Perfluorosulfonic acids (PFSAs) are chemical compounds of the formula CnF(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.
Properties Perfluorosulfonic acids are organofluoroanalogues of conventional alkanesulfonic acids, but they are several pKA units stronger (and are therefore strong acids). Their perfluoroalkyl chain has a highly hydrophobic character.
Use 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.
PFSA resins are specialty polymers consisting of a fluoropolymer backbone of polytetrafluoroethylene with a side chain of perfluorinated vinyl ether comonomer bearing sulfonic acid functional groups. The side chain may vary in length, which imparts different properties. These polymers are used as membranes in fuel cells and water electrolyzers for example. Chemical brand names include Nafion, Aquivion, and Fumapen.
Regulation Perfluorooctanesulfonic acid was included in Annex B of the Stockholm Convention in 2009 and subsequently in the EU POPs Regulation.Regulation (EU) 2019/1021 of the European Parliament and of the Council of 20 June 2019 on persistent organic pollutants
Perfluorohexanesulfonic acid was included in Annex A of the Stockholm Convention in 2022.
Examples Name Abbreviation Structural formula Molecular weight (g/mol) CAS No. Perfluoropropanesulfonic acid PFPrS C3F7SO3H 250.09 423-41-6 Perfluorobutanesulfonic acid PFBS C4F9SO3H 300.10 375-73-5 Perfluoropentanesulfonic acid PFPS C5F11SO3H 350.11 2706-91-4 Perfluorohexanesulfonic acid PFHxS C6F13SO3H 400.12 355-46-4 Perfluoroheptanesulfonic acid PFHpS C7F15SO3H 450.12 375-92-8 Perfluorooctanesulfonic acid PFOS C8F17SO3H 500.13 1763-23-1 Perfluorononanesulfonic acid PFNS C9F19SO3H 550.14 68259-12-1 Perfluorodecanesulfonic acid PFDS C10F21SO3H 600.15 335-77-3
See also Perfluoro(4-ethylcyclohexane)sulfonic acid, a cyclic analogue
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