US2535190A

US2535190A - Manufacture of alkyllead compounds

Info

Publication number: US2535190A
Application number: US85053A
Authority: US
Inventors: Calingaert George; Shapiro Hymin
Original assignee: Ethyl Corp
Current assignee: Ethyl Corp
Priority date: 1949-04-01
Filing date: 1949-04-01
Publication date: 1950-12-26
Anticipated expiration: 1967-12-26
Also published as: FR997064A; DE888696C; GB673871A

Description

Patented Dec. 26, 1950 UNITED STATES PATENT OFFICE N Drawing. Application April 1, 1949, Serial No. 85,053

4 Claims. (01. 260-437) This invention relates to a process for the manufacture of alkyllead compounds. More specifically our invention is directed to an improved process for the manufacture of tetraethyllead.

The process employed in present commercial practice for the manufacture of tetraethyllead, has been in use for a number of years and, in general, is satisfactory. However, it has certain disadvantages which are overcome by practicing our invention. It proceeds by reacting a so dium-lead alloy, of composition controlled to correspond substantially to NaPb, with ethyl chloride according to the following equation:

With the highest yields obtained thereby, only about 22 per cent of the lead present in the NaPb alloy is converted to tetraethyllead. Under conditions of best operation no one heretofore, as far as we are aware, has been able to increase this yield of tetraethyllead by even a few per cent, due to the inherent limitation in yield as is apparent from the consideration of the above equation. It should be noted that in this reaction at least 75% of the lead originally employed is not alkylated. Thus in this reaction, large quantities of lead must be recovered and reprocessed to NaPb alloy in order to make it economical. A further disadvantage of such a large quantity of unreacted lead is that valuable reaction space in the reaction vessel is cocupied by materials which are essentially inert for the manufacture of tetraethyllead under present conditions and mode of operation. Despite these facts the present commercial operation is a more efficient and desirable process than any based upon the Grignard reaction due in part to the high cost of lead chloride and the expense involved in reconverting the free lead to lead chloride.

Various other processes for the production of alkyllead compounds have been described in the literature. For the most part, however, these prior art methods are subject to the same disadvantage that very large amounts of the lead alloy or lead salt entering into the reaction are converted to free lead instead of the desired alkyllead compound. For example, the wellknown Grignard reaction has been suggested frequently for the manufacture of these compounds, as exemplified by U. S. Patents Nos. 1,690,075; 1,705,723; 1,798,593; 1,805,756; 1,863,451; 1,949,948, and other United States or foreign patents of a similar nature. While these patents attempt to improve the efficiency of the Grignard reaction upon which they are dependent, they are all subject to the disadvantage that even though the yield approaches the theoretical, 50% or more of the lead which enters into the reaction is not converted to alkyllead but is left as free lead. It is evident from a consideration of the following equation that a maximum of 50% of the lead in the lead chloride can be converted to tetraethyllead;

The free lead produced in the above reaction will not react with additional quantities of C2H5MgCl and thus it must be recovered, purified, and if reused, converted to lead chloride. This is tedious, expensive and inefilcient. In part, it accounts for the fact that, so far as we are aware, the Grignard reaction has never been applied to any extent commercially to the production of tetraethyllead or any other organic lead compound.

It is therefore an object of our invention to provide a process for the manufacture of alkyllead compounds which overcomes the above objections to the present commercial process and which is far superior to the Grignard process. Particularly it is an object of our invention to increase the conversion of lead to tetraethyllead above that obtained in the present commercial practice. Another object of ourinvention is to increase the product output of tetraethyllead using the existing equipment of the present com mercial process. It is a further object to produce tetraethyllead and related compounds by a process which can convert most of the lead charged to the reaction into the desired end product, thereby avoiding the expensive reprocessing of large quantities of lead.

We accomplish these objects by reacting lead such as the lead produced in the present commercial process with an alkylating agent such as an alkyl chloride, in the presence of magnesium such as magnesium chips, and a catalyst, such as an alkyl ether.

In accordance with our invention, we have found that to produce alkyllead compounds it is unnecessary to start with either a lead alloy, such as the sodium-lead alloy used in the present commercial process, or with a lead salt such as lead chloride, as in the Grignard process. On the contrary, our invention is in the surprising discovery that alkyllead compounds can be made by reacting an alkylating agent with free lead and magnesium in the presence of a catalyst.

Further, we have found that lead can thus be alkylated directly at relatively low temperatures.

