Alkali Fluorides

Sodium fluoride is utilized in the manufacture of organofluoro-compounds (halogen exchange reaction), as a preservative, and as a source of fluorine for toothpaste additives (sodium monofluorophosphate). 

Potassium hydrogen fluoride is used as a frosting agent in the glass industry and as a starting material for the manufacture of elemental fluorine. 

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Hot oleum (>50°C), strong alkalis, fluoride solutions, sulphur trioxide Strong alkalis, especially >54°C, distilled water >82°C, hydrofluoric acid, acid fluorides, hot concentrated phosphoric acid, lithium compounds >1 77°C, severe shock or impact applications Strong oxidizers, very strong solvents... 

Chlorination and bromination of perfluoroketimines take place only in the presence of alkali fluorides as catalyst [267] Chlorine fluoride adds readily across the CO or CN bond of polyfluonnated ketones and immes [268, 269]... 

Three kinds of niobium-containing initial solutions were used, with different Nb F ratios 1 9, 1 18 and 1 6. The first two initial solutions contained mostly NbF6" ions, whereas the third was composed primarily of NbOF52 ions. Table 5 presents the composition of the compounds that were precipitated following the addition of certain alkali fluorides to the initial solutions. 

Fig. 76. IR spectra of the systems Na2TaF7 - NaF (a), K2TaF7 - KF (b), Rb2TaF7 - RbF (c). Curves 1, 2, 3 etc. correspond to 0, 0.1, 0.3 etc. molar fraction of alkali fluoride. The CsTaFf, - CsF system (d) is represented by spectra of CsTaF6 (curve 1), Cs2TaF7 (curve 2) and Cs2TaF8 (curve 3). Reproduced from [358], A. I. Agulyansky, Zh. Neorg. Khim. 25 (1980) 2998, Copyright 1980, with permission of Nauka (Russian Academy of Sciences) publishing.

If an acid solution of a fluorosilicate is rendered faintly alkaline with aqueous sodium hydroxide and then shaken with freshly precipitated cadmium oxide, all the silicic acid is adsorbed by the suspension. The alkali fluoride is then determined in the filtrate. 

The cobalt complex is usually formed in a hot acetate-acetic acid medium. After the formation of the cobalt colour, hydrochloric acid or nitric acid is added to decompose the complexes of most of the other heavy metals present. Iron, copper, cerium(IV), chromium(III and VI), nickel, vanadyl vanadium, and copper interfere when present in appreciable quantities. Excess of the reagent minimises the interference of iron(II) iron(III) can be removed by diethyl ether extraction from a hydrochloric acid solution. Most of the interferences can be eliminated by treatment with potassium bromate, followed by the addition of an alkali fluoride. Cobalt may also be isolated by dithizone extraction from a basic medium after copper has been removed (if necessary) from acidic solution. An alumina column may also be used to adsorb the cobalt nitroso-R-chelate anion in the presence of perchloric acid, the other elements are eluted with warm 1M nitric acid, and finally the cobalt complex with 1M sulphuric acid, and the absorbance measured at 500 nm. 

There are some means for synthesis of defined primary or secondary esters. Monoester salts of phosphoric acid, for instance, are prepared by addition of alcohol or ethoxylated alcohol, alkali fluoride, and pyrophosphoryl chloride (C12P0)20 in a molar ratio of 0.9-1.5 0.05-1 1.0 at -50 to +10°C and hydrolysis of the Cl-containing intermediates with base. Thus, 32.3 g (C12P0)20 was treated at -50°C with 23.9 g lauryl alcohol in the presence of 0.7 g KF and the mixture was slowly warmed to room temperature and hydrolyzed with H20 and 40% NaOH to give 83% sodium monolauryl phosphate. The monoester salts showed comparable or better washing and foaming efficiency than a commercial product [12]. 

Thus removal of water from classical rather inactive fluoride reagents such as tetrabutylammonium fluoride di- or trihydrate by silylation, e.g. in THF, is a prerequisite to the generation of such reactive benzyl, allyl, or trimethylsilyl anions. The complete or partial dehydration of tetrabutylammonium fluoride di- or trihydrate is especially simple in silylation-amination, silylation-cyanation, or analogous reactions in the presence of HMDS 2 or trimethylsilyl cyanide 18, which effect the simultaneous dehydration and activation of the employed hydrated fluoride reagent (cf, also, discussion of the dehydration of such fluoride salts in Section 13.1). For discussion and preparative applications of these and other anhydrous fluoride reagents, for example tetrabutylammonium triphenyldifluorosilicate or Zn(Bp4)2, see Section 12.4. Finally, the volatile trimethylsilyl fluoride 71 (b.p. 17 °C) will react with nucleophiles such as aqueous alkali to give trimethylsilanol 4, HMDSO 7, and alkali fluoride or with alkaline methanol to afford methoxytri-methylsilane 13 a and alkali fluoride. 

