Tetraethyllead

TEL is produced on an industrial scale by reacting chloroethane (ethyl chloride) with a sodium–lead alloy. The product is recovered by steam distillation, leaving a sludge of lead and sodium chloride. TEL is a viscous colorless liquid with a sweet odor. 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 allowed easy absorption by body fats and lipids and diffusion through the blood–brain barrier (BBB). The lead (II) ions (Pb2+) would accumulate within the limbic forebrain, frontal cortex, and hippocampus. Practically speaking, TEL is a "central nervous system toxin which produces an acute toxic psychosis." There is no cure for direct poisoning by TEL. Inorganic lead compounds, such as those present in engine exhausts, could be removed from the system through the administration of chelating agents, which bind to the inorganic lead and flush them out of the body. However, highly lipid-soluble TEL cannot be removed this way, and treatments are of a supportive nature. Despite decades of research, no reactions were found to improve upon this process; it is rather difficult, involves reactive metallic sodium, and converts only 25% of the lead to TEL. A related compound, tetramethyllead, was commercially produced by a different electrolytic reaction. However, tetramethyllead was even more difficult to make, and it did not find use beyond niche applications. == 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 pyrolyzed 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. Pb(C2H5)4 + C2H4X2 + 16 O2 -> 10 CO2 + 12 H2O + PbX2 == In motor fuel ==

TEL was extensively used as a gasoline additive beginning in the 1920s, Valve wear preventive Tetraethyllead helps cool intake valves and is an excellent buffer against microwelds forming between exhaust valves and their seats. 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. Antiknock agent A gasoline-fueled reciprocating engine requires fuel of sufficient octane rating to prevent uncontrolled combustion (pre-ignition and detonation). and peak power. 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. In military aviation, TEL manipulation allowed a range of different fuels to be tailored for particular flight conditions. In 1935 a license to produce TEL was given to IG Farben, enabling the newly formed German to use high-octane gasoline for high altitude flight. A company, Ethyl GmbH, was formed that produced TEL at two sites in Germany with a government contract from 10 June 1936. 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. "Ethyl Fluid" For mixing with raw gasoline, TEL was most commonly supplied in the form of "Ethyl Fluid", consisting of TEL blended with 1,2-dichloroethane and 1,2-dibromoethane, which prevent lead from building up in the engine. 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. 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. Potential use of TEL would need to be authorized through the REACH authorization procedure. While not a complete ban, it introduces significant obligations such as a mandatory analysis of alternatives and socioeconomic analysis. 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. 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. Unleaded fuel was first introduced in the United Kingdom in June 1986. 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. An exemption to the ban exists for owners of classic cars. 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, or by use of additives. 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 ), and/or by retarding ignition timing. Leaded gasoline remained legal as of late 2014 in parts of Algeria, Iraq, Yemen, Myanmar, North Korea, and Afghanistan. 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. 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. the UNEP-sponsored phase-out was nearly complete: only Algeria, Iraq, and Yemen continued widespread use of leaded gasoline, although not exclusively. In July 2021, Algeria had halted its sale. • Austria: 1989 • Belarus: 1998 • Bulgaria: 2002 • Bosnia and Herzegovina: 2009 • Croatia: 2006 • Cyprus: 2004 • Czech Republic: 2001 • Denmark: 1994 • European Union: 1 January 2000 • Finland: 1994 • France: 2000 • Germany: 1996 • Gibraltar: 2001 • Greece: 2002 • Hungary: 1999 • Ireland: 1 January 2000 • Italy: 1 January 2002 • Malta: 2003 • Monaco: 2000 • Netherlands: 1998 • Norway: 1997 • Poland: December 2000 • Slovenia: 2001 • Spain: 1 August 2001 • Portugal: 1999 • Romania: 2005 • Russia: 2003 • Serbia: 2010 • Sweden: 1995 • Switzerland: 2000 • Ukraine: 2003 • United Kingdom: 1 January 2000 North America • Anguilla: 1998 • Antigua and Barbuda: 1991 • Aruba: 1997 • Bahamas: 1996 • Belize: 1997 • Bermuda: 1990 • Cayman Islands: 1999 • Canada: December 1990 • Costa Rica: 1996 • Dominican Republic: 1999 • El Salvador: 1992 • Guatemala: 1991 • Haiti: 1998 • Honduras: 1996 • Jamaica: 2000 • Mexico: 1998 • Nicaragua: 1995 • Panama: 2002 • Trinidad and Tobago: 2000 • United States (including Puerto Rico): 1 January 1996 • California: 1992 South America • Argentina: 1998 • Bolivia: 1995 • Brazil: 1989 or 1991 or 2005 • Guyana: 2000 • Peru: 2004 • Suriname: 2001 • Uruguay: 2004 • Venezuela: 2005 Asia • Afghanistan: 2016 • Bangladesh: 1999 • China: 2000 • Hong Kong: 1999 • India: March 2000 • Saudi Arabia: 2001 • Indonesia: 2006 • Iran: 2003 • Iraq: 2018 • Japan: 1986 • Malaysia: 2000 • Myanmar: 2016 • Philippines: 2000 • Singapore: 1998 • South Korea: 1993 • Sri Lanka: 1999 • Taiwan: 2000 • Thailand: 1996 • Turkey: 2006 • United Arab Emirates: 2003 • Vietnam: 2001 • Yemen: 2018 • New Zealand: 1996 • Guam: 1 January 1996 (USA) • Samoa: 2001 Africa • Egypt: 1999 • South Africa: 2006 • Leaded petrol was supposed to be completely phased out continent-wide on 1 January 2006, following a ban initiated from the 2002 Earth Summit. However, in Algeria refineries needed to be altered; as a result, leaded fuel remained available in parts of Algeria, In motor racing Leaded fuel was commonly used in professional motor racing, until its phase out beginning in the 1990s. Since 1992, Formula One racing cars have been required to use fuel containing no more than 5 mg/L of lead. NASCAR began experimentation in 1998 with an unleaded fuel, and in 2006 began switching the national series to unleaded fuel, completing the transition at the Fontana round in February 2007 when the premier class switched. This was influenced after blood tests of NASCAR teams revealed elevated blood lead levels. Aviation gasoline TEL remains an ingredient of 100 octane avgas for piston-engine aircraft. The current formulation of 100LL (low lead, blue) aviation gasoline contains of TEL, half the amount of the previous 100/130 (green) octane avgas (at 4.24 grams per gallon), and twice as much as the 1 gram per gallon permitted in regular automotive leaded gasoline prior to 1988 and substantially greater than the allowed 0.001 grams per gallon in automotive unleaded gasoline sold in the United States today. The United States Environmental Protection Agency, FAA, and others are working on economically feasible replacements for leaded avgas, which still releases 100 tons of lead every year. Alternative antiknock agents Antiknock agents are classed as high-percentage additives, such as alcohol, and low-percentage additives based on heavy elements. Since the main problem with TEL is its lead content, many alternative additives that contain less poisonous metals have been examined. A manganese-carrying additive, methylcyclopentadienyl manganese tricarbonyl (MMT or methylcymantrene), was used for a time as an antiknock agent, though its safety is controversial and it has been the subject of bans and lawsuits. Ferrocene, an organometallic compound of iron, is also used as an antiknock agent although with some significant drawbacks. High-percentage additives are organic compounds that do not contain metals, but require much higher blending ratios, such as 20–30% for benzene and ethanol. It had been established by 1921 that ethanol was an effective antiknock agent, but TEL was introduced instead mainly for commercial reasons. Oxygenates such as TAME derived from natural gas, MTBE made from methanol, and ethanol-derived ETBE, have largely supplanted TEL. MTBE has environmental risks of its own and there are also bans on its use. Improvements to gasoline itself decrease the need for antiknock additives. Synthetic iso-octane and alkylate are examples of such blending stocks. Benzene and other high-octane aromatics can be also blended to raise the octane number, but they are disfavored today because of toxicity and carcinogenicity. == Toxicity ==