"By practicing our invention, yields of 80 per cent and higher based on the lead charged to the reaction zone have been obtained. Thus almost a fourfold increase in yield of alkylleads over the present commercial process and almost a two-fold increase over the Grignard process, are obtainable by practicing our invention. Such a yield improvement is remarkable and as far as we are aware such high emciencies in the use of the lead charged are not shown in any of the processes described in the literature, and have not been obtained by the present commercial process? The lead used in the process of our invention is any form of metallic lead, which from its physical state, degree of comminution, and conditions of surface is reactive with an alkylating agent in the presence of magnesium metal and a catalyst to produce an alkyllead. In general the lead should be finely divided and its surface should be free from oxidation, which would decrease its activity. It is to be noted that substantial yields of tetraethyllead have been obtained in our process from an oxidized form of lead, which, to our knowledge, has never before been accomplished. However, the removal of, or the prevention of the formation of oxidized material on the lead surface materially increases the yield obtainable. The unreacted lead remaining from known processes in which some alkyllead is formed is an especially excellent form of lead for use in our invention. For example, the

unreacted lead remaining from the present commercial process, when treated according to our invention with ethyl chloride, magnesium, and ethyl ether, results in a yield of about '75 per cent of alkyllead based on the unreacted lead charged. Thus based on the above actual yield, the lead efficiency i. e. utilization of the lead in converting it to an alkyllead, is 50% greater than that theor tically possible for the Grignard reaction. Based on actual yields obtainable by the most careful control of the Grignard reaction, the lead emciency in our process is almost 100% greater.

Further examples of lead which can be successfully employed in our process include lead powders resulting from the decomposition of organo-lead compounds by heat, such as for instance, the lead deposited during the thermal decomposition of crgano-lead compounds. Certain other forms of lead powders which are sumciently active for use in making tetraethyllead by our process can be prepared by grinding or otherwise comminuting lead metal, especially when this is done in an atmosphere of nitrogen which prevents the oxidation of the lead surface. A further example of a method of preparing a finely divided lead suitable for practicing our invention is the reductive precipitation of lead from its compounds. Other methods such as electrolytic deposition will occur to those skilled in the art.

Lead alloys, particularly alloys containing alkaline earth and alkali metals, are also a good source of lead and have been successfully employed. Sodium-lead alloy is an especially good alloy for such use. Other examples of metals alloyed with the lead which have been successfully used in practicing our invention are calcium, potassium, and magnesium. In general any alloy which will react in the following equation can be employed as a source of lead for our PIOGGSSZ Metal-lead alloy+ethyl chloridetetraethyllead+lead+metal chloride Further, certain alloys which enter into the above reaction with difficulty or which require the employment of relatively high temperatures react satisfactorily and at a lower temperature when employed as the source of lead for our process. For example, instead of mono-sodium lead alloy, alloys corresponding to Na2Pb5 and NasPbi have been successfully employed in our process with an efiiciency in converting the lead to tetraethyllead higher than in any process heretofore known. Various combinations of the forms of lead can also be used in the practice of our invention.

Our invention is adaptable to the production of alkyllead compounds generally, such as tetraethyllead, tetramethyllead, dimethyldiethyllead, triethylphenyllead and tetrapropyllead. Nevertheless, for convenience in describing our invention hereafter, specific reference will be made to tetraethyllead, the most widely known because of its use as an antiknock agent. Whenever in the following description this material is referred to, it is to be understood that other alkyllead compounds or mixtures can be made by our process.

Generally, the process of our invention is conducted as follows: The solid materials including lead, for example in the form of sodium-lead alloy, and the desired quantity of magnesium, in the form of powder or chips, are first placed in a reaction vessel such as the autoclave of the present commercial process. While it is convenient to introduce the magnesium along with the lead, it is to be understood that the magnesium may be added separately at any stage of the reaction keeping in mind that no improvement in yield and in some cases no alkylation is obtained by using the magnesium until the catalyst is added.

The vessel is then closed except for the liquid feed line through which the fluid reactants are i passed. The necessary quantity of the alkylating agent such as ethyl chloride is then introduced into the autoclave followed by delivery of the catalyst such as diethyl ether, or the latter can be added along with the ethyl chloride. In the former method, if the lead is introduced in the form of sodium-lead alloy, the ethyl ether is added after the customary or non-catalytic commercial reaction is initiated and in one preferred modification of our'invention the catalyst is not added until most of the non-catalytic reaction has occurred. In both methods of operation a dual process is occurring, namely the noncatalytic reaction between the sodium-lead alloy and the ethyl chloride, and the catalytic reaction between the free lead formed in the customary reaction and the alkylating agent, due to the presence of the magnesium and the catalyst.

Thus, the preferred methods of operating our process using a lead alloy such as sodium-lead alloy, are the method of reaction wherein the catalyst is added concurrently with the alkylating agent hereinafter referred to as the one stage process, and the method wherein most of the catalyst along with the additional alkylating agent is added after the non-catalytic standard reaction is substantially completed, hereafter referred to as the two-stage process. Of course variations in the above modifications can be made such as introducing part of the catalyst along with the initial feed of the alkylating agent followed by additional catalyst after most of the customary reaction has Occurred. Also while it is preferable in our two-stage embodiment to add only the amount of alkylating agent usually employed for the first non-catalytic stage and then add the amount required for the second stage, it is within the scope of our invention to add most of the alkylating agent in the first stage and primarly only the catalyst in the second stage. In all the above modifications it is understood that magnesium must be present and it is added as heretofore mentioned. It should be noted that while the reaction of the presently used commercial process proceeds without a catalyst and is essentially non-catalytic our reaction is catalytic and requires a catalyst.