For the preparation of monofluorophosphates there are quite a lot of methods found in literature. The alkali salts are obtained by shortly melting poly- or trimetaphosphate with alkali fluoride (29,30) - the application of graphite vessels yielding particulary pure products (31) ... 

The ionic model, developed by Bom, Lande, and Lennard-Jones, enables lattice energies (U) to be summed from inverse square law interactions between spherically symmetrical charge distributions and interactions following higher inverse power laws. Formation enthalpies are related to calculated lattice energies in the familiar Bom-Haber cycle. For an alkali fluoride... 

If anhydrous hydrofluoric acid is used as the acid phase, a further fact about one variable in (12b) can easily be introduced. It is known from the investigations of Fredenhagen (1939 Fredenhagen and Cadenbach, 1930) that alkali fluorides are practically completely dissociated in anhydrous HF. The acidity of HF can therefore be varied over a wide range by the addition of alkali fluoride or BF3, with the acidity being reduced by the addition of alkali fluoride but increased by the addition of BFs as a result of the reaction ... 

Because of the complete dissociation of NaF in HF the concentration Cx-, i.e. the concentration of fluoride ions in the present instance, may be expressed by the stoicheiometric concentration of the alkali fluoride. Hence... 

Equation (19) is valid for a large number of aromatic substances investigated in the system HE + NaF. A higher alkali fluoride concentration was necessary for aromatic substances of high basicity. For solubility... 

Benzoyl fluoride can also be prepared by the reaction of anhydrous hydrogen fluoride or potassium fluoride with benzoic anhydride and by the halogen exchange of benzoyl chloride with alkali fluorides, such as NaF/ KF/ KHF2, Na2SiFe, or various other metal fluorides. ... 

Polarized Raman spectra from the alkali fluorides LiF, NaF and CsF habe been observed with argon laser excitations by Evans and Fitchen 09). These spectra are of interest as an extreme test of lattice dynamics theories and polarizability models. 

When no catalyst is used or if KF and NaF are present as catalysts, CIF is the main by-product. When the more basic alkali metal fluorides, RbF and CsF, are used, CIF3 is the favored coproduct. The formation of CIF 3 rather than CIF is presumably associated with the more ready formation of C1F2 intermediates with RbF and CsF. Yields of CIF3O from CljO are rather variable and may be affected by the particular alkali fluoride present. Yields of over 40% have been consistently obtained and have reached over 80% using either NaF or CsF. Since NaF does not form an adduct with CIF3O (64), stabilization of the product by complex formation does not seem to influence the CIF3O yields strongly. 

The interaction of alkali salts with inorganic and organic acids has been extensively studied by the same group. In the case of alkali fluorides it was shown that milling leads to proton transfer and to formation of KHF2, while the reactivity of fluorides follows the order KF>NH4F>NaF>LiF, Cap2 [71b,c]. 

Reaction with alkali fluorides (except LiF) yields double salts, such as K3[Mo03F3], formed as colorless cubic crystals. 

Degrees of Polarity and Mutual Polarization of Ions in the Molecules of Alkali Fluorides, SrO, and BaO... 

A precise quantitative theory of the mutual polarization of ions in molecules is not possible as long as one cannot take into account the inhomogeneity of the field of the polarizing ion and the dependence of the polarizability of the polarized ion on its surroundings. It is therefore attempted to correlate the observed dependence of the p values on r and the polarizability of the ions in a semi-quantitative and semi-empirical fashion. This proves to be successful for the alkali fluorides but explains only qualitatively why the degree of polarity is smaller for BaO than for SrO. 

In the meantime, precise values of and r became available for the four other alkali fluorides and their degrees of polarity, not discussed yet elsewhere, will be compared here. 

Table 1. Internuclear distances (r in A.), dipole moments (fi in T)) and degrees of polarity (p) of alkali fluoride molecules...

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