Preparation of tetraethyllead

One of the chemical techniques for the preparation of tetraethyllead is based on the interaction of lead and sodium alloy with ethylchloride. 

This overall reaction, however, does not show all the stages of the process, since apart from the substances mentioned it forms hexaethyldilead, ethylene, ethane and butane, which demonstrates some secondary reactions. In particular, at the first stage of the reaction ethylchloride seems to interact with metallic sodium forming free ethyl radicals, i.e. the reaction uses the radical mechanism and ethyl radicals are responsible for further synthesis. 

C2HsCI Na C2H5 Pb - PbC2H5] C2tl5 Pb(C2Hs)2 (5.58) NaCI 

Diethyllead decomposes at the synthesis temperature, forming tetraethyllead and metallic lead. The main reaction is accompanied by some by-processes E.g., we find triethyllead, which can easily turn into a dimer, hexaethyldilead. 

The dimer disintegrates at a temperature above 20 °C to form tetraethyllead. 

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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 ... 

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. 

The reaction of (4) with a sodium-lead alloy has long been used for the industrial preparation of tetraethyllead (7) (10,64)- Traditionally the reaction has been written ... 

Thus Cahours (1862) prepared tetramethyllead from methyl iodide,475 and Polis476 prepared tetraphenyllead from bromobenzene. Industrial importance attaches to the preparation of tetraethyllead from ethyl chloride and a lead-sodium alloy at a low or moderate temperature.477... 

Fig. 14 11. Flow diiigranii for the preparation of tetraethyllead. Yield is 85 to 90 per cent on Na with 10 p cent of the Na caiuing aide reactions leading to CiHi, CiH<, and CJI .

Ziegler and collaborators 162, 283) succeeded in the electrolytic preparation of tetraethyllead, a process which is also suitable for obtaining other ethyl metal compounds. The electrolysis of alkali aluminum (or boron) tetraethyl with a lead anode and a mercury cathode yields at the anode a... 

This reaction was first used for preparation of tetraethyllead by electrolysis of a solution or suspension of ethyl iodide in ethanolic alkali [26, 27]. It was later found that the yield of tetraethyllead could be increased to 70% in an aprotic solvent, e.g., acetonitrile [28]. 

TABLE 9. Preparation of Tetraethyllead by Electrolysis of Aluminum Complexes (Lead Anode)... 

Since a potassium electrolyte has better conductivity but separation of metallic potassium from the amalgam is difficult, a method for regeneration of potassium-containing electrolytes has been developed on the basis of the reaction of the potassium amalgam with NaAlR4 [57, 102]. Use of this double-decomposition reaction has made it possible to develop a scheme for the preparation of tetraethyllead with complete regeneration of the electrolyte ... 

Fig, 6. Conical electrolyzer for preparation of tetraethyllead. 1) Porous screen 2) perforated plate 3) diaphragms 4) tubes for removal of gaseous products ... 

Fig. 7. Electrolyzer of column type for preparation of tetraethyllead. 1) Graphite anode 2) cathode 3) screen 4) anode compartment, filled with lead granules ...

While considering electrolyzers for preparation of tetraethyllead the process in which use is made of liquid anode and... 

The electrolysis of halogen-containing organic compounds at a sacrificial cathode commonly produces homoleptic organometallic compounds. For example, the electrolysis of aqueous solutions of iodopropionitrile at a tin, lead, or mercury cathode yields respectively [Sn(CH2CH2CN)4], [Pb(CH2CH2CN)4l, or [Hg(CH2CH2CN)2]. The electrolysis of ethyl chloride or ethyl bromide at a lead cathode has been proposed as a mefiiod for ttie preparation of tetraethyllead. ... 

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 ... 

As was mentioned in Section 1, the first synthesis of an organolead compound was reported by Lowig 210>211), who synthesized tetraethyllead by the reaction of a sodium-lead alloy with ethyl iodide. Some 35 years later, Polis 247,248) prepared the first aryl lead derivative by the reaction of bromobenzene with a sodium-lead alloy. Since 1923, the sodium-lead alloy-ethyl chloride reaction has been used for the commercial production of tetraethyllead. A similar reaction has also been used for the commercial production of tetramethyllead since 1960. The sodium-lead alloy-alkyl chloride reaction is discussed in Section 6. 

In the first step of manufacture of tetraethyllead, sodium-lead alloy is prepared by combining metallic sodium with molten lead in a ratio of 10 parts to 90 parts by weight. This ratio is one to one on an atom basis, and the resulting intermetallic compound NaPb is analyzed, cast, and broken up. Under a nitrogen atmosphere it is then loaded into hoppers holding a single autoclave charge. 

Whelen, M. S. Preparation of Alkyl Mercurials with Tetraethyllead. In Metal-Organic Compounds, Advances in Chemistry Series, Vol. 23, pp. 82—86. Washington, D. C. American Chemical Society 1959. 

A recent procedure for the preparation of lead and other alkyls of potential industrial application is an electrolytic process utilizing an aluminum cathode, a lead anode, and an electrolyte of NaF 2Al(C2H5)3. Passage of current leads to a quantitative formation of tetraethyllead at the anode and the deposition of high-purity aluminum on the cathode. It has been suggested that the purified aluminum obtained as a by-product may help meet the cost of electrical current and raw materials (14<5). ... 

The production of lead alkyls takes the form primarily of tetraethyllead (TEL) and tetramethyllead (TML). Mixed alkyls, such as diethyldimethyllead may be prepared subsequently by reaction of TML and TEL in the presence of a Lewis acid, but this is relatively unimportant. 

The development of the chemistry of organic lead compounds can be divided into three stages. Following the preparation of the first alkyllead compound, hexaethyldiplumbane, in 1853 by Lowig 171), attention was focused on the concept of valence and also the development of the structural theory of organic chemistry, mainly in view of early theories of radicals. Then in 1929 Paneth and collaborators 214, 215), in their classical experiment with tetramethyllead and tetraethyllead, were able to prove beyond doubt the existence of short-lived free radicals, long before anything was known of electron spin resonance spectroscopy. 

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