When the lead charged to the reaction zone is free lead, preferably the catalyst and alkylating agent are added concurrently although they may be added in any other manner, bearing in mind that little or no reaction between the free lead and alkylating agent occurs until the magnesium and the catalyst are added.

While the above modifications were discussed in connection with a batch operation, they can be successfully adapted to a continuous process. In addition to applying the above modifications to a continuous process, other modifications of a continuous process can be made such as first mixing together all the reaction materials and then passing them continuously through a suitable reaction zone.

In all modes of operation of our invention most of the catalyst, such as ether, as well as excess alkylating agent, such as ethyl chloride, can be recovered. Part is recoverable during the reaction by venting or other means, and part during the recovery of the alkyllead product. During the alkylation process the pressure is controlled by Venting which releases part of the ether along with excess ethyl chloride, both of which may be recovered by condensation. Additional quantities of ether as well as excess ethyl chloride are recoverable during the separation of the alkyllead product by steam distillation, solvent extraction or other suitable means. The ether so recovered as well as the excess ethyl chloride may then be reused or recycled to the system.

In general when using a lead alloy with any specific combination of catalyst, alkylating agent, form of magnesium and operating conditions, better results are obtained in a two-stage operation than in a one-stage. A possible explanation for this is that the free lead is more available for reaction. However, for economic and other reasons a one-stage reaction may be preferred in some cases.

Unless otherwise stated all parts and percentages herein are by weight. Further in the following examples, ether refers to diethyl ether unless otherwise specified.

Our invention can be further understood by referring to the following illustrations of detailed working examples:

Two stage reaction using sodium-lead alloy and ethyl chloride: A charge of 100 parts of NaPb alloy and 15.8 parts of magnesium chips is added to a reaction vessel. equipped with an agitator, a jacket for circulation of heating or cooling liquids, a reflux condenser, charging and discharging ports, liquid feed lines, and means for releasing the pre sure. Liquid ethyl chloride in the amount of 111 parts is added under pressure to the stirred solids in the vessel over a period of one-half hour. By controlling the flow of liquid in the autoclave jacket and in the reflux condenser the temperature of the reaction mass is permitted to rise from an initial temperature of 50 C. to a temperature of C. during this feed period. The pressure in the autoclave during this feed rises to pounds per square inch gauge where it is maintained. The temperature of the stirred reaction mixture is maintained at 70 C. for an additional 15 minutes maintaining the 75 pound pressure. For the second stage, an additional quantity of 56 parts of ethyl chloride, with which has been premixed 15 parts of ether, is added uniformly under pressure as a liquid to the autoclave over a period of 15 minutes, again maintaining the 75 pounds pressure. The temperature of the stirred reaction mass is maintained at 70 C., while maintaining 75 pounds pressure, for an additional minutes. At the end of this period the pressure in the autoclave is reduced to atmospheric by venting for 15 minutes while the temperature is maintained at 70 C. For an additional 15 minutes period at 70 C. nitrogen is passed over the reaction mass while the autoclave is open to the atmosphere. The mass is then cooled to 45 C. over an additional 30 minute period while flushing with a stream of nitrogen. The reaction mass is then discharged to a steam-still containing 250 parts of water. With -steam fed to the jacket of the steam-still, a forecut of ethyl chloride and ether is taken, up to a vapor temperature of 70 C. At this point the steam jets are. then turned on, and with the jacket steam off, the tetraethyllead is distilled for one and one-half hours after the first drop of tetraethyllead appears in the distillation receiver. The yield of product is 68 parts, or a yield of 76 per cent based on the lead present in the sodium-lead alloy.

One stage reaction using sodium-lead alloy and ethyl chloride: Using substantially the same operating procedure as described in the above detailed example, a one-stage modification is carried out with the variation that all the ether and ethyl chloride are added simultaneously to the system during a 45 minute period. In this charge, 100 parts of sodium lead alloy, 167 parts of ethyl chloride, 15.8 parts of magnesium and 15 parts of ether are employed. The operations of cooking, venting, cooling, discharging and recovery of the product are conducted substantially as above. The yield of product was 103 parts, or 74 per cent based on the lead present in the sodium-lead alloy.

Using free lead produced in the reaction between ethyl chloride and sodium-lead alloy: Using substantially the same procedure as in the above examples, 100 parts of free lead, 182 parts of ethyl chloride, 23 parts of magnesium and 14 parts of ether were employed. Again the operations of cooling, venting. discharging and recovery of product are conducted substantially as above. The yield of prod ct was 112 parts, or 72 per cent based on the lead charged.

