Lithium fluoride solubility

Properties. Lithium fluoride [7789-24-4] LiF, is a white nonhygroscopic crystaUine material that does not form a hydrate. The properties of lithium fluoride are similar to the aLkaline-earth fluorides. The solubility in water is quite low and chemical reactivity is low, similar to that of calcium fluoride and magnesium fluoride. Several chemical and physical properties of lithium fluoride are listed in Table 1. At high temperatures, lithium fluoride hydroly2es to hydrogen fluoride when heated in the presence of moisture. A bifluoride [12159-92-17, LiF HF, which forms on reaction of LiF with hydrofluoric acid, is unstable to loss of HF in the solid form. 

Manufacture. Lithium fluoride is manufactured by the reaction of lithium carbonate or lithium hydroxide with dilute hydrofluoric acid. If the lithium carbonate is converted to the soluble bicarbonate, insolubles can be removed by filtration and a purer lithium fluoride can be made on addition of hydrofluoric acid (12). High purity material can also be made from other soluble lithium salts such as the chloride or nitrate with hydrofluoric acid or ammonium bifluoride (13). 

In both cases, the fluorination of the complex oxides of tantalum and niobium leads to the formation of the water-soluble compounds (NH4)2TaF7 and (NH4)3NbOF6, the insoluble lithium fluoride and die gaseous components H20, NH3 and HF. 

The addition of lithium fluoride, due to its solubility in a fluorine bath, can suppress the occurrence of the anode effect.2 Nakajima and co-workers reported that the carbon/hydrogen fluoride/fluorine system formed the graphite fluoride intercalation compound C4F as a solid... 

Lithium fluoride. CAS 7789-24-4. LiF, mp 848 C, soluble in HyO tslighl I Used in enamel and glass formulations as a component of w elding and brazing fluxes in the eiectrowinning of aluminum and as an ingredient of molten salts. 

In spite of the efficiency of lithium fluoride to initiate formation of an azomethine ylid from aminomethylethers, sonication of the reaction medium proved useful. It is likely that sonication improves the solubility of lithium fluoride in the solvent. This is illustrated by the following two examples. Chiral pyrrolidinylfuranones are obtained from 5-(S)-5-menthyloxy-4-vinylfuran-2(5H)-one. Sonication increases the yield from 55 to 88%, but does not change the stereoselectivity.440... 

Reference has already been made to the high lattice energies of crystalline compounds containing small ions lithium fluoride is such a compound, and its high heat of formation and low solubility are not unexpected. 

Ue have found that sonication of the reaction mixture decreases the time needed for reaction and also substantially increases the yield. This is probably related to an increase in the solubility of lithium fluoride in acetonitrile or is a consequence of surface effects on the metal. 

A more quantitative approach to this problem (Swain et al., 1960) reveals that solubilities of metal halides are generally higher in H2O than in D2O. Lithium fluoride was the exception, as might be expected for an anion which forms exceptionally strong hydrogen bonds. 

It has been recognized that Li-O compounds are not the only phases present in the discharge product. Side reactions (i.e., reactions involving decomposition of the salt, solvent, or positive electrode) have been observed to produce other compounds, such as lithium carbonate, lithium acetate, lithium formate, and lithium fluoride [65, 66]. The products of these side reactions can comprise a substantial fraction of the discharge product one experiment found that in a typical Li-02 cell with an ethereal solvent, the yield of Li202 was at best 91 % of the theoretical amount expected from coulometry [65]. It is important to note that in addition to the precipitated side reaction products, there may be additional soluble side reaction products. Side reactions are discussed in more detail in Sect. 3.3.4. 

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