMINUM TRIOGANOHYDRIDE COMPLEX FROM (D) WITH AN OLEFIN CORRESPONDING TO THE ALKYL OF THE LEAD TETRAALKYL PRODUCT, AND COVERING THEREBY THE SAID COMPLEX TO THE BIMETALLIC ORGANOMETALLIC COMPLEX ELECTROLYZED, AND RETURNING TO THE ELECTROLYSIS ZONE.