While the process of our invention is operable over a wide range of temperatures we have found that our preferred temperature is within the range of 45 C. to -85 C. When our two-stage reaction is employed it is sometimes advantageous to operate the second stage at a different temperature than the first stage, However, temperatures preferably in the neighborhood of 70 C. are employed in both the one-stage and two-stage operations. In general for a given method of operation, catalyst employed, concentration of reactants and catalyst, and reaction time, there is an optimum temperature of operation. For ex- 75 ample, in a series of operations carried out with 3.2 parts of magnesium, 112 parts of ethyl chlo-' ride and parts of diethyl ether, to 100 parts of sodium-lead alloy, and with all the ingredients added to the reaction vessel at the beginning of the reaction, the yields of tetraalkyllead obtained after three hours of heating were 32, 33, 34 and 29% of the lead present, respectively, when the temperature of the reaction mixture was maintained at 45, 60, 70 and 85 C.

In general, the reaction of our process is completed within a few hours i. e. to 8 hours. When it is coupled with the present sodium-lead alloy method, we have found that a total time within the rangeof approximately to 6 hours is suflicient.

It is desirable to introduce the alkylating agent such as ethyl chloride as a liquid. Therefore the autoclave is operated under a pressure sufliciently high to maintain the fluid reactants in the liquid phase. Thus the pressure of the reaction using ethyl chloride preferably is maintained within the range of 70 to 125 pounds per square inch. Also the catalyst, such as ethyl ether, preferably is fed in the liquid phase under pressure. If desired the ethyl chloride and the ethyl ether can be mixed and the mixture introduced under pressure into the autoclave.

The state of comminution of the magnesium used in our process is not critical. For example, We have obtained good yields of tetraethyllead when using magnesium in the form of flakes, chips, dust, turnings, and various combinations of particle size. At present we prefer the use of chips because of their cheapness.

The yield of alkyllead obtainable in our process for a given amount of lead increases with the amount of magnesium employed up to about 17.6 parts of magnesium to 100 parts of lead as sodium-lead alloy. Above this quantity of magnesium the additional yield obtainable is small. When free lead is employed little improvement in yield is obtained above 23 parts of magnesium per 100 parts of lead. To illustrate, under comparable conditions and using ethyl chloride and ethyl ether, when 26.3, 17.6, 13.2, 8.8, 3.5, 2.1, 1.4 and 0.0 parts of magnesium per 100 parts of lead charged as sodium-lead alloy were used, yields of 77%, 71%, 59%, 33%, 33%, 29%, 26% and 21% respectively of alkyllead based on the lead charged were obtained.

Thus it can be seen that there is a well-defined relationship between the amount of magnesium employed in our process and the amount of alkyllead compound formed. In general we have found that magnesium quantities between 1 and 30 parts to 160 parts of free lead can be successfully employed in our process. Further. in making tetraethyllead from sodium lead-alloy, ethyl chloride and an alkyl ether, good yields are obtained for quantities of magne ium between about 2 and 13 parts to 100 parts of lead ba ed on the lead in the lead-alloy. The choice of the amount of magnesium used within the above ranges is primarily one of economics depending on such factors as the availability of equipment, the cost of magnesium, the product output desired, the cost of recovery of unreacted lead, and other com mercial considerations. It should be noted that, in many of the examples given subsequently herein. only 3.5 parts of magnesium to 100 parts of lead as sodium-lead alloy were employed in existing equipment. Although higher yields could be obtained by using more magnesium, these examples illustrate the complete freedom of choice, permissible in our process, to select the amount of magnesium in accordance with the above-mentioned economic consideration, unrestricted by any stoichiometric relationship.

For the purpose of the above comparison of different amounts of magnesium the quantity of catalyst was held constant. It is to be understood, however, that for each magnesium level, usually there is a preferred catalyst concentration range, not necessarily that employed in the above examples, and that therefore the above yields do not represent the highest obtainable in every case. In general, the ratio of catalyst weight to magnesium weight employed in our process should be between the limits of about 8 to 1 and 1 to 20, while We prefer to operate our process between the limits of 1 to 1 and l to 15.

The magnesium need not be added along with the lead. Another way of adding the magnesium to the system is to premix it with the ether and part of the ethyl chloride and then introduce the resulting solution or suspension into the reaction vessel at the desired stage. Furthcr, the solution or suspension can be concentrated by evaporation and then added in the second or catalytic stage. For example, 15.8 parts of magnesium was dissolved in a mixture of 42 parts of ethyl chloride and 150 parts of diethyl ether. The resulting solution was concentrated by removing most of the ether by evaporation and the solid material obtained, containing 25 parts of ether, plus additional ethyl chloride was added to the reaction vessel after the non-catalytic reaction of parts of sodium-lead alloy was substantially complete. In this modification, a yield of alkyllead compound of 46% based on the lead present was obtained. Further, the use of magnesium alloyed with lead or another metal will reduce, at least in part, the amount of free magnesium required.

