Alloy, sodium-lead

Sodium—lead alloys that contain other metals, eg, the alkaline-earth metals, are hard even at high temperatures, and are thus suitable as beating metals. Tempered lead, for example, is a beating alloy that contains 1.3 wt % sodium, 0.12 wt % antimony, 0.08 wt % tin, and the remainder lead. The German BahnmetaH, which was used ia axle beatings on railroad engines and cars, contains 0.6 wt % sodium, 0.04 wt % lithium, 0.6 wt % calcium, and the remainder lead, and has a Brinell hardness of 34 (see Bearing MATERIALS). 

Sodium amalgam is employed ia the manufacture of sodium hydroxide sodium—potassium alloy, NaK, is used ia heat-transfer appHcations and sodium—lead alloy is used ia the manufacture of tetraethyllead and tetramethyUead, and methylcyclopentadienylmanganesetricarbonyl, a gasoline additive growing ia importance for improving refining efficiency and octane contribution. 

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 ... 

The checkers dried benzene over sodium-lead alloy (dri-Na, Baker). Its water content was less than 0.1 mg. per ml. by Karl Fischer titration. 

Sodium forms alloys with a number of metals including lead, chromium, mercury, aluminum, silicon, and iron. With mercury, it forms sodium amalgam. Sodium-lead alloy is commercially used to produce tetraethyllead, which was used historically as an additive to gasoline ... 

The bimolecular reduction of aromatic nitro compounds, depending on reaction conditions, may produce azoxy compounds, azo compounds, hydrazo compounds (1,2-diarylhydrazines), benzidines, or amines. Whereas the reduction with zinc and sodium hydroxide leads to azo compounds, zinc and acetic acid/acetic anhydride produces azoxy compounds. Other reducing agents suggested are stannous chloride, magnesium with anhydrous methanol, a sodium-lead alloy in ethanol, thallium in ethanol, and sodium arsenite. 

The electrolysis Of fused alkali salts.—Many attempts have been made to prepare sodium directly by the electrolysis of the fused chloride, since that salt is by far the most abundant and the cheapest source of the metal. The high fusion temp. the strongly corrosive action of the molten chloride and the difficulty of separating the anodic and cathodic products, are the main difficulties which have been encountered in the production of sodium by the electrolysis of fused sodium chloride. Attention has been previously directed to C. E. Acker s process for the preparation of sodium, or rather a sodium-lead alloy, by the electrolysis of fused sodium chloride whereby sodium is produced at one electrode, and chlorine at the other but the process does not appear to have been commercially successful. In E. A. Ashcroft s abandoned process the fused chloride is electrolyzed in a double cell with a carbon anode, and a molten lead cathode. The molten lead-sodium alloy was transported to a second chamber, where it was made the anode in a bath of molten sodium hydroxide whereby sodium was deposited at the cathode. A. Matthiessen 12 electrolyzed a mixture of sodium chloride with half its weight of calcium chloride the addition of the chloride of the alkaline earth, said L. Grabau, hinders the formation of a subchloride. J. Stoerck recommended the addition of... 

The xylene is dried over sodium wire or sodium-lead alloy before use. 

Large quantities of tetramethyl lead (TML) were used back in the 1960s as an antiknock additive in high-octane gasoline before they were banned because of air pollution problems. TML was produced in a batch reactor that had the interesting feature of requiring the removal of a byproduct during the batch. The main reaction involves a solid sodium-lead alloy and liquid methyl chloride ... 

The variability of the sizes of the solid sodium-lead alloy particles introduces another factor. The smaller the particle size, the more surface area is exposed to reaction, which increases the effective reaction rate. Big particles react slowly small particles react quickly. So, for the same pressure-time trajectory, significantly different heat load-time requirements can occur. If the alloy charge contains very small particles, a runaway reaction can occur if the pressure controller setpoint is ramped up too quickly. 

Organolead compounds are those in which a lead atom is bound directly to one or more carbon atoms. It is generally accepted that L5wig 210,211) first synthesized an organolead compound in 1853 by reacting a sodium-lead alloy with ethyl iodide. Lowig s product was either or both tetraethyl-... 

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. 

Lead alloys other than sodium-lead alloy are also reactive with alkyl halides to form R4Pb compounds. Dimagnesium-lead alloy, Mg2Pb, is reactive with alkyl halides in the presence of a diethyl ether-iodine catalyst mixture to form R4Pb 285>. The reaction with ethyl chloride was considered at one time for the commercial production of tetraethyllead, but the high yields obtained in the laboratory could not be duplicated in pilot plant equipment 284>. A main advantage of the use of Mg2Pb in place of NaPb is that no by-product lead metal is formed under ideal conditions. 

