Tetraalkyllead compounds

Tetraalkyllead compounds can also be used as starting materials for the synthesis of functionalized and specific organoplumbanes. In the latter case, cleavage of one or more of the attached alkyl groups is achieved so as to introduce subsequently new groups, different from the original ones. 

The concentration factor may also be expressed as ng Pbkg-1 (fish)/ngPbl 1 (water), for the individual tetraalkyllead compounds and for the various species of fish in which they were detected, and data for inorganic lead were derived in a similar manner. The concentration factors are summarized in Table 20. 

The major organolead compounds found in the environment are the tetraalkyllead compounds and their di- and trialkyl decomposition products. Elevated levels of tetraalkyl-leads have two possible sources either (i) anthropogenic leaded petroleum inputs or (ii) environmental methylation of natural lead compounds. While the former is well established, the latter is the subject of some controversy in the literature. Interest in the environmental methylation process derives from the increased toxicity of methyllead compounds compared to their inorganic analogs. 

Tetraalkyllead compounds can be obtained by reaction of Grignard reagents with lead(II) halides or by reaction of 3RLi and RI with PbX2. ... 

The application of a combination of gas chromatography and atomic absorption spectrometry to the determination of tetraalkyllead compounds has been studied by Chau et al. [f 7] and by Segar [20], In these methods the gas chromatography flame combination showed a detection limit of about O.lpg Pb. Chau et al. [f 7, 18] have applied the silica furnace in the atomic absorption unit and have shown that the sensitivity limit for the detection of lead can be enhanced by three orders of magnitude. They applied the method to the determination of tetramethyllead in sediment systems. 

De Jonghe, W., Chakraborti, D. and Adams, F. (1980) Graphite furnace atomic absorption as a metal specific detection system for tetraalkyllead compounds separated by gas-liquid chromatography. Anal. Chim. Acta, 115, 89-105. 

Hewitt, C.N. and Harrison, R.M. (1985) A sensitive, specific method for the determination of tetraalkyllead compounds in air by gas chromatography/atomic absorption spectrometry. Anal. Chim. Actarom., 167, 277-287. 

Tetraalkyllead compounds tend to be clear, colorless liquids and are soluble in common organic solvents, such as hydrocarbons, chloroform and ether. The tetraaryl derivatives are beautifully crystalline solids most are white or colorless, but the more highly substituted phenyllead compounds tend to be yellow in color. The tetraaryl derivatives tend to be soluble in chloroform, acetone and aromatic hydrocarbons, and insoluble in such solvents as ether, alcohol and aliphatic hydrocarbons. 

The price of tetraalkyllead compounds is quite dependent on the price of lead metal, the most expensive raw material component. Thus, prices of commercial antiknock fluids fluctuate from time to time. The price of tetramethyllead fluid is generally several cents per pound higher than that of tetraethyllead fluid, reflecting the higher cost of manufacture. Because of the higher price of tetramethyllead, comparatively little of it is used alone 16,200). 

Several other electrolytic systems have been proposed for manufacturing tetraalkyllead compounds, but are not being used commercially. Electrochemical syntheses have been reviewed by Shapiro and Frey 289>, Lehmkuhl 204>, Marlett 215), and to some extent, Fioshin and Tomilov 136). 

Other interesting electrolytic systems have been developed based on electrolysis of triethylsulfonium bromide in acetonitrile with a lead cathode H8,ii9)j and electrolyses of aqueous solutions of sodium tetra-alkylboron compounds 245,337) Altogether, the breadth and depth of the research effort that has been devoted to the various electrolytic methods for the synthesis of tetraalkyllead compounds is remarkable. However, the successful development of a commercial process has not been accomplished, and indeed, it is probably less likely today than it was several years ago. 

The mixed methyl-ethyl tetraalkyllead compounds have become quite important commercially in the past several years because of their excellent antiknock effects and volatilities (see Extent of Antiknock Effect). Sometimes tetramethyllead and tetraethyllead are simply mixed together in motor fuel, but usually the compounds are subjected to "redistribution of the methyl and ethyl groups. The redistribution reaction involves the exchange of the organic groups between the compounds, yielding practically a random equilibrium production of all the possible products in a statistical distribution, as shown in the equation ... 

Outside of the antiknock field, the commercial applications of organolead compounds are relatively few and quite small. The largest of these applications is in the manufacture of organomercury fungicides by alkylation. This application is old and is relatively static. Other alkylations consume a little tetraalkyllead compound. A small amount of tetra-methyllead has long been used to fill Geiger counters. 

In the laboratory, work with organolead compounds is carried out exclusively in fume hoods with excellent mechanical ventilation. Inhalation is thus prevented, together with dispersal of dust and contamination of the body. Spilling of tetraalkyllead compounds or solutions on the hands is avoided, as in the manufacturing plants, by the use of rubber gloves or special impervious gloves containing an impervious inner layer. 

There is no known antidote for tetraalkyllead intoxication. Therefore, even in serious cases treatment is usually confined to intensive supportive care and adequate sedation. Although chelating agents are useful in inorganic lead intoxication, they have not been shown conclusively to be of any aid in intoxication due to tetraalkyllead compounds. It has been speculated that to be effective a therapeutic compound would be required to combine with trialkyllead compounds and thus increase their elimination from the body 101>. 

F. G. Noden, The determination of tetraalkyllead compounds and their degradation products in natural water, In M. Branica, Z. Konrad (Eds.), Lead in Marine Environment, 1980, Pergamon Press, Oxford, 83-91. 

The most widely used technique for trapping of tetraalkyllead compounds from an air stream is their collection on GC-packing in a cooled U-tube " or on an appropriate solid sorbent. By heating the U-tube or the solid sorbent the species are desorbed into a GC column or directly into the detector system for analysis. 

Tetraalkyllead compounds are either removed from water phase by the purge and trap method (similar to its trapping from air) or by solvent extraction. In the latter method, the species are quantitatively extracted from water saturated with NaCl into a smaller amount of hexane. 

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