The process of our invention is carried out in the presence of catalysts. We have found that organic compounds containing an atom capable of chemical coordination with magnesium-containing compounds are particularly effective.

5 Among the compounds which are effective catalysts for the process of our invention are ethers such as alkyl and aralkyl ethers, ammonium derivatives such as tetraalkylammonium and aralkylammonium iodides, and amines such as trialkyland aralkylamines.

Examples of ethers that we have successfully used in our proczss are diethyl ether, methylethyl ether, dibutyl ether, dihexyl ether, dimethyl ether of ethylene glycol, 1,4-dioxane and anisole. Of the ethers, the lower alkyl ethers including methyl ethyl through hexyl, are prcferred. Examples of hydrocarbon-substituted ammonium iodides which are eifective in catalyzing the process of our invention are tetraethylammonium iodide, and trimethyhthylammonium iodide. Among the amines which catalyze the process of our invention, are triethylamine, trimethylamine, and dimethylaniline. It is also to be understood that combinations of the above mentioned catalysts can be employed.

The various catalysts do not all act in the same manner. Except for dimethyl ether the lower alkyl ethers give about the same yield for both one and two-stage operations on sodium-lead alloy although slightly higher yields have been observed for the two-stage operation. However for tertiary amines, the alkyl ammonium iodides and to some extent methylethyl ether, better yields are obtained in the two-stage operation,

especially when relatively larger quantities of catalysts are used.

We have found that the yield of alkyllead compounds is affected by varying the amount of catalyst. catalyst depends on the operating conditions. For example, in using ethyl chloride, sodiumlead alloy and magnesium for making tetraethyllead with diethyl ether as a catalyst in a process whereby all the reactants of our invention are added to the reaction vessel at the same time, and 3.2 parts of magnesium are used per 100 parts of sodium-lead alloy, the yields obtained with 0, 1, 3, and 10 parts of ether per 106 parts of alloy at a temperature of about 70 C. are 21, 25, 27.4, 34, and 34.7 per cent, respectively, based on the lead present. Further, under the same conditions, when employing 15.8 parts magnesium per 100 parts of sodium-lead alloy, the yield of alkyllead compound obtained using 0, 2.5, 5, l5 and 40 parts of diethyl ether per 100 parts of sodium-lead alloy are 21, 66, 69, 71 and 28 per cent of the lead present, respectively. The same effect has been observed when alkylamines are used as the catalysts of our invention. To illustrate; in conducting our process as above, and employing 15.8 parts of magnesium per 100 parts of sodium-lead alloy, the yields of alkyllead comnound obtained with 0, 0.7, 6.5, 13 and 20 parts of triethylamine per 100 parts of sodiumlead alloy at a temperature of about 79 C. were 21, 26, 51, 57 and 48 per cent of the lead present, respectively. It should be noted that when no catalyst is used the yield is only 21 per cent which is abo t standard for the present commercial process.

As further examples of the variations obtained with different amounts of catalyst, we have carried out our process under conditions permitting the non-catalytic reaction between sodium-lead alloy and ethyl chloride to proceed, in the presence of 15.8 parts of magnesium per 100 parts of sodium-lead alloy, substantially to completion, whereupon an additional quantity of alkylating agent was added to the reaction mixture along with the catalyst. Under the conditions of this embodiment of our invention in which the temperature was maintained at about 70 C. we obtained yields of tetraethyllead of 21, 26, 40 and 74% respectively, based on the lead initially introduced into the reaction zone when employing 0, 1, 5, and parts of diethyl ether per 100 parts of sodium-lead alloy introduced in the first stage of the process.

Similar results are obtained using triethylamine as the catalyst in this type of two-stage operation. Thus, yields of 21, 38, 56 and 43% of tetraethyllead, based upon the lead present, were obtained with 0, 3, 13 and 55 parts respectively of triethylamine per 100 parts of sodiumlead alloy in the presence of 15.8 parts of magnesium per 100 parts of the sodium-lead alloy.'

Similar results have been obtained when substituting other others for diethyl ether. In a typical one-stage reaction with 15.8 parts of magnesium per 100 parts of sodium-lead alloy at a temperature of about 70 C. the yield of alkyllead compound with 38 parts of dihexyl ether per 100 parts of sodium-lead alloy was 70% based on the lead present. Methylphenyl ether similarly employed produced a 26% yield of alkyllead compound. Methylethyl ether when employed at a concentration of 4 parts per 100 parts of alloy, with 3.2 parts of magnesium produced a yield of 33% of allsyllead compound. With 15.8 parts of The optimum amount of a specific magnesium and 4 parts of methylethyl ether per parts of sodium-lead alloy 57% of the lead present was converted to alkyllead compound. As still further examples of the effectiveness of other catalysts which can be employed successfully in the process of our invention, under the conditions of the previous example 9 parts of the dimethylether of ethylene glycol per 106 parts of sodium-lead alloy gave a 29% yield of alkyllead compound, While 9 parts of 1,4-dioxane gave a yield of 34%. Further, under these same conditions when using 1.7 and 5.0 parts of tetraethylammonium iodide, we obtained yields of 23, and 24 per cent. Little product was obtained when no magnesium was used.