Mg2Pb alloy is also reactive with alkyl halides higher than ethyl halides whereas sodium-lead alloy is not, except in the presence of water and pyridine 167,274) xhis hydrous system was used briefly in the 1920 s for the commercial production of tetraethyllead 67). 

R4Pb, but these systems offer no advantage, economic or otherwise, over the sodium-lead alloy systems. 

Diethyl sulfate is also reactive with sodium-lead alloy 293> and calcium-lead alloy 200,201) to form R4Pb. With NaPb, the stoichiometry is ... 

These reactions of lead metal and lead alloys with alkyl esters are conducted at elevated temperatures (usually above 80 °C) and at elevated pressure (autogenous pressure of RX), and in the presence of a suitable catalyst, such as ethers, amines, iodides, dependent on the particular system involved. Despite the large number of systems which have been investigated, none has been found to be as economical for the commercial production of tetramethyllead and tetraethyllead as the sodium-lead alloy reaction, with the possible exception of the electrolytic process developed by Nalco Chemical Company for tetramethyllead. Electrolytic processes are discussed in Section 6. 

The initial large-scale production of tetraethyllead was based on the batchwise reaction of sodium-lead alloy with ethyl chloride. Although various details in this process have been changed over the years, the basic method remains the same for the manufacture of most of the tetraethyllead produced in the world today. 

The reaction of NaPb (and other sodium-lead alloys) with ethyl chloride undoubtedly proceeds via a free radical sequence, in which the alloy reacts to form sodium chloride and ethyl radicals ethane, ethylene, and butane are by-products formed by combination and disproportionation of the ethyl radicals. Shushunov and his colleagues 230,296) have carried out a detailed investigation of the kinetics of the NaPb-C2H5Cl reaction. The reaction sequence below was proposed for the ethylation reaction ... 

The manufacture of tetraethyllead presented many problems historically because there was no prior experience in the large-scale production of any organometallic compounds. There have been innumerable patents issued to protect various modifications of the basic process. The original major contribution to the development of a commercially successful alloy process for tetraethyllead was the demonstration by Kraus and Callis 194,193) 0f the conditions required for the facile reaction of the sodium-lead alloy with ethyl chloride. The development of the process has been reviewed by several writers 120,121,277,289,290,310,315), Additional important early patents on the process are those of Calcott and Daudt 64,103). 

The reaction of alkyl halides with sodium-lead alloy is quite sensitive to many reaction factors. The monosodium-lead alloy reacts at a fast rate only with ethyl chloride. The presence of other ethyl halides or methyl halides in the ethyl chloride inhibits the reaction severely, and the presence of as little as 0.0025% acetylene in the ethyl chloride retards the reaction strongly 284>. 

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. 

Sacrificial anode — is a piece of metal used as an anode in electrochemical processes where it is intended to be dissolved during the process. In -+ corrosion protection it is a piece of a non-noble metal or metal alloy (e.g., magnesium, aluminum, zinc) attached to the metal to be protected. Because of their relative -+ electrode potentials the latter is established as the -+ cathode und thus immune to corrosion. In -+ electroplating the metal used as anode may serve as a source for replenishing the electrolyte which is consumed by cathodic deposition. The sodium-lead alloy anode used in the electrochemical production of tetraethyl lead may also be considered as a sacrificial anode. 

The major commercial synthesis is by the interaction of a sodium-lead alloy with CH3C1 or C2H5C1 in an autoclave at 80 to 100°C, without solvent for QH5CI but in toluene at a higher temperature for CH3C1. The reaction is complicated and not fully understood, and only a quarter of the lead appears in the desired product ... 

Dioxane may be dried by refluxing over sodium-lead alloy, followed by distillation. 

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 ... 

The sodium-lead alloy has to be specifically prepared (65), and quite a variety of reaction conditions have been reported (10). The surface needs to be oxygen free. Partial replacement of sodium by potassium enhances yields, as does treatment with iodine. The system s temperature and pressure of (4) also are crucial factors in determining reaction rate. The following mechanism was proposed (10) ... 

The use of a sodium-tin alloy for the preparation of tetramethyltin preceded use of the corresponding sodium-lead alloy (64,66), but was subsequently displaced by other methods. Currently, the Direct Reaction is used to prepare dialkyltin dihalides, and generally requires an oxygen-containing solvent plus another metal as accelerator (66) ... 

Lead tetraphenyl, Pb(CJl5)4.—body was first prepared from sodium-lead alloy, bromobenzene, and ethyl acetate by heating the mixture to boiling in an oil-bath for sixty hours. It is much more... 

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