Tetra-ethyl lead

Unbumt gasoline and cracked hydrocarbons such as ethylene and propylene are also substantial constituents of exhaust. Gasoline contains additives such as benzene, toluene and branched hydrocarbons to achieve the necessary octane numbers. The direct emission of these volatile compounds, e.g. at gas stations, is a significant source of air pollution. Leaded fuels, containing antiknock additions such as tetra-ethyl-lead, have been abandoned because lead poisons both human beings and the three-way exhaust catalyst, especially for the removal of NO by rhodium. 

Equipment Leaks of VOC in the Synthetic Organic Chemicals Manufacturing Industry (SOCMI)—chemicals produced by affected facilities (tetra ethyl lead, tetramethyl lead)... 

MachleWR. 1935. Tetra-ethyl lead intoxication and poisoning by related compounds of lead. JAMA 105 578-585. 

Tetra ethyl lead (TEL) was used as an anti-knock agent in automotive gasoline. Small amounts were normally added. During the compression stroke TEL reacts with the air to form very small lead oxide particles. Give an explanation why you believe TEL would be an effective anti-knock agent. 

As early as 1925, two of the first automobile engineers became aware of the need to improve the octane number of fuels. Charles Kettering advocated the use of a newly developed compound called tetra-ethyl lead, Pb(C2H5)4. This compound acts as a catalyst to... 

Tetra-ethyl lead became the chosen fuel additive. Over many decades, lead emissions from car exhausts accumulated in urban ponds and water systems. Many waterfowl that live in urban areas experience lead poisoning. Lead is also dangerous to human health. 

Antiknock gasoline a gasoline to which a low percentage of tetra-ethyl-lead, or similar compound, has been added to increase octane number and eliminate knocking. Such gasolines have an octane number of 100 or more and are now used chiefly as aviation fuel. 

Tetra-ethyl lead is added to petrol as an anti-knock agent. When the petrol is burnt in the engine, the organic lead is converted to inorganic compounds. Ethylene dibromide is added to the tetra-ethyl... 

As early as 1937, R.A. Kehoe began to investigate the human uptake of lead at the Kettering Laboratory, Cincinnati. A full account of the work, with statistical analysis, has been published by Gross (1981). In this and later work by Griffin et al. (1975), lead aerosol was produced by burning tetra-ethyl lead in propane and was passed into chambers. Volunteers were exposed in the chambers to the lead aerosol daily over periods of several months. The concentration of lead in the air (PbA) was monitored continuously, and samples of venous blood were taken from the volunteers at intervals for measurement of blood lead (PbB). It was found that PbB increased during the first month or two and then reached a quasi-equilibrium in which the intake from inhalation was balanced by excretion. 

Pb was obtained as a solution of PbCl2. Tetra-ethyl lead was synthesised by a Grignard reaction and added to petrol together with ethylene dibromide. The petrol was burnt in a 50-cc four-stroke engine, and the exhaust passed into a wind tunnel (Fig. 7.8). The airflow in the tunnel gave sufficient dilution to limit the concentration of CO to 1000... 

Fig. 7.8. The effect of two types of anti-knock on the characteristics of two-stage ignition measured in a rapid compression machine. Ti is the time from the end of compression to the cool-flame is the subsequent time to the true ignition AT is the temperature rise over the cool-flame. Conditions 0.5 stoichiometric mixture of 2-methyl pentane and air at 720 K and total concentration 3.2 x 10 mol cm . TEL (tetra-ethyl lead) affects the second stage, but not ti, NMA (N-methyl aniline) affects both ti and t2. From [42],...

Both types of anti-knock are more effective in paraffinic fuels then in olefinic or aromatic fuels, and can even promote knock when added to some alcohols. In Fig. 7.9 the response of some pure hydrocarbons to the addition of 3ml/US gal of tetra-ethyl lead is shown, in terms of Performance Number. Almost all the alkanes lie on a steeper line than the alkenes. The exceptions are low octane number alkenes, which are largely straight alkane chains, and a few highly-branched alkanes (which also have high sensitivity, see Section 7.2.3). Notwithstanding the subtleties of lead additives, a broad explanation in chemical kinetic terms is that the antiknock acts to increase radical termination rates and, consequently, has proportionately less effect in those fuels where the termination rates are already high. 

Fig. 7.9. Effect on octane quality of adding 3 ml/US gal tetra-ethyl lead to pure alkane and alkene fuels. The Performance Number is a practical measure of the propensity of a fuel to knock and related to the research octane number, RON, by the empirical formula PN = 2800/(128-RON). Except for a few highly branched species, the TEL increases the the performance number of alkanes by a constant factor of 1.5. It is less effective in alkene...

