Tetraalkyllead

The transfer of an ethyl group, in particular, can be performed with high diastereoselectivity by the use of tetraalkyllead, activated with titanium(IV) chloride14"15 (Table 4). The order of addition of the reagents exhibits a strong influence on the chemical yield and diastercoselectiv-ity of the addition reaction. Typically, titanium(IV) chloride is added at -78CC to the aldehyde, followed by addition of tetraethyllead. Poor yields and diastereoselectivity are observed if titanium(IV) chloride is first added to tetraethyllead followed by addition of the aldehyde ... 

Determination of organolead metabolites of tetraalkyllead in urine can be carried out after solid-phase enrichment and end analysis using reversed-phase HPLC with chemical reaction detector and by LC-MS (thermospray127). The chemical derivation consists of conversion to the dialky Head form, as shown in reaction 1, followed by complex formation with 4-(2-pyridylazo)resorcinol (11) and spectrophotometic measurement at 515 nm128. 

A combination of FLA and iodination of tetraalkyllead in emulsions, followed by AAS Pb determination, was proposed. The different behaviour shown by TEL and TML can be used for speciation of these compounds142. 

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. 

TABLE 17. Oxidation potential of several tetraalkyllead derivatives under three current densities i/A (mAcirr2)191... 

The vast majority of measurements of organolead compounds in the environment do not constitute evidence for biomethylation of lead. Most environmental organic lead comes from incomplete combustion or spillage of methyl- or ethyl-lead gasoline additives (viz tetraalkylleads or TALs). A literature search will produce several hundred TAL or ionic alkyllead results, but few of them are evidence for methylation in or by the environment. 

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. 

Tetraalkylleads are highly lipid, soluble, rapidly metabolized and readily cross the blood-brain barrier. These physicochemical properties make the central nervous system the main site of the toxic action of the alkyllead species138. The earliest symptoms include insomnia, which may be followed by lack of appetite, nausea, vomiting, diarrhea hallucinations, delusions, delirium and ultimately death141. Continuing exposure may lead to complaints associated with central nervous system disturbances141. 

The most toxic organoleads are the trialkylleads, whose toxicity increases with alkyl chain length. Tetraalkylleads themselves are completely nontoxic and their apparent toxicity is due to their trialkyllead breakdown products136. 

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

Huber, F., Petz, W., Eds. Tetraalkyllead, Tetraaryllead. In Gmelin Handbook of Inorganic and Organometallic Chemistry, 8th ed., Organolead Compounds, Part 3 Springer Berlin, 1992. 

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. 

Seeber A, Kiesswetter E, Neidhart B, et al Neurobehavioral effects of long term exposure to tetraalkyllead. Neurotoxicol Teratol 12 653-655, 1990... 

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