US3156716A - Process for preparing tetravinyl lead - Google Patents

Description

United States Patent 3,156,716 PRQCESS FGR PREPARl-NG TETRAVINYL LEAD Hugh ll. Ramsden and Hugh F. Shannen, Scotch Plains,

N..l., assiguors to Esso Research and Engineering (Compauy, a corporation of Delaware No Drawing. Filed .Tan. 24, 1963, Ser. No. 253,742 7 Claims. (Cl. 260-437) The present invention is concerned with the preparation of organolead compounds. In particular, it is concerned with an improved process for the preparation of tetravinyl lead.

It is known in the art that olefinic lead compounds, either alone or in combination with other suitable lead alkyl anti-knock additives in motor fuel, are elfective antiknock agents. These lead olefinic anti-knock additives include those organo-lead compounds that possess one or more olefinic groups wherein the said olefinic groups are attached directly to the lead atom and comprise from 2 to 8 carbon atoms in each group or 8 to 32 carbon atoms in total. In particular, those olefinic lead compounds having olefinic radicals comprising one or more vinyl groups, such as tetra-allyl lead, tetracrotyl lead, tetrapropenyl lead, tetramethylallyl lead, mixed lead alkenyls such as divinyl diallyl lead, vinyl allyl dicrotyl lead and vinyl allyl crotyl methylallyl lead and other suit able combinations of the foregoing olefinic compounds are desirable additives for motor fuels.

A preferred anti-knock agent from the above class of compounds has been found to be tetravinyl lead. Use of minor amounts of tetravinyl lead in gasoline gives very effective anti-knock activity. In fact, it has been discovered that tetravinyl lead is superior in anti-knock ability to the lead alkyl compounds, in particular tetraethyl lead, at the same additive levels. Therefore, a process adaptable to the commercial production of tetravinyl lead is of great interest and extreme importance to the members of the automotive and petroleum industries.

Tetravinyl lead is a relatively new compound which has been recently synthesized. Two methods for the preparation of tetravinyl lead are described in the article in Angewandte Chemie, volume 71, page 161 (February 21, 1959), entitled Preparation of Tetravinyl Lead, by Ludwig Maier. These methods, as disclosed by the aforementioned reference, can be summarized by the following two reactions:

(2) PbCl -I- 4CH =CHMgBr Pb (CH:

While both methods do produce the desired tetravinyl lead product, the yields are so poor as to make the proccases of little value outside of producing small laboratory size amounts of the compound. Typical yields reported by Maier are 17.2% of theory for method (1) and 9.1% by method (2).

A contemporary article of Maiers described a procedure which was analogous to method (2).

The article. entitled Preparation of Tetravinyllead and Some Phenyl- 3,156,716 Patented Nov. 10, 1964 method (1) since ammonium chloride is a product of that method and therefore the deficiency of yield is seemingly inherent in the reaction itself. The method using lead chloride (PbCI as practiced by Juenge and Cook, proved to be an extremely difficult reaction to control. During the addition of solid lead chloride to the vinyl Grignard solution, heat surges occurred accompanied by the generation of great volumes of gas. The reaction was carried out at high temperatures with an excess of the Grignard in order to prevent the formation of hexavinyldilead. This compound can be converted to tetravinyl lead only by repeated and hazardous redistillations; hazardous because of the likelihood of explosive decompositions.

The conditions employed in the above .preparation result in a large amount of decomposition as evidenced by the large amounts of gas evolved. It is further evidenced by the great amounts of solid, presumably polymers, obtained by Juenge and Cook during their work-up. Thus it is not so surprising that the over-all yield was so poor. Special care was required during the work-up and purification of the reaction product since the tetravinyl lead so obtained decomposed explosively when heated over C. Furthermore the product prepared by this procedure was found to be unstable at room temperature and required careful storage at very low temperatures in the absence of light. Over-all this procedure could not be considered suitable for large scale preparations due to the combined factors of poor yield, hazardouswork-up conditions and the instability of the product obtained.

It has now been found that tetravinyl'lead can be prepared from lead chloride and vinyl .Grignard by an improved process whereby high yields, safe work-up and a stable product are obtained. This process is easily controlled and eliminates the heat surges previously associated with this synthesis. Decomposition during the reaction is minimal so that little or no gas evolution is found. This also results in a very great reduction in the amount of polymer produced. The relative absence of polymer aids in simplifying both the solvent stripping and product distillation steps.

