Tetraalkyl lead

The main concern regarding tetraalkyl lead has been about human health hazards, a concern that has resulted in the progressive replacement of leaded petrol by unleaded petrol in most countries (Environmental Health Criteria 85). There has been particular concern about possible brain damage to children in polluted urban areas. Little work has been done on the effects of organolead compounds on wildlife or ecosystems, so the following account will be brief. 

Organic Lead. Following a single exposure to vapors of tetraalkyl lead compounds (approximately 1 mg/m3 breathed through a mouthpiece, 10-40 breaths of approximately 1 L volume) in four male subjects, 37% and 51% of inhaled tetraethyl and tetramethyl lead, respectively, were initially found in the respiratory tract, but a considerable percentage of these volatile compounds was lost through exhalation (Heard et al. 1979). Approximately 60-80% of the deposited tetraalkyl lead was absorbed by the lungs. 

Organic Lead. Urinary lead levels were elevated for 4 days in a man accidentally exposed to an unknown quantity of tetramethyl lead (Gething 1975). Exhalation of the tetraalkyl lead compounds following inhalation exposure is a major route of elimination in humans. At 48 hours postexposure, 40% and 20% of the initially inhaled tetramethyl and tetraethyl lead doses, respectively, were exhaled with low urinary excretion (Heard et al. 1979). 

Biomarkers of exposure for inorganic and organic forms of lead are usually the measurement of total lead levels in tissues or fluids. Total lead measurements of biological media includes all metabolites and endogenous lead sources as well as any original lead-containing exposure agent. Tetraalkyl lead compounds may also be measured in the breath. 

In water, tetraalkyl lead compounds are subject to photolysis and volatilization with the more volatile compounds being lost by evaporation. Degradation proceeds from trialkyl lead to dialkyl lead to inorganic lead. Tetraethyl lead is susceptible to photolytic decomposition in water. Triethyl and trimethyl lead are more water-soluble and therefore more persistent in the aquatic environment than tetraethyl or tetramethyl lead. The degradation of trialkyl lead compounds yields small amounts of dialkyl lead compounds. Removal of tetraalkyl lead compounds from seawater occurs at rates that provide half-lives measurable in days (DeJonghe and Adams 1986). 

Birch J, Harrison RM, Laxen DPH. 1980. A specific method for 24-48 hour analysis of tetraalkyl lead in air. Sci Total Environ 14 31-42. 

Chau YK, Wong PTS, Bengert GA, et al. 1979. Determination of tetraalkyl- lead compounds in water, sediments, and fish samples. Anal Chem 51 186-188. 

DeJonghe WRA, Chakraborti D, Adams FC. 1981. Identification and determination of individual tetraalkyl lead species in air. Environ Sci Technol 15 1217-1222. 

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. 

Sirota, G.R. and J.F. Uthe. 1977. Determination of tetraalkyl lead compounds in biological materials. Anal. Chem. 49 823-825. 

Hazards Associated with Organic Chemical Manufacturing Tetraalkyl Lead by Lead Alkylation, Mitre Corp., McLean, VA, Report No. MTR-78W00364-03, May 1979. 

Tetramethyllead has been also put forward as an antishock additive for engine fuel. Comparison tests have shown that tetramethyllead is more efficient that tetraethyllead, especially in petrols with high content of aromatic hydrocarbons. Tetraalkyl lead derivatives can also be used in the production of lead alkylhalogenides and their derivatives. 

Suggest cathodes and anodes for the following processes, giving a full rationalization of your choices (a) methyl chloride to tetraalkyl lead, (b) acetone to pinacol, and (c) nitrobenzene to /t-amino phenol. Your choices need not be limited to the electrode materials mentioned here. (Bockris)... 

Speciation of lead in air and atmospheric particulates is still a topic of great environmental relevance. Sodium tetrahydroborate may be used to hydrogenate inorganic lead ions and alkyl-lead species.60 As in the study by Balls outlined above, cryogenic trapping may again be used to trap temporarily the plumbane and alkyl- and tetraalkyl-lead compounds, which are then released sequentially by heating for detection by flame AAS. 

O3) have not been attained. In contrast, MTBE was incorporated in European gasoline as an octane enhancer to replace banned tetraalkyl lead compounds and increasing restrictions on aromatics content. 

The electrochemiral synthesis of tetraalkyl lead by the Nalco proc ... 

In the sediments, lead is mobilized and released when the pH decreases suddenly or ionic composition changes. However, there was no significant release of lead from dredge spoils suspended in estuarine waters of different salinities for 4 weeks. Some Pb " in sediments may be transformed to tetraalkyl lead... 

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