Hexafluorophosphoric acid

All three fluorophosphoric acids are commercially available. The mono- and difluoro acids can be made as anhydrous or hydrated Hquids. Commercial hexafluorophosphoric acid is an aqueous solution. Anhydrous hexafluorophosphoric acid maybe prepared at reduced temperatures and pressures but it dissociates rapidly into PF and HF at 25°C (56). When diluted with water all the fluorophosphoric acids hydrolyze producing orthophosphoric acid. The hexafluoro acid is the most stable of the three fluorophosphoric acids. 

A number of salts of the monofluoro- and hexafluorophosphoric acids are known and some are commercially important. The salts of difluorophosphoric acid are typically less stable toward hydrolysis and are less well characterized. Sodium monofluorophosphate [7631-97-2] the most widely used dentifrice additive for the reduction of tooth decay, is best known (see Dentifrices). Several hexafluorophosphates can be prepared by neutralization of the appropriate base using hexafluorophosphoric acid. The monofluorophosphates are usually prepared by other methods (57) because neutralization of the acid usually results in extensive hydrolysis. 

The commercially available difluorophosphoric acid has a formula approximating 2 HPO2F2 H20 and contains some monofluorophosphoric acid (1) and some hexafluorophosphoric acid (3) as well as HF. It is primarily used ia catalytic appHcations. 

Hexafluorophosphoric Acid. Hexafluorophosphoric acid (3) is present under ambient conditions only as an aqueous solution because the anhydrous acid dissociates rapidly to HF and PF at 25°C (56). The commercially available HPF is approximately 60% HPF based on PF analysis with HF, HPO2F2, HPO F, and H PO ia equiUbrium equivalent to about 11% additional HPF. The acid is a colorless Hquid which fumes considerably owiag to formation of an HF aerosol. Frequently, the commercially available acid has a dark honey color which is thought to be reduced phosphate species. This color can be removed by oxidation with a small amount of nitric acid. When the hexafluorophosphoric acid is diluted, it slowly hydrolyzes to the other fluorophosphoric acids and finally phosphoric acid. In concentrated solutions, the hexafluorophosphoric acid estabUshes equiUbrium with its hydrolysis products ia relatively low concentration. Hexafluorophosphoric acid hexahydrate [40209-76-5] 6 P 31.5°C, also forms (66). This... 

Many of the organic and inorganic hexafluorophosphates can be prepared by reaction of hexafluorophosphoric acid and the appropriate base. Another method involves reaction of the appropriate chloride and PCI3 with anhydrous HF (87). 

A. o-Bromobenzenediazonium hexafluorophosphate. A solution of 95 ml. of 12N hydrocMoric acid in 650 ml. of water is added with stirring to 60 g. of o-bromoaniline (0.35 mole Note 1) in a 2-1. three-necked flask equipped with stirrer and thermometer. Solution is effected by heating the mixture on a steam bath (Note 2). A solution of 29 g. (0.42 mole) of sodium nitrite in 75 ml. of water is added with stirring while the mixture is maintained at — 5° to —10° by means of a bath of ice and salt or of dry ice and acetone. At the end of the addition there is an excess of nitrous acid, which can be detected with starch iodide paper. Seventy-four milliliters (134 g., 0.60 mole) of 65% hexafluorophosphoric acid (Note 3) is added in one portion, with vigorous stirring, to the cold solution of the diazonium salt. Cooling and slow stirring are continued for an additional 30 minutes, and the precipitated diazonium hexafluorophosphate is then collected on a Bilchner funnel. The diazonium salt is washed on the funnel with 300 ml. of cold water and with a solution of 80 ml. of methanol in 320 ml. 

Hexafluorophosphoric acid and its salts can be employed for halogen- and alkoxy-exchange fluorination at germanium and silicon atoms in transition metal complexes3 or chloro(or-gano)silanes,4 to give, for example, 33 and 4.4... 

Hexafluorophosphoric acid is a useful reagent for the conversion of arylamines into aryl fluorides 6 via decomposition of intermediate arenediazonium hexafluorophosphates 5 (see also Section 26.1.4.3.) and in some cases this procedure has a marked advantage over the use of fluoroboric acid (see Section 26.1.3.) in the same reaction.5... 

An appreciable increase in the yield of some aromatic fluorides with hexafluorophosphoric acid, compared to the fluoroboric acid method, has been observed. Outstanding in this respect is the increase in yields of 2-fluorobenzoic acid (+52%), 4-fluorobenzoic acid ( + 49%),... 

Reaction of the ketosulfone (ix) with 2-chloro-1,3-bis(dimethylamino)trimethinium salt (xix) in the presence of an equimolar amount of tert-BuOK followed by treatment with acetic acid and TFA and reflux with an excess of ammonium hydroxide. 2-Chloro-1,3-bis(dimethylamino)trimethinium hexafluoro-phosphat (xix) is obtained by reaction of chloroacetic acid with hot dimethylformamide and POCI3. Finally the reaction mixture is treated with NaOH and hexafluorophosphoric acid in water. 

The diazonium hexafluorophosphates, prepared similarly from the appropriate diazonium chloride solution and hexafluorophosphoric acid, may in general be used instead of the fluoroborates with advantage. The thermal decomposition of diazonium hexafluorophosphates to aryl fluorides generally proceeds smoothly and in better yield.29... 

Addition of concentrated hexafluorophosphoric acid to a mixture of iosobutyric anhydride and 3-ethyl-3-pentanol leads to 4-ethyl-2,6-diisopropyl-3,5-dimethylpyrylium hexafluorophosphate, a reaction that proceeds via a rapid exothermal diacylation (Equation 466) <2004JOC536>. 

Protonation of dienol complexes (53) with hexafluorophosphoric acid in diethyl ether affords air-stable salts (55) in high yield [Eq. (27)] (206). While the iron derivatives (21) are rapidly hydrolyzed, the cyclopentadienyl rhodium and iridium salts (55) are much less reactive (207). 

The reaction of 5-chloropent-l-yne with 92 in refluxing methanol with aqueous hexafluorophosphoric acid affords a one-pot synthesis of the cyclic... 

Heating AH-1 -benzotellurins in glacial acetic acid in the presence of hexafluorophosphoric acid on a steam bath yielded benzotellurinium hexafluorophosphales4. 

Guaiazulene reacts with thiophene 2-carbaldehyde in methanol in the presence of hexafluorophosphoric acid to give the stabilized carbenium ion 183 in 98% yield <2005T10349>. Reduction of this with zinc powder gives a mixture of stereoisomeric dimers (Equation 83). 

HEXAFLUOROKIEZELZUUR (DUTCH) see SC0500 HEXAFLUOROPHOSPHORIC ACID see HDEOOO... 

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