Tetraethyllead

Names
Preferred IUPAC name Tetraethylplumbane
Other names Lead tetraethyl Tetraethyl lead Tetra-ethyl lead
Identifiers
CAS Number	78-00-2 Y
3D model (JSmol)	Interactive image
Abbreviations	TEL
Beilstein Reference	3903146
ChEBI	CHEBI:30182 Y
ChemSpider	6265 Y
ECHA InfoCard	100.000.979
EC Number	201-075-4
Gmelin Reference	68951
MeSH	Tetraethyl+lead
PubChem CID	6511
RTECS number	TP4550000
UNII	13426ZWT6A Y
UN number	1649
CompTox Dashboard (EPA)	DTXSID7023801
InChI InChI=1S/4C2H5.Pb/c4*1-2;/h4*1H2,2H3; Y Key: MRMOZBOQVYRSEM-UHFFFAOYSA-N Y
SMILES CC(CC)(CC)CC
Properties
Chemical formula	C8H20Pb
Molar mass	323.4 g·mol−1
Appearance	Colorless liquid
Odor	pleasant, sweet[1]
Density	1.653 g cm−3
Melting point	−136 °C (−213 °F; 137 K)
Boiling point	84 to 85 °C (183 to 185 °F; 357 to 358 K) 15 mmHg
Solubility in water	200 parts per billion (ppb) (20 °C)[1]
Vapor pressure	0.2 mmHg (20 °C)[1]
Refractive index (nD)	1.5198
Structure
Molecular shape	Tetrahedral
Dipole moment	0 D
Hazards
Occupational safety and health (OHS/OSH):
Main hazards	Flammable, extremely toxic
GHS labelling:
Pictograms
Hazard statements	H300+H310+H330, H360, H373, H410
Precautionary statements	P201, P202, P260, P262, P264, P270, P271, P273, P280, P281, P284, P301+P310, P302+P350, P304+P340, P308+P313, P310, P314, P320, P321, P322, P330, P361, P363, P391, P403+P233, P405, P501
NFPA 704 (fire diamond)	4 2 3
Flash point	73 °C (163 °F; 346 K)
Explosive limits	1.8%–?[1]
Lethal dose or concentration (LD, LC):
LD50 (median dose)	35 mg/kg (rat, oral) 17 mg/kg (rat, oral) 12.3 mg/kg (rat, oral)[2]
LDLo (lowest published)	30 mg/kg (rabbit, oral) 24 mg/kg (rat, oral)[2]
LC50 (median concentration)	850 mg/m3 (rat, 1 hr)[2]
LCLo (lowest published)	650 mg/m3 (mouse, 7 hr)[2]
NIOSH (US health exposure limits):
PEL (Permissible)	TWA 0.075 mg/m3 [1]
REL (Recommended)	TWA 0.075 mg/m3 [1]
IDLH (Immediate danger)	40 mg/m3 (as Pb)[1]
Related compounds
Related compounds	Tetramethyllead Tetraethylmethane Tetraethylsilane Tetraethylgermanium Tetraethyltin
Except where otherwise noted, data are given for materials in their standard state (at 25 °C , 100 kPa). Y verify (what is YN ?) Infobox references

Tetraethyllead (commonly styled tetraethyl lead), abbreviated TEL, is an organolead compound with the formula Pb(C₂H₅)₄. It was widely used as a fuel additive for much of the 20th century, first being mixed with gasoline beginning in the 1920s. This "leaded gasoline" had an increased octane rating that allowed engine compression to be raised substantially and in turn increased vehicle performance and fuel economy.^[3][4] TEL was first synthesised by German chemist Carl Jacob Löwig in 1853. American chemical engineer Thomas Midgley Jr., who was working for the U.S. corporation General Motors, was the first to discover its effectiveness as an antiknock agent in 1921, after spending several years attempting to find an additive that was both highly effective and inexpensive.

