Potassium, hydrogen fluoride

Fluorine cannot be prepared directly by chemical methods. It is prepared in the laboratory and on an industrial scale by electrolysis. Two methods are employed (a) using fused potassium hydrogen-fluoride, KHFj, ill a cell heated electrically to 520-570 K or (b) using fused electrolyte, of composition KF HF = 1 2, in a cell at 340-370 K which can be electrically or steam heated. Moissan, who first isolated fluorine in 1886, used a method very similar to (b) and it is this process which is commonly used in the laboratory and on an industrial scale today. There have been many cell designs but the cell is usually made from steel, or a copper-nickel alloy ( Monel metal). Steel or copper cathodes and specially made amorphous carbon anodes (to minimise attack by fluorine) are used. Hydrogen is formed at the cathode and fluorine at the anode, and the hydrogen fluoride content of the fused electrolyte is maintained by passing in... 

Zirconium is readily attacked by acidic solutions containing fluorides. As Httle as 3 ppm flouride ion in 50% boiling sulfuric acid corrodes zirconium at 1.25 mm/yr. Solutions of ammonium hydrogen fluoride or potassium hydrogen fluoride have been used for pickling and electropolishing zirconium. Commercial pickling is conducted with nitric—hydrofluoric acid mixtures (see Metal surface treatments). 

Fluorosilicate Fusion. The fusion reaction of milled zircon with potassium hydrogen fluoride was used to prepare potassium hexafluorozirconate [16923-95-8] for studies leading to the first separation of hafnium and zirconium (30). Similar reactions using potassium hexafluorosihcate have been used (31,32) commercially in the United States and the former USSR ... 

Potassium hydrogen fluoride [7789-29-9] M 78.1. Crystd from water. 

Cyclopropyl methanols when treated with a combination of hydrogen fluoride, pyridine, potassium hydrogen fluoride, and diisopropylamine undergo fluonnation and rearrangement to give excellent yields of homoallylic fluorides Chlorobenzene substituted cyclopropyl methanols at low temperatures leads to ring expansion to give... 

According to E. Fremy s Recherches sur les fluorures (1856), the acid furnished by the action of sulphuric acid on fluorspar always contains water, sulphuric acid, sulphurous acid, hydrofluosilicic acid, and other impurities. After many fruitless attempts to puiify and dehydrate the crude material so obtained, he sought other means of preparation, and found that anhydrous hydrofluoric acid could be satisfactorily obtained by heating well-dried potassium hydrogen fluoride in a platinum retort attached to a platinum receiver which was cooled by immersion in a freezing mixture. The first portions of the acid which distilled over contained a little moisture. H. Moissan thus describes the operation ... 

The second organic fluoride was not made until 20 years later. Fremy (with whom Moissan studied in the 1870 s) generated pure anhydrous hydrogen fluoride for the first time by heating potassium hydrogen fluoride (KHF2). The latter (Fremy s salt) was heated with ethyl potassium sulfate in a platinum apparatus to give fluoroethane.12... 

Moreover, interesting ring-formation reactions to give 7 have also been reported for substituted mclhoxyallenyl(cyclopropyl)methanols using 70% hydrogen fluoride/pyridine in combination with sodium fluoride or potassium hydrogen fluoride.82... 

With Potassium Fluoride and Potassium Hydrogen Fluoride... 

Analogous to sulfonyl fluorides, acid fluorides can be prepared in good yields by treating acid chlorides with potassium fluoride in the presence or absence of a solvent.28 Potassium hydrogen fluoride is used in excess for the preparation of 4-methyl- and 4-fluorobenzoyl fluorides 2 from the corresponding acid chlorides 1 by slow distillation from a mixture of both the reactants.29... 

Chloromethyl)oxirane (3) affords 1,3-difluoro- and l-chloro-3-fluoropropan-2-ol (4 and 5) on reaction with potassium hydrogen fluoride in diethylene glycol.76 There is no reaction when potassium fluoride is used which indicates that the epoxy ring in 3 is opened by the hydrogen fluoride present in potassium hydrogen fluoride and later the chlorine is exchanged for fluorine. 

Potassium hydrogen fluoride is also used to open the epoxide ring in the /1-D-galactopyranose 6 with concomitant formation of the fluoride 7.7 7... 

A mixture of potassium hydrogen fluoride, 1 M hydrofluoric acid and (V-iodosuccinimide in the presence of tetrabutylammonium fluoride (TBAF) as a phase-transfer catalyst has been shown to effect iodofluorination of alkenes in good yield.163 Dodec-l-ene (6) has been transformed to 2-fluoro-l-iodododecane (7) in 82% yield. TBAF is essential for the reaction to proceed quickly and to improve the yield. The percentage of the side product 1-iodododecan-2-ol is kept to a minimum (0.2%). Many alkenes have been transformed to the corresponding fluoroiodo derivatives by this method.163... 

For minerals in which the titanium content is high it has been found preferable to attack the ore with potassium hydrogen fluoride, KHF2, or concentrated hydrofluoric acid.13 In one such process the powdered... 

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