Fluorosulfuric acid, properties

Fluorosulfuric acid is stable to heat up to decomposition at about 900°C (13), where vapor-phase dissociation into hydrogen fluoride and sulfur trioxide probably occurs. Reviews of the chemistry and properties of fluorosulfuric acid have been pubUshed (14—16). 

Other studies which have been reported describe unusual chemistry such as HSO F—Nb(S02F) systems (42). Also the unique properties of fluorosulfuric acid have been found to provide unusual solvent systems, which can vary properties such as acidity, heats of solution, enthalpy, and heats of neutralization (43). 

Fluorosulfuric acid can be very corrosive. A study of the corrosive properties of fluorosulfuric acid during preparation and use showed carbon steel to be acceptable up to 40°C, stainless steel up to 80°C, and aluminum alloys up to 130°C (52). 

Fluorosulfonate ion, 2 124-125 Fluorosulfonic acid, 2 123-124, 145, see also Fluorosulfuric acid esters, 2 126-127, 145 Fluorosulfonylamide ions, 19 193-206 Fluorosulfonyl-nitrogen compounds, syntheses and properties of, 14 363-372 iV-Fluorosulfonylpentafluorosulfanylamine, 19 190, 191... 

Radical cations that are produced by electrochemical oxidation are not stable in solvents with appreciable base character. This results because such radicals are subject to attack by available nucleophiles, and solvents that contain donor electron pairs are good nucleophiles. Cation radicals are most stable in solvents that are good Lewis acids and show negligible basic properties. Some of the solvent systems that have been employed to stabilize electrochemically produced cation radicals include nitromethane and nitrobenzene,21 dichloro-methane,22 trifluoroacetic acid-dichloromethane (1 9),23 nitromethane-AlCl3,24 and AlCl3-NaCl (1 l).25 Organic chemists should be familiar with the stabilization of carbonium ions by superacid media.26 These media usually contain fluorosulfuric acid, or mixtures of fluorosulfuric acid with antimony pen-tachloride and sulfur dioxide, and are potent solvents for the production and stabilization of organic cations. 

A different distribution was observed when a-deutero-enrfo-armilenol was treated with similar reagents. This four-fold random distribution of deuterium, only among a, y, 5 and 0 carbons is consistent with [458] or rearranging [457]. Only four-fold randomization was observed when selectively a-deuterated [460] was transformed into the cation [457] (or [458]) by fluorosulfuric acid. Thus it necessarily follows that the 11-fold automerization is not a property of the armilenyl cation [457] (or [458]) but rather of a precursor which more resembles the [4.3.2]-system. 

The ready availability of the strong anhydrous acids fluorosulfuric acid and trifluoromethanesulfonic acid in recent decades prompted more chemistry 179). The electron-withdrawing properties of the CF3—, F—, and —SO2— groups suggested that FSO3 and CF3S03 ... 

The facts given above and the close parallel between 7/s values and the three acidity functions—%H2S04, IIQ and (H0 + log [H+]) suggest that linear relationships may be found which would permit the estimation of otherwise inaccessible H0 values or AHS values. This was indeed done in order to estimate the H0 acidity of fluorosulfuric acid (Fig. 3) and HSO3F—SbF5 with independent corroboration of the former value within 1 3 H0 unit (Arnett et al., 1972b). Unfortunately, we have not been able to find any objective treatment of such data which would yield reliable thermodynamic properties for ionization of weak bases in water as a standard state. 

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