6 mL of tetraethyllead is enough to induce severe lead poisoning. The hazards of TEL content are heightened due to the compound's volatility and high lipophilicity, enabling it to easily cross the blood–brain barrier. Early symptoms of acute exposure to tetraethyllead can manifest as irritation of the eyes and skin, sneezing, fever, vomiting, and a metallic taste in the mouth. Later symptoms of acute TEL poisoning include pulmonary edema, anemia, ataxia, convulsions, severe weight loss, delirium, irritability, hallucinations, nightmares, fever, muscle and joint pain, swelling of the brain, coma, and damage to cardiovascular and renal organs. Chronic exposure to TEL can cause long-term negative effects such as memory loss, delayed reflexes, neurological problems, insomnia, tremors, psychosis, loss of attention, and an overall decrease in IQ and cognitive function. The carcinogenity of tetraethyllead is debatable. It is believed to harm the male reproductive system and cause birth defects. Concerns over the toxicity of lead eventually led to the ban on TEL in automobile gasoline in many countries. Some neurologists have speculated that the lead phaseout may have caused average IQ levels to rise by several points in the US (by reducing cumulative brain damage throughout the population, especially in the young). For the entire US population, during and after the TEL phaseout, the mean blood lead level dropped from 16 μg/dL in 1976 to only 3 μg/dL in 1991. == History ==

In 1853, German chemist Karl Jacob Löwig (1803–1890) first prepared what he claimed was Pb2(C2H5)3 from ethyl iodide and an alloy of lead and sodium. In 1859, English chemist George Bowdler Buckton (1818–1905) reported what he claimed was Pb(C2H5)2 from zinc ethyl (Zn(C2H5)2) and lead(II) chloride. Later authors credit both methods of preparation with producing tetraethyl lead. In fuel TEL remained unimportant commercially until the 1920s. In 1921, at the direction of DuPont Corporation, which manufactured TEL, it was found to be an effective antiknock agent by Thomas Midgley Jr., working under Charles Kettering at General Motors Corporation Research. General Motors patented the use of TEL as an antiknock agent and used the name "Ethyl" that had been proposed by Kettering in its marketing materials, thereby avoiding the negative connotation of the word "lead". In 1924, Standard Oil of New Jersey (ESSO/EXXON) and General Motors created the Ethyl Gasoline Corporation to produce and market TEL. Deepwater, New Jersey, across the river from Wilmington, was the site for production of some of DuPont's most important chemicals, particularly TEL. After TEL production at the Bayway Refinery was shut down, Deepwater was the only plant in the Western hemisphere producing TEL up to 1948, when it accounted for the bulk of the Dupont/Deepwater's production. Initial controversy The toxicity of concentrated TEL was recognized early on, as lead had been recognized since the 19th century as a dangerous substance that could cause lead poisoning. In 1924, a public controversy arose over the "loony gas", after five workers died, and many others were severely injured, in Standard Oil refineries in New Jersey. There had also been a private controversy for two years prior to this controversy; several public health experts, including Alice Hamilton and Yandell Henderson, engaged Midgley and Kettering with letters warning of the dangers to public health. The New York Times editorialized in 1924 that the deaths should not interfere with the production of more powerful fuel. The conference was initially expected to last for several days, but reportedly the conference decided that evaluating presentations on alternative anti-knock agents was not "its province", so it lasted a single day. Kettering and Midgley stated that no alternatives for anti-knocking were available, although private memos showed discussion of such agents. One commonly discussed agent was ethanol. The Public Health Service created a committee that reviewed a government-sponsored study of workers and an Ethyl lab test, and concluded that while leaded gasoline should not be banned, it should continue to be investigated. In the late 1920s, Robert A. Kehoe of the University of Cincinnati was the Ethyl Corporation's chief medical consultant and one of the lead industry's staunchest advocates, who would not be discredited until decades later by Dr. Clair Patterson's work on human lead burdens (see below) and other studies. As the head of Kettering Laboratories for many years, Kehoe would become a chief promoter of the safety of TEL, an influence that did not begin to wane until about the early 1960s. But by the 1970s, the general opinion of the safety of TEL would change, and by 1976 the U.S. government would begin to require the phaseout of this product. In the late 1940s