The product obtained from this improved process is of very high purity (about 99%) as determined by lead analysis. Unlike the material prepared by the previous ly known processes, the tetravinyl lead of the present process has been found to be stable on storage at room temperature in dark bottles. Samples stored under those conditions for as long as six months did not show any sign of decomposition.

This improved process consists of adding a solution of vinyl Grignard, previously prepared by methods well known in the art, i.e. by reacting a vinyl halide, e.g. vinyl chloride, with magnesium, to a slurry of lead chloride in a suitable inert solvent. Suitable inert solvents for the preparation of the vinyl Grignard and for use in the lead chloride slurry include te'trahydrofura'n, diglyme and related diethers of ethylene and polyethylene glycols, e.g. ethylene glycol dimethyl ether. An especially preferred inert solvent is tetrahydrofuran. The solvent used in preparing the Grignard and that used in the lead chloride slurry may be the same, difierent, or each may be mixtures of the above type of solvents.

Furthermore, it has been found that inert liquid hydrocarbons may be added to the reaction mixture to thin the slurry thereby allowing efiicient mixing. Suitable inert liquid hydrocarbons include normal and iso alkanes, cycloalkanes, aromatics, alkyl substituted aromatics, etc; It is preferred that the hydrocarbon boil below about roe- C. in order to allow the stripping of the solvent to be accomplished without excessive heating. Preferred liquid hydrocarbons include n-pentane, benzene and cy- Gt clohexane. A most preferred liquid hydrocarbon is n-pentane. The addition of the hydrocarbon diluent may be made before the Grignard solution is added or during the course of the Grignard addition. The temperature (during the addition of the major part of the Grignard solution) is kept below 40 C. After the addition is completed, the mixture is heated at reflux for several hours, e.g. 1-6 hours, preferably 2-4 hours. After cooling and filtration, the filtrate is stripped of all solvents. The concentrated mixture is then distilled under vacuum to yield the desired tetravinyl lead, which is collected in the temperature range of about 24-35 C. at l-3 mm. pressure. During this distillation the pot temperature is maintained below 75 C. By keeping the lead chloride concentration in great excess during the addition and by careful temperature control, yields of 80% and greater are readily obtainable.

The process will be more completely understood from a consideration of the following examples. It is understood that these examples are advanced for the purpose of illustration and should not be construed as limiting the scope of the invention in any manner.

Example I A solution of 5.0 moles of vinylmagnesium chloride (prepared by reacting 5.5 moles of vinyl chloride and 5 gram atoms of magnesium) in 1200 ml. of tetrahydrofuran was added dropwise to a stirred suspension of 667.4 grams of lead chloride in 1000 ml. of tetrahydrofuran. After about one-quarter of the Grignard solution had been added, the suspension, which had been black from the first addition, became thick. At this point 1000 ml. of pentane was added to break up the slurry. The Grignard solution was completely added in about 4 hours and during the major part of this time the temperature was maintained below 40 C. Near the end of the addition the temperature was allowed to rise until it reached a final value of about 46 C. The reaction mixture was then heated to reflux and maintained at that temperature (49 C.) for about 2 hours. It was then allowed to stand overnight during which time a black precipitate settled out. This precipitate was filtered off and the filtrate was stripped of solvent under reduced pressure. The residue, including some precipitated salts and polymer, was then vacuum distilled. Tetravinyl lead was obtained in the fraction distilling from 24 C. to 34 C. at 1-3 mm. (absolute). During this distillation, the pot was heated by means of a water bath and the pot temperature was not allowed to exceed 65-75 C. The bath temperature at final dry point was 80 C. Tetravinyl lead was obtained in a yield of 298.4 grams or 79%. However, additional amounts of product were found to be present in both the residual salt cake and the distillation fore runs so by recycling these materials, even higher process yields can be obtained.

Example II The process of Example I was scaled up by a factor of 20 times (29-30 pounds of lead chloride) and run in pilot plant equipment without any noticeable difiiculty. It is therefore evident that this process can be used safely in the large scale preparation of tetravinyl lead.

Example III The process of Example I wherein ethylene glycol dimethyl ether is used as solvent yields tetravinyl lead in high yield.