Various alkylating agents can be employed in our invention. For the most part the alkylating agents of our process are esters of inorganic acids having the desired alkyl group such as alkyl chlorides, alkyl bromides, alkyl iodides, and alkyl phosphates. In general the inorganic acid ester alkylating agents are the mono-chloro, -b1'omo and -iodo derivatives of the paraifin hydrocarbons such as, methane, ethane, propane, and pentane, and the corresponding trialkyl phosphates. For example methyl chloride, methyl iodide, ethyl chloride, ethyl bromide, ethyl iodide, 11-- propyl chloride, n-butyl bromide, n-amyl chloride, n-amyl iodide, and triethyl phosphate can be successfully employed. Instead of the normal alkyl halides, other isomers such as the iso compounds, can be used. Various combinations of these alkylating agents can also be used. For example two or more alkylating agents can be used simultaneously in the oneand two-stage process or diflerent alkylating agents can be used in each stage of the twoestage process.

The different alkylating agents mentioned above do not all behave in the same manner. The operating conditions can be varied within the scope of our invention in order to obtain the best results with the particular alkylating agent or agents employed. For example, except for methyl chloride, the lower alkyl chlorides particularly ethyl chloride give excellent yields of tetraalkyllead in both the oneand two-stage operations on sodium-lead alloy. However, methyl chloride and the alkyl bromides and iodides are preferably employed in the second step of the two-stage operation since better yields are thereby obtained.

In general, the alkylating agents which are well known for use in the present commercial process, or which can be used in our process with a lead alloy, give excellent results when employed in all embodiments of our invention. Those a1- kylating agents which give relatively low yields in the present commercial process, or in our process in which a lead alloy is employed, do, howeve give excellent results when free lead or the lead resulting from the processes of the prior art are employed, or are employed in the second stage of the two-stage embodiment of our invention, regardless of the form in which the lead is employed in the first stage.

As an example of a preferred embodiment of the process of our invention using a chloride alkylating agent, we obtained a 74 per cent yield of alkyllead compound based on the lead present in 100 parts of sodium-lead alloy by adding to this alloy 168 parts of ethyl chloride, 15.8 parts of magnesium and 7.5 parts of ethyl ether in a reaction vessel and heating the mixture for two hours at a temperature of 70 C. Substitution of 16.3 parts of n-propyl chloride for the ethyl chloride of this example and parts of ethyl ether, resulted in a yield of alkyllead compound of 41% based on the lead employed. Another embodiment of our process in which the alkylating agent is also ethyl chloride is a two-stage operation in which 100 parts of sodium-lead alloy was maintained at a temperature of 70 C. for one hour in the presence of 15.8 parts of magnesium, and 168 parts by weight of ethyl chloride. At the end of this period the reaction vessel was cooled to below C., opened, and 15 parts of ether were added, and heating of the mixture was continued for an additional two and one-half hours at 70 C. The yield of alkyllead compound thus obtained was 74% of the lead present.

To illustrate a preferred embodiment of our process when employing ethyl bromide as the alkylating agent, we have prepared metallic lead by alkylating 100 parts of sodium-lead alloy with 168 parts of ethyl chloride for one-half hour at a temperature of 70 C. At the end of this period the reaction vessel was cooled, opened and the ethyl chloride evaporated oil, and 15.8 parts of magnesium, 15 parts of ether and 280 parts of ethyl bromide, were added, and the mixture was maintained at a temperature of 70 C. for an additional period of one and one-half hour. The total yield of alkyllead compound which was obtained was 82% of the lead initially introduced.

In a process similar to the above-mentioned example, we substituted 132 parts of methyl chloride for the ethyl bromide as the alkylating agent of the second stage. *With this embodiment the total yield of alkyllead compound was 37 of the lead initially introduced.

In a further modification of our process we obtained metallic lead as described above by the reaction of ethyl chloride and sodium-lead alloy, and in the second stage we added 300 parts of ethyl iodide along with the 15.8 parts of magnesium and 15 parts of ether, all per 100 parts of the sodium-lead used in the first stage. In this embodiment of our invention the second stage of the reaction was carried out at temperature of 50 C. and an overall yield of 'alkyllead com pound of 77% of the lead employed was obtained.

