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'''Tetraethyl lead''' (TEL) is a liquid with the chemical formula (CH<sub>3</sub>CH<sub>2</sub>)<sub>4</sub>Pb. Once widely used (circa 1925 to 1990) to increase the [[octane rating]] of [[gasoline]] ([[petrol]]), TEL usage in gasoline has been largely phased out by most nations<ref>
[http://www.uneptie.org/energy/transport/documents/pdf/phasingLead.pdf Phasing Lead Out of Gasoline] A report issued by the [[United Nations Environmental Programme]] (UNEP). See page 8 of 23 pdf pages.</ref> primarily because of the toxicity of the [[lead]] [[emission]]s from spark-ignited [[internal combustion engines]] burning gasoline containing TEL. Another reason for discontinuing TEL usage was that it degraded the efficiency of the [[catalytic converters]] installed in automotive vehicles to reduce their emissions of [[Air pollution|air pollutant]]s.


==Manufacture and properties==
TEL is produced by the alkylation of a [[sodium]]-[[lead]] [[alloy]] using [[chloroethane]] as expressed by this chemical equation:
:4 CH<sub>3</sub>CH<sub>2</sub>Cl + 4 NaPb →  (CH<sub>3</sub>CH<sub>2</sub>)<sub>4</sub>Pb + 4 NaCl + 3 Pb
which can also be written as:
:4 [[mole]]s of chloroethane + 4 moles of sodium-lead alloy → 1 mole of tetraethyl lead + 4 moles of sodium chloride + 3 moles of lead
{| border="0" width="360" align="right" cellpadding="0" cellspacing="0" style="wrap=no"
|
{| class = "wikitable" align="right" style="font-size:85%;"
|+ <font size=3px> Properties </font>
! width=120px|Property!! Width=185px|Value
|-
| align="left"|'''Common name'''|| align="left"|tetraethyl lead
|-
| align="left"|'''Other names'''|| align="left"|tetra-ethyl lead, lead tetraethyl,<br/>tetraethyl plumbane, TEL
|-
| align="left"|'''IUPAC name''' || align="left"|tetraethylplumbane
|-
| align="left"|'''CAS number'''|| align="left"|78-00-2
|-
| align="left"|'''Molecular formula''' || align="left"|(CH<sub>3</sub>CH<sub>2</sub>)<sub>4</sub>Pb
|-
| align="left"|'''[[Molecular mass]]''' || align="left"|323.4 g/mol<ref name=NIST>[http://webbook.nist.gov/cgi/cbook.cgi?Name=tetraethyl+lead&Units=SI NIST Chemistry WebBook]</ref>
|-
| align="left"|'''[[Density]]''' || align="left"|1.653 g/ml for liquid at 20 °[[Celsius|C]], 1 [[Pressure|atm]]
|-
| align="left"|'''[[Boiling point]]''' || align="left"|455.7 K (182.6 °C) at 1 atm<ref name=NIST/>
|-
| align="left"|'''Melting point''' || align="left"|142.94 K (-130.2 °C)<ref name=NIST/>
|-
| align="left"|'''[[Specific heat]], c<sub>p</sub>''' || align="left"|0.956 J/(g·K) for liquid at 20 °C<ref name=NIST/>
|-
| align="left"|'''Heat of vaporization'''|| align="left"|175.0 J/g for liquid at 182.6 °C<ref name=NIST/>
|-
| align="left"|'''Heat of fusion'''|| align="left"|27.2 J/g for solid at -130.2 °C<ref name=NIST/>
|-
| align="left"|'''Viscosity'''||align="left"|
|-
| align="left"|'''Refractive index'''||align="left"|
|}
|}
The product tetraethyl lead is a [[Viscosity|viscous]] colorless liquid that is highly [[Lipophilicity|lipophilic]] and soluble in fats, oils and [[lipids]] as well as gasoline and other [[non-polar]] [[hydrocarbon]]s. Other properties of tetraethyl lead are listed in the adjacent table.
At the temperatures found in spark-ignited internal combustion engines, TEL decomposes completely into lead and [[lead oxide]] (PbO) and combustible, short-lived ethyl [[Radical (chemistry)|radical]]s. Lead itself is the reactive agent that enhances the octane rating of gasolines and tetraethyl lead serves as a gasoline-soluble lead carrier.
==TEL fluid formulation==
When TEL burns, it produces not only [[carbon dioxide]] (CO<sub>2</sub>) and [[water]] (H<sub>2</sub>O), but also lead (Pb):
: (CH<sub>3</sub>CH<sub>2</sub>)<sub>4</sub>Pb  +  13 O<sub>2</sub>  →  8 CO<sub>2</sub>  +  10 H<sub>2</sub>O  +  Pb
The lead can the oxidize further to give lead oxide (PbO):
: 2 Pb  + O<sub>2</sub> → 2 PbO
The Pb and PbO would soon accumulate and destroy an engine. For this reason, the TEL used in gasoline was  actually part of a blended liquid formulation known as '''''TEL fluid''''' or '''''ethyl fluid''''' that contained [[1,2-Dibromoethane|1,2-dibromoethane]] and [[1,2-Dichloroethane|1,2-dichloroethane]] liquids known as ''lead scavengers''. Those scavengers formed [[lead bromide]] (PbBr) and [[lead chloride]] (PbCl) which are volatile and were emitted from the engine exhaust to the [[atmosphere]]. The complete composition of TEL fluid was:<ref>[http://www.epa.gov/OUST/cat/Section_2-Historical_Usage.pdf Historical Uses] A publication of the [[U.S. Environmental Protection Agency]]</ref>
*Tetraethyl lead &nbsp; &nbsp; &nbsp; 61.45%
*1,2-Dibromoethane 17.85%
*1,2-Dichloroethane 18.80%
*Inerts & color dye &nbsp; &nbsp;1.90%
The addition of as little as 0.8 ml of TEL fluid per [[liter]] of gasoline (3 ml/[[U.S. customary units|gallon]]) of gasoline was equivalent to adding 0.5 g of lead per liter of gasoline and resulted in significant increases in the octane rating of the gasoline.
==History of tetraethyl lead as a gasoline octane enhancer==
{{main|Lead|Gasoline|Octane rating}}
Good sources for TEL history.<ref>[http://pubs.acs.org/doi/pdf/10.1021/om030621b The Rise and Fall of Tetraethyllead. 2.] Dietmar Seyferth, Department of Chemistry, [[Massachusetts Institute of Technology]], Organometallics, 2003, 22 (25), pp 5154–5178</ref>
<ref>[http://www.runet.edu/~wkovarik/papers/kettering.html Charles F. Kettering and the 1921 Discovery of Tetraethyl Lead In the Context of Technological Alternatives]</ref>
==References==
{{reflist}}

Revision as of 13:31, 15 May 2009

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