Example IV The process of Example I wherein benzene is added as the hydrocarbon diluent yields tetravinyl lead in high yield.

Example V The process of Example I wherein cyclohexane is added as the hydrocarbon diluent yields tetravinyl lead in high yield.

Example VI The process of Example I wherein the vinyl Grignard is prepared from vinyl bromide and magnesium yields tetravinyl lead in high yield.

What is claimed is:

1. An improved process for the preparation of tetravinyl lead comprising (1) slowly adding a vinyl Grignard solution to a slurry of lead chloride each in an organic ethereal solvent at a temperature maintained below about 40 C. during the major part of said addition the amount of said organic ethereal solvent being sufiicient to allow efiicient mixing of said slurry, (2) refluxing the mixture and (3) distilling under reduced pressure while maintaining the pot temperature below about C. to recover said tetravinyl lead as a distillate fraction.

2. An improved process for the preparation of tetravinyl lead comprising (1) slowly adding a solution of vinyl magnesium chloride to a slurry of lead chloride each in an organic ethereal solvent at a temperature maintained below about 40 C. during the major part of said addition, (2) adding a slurry thinning amount sufficient to allow efficient mixing of said slurry of an inert hydrocarbon diluent, (3) refluxing the mixture and (4) distilling under reduced pressure while maintaining the pot temperature below about 75 C. to recover said tetravinyi lead as a distillate fraction.

3. The process of claim 2 wherein the inert solvent of step (1) is tetrahydrofuran.

4. The process of claim 2 wherein the inert hydrocarbon diluent of step (2) is n-pentane.

5. An improved process for the preparation of tetravinyl lead comprising (1) slowly adding a solution of vinylmagnesium chloride in tetrahydrofuran to a slurry of lead chloride in tetrahydrofuran at a temperature maintained below about 40 C. during the major part of said addition, (2) adding a slurry "thinning amount sufficient to allow efiicient mixing of said slurry of n-pentane, (3) refluxing the mixture and (4) distilling under reduced pressure while maintaining the pot temperature below about 75 C. to recover said tetravinyl lead as a distillate fraction.

6. The process of claim 5 wherein the refluxed mixture of step 3 is allowed to stand at a lower temperature until a precipitate settles out, is filtered free from said precipitate and is stripped of solvent prior to the distillation of step 4.

7. An improved process for the preparation of tetravinyl lead comprising (1) slowly adding a solution of vinylmagnesium chloride in an inert organic ethereal solvent selected from the class consisting of tetrahydrofuran, the di-ethers of ethylene glycols and the di-ethers of polyethylene glycols to a slurry of lead chloride in an organic ethereal solvent selected from said class at a temperature maintained below about 40 C. during the major part of said addition; (2) adding a slurry thinning amount sufficient to allow efiicient mixing of said slurry of an inert hydrocarbon solvent boiling below about C.; (3) refluxing the resulting mixture; (4) cooling said mixture until a precipitate settles out; (5) filtering off said precipitate to yield a solids free filtrate; (6) stripping off said inert solvent from said filtrate and (7) distilling the residuum of step (6) under reduced pressure while maintaining the pot temperature below about 75 C. to recover said tetravinyl lead as a distillate fraction.

References Cited in the file of this patent UNITED STATES PATENTS 3,071,607 Juenge Jan. 1, 1963

Claims (1)

1. AN IMPROVED PROCESS FOR THE PREPARATION OF TETRAVINYL LEAD COMPRISING (1) SLOWLY ADDING A VINLY GRIGNARD SOLUTION TO A SLURRY OF LEAD CHLORIDE EACH IN AN ORGANIC ETHEREAL SOLVENT AT A TEMPERATURE MAINTAINED BELOW ABOUT 40*C. DURING THE MAJOR PART OF SAID ADDITION THE AMOUNT OF SAID ORGANIC ETHEREAL SOLVENT BEING SUFFICIENT TO ALLOW EFFICIENT MIXING OF SAID SLURRY, (2) REFLUXING THE MIXTURE AND (3) DISTILLING UNDER REDUCED PRESSURE WHILE MAINTAINING THE POT TEMPERATURE BELOW ABOUT 75*C. TO RECOVER SAID TETRAVINYL LEAD AS A DISTILLATE FRACTION.