Tetraethyllead reactions

SECOND-ORDER RATE COEFFICIENTS (l.mole 1. Sec" ) FOR THE ACETOLYSIS OF TETRAETHYLLEAD (REACTION (32)) AND TRIETHYLLEAD ACETATE (REACTION (33))... 

Tetraethyllead can be manufactured by the reaction of ethyl chloride with lead-sodium alloy (see Lead compounds). 

The halogen influences the rate of reaction, and, in general, the order of reactivity is HI > HBi > HCl. Impoitant uses of etfiyl chloiide include the manufacture of tetraethyllead and ethylceUulose. Ethyl bromide can be used to produce ethyl Grignard reagent and various ethyl amines. 

Ethyl Chloride. Previously a significant use for industrial ethanol was the synthesis of ethyl chloride [75-00-3] for use as an intermediate in producing tetraethyllead, an antiknock gasoline additive. Ethanol is converted to ethyl chloride by reaction with hydrochloric acid in the presence of aluminum or zinc chlorides. However, since about 1960, routes based on the direct addition of hydrochloric acid to ethylene or ethane have become more competitive (374,375). 

The transfer of an ethyl group, in particular, can be performed with high diastereoselectivity by the use of tetraalkyllead, activated with titanium(IV) chloride14"15 (Table 4). The order of addition of the reagents exhibits a strong influence on the chemical yield and diastercoselectiv-ity of the addition reaction. Typically, titanium(IV) chloride is added at -78CC to the aldehyde, followed by addition of tetraethyllead. Poor yields and diastereoselectivity are observed if titanium(IV) chloride is first added to tetraethyllead followed by addition of the aldehyde ... 

The best known example is the electrosynthesis of tetraethyllead (TEL) Pb(C2Hj)4, which has been in wide use as an antiknock additive of gasoline, and still is in a number of countries. This substance is readily produced by reaction of ethyl radicals with the lead electrode ... 

Anodic processes can also be used for tetraethyllead electrosynthesis. Here solutions of organometallic compounds are used the overall reaction is replacement of the metal in these compounds by another metal, lead. One such process uses a melt of the compound NaAl(C2H5)4, from which radicals QHj are produced anodically. The process is highly efficient, but it is not easy to isolate the TEL produced from the melt. More convenient is a commercial process involving the anodic oxidation of the Grignard reagent C2H5MgCl ... 

Before its use as a fuel additive to reduce engine knock was banned in the United States, tetraethyllead was produced in enormous quantities. One method of producing the compound was the reaction between lead and ethyl chloride, in which the reactivity of lead was enhanced by its amalgamation with sodium. 

Allyllead compounds, which are very unstable, can be prepared from tetraethyllead by reaction with 2-methyl-3-chloropropene170 ... 

Another study on the electrosynthesis of (alkyl) M compounds (M = Ge, Pb, Sn n = 2, 4) provides illustrative examples37. Sacrificial cathodes of Cd, Zn and Mg were used to produce the corresponding metal alkyls which are subsequently oxidized on sacrificial anodes of Ge, Sn and Pb. The cells are of very simple construction, with the proper metal electrodes. Diethylcadmium is utilized in this way for the manufacture of tetraethyllead from lead acetate and triethylaluminum in the following reaction sequence ... 

Heterogeneous route, at the electrode surface. The lead anode is attacked and yields tetraethyllead as the main product. For this stage, several reaction routes are possible, e.g. diethylcadmium may be oxidized on the lead anode to produce ethyl radicals which, in turn, may oxidize metallic lead. Partially alkylated lead compounds thus formed are alkylated to tetraethyllead by ethyl iodide. 

In several studies, electrosynthesis of tetraethyllead from EtBr on a Pb anode has been carried out in a two-phase system and empirical evaluation of reaction conditions was... 

The classical large-scale method for preparation of tetraethyllead and tetramethyllead is by reaction of alkyl halide with sodium/lead alloy (composition Pb Na 1/1 )38. The product is isolated by steam distillation and yields are high ... 

Further reaction of Ph3P+ and Hg contributes the second ET for the overall two-electron oxidation. This was studied in detail for oxidations of tetraphenyllead, tetraethyllead and tetramethyllead at mercury electrodes in dichloromethane. The rationale of the mechanisms proposed above is based on the following observations122. 

Kharasch, M.S., Jensen, E.V., and Weinhouse, S., Alkylation reactions of tetraethyllead. A new synthesis of ethyldichloroarsine and related compounds,... 

Since a radical is consumed and formed in reaction (3.3) and since R represents any radical chain carrier, it is written on both sides of this reaction step. Reaction (3.4) is a gas-phase termination step forming an intermediate stable molecule I, which can react further, much as M does. Reaction (3.5), which is not considered particularly important, is essentially a chain terminating step at high pressures. In step (5), R is generally an H radical and R02 is H02, a radical much less effective in reacting with stable (reactant) molecules. Thus reaction (3.5) is considered to be a third-order chain termination step. Reaction (3.6) is a surface termination step that forms minor intermediates (T) not crucial to the system. For example, tetraethyllead forms lead oxide particles during automotive combustion if these particles act as a surface sink for radicals, reaction (3.6) would represent the effect of tetraethyllead. The automotive cylinder wall would produce an effect similar to that of tetraethyllead. 

