Perfluorosulfonic acids

Perfluorosulfonic acids (PFSAs) are chemical compounds of the formula C_nF_(2n+1)SO₃H and thus belong to the family of perfluorinated and polyfluorinated alkyl compounds (PFASs). The simplest example of a perfluorosulfonic acid is the trifluoromethanesulfonic acid. Perfluorosulfonic acids with six or more perfluorinated carbon atoms, i.e. from perfluorohexanesulfonic acid onwards, are referred to as long-chain.^[1]

Perfluorosulfonic acids are organofluoroanalogues of conventional alkanesulfonic acids, but they are several pK_A units stronger (and are therefore strong acids). Their perfluoroalkyl chain has a highly hydrophobic character.

Perfluorooctanesulfonic acid, for example, has been used in hard chromium plating. Since the early 2000's 6:2 fluorotelomersulfonic acid has been used as a replacement for perfluorooctanesulfonic acid.^[2]

Perfluorooctanesulfonic acid was included in Annex B of the Stockholm Convention in 2009 and subsequently in the EU POPs Regulation.^[3]

Perfluorohexanesulfonic acid was included in Annex B of the Stockholm Convention in 2022.^[4]

• Perfluoro(4-ethylcyclohexane)sulfonic acid, a cyclic analogue

• OECD, ed. (2022), "3. Perfluoroalkane sulfonic (a) and sulfinic (b) acids", Fact Cards of Major Groups of Per- and Polyfluoroalkyl Substances (PFASs), OECD Environment, Health and Safety Publications 68 Series on Risk Management, pp. 31–41