and early 1950s, Clair Cameron Patterson accidentally discovered the pollution caused by TEL in the environment while determining the age of the Earth. As he attempted to measure lead content of very old rocks, and the time it took uranium to decay into lead, the readings were made inaccurate by lead in the environment that contaminated his samples. He was then forced to work in a cleanroom to keep his samples uncontaminated by environmental pollution of lead. After coming up with a fairly accurate estimate of the age of the Earth, he turned to investigating the lead contamination problem by examining ice cores from countries such as Greenland. He realized that the lead contamination in the environment dated from about the time that TEL became widely used as a fuel additive in gasoline. Being aware of the health dangers posed by lead and suspicious of the pollution caused by TEL, he became one of the earliest and most effective proponents of removing it from use. In the 1960s, the first clinical works were published proving the toxicity of this compound in humans, e.g. by Mirosław Jan Stasik. In the U.S. in 1973, the United States Environmental Protection Agency issued regulations to reduce the lead content of leaded gasoline over a series of annual phases, which therefore came to be known as the "lead phasedown" program. EPA's rules were issued under section 211 of the Clean Air Act, as amended 1970. The Ethyl Corp challenged the EPA regulations in federal court. Although the EPA's regulation was initially invalidated, Additional regulatory changes were made by EPA over the next decade (including adoption of a trading market in "lead credits" in 1982 that became the precursor of the Acid Rain Allowance Market, adopted in 1990 for SO2), but the decisive rule was issued in 1985. The EPA mandated that lead additive be reduced by 91 percent by the end of 1986. A 1994 study had indicated that the concentration of lead in the blood of the U.S. population had dropped 78% from 1976 to 1991. The U.S. phasedown regulations also were due in great part to studies conducted by Philip J. Landrigan. In Europe, Derek Bryce-Smith was among the first to highlight the potential dangers of TEL and became a leading campaigner for removal of lead additives from petrol. From 1 January 1996, the U.S. Clean Air Act banned the sale of leaded fuel for use in on-road vehicles although that year the US EPA indicated that TEL could still be used in aircraft, racing cars, farm equipment, and marine engines. Thus, what had begun in the U.S. as a phase down ultimately ended in a phase-out for on-road vehicle TEL. Similar bans in other countries have resulted in lowering levels of lead in people's bloodstreams. Taking cue from the domestic programs, the U.S. Agency for International Development undertook an initiative to reduce tetraethyl lead use in other countries, notably its efforts in Egypt begun in 1995. In 1996, with the cooperation of the U.S. AID, Egypt took almost all of the lead out of its gasoline. The success in Egypt provided a model for AID efforts worldwide. By 2000, the TEL industry had moved the major portion of their sales to developing countries whose governments they lobbied against phasing out leaded gasoline. India banned leaded petrol in March 2000. The announcement was slightly premature, as a few countries still had leaded gasoline for sale as of 2017. Effect on crime rates Reduction in the average blood lead level is believed to have been a major cause for falling violent crime rates in the United States. A statistically significant correlation has been found between the usage rate of leaded gasoline and violent crime: the violent crime curve virtually tracks the lead exposure curve with a 22-year time lag. After the ban on TEL, blood lead levels in U.S. children dramatically decreased. Taking into consideration other factors that are believed to have increased crime rates over that period, Reyes found that the reduced exposure to lead led to an actual decline of 34% over that period. Lingering issues over time Although leaded gasoline has long since ended its history of regular use in U.S. transportation, it has left high concentrations of lead in the soil adjacent to roads that were heavily used prior to its phaseout. These contaminated materials present health dangers even when merely touched or when components of it get breathed in. Children, especially those in poverty inside of the U.S., are particularly at risk. == See also ==