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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 nationsprimarily 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.

Properties Property Value Common name tetraethyl lead Other names tetra-ethyl lead, lead tetraethyl, tetraethyl plumbane, TEL IUPAC name CAS number 78-00-2 Molecular formula (CH3CH2)4Pb Molecular mass 323.4 g/mol Density 1.653 g/ml for liquid at 20 °C, 1 atm Boiling point 455.7 K (182.6 °C) at 1 atm Melting point 142.94 K (-130.2 °C) Specific heat, cp 0.956 J/(g·K) for liquid at 20 °C Heat of vaporization 175.0 J/g for liquid at 182.6 °C Heat of fusion 27.2 J/g for solid at -130.2 °C Viscosity Refractive index

Manufacture and properties

TEL 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, TEL 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 formulation

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 lead oxide (PbO):

2 Pb + O₂ → 2 PbO

The Pb and PbO would quickly accumulate and destroy an engine. For this reason, the TEL used in gasoline was actually part of a formulated liquid fluid known as TEL fluid or ethyl fluid that contained 1,2-dibromoethane and 1,2-dichloroethane liquids which served to scavenge the Pb and PbO from the engine.