Ternary Superacids

As mentioned in Section 2.3.1, fluorosulfuric acid used in common laboratory practice always contains HF. A mixture of HSO3F and CF3SO3H is, in fact, the ternary superacid HSO3F-HF-CF3SO3H. 

Considerable use has been made of superacid systems, particularly the HSOsF—SbFs system, for the preparation and identification of the conjugate adds of some very weak bases. The ternary system HSOsF—SbF(—SO2 has also often been used for such studies. Although SO2 is completely misdble with HSO3F—SbFj mixtures, it is not protonated to any measurable extent and it does not appear to cause any appreciable reduction of the very high acidity of HSOsF—SbFg. Sulphur dioxide also considerably reduces the rather high viscosity of SbFj— HSOsF solutions and this gives rise to sharper and better resolved n.m.r. spectra. 

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