In the mid-20th century, scientists discovered TEL caused lead poisoning and was toxic to the human brain, especially in children.^[5] The United States and many other countries began phasing out the use of TEL in automotive fuel in the 1970s. By the early 2000s, most countries had completely banned the use of TEL in gasoline. Since 2011, leaded gasoline has been banned in every country. A 2011 study backed by the United Nations estimated that the removal of TEL had resulted in $2.4 trillion in annual benefits, and 1.2 million fewer premature deaths.^[6]

Despite being banned from use in automotive fuel, TEL is sometimes still used in certain grades of aviation fuel. Innospec has claimed to be the last firm legally making TEL but, as of 2013^[update], TEL was being produced illegally by several companies in China.^[7] In July 2021, the sale of leaded gasoline for cars was completely phased out worldwide, prompting the United Nations Environment Programme (UNEP) to declare an "official end" of its use in cars on August 30, 2021.^[8]

Synthesis and properties

TEL is produced by reacting chloroethane with a sodium–lead alloy.^[9][10]

The product is recovered by steam distillation, leaving a sludge of lead and sodium chloride.^[11] TEL is a viscous colorless liquid with a sweet odor.^[12] Because TEL is charge neutral and contains an exterior of alkyl groups, it is highly lipophilic and soluble in petrol (gasoline). This property, which allows it to dissolve so evenly and effectively in motor fuel, also allows it to dissolve oils and fats well, and therefore, diffuse through the blood–brain barrier and accumulate within the limbic forebrain, frontal cortex, and hippocampus.^[13]

Despite decades of research, no reactions were found to improve upon this process, which is rather difficult, involves metallic sodium, and converts only 25% of the lead to TEL. A related compound, tetramethyllead, was commercially produced by a different electrolytic reaction.^[9] A process with lithium was developed but never put into practice.^[14]

Reactions

A noteworthy feature of TEL is the weakness of its four C–Pb bonds. At the temperatures found in internal combustion engines, TEL decomposes completely into lead as well as combustible, short-lived ethyl radicals. Lead and lead oxide scavenge radical intermediates in combustion reactions. Engine knock is caused by a cool flame, an oscillating low-temperature combustion reaction that occurs before the proper, hot ignition. Lead quenches the pyrolysed radicals and thus kills the radical chain reaction that would sustain a cool flame, preventing it from disturbing the smooth ignition of the hot flame front. Lead itself is the reactive antiknock agent, and the ethyl groups serve as a gasoline-soluble carrier.^[9]

When TEL burns, it produces not only carbon dioxide and water, but also lead and lead(II) oxide:^[15]

Pb and PbO would quickly over-accumulate and foul an engine. For this reason, 1,2-dichloroethane and 1,2-dibromoethane were also added to gasoline as lead scavengers—these agents form volatile lead(II) chloride and lead(II) bromide, respectively, which flush the lead from the engine and into the air:^[15]

In motor fuel

TEL was extensively used as a gasoline additive beginning in the 1920s,^[16] wherein it served as an effective antiknock agent and reduced exhaust valve and valve seat wear. Concerns were raised in reputable journals of likely health outcomes of fine particles of lead in the atmosphere.^[17][18][19]

Valve wear preventive

Tetraethyllead helps cool intake valves and is an excellent buffer against microwelds forming between exhaust valves and their seats.^[20] Once these valves reopen, the microwelds pull apart and abrade the valves and seats, leading to valve recession. When TEL began to be phased out, the automotive industry began specifying hardened valve seats and upgraded materials which allow for high wear resistance without requiring lead.^[21]

Antiknock agent

A gasoline-fuelled reciprocating engine requires fuel of sufficient octane rating to prevent uncontrolled combustion (preignition and detonation).^[9] Antiknock agents allow the use of higher compression ratios for greater efficiency^[22] and peak power.^[23] Adding varying amounts of additives to gasoline allowed easy, inexpensive control of octane ratings. TEL offered the business advantage of being commercially profitable because its use for this purpose could be patented.^[16] Aviation fuels with TEL used in WWII reached octane ratings of 150 to enable turbocharged and supercharged engines such as the Rolls-Royce Merlin and Griffon to reach high horsepower ratings at altitude.^[24] In military aviation, TEL manipulation allowed a range of different fuels to be tailored for particular flight conditions.^{[citation needed]}

In 1935 a licence to produce TEL was given to IG Farben, enabling the newly formed German Luftwaffe to use high-octane gasoline. A company, Ethyl GmbH, was formed that produced TEL at two sites in Germany with a government contract from 10 June 1936.^[25]

In 1938 the United Kingdom Air Ministry contracted with ICI for the construction and operation of a TEL plant. A site was chosen at Holford Moss, near Plumley in Cheshire. Construction started in April 1939 and TEL was being produced by September 1940.^[26]

