Hydrogen fluoride as a solvent

Fluoroolefins add mercuric fluoride at 50- 100 °C to give bis(polyfluoroalkyl)-mercury derivatives. Reaction is usually carried out in hydrogen fluoride as a solvent. This process was reviewed and the electrophilic nature of this process established [6]. Addition to olefin starts by the attack of cation 3 (Eq. 5) on the double bond of fluoroolefin. 

Katz, J. J. Anhydrous hydrogen fluoride as a solvent for proteins and other biologically important substances. Arch. Biochem. Biophys. 51, 293 (1954) Anhydrous trifluoroacetic acid as a solvent for proteins. Nature 174, 509 (1954) A. L. Koch, W. A. Lamont and J. J. Katz The effect of anhydrous strong acids on ribonuclease and lysozyme. Arch. Biochem. Biophys. 63, 106 (1956). 

In the case of cysteine (5) the product obtained is contaminated by cystine and also by thiazolidine carboxylic acid (obtained by reaction of cysteine and formaldehyde, the latter arising from hydrolytic decomposition of acetamidomethanol, see section VI). However, the product could easily be purified by using ion exchange columns. On the other hand, anhydrous conditions should avoid the decomposition of the acetamidomethanol and indeed a reaction using hydrogen fluoride as a solvent results in quantitative yield of the pure product". 

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