Abstract

Perfluoroalkanesulfonic acids and their derivatives are of commercial significance because of their unusual acid strength, chemical stability, and the surface activity of the higher members of the series (eight carbons and larger). The best method of preparation is via the perfluorinated sulfonyl fluorides derived from electrochemical fluorination, although other methods including direct fluorination with fluorine gas are known. The first member of the series, trifluoromethanesulfonic acid, is one of the strongest acids known. Alkyl esters of trifluoromethanesulfonic acid are among the best leaving groups known and are commonly used in that capacity in displacement reactions. Lithium trifluoromethanesulfonate solutions are very conductive and can find application as electrolytes in primary lithium batteries and as antistats for films.

Derivatives of the longer-chain perfluoroalkanesulfonic acids have a number of unique surface-active properties and have formed a basis for a number of commercial products. The longer-chain acids and their salts, particularly C₈F₁₇SO₃H and higher, are surface-active agents in aqueous media. They reduce the surface tension of water to levels not possible with hydrocarbon surfactants. Preparation of difunctional perfluoroalkanesulfonates and their derivatives is discussed, including fluorosulfonylacetyl fluoride. Fluorosulfonyldifluoracetyl fluoride is an important industrial intermediate used in the production of Du Pont's Nafion ion-exchange membranes and in many other applications.