"Ethyl Fluid"

For mixing with raw gasoline, TEL was most commonly supplied in the form of "Ethyl Fluid", which consisted of TEL blended with 1,2-dichloroethane and 1,2-dibromoethane. Ethyl Fluid also contained a reddish dye to distinguish treated from untreated gasoline and discourage the use of leaded gasoline for other purposes such as cleaning.^[27]

In the 1920s before safety procedures were strengthened, 17 workers for the Ethyl Corporation, DuPont, and Standard Oil died from the effects of exposure to lead.^[16]

Ethyl Fluid's formulation consisted of:^[9]

• 61.45% tetraethyllead
• 18.80% 1,2-dichloroethane
• 17.85% 1,2-dibromoethane
• 1.90% inerts and dyes

Dichloroethane and dibromoethane act in a synergistic manner, where equal or approximately equal quantities of both provide the best scavenging ability.^[9]

Phaseout and ban

In most industrialized countries, a phaseout of TEL from road vehicle fuels was completed by the early 2000s because of concerns over air and soil lead levels and the accumulative neurotoxicity of lead. In the European Union, tetraethyllead has been classified as a Substance of Very High Concern and placed on the Candidate List for Authorisation under Registration, Evaluation, Authorisation and Restriction of Chemicals (REACH).^[28] Potential use of TEL would need to be authorised through the REACH authorisation procedure. While not a complete ban, it introduces significant obligations such as a mandatory analysis of alternatives and socioeconomic analysis.^{[citation needed]}

The use of catalytic converters, mandated in the United States for 1975 and later model-year cars to meet tighter emissions regulations, started a gradual phase-out of leaded gasoline in the U.S.^[29] The need for TEL was lessened by several advances in automotive engineering and petroleum chemistry. Safer methods for making higher-octane blending stocks such as reformate and iso-octane reduced the need to rely on TEL, as did other antiknock additives of varying toxicity including metallic compounds such as methylcyclopentadienyl manganese tricarbonyl (MMT) as well as oxygenates including methyl tertiary-butyl ether (MTBE), tert-amyl methyl ether (TAME), and ethyl tert-butyl ether (ETBE).^{[citation needed]}

The first country to completely ban leaded gasoline was Japan in 1986.^[30]

Since January 1993 all gasoline powered cars sold in the European Union and the United Kingdom have been required to use unleaded fuel. This was to comply with the Euro 1 emission standards which mandated that all new cars to be fitted with a catalytic converter.^[31] Unleaded fuel was first introduced in the United Kingdom in June 1986.^[32]

Leaded gasoline was removed from the forecourts in the United Kingdom on January 1, 2000, and a Lead Replacement Petrol was introduced although this was largely withdrawn by 2003 due to dwindling sales.^[33][34] An exemption to the ban exists for owners of classic cars.^{[citation needed]}

Vehicles designed and built to run on leaded fuel often require modification to run on unleaded gasoline. These modifications fall into two categories: those required for physical compatibility with unleaded fuel, and those performed to compensate for the relatively low octane of early unleaded fuels. Physical compatibility requires the installation of hardened exhaust valves and seats. Compatibility with reduced octane was addressed by reducing compression, generally by installing thicker cylinder head gaskets and/or rebuilding the engine with compression-reducing pistons, although modern high-octane unleaded gasoline has eliminated the need to decrease compression ratios.^{[citation needed]}

Leaded gasoline remained legal as of late 2014^[35] in parts of Algeria, Iraq, Yemen, Myanmar, North Korea, and Afghanistan.^{[36][37][needs update]} North Korea and Myanmar purchased their TEL from China, while Algeria, Iraq, and Yemen purchased it from the specialty chemical company Innospec, the world's sole remaining legal manufacturer of TEL.^[38] In 2011 several Innospec executives were charged and imprisoned for bribing various government state-owned oil companies to approve the sale of their TEL products.^[37][39]

As of June 2016^[update] the UNEP-sponsored phase-out was nearly complete: only Algeria, Iraq, and Yemen continued widespread use of leaded gasoline, although not exclusively.^[40] In July 2021, Algeria had halted its sale.^[8]

Leaded-fuel bans

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Leaded-fuel bans for road vehicles came into effect as follows: