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]

Perfluorooctanesulfonic acid

Trifluoromethanesulfonic acid

Properties

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.

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.^[2]

Regulation

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]

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

Literature

• 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

References

1. "Terminology | FluoroCouncil".
2. Bohannon, Meredith E; Narizzano, Allison M; Guigni, Blas A; East, Andrew G; Quinn, Michael J (2023). "Next-generation PFAS 6:2 fluorotelomer sulfonate reduces plaque formation in exposed white-footed mice". Toxicological Sciences. 192 (1): 97–105. doi:10.1093/toxsci/kfad006.
3. Regulation (EU) 2019/1021 of the European Parliament and of the Council of 20 June 2019 on persistent organic pollutants
4. "UN experts recommend elimination of additional hazardous chemicals to protect human health and the environment".