Primary pollutants are those emitted directly to the atmosphere while secondary pollutants are those formed by chemical or photochemical reactions of primary pollutants after they have been admitted to the atmosphere and exposed to sunlight. Unbumed hydrocarbons, NO, particulates, and the oxides of sulfur are examples of primary pollutants. The particulates may be lead oxide from the oxidation of tetraethyllead in automobiles, fly ash, and various types of carbon formation. Peroxyacyl nitrate and ozone are examples of secondary pollutants. 

Taylor in 1925 demonstrated that hydrogen atoms generated by the mercury sensitized photodecomposition of hydrogen gas add to ethylene to form ethyl radicals, which were proposed to react with H2 to give the observed ethane and another hydrogen atom. Evidence that polymerization could occur by free radical reactions was found by Taylor and Jones in 1930, by the observation that ethyl radicals formed by the gas phase pyrolysis of diethylmercury or tetraethyllead initiated the polymerization of ethylene, and this process was extended to the solution phase by Cramer. The mechanism of equation (37) (with participation by a third body) was presented for the reaction, - which is in accord with current views, and the mechanism of equation (38) was shown for disproportionation. Staudinger in 1932 wrote a mechanism for free radical polymerization of styrene,but just as did Rice and Rice (equation 32), showed the radical attack on the most substituted carbon (anti-Markovnikov attack). The correct orientation was shown by Flory in 1937. In 1935, O.K. Rice and Sickman reported that ethylene polymerization was also induced by methyl radicals generated from thermolysis of azomethane. 

The hydrocarbon-type analysis of the Platformate discussed above was based on the product having an octane number of 92.9 (F-l plus 3 ml. of tetraethyllead per gallon). The aromatic content (based on charge) increases continually with increased severity. At the two highest severities, the aromatic yield (based on the charge) is in excess of the total naphthenes and aromatics present in the charge. This indicates the participation of the dehydrocyclization reaction of paraffins to form aromatics. 

Meanwhile, extensive investigation of other of the many reactions by which tetraethyllead can be synthesized, such as the substitution of magnesium and other alkylating metals for sodium and of other ethyl esters for ethyl chloride, has led to the conclusion that none of these is likely to replace the lead-sodium-ethyl chloride method in the foreseeable future. Further reduction in cost would appear most likely to come from refinements in the existing process, and further reduction in operating hazards. One important factor in the cost is not susceptible to improvement by research—the cost of pig lead, which today represents about 18% of the selling price of tetraethyllead as motor fluid. The present price of pig lead is about three times that during most of the past 25 years. 

Next to the formation of Grignard reagents, the most important application of this reaction is the conversion of alkyl and aryl halides to organolithium compounds,435 but it has also been carried out with many other metals, e.g., Na, Be, Zn, Hg, As, Sb, and Sn. With sodium, the Wurtz reaction (0-86) is an important side reaction. In some cases where the reaction between a halide and a metal is too slow, an alloy of the metal with potassium or sodium can be used instead. The most important example is the preparation of tetraethyllead from ethyl bromide and a Pb-Na alloy. 

Many dialkyl and diaryl cadmium compounds have found use as polymerization catalysts. For example, the diethyl compound catalyzes polymerization of vinyl chloride, vinyl acetate, and methyl methacrylate (45), and when mixed with TiCl can be used to produce polyethylene and crystalline polypropylene for filaments, textiles, glues, and coatings (45). With >50% TiCl diethyl cadmium polymerizes dienes. Diethyl cadmium maybe used as an intermediate ethylating agent in the production of tetraethyllead. The diaryl compounds such as diphenylcadmium [2674-04-6]> (C H Cd, (mp 174°C) are also polymerization catalysts. These compounds are also prepared using Grignard or arylUthium reagents in tetrahydrofiiran (THF) solvent but may be prepared by direct metal substitution reactions such as ... 

Pressure development due to preflame reactions of paraffin hydrocarbons is affected little by the presence of tetraethyllead even though autoignition is suppressed 25, 115). In one series of experiments 25), increasing fuel quality 10 octane numbers reduced the pressure development 10 pounds per square inch, while addition of tetraethyllead to achieve the same 10 octane number increase resulted in a decrease of only 2 pounds per square inch. These findings indicate that tetraethyllead is specific in its activity, inhibiting only certain types of reactions leading to the final autoignition step. 

Tetraethyllead is believed to act as an antiknock by changing the course of the complex hydrocarbon oxidations which precede knock (69). It also may improve fuel-ignition resistance by its effects on these preflame reactions it is most effective in fuels that undergo considerable preflame reaction and has little effect on fuels that do not. Some of the products formed in preflame reactions—aldehydes, for example—sensitize fuels to ignition (47, 69, 86). 

Horn and Huber47 have comprehensively studied the acetolysis of tetraethyllead by acetic acid in solvent anhydrous toluene. In contrast to Robinson2 who observed only reaction (32) when acetic acid was used as solvent, Horn and Huber showed that the two competitive consecutive reactions (32) and (33)... 

The activation energies for reactions (32) and (33) in solvent toluene differ by 7 kcal.mole-1 and hence the ratio of the rate coefficients k33/k32 is temperature-dependent, being 48 at 60 °C and 214 at 100 °C. A normal second-order plot of x/a(a—x) versus t for the case of equal initial concentrations (0.2 M) of tetraethyllead and acetic acid at 60 °C gives a good straight line for the first 13 % reaction, but a similar plot at 100 °C deviates from a straight line even at 5 % reaction, due to the much faster relative rate of reaction (33) at 100 °C compared with that at 60 °C. 

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