Leaded fuels, containing antiknock additions such as tetra ethyl lead, have been abandoned nowadays because lead is a poison for human beings and for the three-way catalyst, especially for the removal of NO by rhodium. 

One of the most widely known examples of catalyst poisoning is taken from the automobile industry. Though tetra-ethyl lead has been removed from essentially all gasoline in North America, the ban on leaded gasoline is not worldwide, and leaded and unleaded gasoline is available in many countries. Catalytic converters, which contain precious metals like platinum, palladium, and rhodium, are used to both reduce NO c and oxidize CO and unburned hydrocarbons. Lead irreversibly destroys the catalytic ability of the converter. Concentrations of lead in leaded gasoline are nominally 150mg/L. 

Polymerization of Propene and Ethene Induced by Tetra-ethyl Lead. 

Cassells DAK, Dodds EC Tetra-ethyl lead poisoning. BM] 2 681-685,1946 Grandjean P, Nielsen T Organolead compounds environmental health aspects. Residue Reviews 72 97-148, 1979... 

Hamilton A, Reznikoff P, Burnham GM Tetra-ethyl lead. JAMA 84 1481-1486, 1925 Hardy HL, Maloof CC Evidence of systemic effect of tetryl with summary of available literature. AMA Archives of Industrial Hygiene and Occupational Medicine... 

Kehoe RA Tetra-ethyl lead poisoning clinical analysis of a series of nonfatal cases. JAMA 85 108-110, 1925... 

Mitchell CS, Shear MS, Bolla KI, et al Clinical evaluation of 58 organolead manufacturing workers. J Occup Environ Med 38 372-378, 1996 Norris C, Gettler AO Poisoning by tetra-ethyl lead postmortem and chemical findings. JAMA 85 818-820, 1925... 

The alkyl leads rapidly became the most cost-effective method of enhancing octane. Up until the late 1960s, alkyl leads were added to gasoline in increasing concentrations to improve octane number. However, in later years, the use of tetra ethyl lead was not encouraged. Presently in most countries of the world, the use of tetra ethyl lead as an additive to gasoline is prohibited by law. 

Most gasoline contain lead additives, which provide the antiknock characteristics that are required by present-day high compression engines. The most common additives contain tetra-ethyl lead or tetra-methyl lead together with organic chlorides and bromides. 

Due to their physical and chemical properties, alkali metals were not regarded as being attractive metals in the classical sense of application of metals. Therefore, these metals were mainly used as intermediates for chemical processes. Sodium, for instance, was largely produced for the synthesis of tetra ethyl lead on the basis of the reaction of ethyl chloride with the sodium lead intermetallic compound NaPb. 

The sodium lead system is important, since NaPb compounds are applied to chemical processes. The intermetallic compound NaPb is fabricated in large amounts as an intermediate for the production of tetra ethyl lead. The Na—Pb phase diagram indicates the formation of several compounds, as shown in Fig. 14. The solubility of lead in liquid sodium is considerably high, the saturated solution contains 3 at- % Pb at 250 °C. The sodium-tin system shows a similar solution and compound formation behaviour. 

Figure 24.9. Vapor pressure of selected compounds versus temperature. (Note Atmospheric pressure is 760mmHg.) (Copyright, 2001, CRC Press, used with permission) (Stegemeier and Vinegar, 2001). TEL, tetra-ethyl lead PCP, pentachlorophenol TCDD, 2,3,7,8-tetrachlorodibenzo-p-dioxin PCB, polychlorinated biphenyls.

Atmospheric lead emissions in Nigeria have been estimated to be 2800 metric tonnes per year with most (90%) derived from automobile tail pipe (Nriagu et al, 1997). Lead in the form of tetra-ethyl lead Pb(C2H5)4 is the most common additive to petrol to raise its octane number. Upon combustion in the petrol engine, the organic lead is oxidized to lead oxide according to the following reaction ... 

Analyses of ice in the core drilled at Camp Century in northwest Greenland revealed that the concentration of lead increased gradually from 0.011 pg/kg in 1753 A.D. to 0.068 pg/kg in 1945 A.D. Subsequently, the concentration of lead rose steeply and reached 0.16 pg/kg in 1960 (Murozumi et al. 1969). The dramatic increase in the concentration of lead in this ice core was attributed to the widespread use of gasoline that contained tetra-ethyl lead as an additive. 

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