History of leaded petrol
methods of eliminating engine knocking. 40% benzene and 1% iodine were plausible alternatives, but the former was too expensive and the latter too corrosive to be used. 5
Tetraethyl Lead
After seven years of trying, Kettering, Midgeley, and the GM research team have found the perfect compound. Working their way down Group VI of the periodic table, they found tetraethyl tin to be effective and finally landed on TEL, which was able to completely silence the engine the team was testing. 6 With the discovery of an extremely effective, apparently practical anti-knock agent, the modern high-compression, high power output internal combustion engine could now become a reality.
TEL fit the criteria for what the team was looking for:
1. It was relatively simple to produce, by reacting chloroethane with a sodium-lead alloy, 4 NaPb + 4 CH 3 CH 2 Cl → Pb(CH 3 CH 2 ) 4 + 4 NaCl + 3 Pb, [6] with both reactants able to be procured cheaply. 2. It was able to eliminate engine knocking, as TEL has 4 weak C-Pb bonds, which decompose upon heating to form 4 ethyl radicals as well as lead, which stops the radical chain reaction that otherwise would have caused spontaneous combustion, preventing premature detonation and engine knocking, with the lead itself being the reactive antiknock agent, with the ethyl radicals only serving as soluble carriers . 7
Figure 3: Skeletal formula of TEL 8
3. TEL was by far the most effective antiknock agent. One fortieth of one percent solution of TEL was equivalent in knock inhibition to 1.3% aniline in kerosene, far superior to any other compound tested under similar circumstances. 9
5 Bill Kovarik, ‘Charles F. Kettering and the 1921 discovery of tetraethyl lead’, accessed 8 th August 2023, https://environmentalhistory.org/people/charles-f-kettering-and-the-1921-discovery-of-tetraethyl-lead/#fears. 6 Ibid. 7 Dietmar Seyferth, ‘The Rise and Fall of Tetraethyl Lead. 2.’, accessed 10 th August 2023, https://pubs.acs.org/doi/epdf/10.1021/om030621b. 8 User Darkness2560, Wikipedia, accessed 4 th August 2023, https://en.wikipedia.org/wiki/Tetraethyllead#/media/File:Tetraethyllead-Skeletal-SVG.svg. 9 Seyferth (note 7).
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