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'''Tetraethyl lead''' (TEL) is a viscous 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> | '''Tetraethyl lead''' (TEL) is a viscous 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. | 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== | |||
Tetraethyl lead 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 mols of chloroethane + 4 mols of sodium-lead alloy → 1 mol of tetraethyl lead + 4 mols of sodium chloride + 3 mols of lead | |||
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 engine]]s, tetraethyl lead 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== | |||
When tetraethyl lead 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 species such as [[lead oxide]] (PbO): | |||
: 2 Pb + O<sub>2</sub> → 2 PbO | |||
The Pb and PbO would quickly accumulate and destroy an engine. For this reason, the lead scavengers [[1,2-Dibromoethane|1,2-dibromoethane]] and [[1,2-Dichloroethane|1,2-dichloroethane]] are used in conjunction with TEL. | |||
==References== | |||
{{reflist}} | |||
Revision as of 23:53, 14 May 2009
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Tetraethyl lead (TEL) is a viscous liquid with the chemical formula (CH3CH2)4Pb. 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[2]primarily because of the toxicity of the lead emissions 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 pollutants.
Manufacture and properties
Tetraethyl lead is produced by the alkylation of a sodium-lead alloy using chloroethane as expressed by this chemical equation:
- 4 CH3CH2Cl + 4 NaPb → (CH3CH2)4Pb + 4 NaCl + 3 Pb
which can also be written as:
- 4 mols of chloroethane + 4 mols of sodium-lead alloy → 1 mol of tetraethyl lead + 4 mols of sodium chloride + 3 mols of lead
The product tetraethyl lead is a viscous colorless liquid that is highly lipophilic and soluble in fats, oils and lipids as well as gasoline and other non-polar hydrocarbons. Other properties of tetraethyl lead are listed in the adjacent table.
At the temperatures found in spark-ignited internal combustion engines, tetraethyl lead decomposes completely into lead and lead oxide (PbO) and combustible, short-lived ethyl radicals. 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
When tetraethyl lead burns, it produces not only carbon dioxide (CO2) and water (H2O), but also lead (Pb):
- (CH3CH2)4Pb + 13 O2 → 8 CO2 + 10 H2O + Pb
The lead can the oxidize further to give species such as lead oxide (PbO):
- 2 Pb + O2 → 2 PbO
The Pb and PbO would quickly accumulate and destroy an engine. For this reason, the lead scavengers 1,2-dibromoethane and 1,2-dichloroethane are used in conjunction with TEL.
References
- ↑ 1.0 1.1 1.2 1.3 1.4 1.5 NIST Chemistry WebBook
- ↑ 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.