As a still further embodiment of the abovedescribed two-stage reaction, we employed trimethyl phosphate as the alkylating agent in the second stage. In this example, we added 405 parts of trimethyl phosphate, 15.8 parts of magnesium and 15 parts by weight of ether to the lead metal prepared from 100 parts of sodiumlead alloy as described above. This reaction mixture was heated for a period of four hours at a temperature of 70 C. The yield of alkyllead compound obtained from the combined stages of the process was 23.3% of the lead employed. Under the same conditions, when no magnesium and no ether was used the yield obtained from the second stage was substantial y zero.

Further, the alkylating agents in addition to having the proper a kyl groups should have an acid or negative radical which will react with the magnesium to form MgX. In our reaction the alkylating agent must react with both the lead and the magnesium. For example the overall equation for our reaction when lead and ethyl chloride are employed is:

and for the dual reaction heretofore referred to, the equation is Catalyst Thus no free lead is formed in our reaction. Similar equations can be written for other alkylating agents.

For best results, the alkylating agents of our process should be employed in excess over the amount required according to the above equations. If less than the amount of alkylating agent required to completely alkylate the lead according to the above equations is used, the yields will be lower, but will still be good when determined on the basis of the amount of alkylating agent. This is especially true when the two stage operation is employed and in an operation wherein the alkylating agent is fed to the system gradually.

In several of the above examples wherein various embodiments of our invention were described using diiferent alkylating agents, we have referred to the preparation of free lead by the preliminary reaction of sodium-lead alloy with an a'kylating agent in the absence of magnesium and a catalyst. It is not necessary, however, for the successful operation of the process of our invention to use lead prepared in this manner. We have found that lead metal from other sources can be successfully alkylated under the conditions of the process of our invention. For example we have treated successfully 100 parts of a flaked lead metal with 187 parts of ethyl chloride, 23 parts of magnesium and 13.5 parts of ether, at a temperature of 70 C. for six hours and converted 59% of the lead metal to akyllead compound. Further, under the same conditions we have used a lead powder, of such particle size that it passed through an B-mesh screen and was held on a ZO-mesh screen, and obtained a 31% yield of alkyllead compound. Under identical conditions, with the exception that in one instance the magnesium was withheld from the reaction mixture, and in the other, ether was withheld from the reaction mixture, no alkyllead compound was produced from these lead metals.

The above examples of the process of our invention in which a sodium-lead alloy has been used as the lead source have referred to the alloy having substantially the composition corresponding to the formula NaPb, the alloy used in the present commercial process. We have found, however, that other alloys of sodium and lead of composition different from NaPb can be employed successfully in our process to produce good yields of alkyllead compound. For example, we have treated, in a one-stage modification of our invention, 100 parts of the alloy Na9Pb4 with 150 parts of ethyl chloride, 8.2 parts of magnesium and 15 parts of ethyl ether at a temperature of 70 C. for hours. The yield of alkyllead compound was 33% based on the lead. We repeated this process without the magnesium and ether in the reaction charge and obtained a yield of alkyllead compound of on y 1.5%, even when operating at the higher temperature of C. We have obtained an excellent result when employing the NaaPbr alloy in the twostage embodiment of our invention as follows: the alloy and alkylating agent in the proportions stated above were heated together at a temperature of C. for one hour, after which period the reaction vessel was cooled and charged with the above quantities of magnesium and ether, and heated for an additional period of two hours at 70 C. The resulting yield of alkyllead compound from both steps was 73% based on the lead introduced in the first step- As further examples of the process of our invention we have treated 100 parts of the alloy NazPbs with 200 parts of ethyl chloride, 20 parts of magnesium, and 15 parts of ether in both the oneand two-stage embodiments described above. The resultant yields, based on the lead present in the alloy were 18% for the one-stage operation, and 9% of the two-stage operation. When no magnesium and no ether was used, the yield was only 2.3%.

Alkali metals other than sodium as well as alkaline earth metals when alloyed with lead also gave good yields by our process. For example we have employed successfully the alloys KPb, CaPb and MgzPb, in both oneand two-stage embodiments of our invention. The conditions employed in each case were similar to those described for the sodium-lead alloys above. For a one-stage operation we obtained yields of alkyllead compound of 32, 66, and 52% with the KPb, CaPb and MgzPb alloys, respectively, and 5, 68, and 54% in the two-stage embodiment. When no magnesium and no ether was used, the yields were 0.3, 40 and 45.2 respectively.

It should be noted that, although many of the foregoing examples of our process employed a reaction time of two hours, the yields are substantially improved, in some cases by as much as 100%, by increasing the reaction time within the range of 2 to 8 hours.

Our process, in common with most of the processes of the prior art, when employed to make tetraethyllead also produces some hexaethyldilead. Its presence is readily detected by noting the color in the final alkyllead product. If there is none present the color is water-white while a yellow color indicates its presence. In view of the widespread commercial use of tetraethyllead, it may be desirable to convert hexaethyldilead to a more valuable product. Therefore any of the latter contained in the final product, can be converted to tetraethyllead and free lead by heating. Actually, by such heating, 82% by weight of tetraethyllead is formed and the free lead so produced can be reprocessed. Further, most of the hexaethyldilead can be prevented from forming in our process by employing temperatures near 85 C. or by lengthening the time of the reaction at a lower temperature, say 70 C.

