The Purification of Lithium

The purification Of lithium salts.—The lithium salts prepared by the above described processes contain salts of the alkalies and alkaline earths. These... 

The purification of lithium carbonate by taking advantage of its negative coefficient of solubility has been described by E. R. Caley and P. J. Elving, Inorganic Syntheses, 1, 1 (1939). 

Sepa.ra.tion of Plutonium. The principal problem in the purification of metallic plutonium is the separation of a small amount of plutonium (ca 200—900 ppm) from large amounts of uranium, which contain intensely radioactive fission products. The plutonium yield or recovery must be high and the plutonium relatively pure with respect to fission products and light elements, such as lithium, beryUium, or boron. The purity required depends on the intended use for the plutonium. The high yield requirement is imposed by the price or value of the metal and by industrial health considerations, which require extremely low effluent concentrations. 

This group of reagents is commercially available in large quantities some of its members - notably lithium aluminium hydride (LiAlH4), calcium hydride (CaH2), sodium borohydride (NaBH4) and potassium boro-hydride (KBH4) - have found widespread use in the purification of chemicals. 

The purification of diethyl ether (see Chapter 4) is typical of liquid ethers. The most common contaminants are the alcohols or hydroxy compounds from which the ethers are prepared, their oxidation products (e.g. aldehydes), peroxides and water. Peroxides, aldehydes and alcohols can be removed by shaking with alkaline potassium permanganate solution for several hours, followed by washing with water, concentrated sulfuric acid [CARE], then water. After drying with calcium chloride, the ether is distilled. It is then dried with sodium or with lithium aluminium hydride, redistilled and given a final fractional distillation. The drying process should be repeated if necessary. 

The ethylmagnesium bromide is prepared in dry tetrahydrofuran and stored no longer than 1 week in a 250-ml. tube fitted with a 3-way vacuum stopcock and a dropping buret. The solution is decanted into the buret, and the correct volume is transferred to the reaction flask with positive nitrogen pressure. The tetrahydrofuran is purified by distillation from lithium aluminium hydride. See Org. Syn., 46, 105 (1966), for warning regarding the purification of tetrahydrofuran. 

Lithium homoenolates derived from carboxylic acids were generated from the corresponding /3-chloro acids by means of an arene-catalyzed lithiation. Chloro acids 186 were deprotonated with n-butyllithium and lithiated in situ with lithium and a catalytic amount of DTBB (5%) in the presence of different carbonyl compounds to yield, after hydrolysis, the expected hydroxy acids (187). Since the purification of these products is difficult, they were cyclized without isolation upon treatment with p-toluenesulfonic acid (PTSA) under benzene reflux, into substituted y-lactones 188 (Scheme 64) . 

Tetrahydrofuran is dried by distillation from lithium aluminum hydride. (See Org. Syn., 46, 105 (1966) for warning note regarding the purification of tetrahydrofuran.)... 

Precipitate with aq. ammonia. Evaporate the soln. down to about 100 c.c., and filter the ot liquid so as to remove calcium sulphate. The cone. soln. is sat. with ammonium alum and allowed to stand for some time. The mixed crystals of potassium, rubidium, and oeesium alums and of lithium salt are dissolved in 100 c.c. of distilled water and recrystal-lized. The recrystallization is repeated until the crystals show no spectroscopic reaction for potassium or lithium. The yield naturally depends on the variety of lepidolite employed. 100. grms of an average sample gives about 10 grms. of crude crystals and about 3 grms. of the purified caesium and rubidium alums. For the purification of caesium and rubidium salts, see the chlorides. The mother-liquors are treated with an excess of barium carbonate, boiled, and filtered. The filtrate is acidified with hydrochloric acid, and evaporated to dryness. The residue is extracted with absolute alcohol in which lithium chloride is soluble, and the other alkali chlorides are sparingly soluble. 

Tetrahydrofuran (THF) was distilled from lithium aluminum hydride under nitrogen (Caution See Org. Synth., Coll., Vol. V1973, 976 for a warning regarding the purification of tetrahydrofuran. The checkers employed THF that had been purified by distillation from sodium and benzophenone.). 

Since lithium salts obtainable by purchase, even of so-called c.p. or reagent quality, frequently contain impurities totaling about 1 per cent, it is desirable to have a rapid method for obtaining such salts in a reasonably pure state. The following simple procedure for the purification of c.p. or reagent grade lithium carbonate provides such a method, since the resulting pure carbonate may be readily converted by treatment with the proper pure acid into practically any lithium salt desired. The procedure is based upon the fact that lithium carbonate, in contrast to the salts that contaminate it, is much less soluble in hot than in cold water. J In other words, simple recrystallization is employed, but the process is carried out in the reverse direction. 

The lithium nitride produced in the second vessel will be 95 to 99% pure, depending on the purity of the lithium that was used in the reaction. On the basis of ammonia obtained by hydrolysis, the ratio Li N is very nearly 3 1. Pure lithium nitride may also be produced in the first vessel if the purification of the nitrogen is complete, but this sample of nitride is sometimes contaminated with small quantities of lithium oxide or hydroxide. 

Since sUyl ynol ethers have an electron-rich triple bond, they are useful for Lewis acid catalyzed synthetic reactions. Lithium ynolates 175 are silylated by TIPSCl or TIPSOTf and TBSCl to afford the corresponding silyl ynol ethers 176 and 177, which are thermally stable and isolable, but sensitive toward acids (equation 71) . See also equations 9 and 10 in Section ll.C. An experimentally improved procedure for the purification of 176 derived from Kowalski s method is described. Lithium ynolate derived from Julia s method is also used for the preparation of 176. TMSCl and TESCl provide silyl ketenes 179, however, by C-silylation. These small silyl chlorides primarily gave the silyl ynol ethers 178, but, upon warming the reaction mixture, isomerization to the more stable silyl ketenes takes place. The soft electrophilic silyl chlorides like PhsSiCl afford silyl ketenes. Disi-lyl ynol ethers, prepared from ynolate dianions, are rearranged to disilylketenes mediated by salts . 

The effectiveness of the purification of molten lithium halides by hydrogen halides is appreciably lower than mentioned above [232], This is explained by the fact that molten lithium halides keep the water, which can dissolve in these melts in considerable quantities. Even mixed-halide mixtures retain this property, e.g. the molten KCl-LiCl eutectic keeps the dissolved water strongly at temperatures of the order of 400 °C [179], and bubbling of dry HC1 during an hour does not result in complete removal of H20. 

V.L. Cherginets and V.V. Banik, Purification of Lithium Chloride and the LiCl KC1 Eutectic from Oxygen-Containing Admixtures (Abstract of Seventh All-Union Conference on Chemistry and Engineering of Rare Alkali Metal Halides, Apatity, 1988) pp. 116-117. 

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