Oleums-polysulfuric acids

Lewis and Bigeleisen,71 who first determined the Hammett acidity function values for oleums, used a method to derive them from the vapor pressure measurements. Brand et al.,72 however, subsequently by the use of nitro compound indicators showed that the H0 values are not directly related to the vapor pressure. The most accurate Ho values for oleums so far have been published by Gillespie et al.7 (Table 2.4). 

The increase in acidity on addition of S03 to sulfuric acid is substantial, and an //0 value of —14.5 is reached with 50mol% S03. The main component up to this S03 concentration is pyrosulfuric (or disulfuric) acid H2S207. Upon heating or in the 

At higher S03 concentration, a series of higher poly sulfuric acids such as H2S3O10, H2S4013, and so on, are formed and a corresponding increase in acidity occurs. However, as can be seen from Table 2.4, the acidity increase is very small after reaching 50mol% of S03 and no data are available beyond 75%. 

Fluorosulfuric Acid-Antimony Pentafiuoride ( Magic Acid ). 

The acidity of the Magic Acid system as a function of SbF5 content has been measured successively by Gillespie,8 Gold,73 Sommer,74 and their co-workers. The increase in acidity is very sharp at low SbF5 concentration and was estimated to 

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The first acids of the sulfuric acid system to be recognized (29) were disulfuric acid, H2S2O7, and the higher polysulfuric acids, H2SSO10 etc., which are present in oleum. Dilute oleum contains mainly disulfuric acid, H2S2O7, and from cryoscopic measurements on such solutions the first dissociation constant of disulfuric acid has been found to be 1.4 X 10 2 (5). It is approximately 30% ionized in a 0.1 m solution ... 

The conductivities of its solutions, which are shown in Pig. 3, are also consistent with this value for its acid-dissociation constant. The higher polysulfuric acids are present in increasing amount in more concentrated oleums and they appear to be somewhat stronger acids than disulfuric... 

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