For example, when reacting 100 parts of sodium-lead alloy with 68 parts of ethyl chloride in the presence of 3.2 parts of magnesium and with quantities of diethylether varying between 1 to parts, no significant amount of hexaethyldilead is formed at a temperature of 85 C. and a reaction time of 2 hours. Likewise substantially none is formed at a temperature of 70 C. for a reaction time of 3 hours. Under both of the above conditions, the quantity of ether employed had no effect on hexaethyldilead formation. Further, where some hexaethyldilead is formed at a given temperature and time, the amount can be reduced by using relatively small quantities of ether.

For the reaction of our invention to proceed effectively it is essential that the reaction zone be free from substantial amounts of certain materials which may be inert and which may act primarily as diluents. However certain materials when used in small concentrations are, in some cases, beneficial even though they do not directly improve the yields. For example, certain thermal stabilizers such as diisobutylene, styrene and naphthalene when added in quantities of the order of a few per cent based on the lead are beneficial in reducing the tendency of the alkyllead compounds in the reaction mass to undergo thermal decomposition. Further certain known accelerators such as acetone, dipropyl ketone, ethyl acetate, ethyl butyrate and butyl acetate may tend to accelerate the eaction when used in small quantities of the order of .04 part to 1 part of lead. Quantities above 1 part to 1 part of lead should be avoided. For example when acetone was used in quantities of .04 part to 1 part of lead, there was no appreciable decrease in yield of alkyllead product. But when 5 parts to 1 part of lead was used substantially no yield was obtained.

Hydrocarbons, such as gasoline and its components, are additional examples of materials which may be beneficial in small quantities, but harmful when used in excess. The presence of hydrocarbons in substantial amounts seriously interferes with the progress of the alkylation reaction although relatively small amounts may be of some help. If one-half part of a hydrocarbon to one part of lead is added to the reactants or" our invention the yield of desired tetraalkyllead compound is seriously impaired. In general as the amount of hydrocarbons is increased, the yield of tetraalkyllead is reduced until finally little, if any, is produced. To illustrate, when 0.5 part, 1.0 part and 5.0 parts of straight run gasoline to 1 part of lead were added to the reactants of our invention the yield of tetraethyllead was reduced by 66%, 98% and 100% respectively. lIhus at 5.0 parts of hydrocarbons no yield of tetraethyllead was obtained. It should be understood that small amounts, of the order of less than one part to one part of lead, of such inert materials may be present without objectionable effects upon the reaction. Actually, such small amount of inerts may be helpful, perhaps because of what appears to be a tendency to cleanse the walls of the reaction vessel thereby maintaining the yields at the normal level. In certain instances, for example where the reaction vessel walls were in pOOr conditions, some improvement in yield when using a small quantity of a hydrocarbon material has been noted.

Thus while small quantities of certain materials such as those enumerated above may benefit our process, in general quantities above 1 part to 1 part of lead should be avoided, or stating it another way, the quantity of such materials should be less than part to 1 part of the total amount of reactants, i. e., lead, magnesium, alkylating agent, and catalyst.

Other embodiments of this invention can be made without departing from the spirit and scope of our invention which is not limited to specific embodiments given herein.

We claim:

1. A process for making alkyllead compounds which comprises alkylating free lead in the presence of free magnesium and a catalyst.

2. A process for making tetraalkyllead which comprises treating free lead with an excess of alkylating agent in the presence of free magnesium and a catalyst.

3. A process for making tetraethyllead which comprises reacting free lead with sufficient ethyl chloride to alkylate more than fifty per cent of said lead in the presence of free magnesium and a lower alkyl ether catalyst.

4. A dual process for making tetraethyllead which comprises reacting a sodium-lead alloy with ethyl chloride, and reacting the free lead 16 UNITED STATES PATENTS so produced with ethyl chloride in the presence Number Name Date of free magnesium and diethyl ether. 1,949,949 Alleman Mar. 6, 1934 2,000,069 Downing et a1. May 7, 1935 GEORGE CALINGAERT- 5 2,012,356 Shapiro Aug. 27, 1935 HYMIN SHAPIRO- ,061,267 Downing et a1 Nov. 17, 1936 REFERENCES CITED 2,270,109 Cahngaert Jan. 13, 1942 The following references are of record in the FOREIGN PATENTS 10 Number Country Date Great Britain July 22, 1925 file of this patent:

Claims

1. A PROCESS FOR MAKING ALKYLLEAD COMPOUNDS WHICH COMPRISES ALKYLATING FREE LEAD IN THE PRESENCE OF FREE MAGNESIUMAND A CATALYST.