Tetraethyllead antiknock compound

Procedures for Pb-Na alloys suitable for synthesizing the tetramethyl- and tetraethyllead antiknock compounds on a large scale are based on the same principles as the laboratory methods but are adapted to handling large amounts" and to obtaining material with proper surface area, gross structure of the alloy, etc.. ... 

Metal carbonyls have been used as antiknock compounds in unleaded gasoline (see Gasoline and other motor fuels). The Ethyl Corp. marketed methylcyclopentadienyknanganese tticarbonyl (MMT) however, as in the case of tetraethyllead (180), its use is prohibited because of environmental concerns. 

In general, it would appear that some degree of trouble must always be expected from deposits—trouble which in some part, though by no means wholly, is due to the antiknock compound. However, progress has been made to the point where the present problems cannot be regarded as critical. Moreover, present research indicates that there is hope for substantial further improvement. In any case, the extent to which tetraethyllead contributes to these problems is a small price to pay for its value as a fuel constituent. 

Both before and after the commercial introduction of tetraethyllead antiknocks, many other substances have been considered as octane-number improvers. Chief among them are hydrocarbons, amines, and other organometallic compounds. 

As indicated above, the largest commercial application of organolead compounds is as antiknock agents. The discovery of the antiknock effect by Midgeley and Boyd 223> led to the present worldwide business in antiknock compounds. Tetraethyllead was sold as early as 1923, but... 

The largest consumption of sodium worldwide, as of the mid-1990s, is the production of tetraethyllead and tetramethyllead antiknock compounds for gasoHne. This production is outside of North America. Sodium is also used for the production of other organometalHc compounds such as methylcyclopentadienyHnanganese tricarbonyl (MMT), another gasoline additive. 

Some works have dealt with the interplay of some of the more recent roles of lead in commercial and industrial history with social and public health issues and their respective proponents. Rosner and Markowitz (1985) detailed the enormous industrial and political pressures brought to bear to ease entry of the gasoline lead additive, tetraethyllead (TEL), into commerce as an effective antiknock compound for high compression engines. Graebner (1987) has detailed the history of the lead industry s participation in lead research with an eye to controlling the flow of such research information. 

Among the latest additives (1957) are methyl cyclopentadienyl manganese tricarbonyl of the Ethyl Corporation, and an organic boron compound of the Standard Oil Company of Ohio. The boron compound in small amounts (0.008—0.03 per cent) not only reduces combustion-zone deposits and surface ignition but also increases the effectiveness of tetraethyllead. Antiknock effects are greatest with leaded straight-run or A[Pg.38]

The octane rating of gasoline can be further improved by adding antiknock compounds to prevent premature combustion. At one time, the preferred additive was tetraethyllead, (C2H5)4Pb. Lead additives have been phased out of gasoline in most countries because lead is toxic, and substitutes such as the oxygenated hydrocarbons methanol and ethanol are used instead. 

Lead, like tin, forms only one hydride, plumbane. This hydride is very unstable, dissociating into lead and hydrogen with great rapidity. It has not been possible to analyse it rigorously or determine any of its physical properties, but it is probably PbH4. Although this hydride is unstable, some of its derivatives are stable thus, for example, tetraethyllead, Pb(C2Hj)4, is one of the most stable compounds with lead in a formal oxidation state of + 4. It is used as an antiknock in petrol. 

Tetraethyllead was the first known organolead compound, synthesized in 1853. Its antiknock properties were discovered in 1922, and since then its consumption has rapidly increased. 

Tetraethyllead was used in the past as an antiknock agent in gasoline, but it has been phased out in most countries. Alkyllead compounds have a detergent-like activity on liposomes and black lipid membranes [232], Tributyllead destroys planar lipid membranes at lower concentrations than tripropyllead, which is again more effective than triethyl- and trimethyllead [232]. Inorganic lead compounds like lead acetate and lead nitrate were effective only at twice as high concentrations [232]. 

Sensitivity to Sulfur. The effectiveness of tetraethyllead as an antiknock is markedly reduced by one of the normal constituents of gasoline—sulfur. The different types of sulfur compounds show varying degrees of tetraethyllead destruction, but all have a deleterious effect, and as much as two thirds of the effectiveness of tetraethyllead may be lost in a gasoline high in sulfur. 

As regards organometallics other than tetraethyllead and other lead alkyls, only iron pentacarbonyl has received much attention, because of its low cost in some fuels it is probably the cheapest known source of antiknock increase (20). However, the great increase in engine wear which its abrasive combustion products produce makes its use impractical, and there appear to be no prospects for its commercial use (20). A new iron compound, dicyclopentadienyliron (ferrocene), also demonstrates the antiknock effectiveness of iron compounds. As an antiknock, it is approximately 50% as effective as tetraethyllead and has other favorable characteristics, but it is not practical for antiknock use for the same reason as iron pentacarbonyl—accumulation of iron oxide in engine cylinders where it has an adverse effect on wear and spark-plug life (2). 

As indicated above, the antiknock effect is shown by many compounds. Outstanding among these are the organometallic compounds of many metals. Effective derivatives of many metals include alkyl compounds, aryls, carbonyls, nitrosyls, phosphines, cyclopentadienyls, and many mixed compounds. The aromatic amines are also good antiknock agents, but far less effective than the organometallic compounds. The reason why commercialization efforts were concentrated on tetraethyllead early in the history of antiknock investigations is evident from Table 1, which is a composite of early data 6 8,216). 

The only commercial competition for tetraethyllead as an antiknock agent is provided by tetramethyllead and mixed methyl and ethyl lead compounds. In 1960, Ethyl Corporation and E. I. DuPont de Nemours and Company inaugurated the manufacture of tetramethyllead in the U.S.A., and in the same year Mobil Oil Company and Standard of California began the marketing of gasoline containing tetramethyllead. Various mixed methylethyllead compounds and mixtures have been patented and have been supplied commercially since this period 65,113,129),... 

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