FLUOROSULFURIC ACID AND RELATED SUPERACID MEDIA

Fluorosulfuric acid is one of the most highly acidic media that have been investigated in any detail. Its physical and chemical properties are described. It has proved to be a very useful solvent for studying the protonation of very weak bases, particularly as its low freezing point, −88.98°, has enabled the nmr spectra of the protonated forms of many weak bases to be observed. The acidity of fluorosulfuric acid may be further increased by the addition of SbF5 and of both SbF5 and SO3. Acids such as H [SbF5(SO3F)] and H[SbF2(SO3F)4] are formed in these systems. These still more acidic media have also proved very useful in the study of protonation reactions and for the formation of carbonium ions and related species. By oxidizing iodine with S2O6F2 the cations I2+, I3+, I5+, and I42+ have been obtained in solution in fluorosulfuric acid, and by the oxidation of selenium with S2O6F2 in HSO3F the cations Se42+ and Se82+ have been obtained. From a solution of Se42+in HSO3F the compound Se4(SO3F)2 has been obtained. Fluorosulfuric acid is a useful reagent for preparing oxyfluorides from oxides and oxy acid salts, e.g., KMnO4 gives MnO3F, BaSeO4 gives SeO2F2, and KCIO4 gives ClO3F. © 1968, American Chemical Society. All rights reserved.