Perfluoroalkyl carboxylic acids
Class of chemical compounds
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Through Carboxylic acid, Peptide and Montreal Protocol
Applications
Trifluoroacetic acid is a widely employed acid, used for example in the synthesis of peptides. Its esters are useful in analytical chemistry.
Longer-chain perfluoroalkyl carboxylic acids, e.g. with five to nine carbons, are useful fluorosurfactants and emulsifiers used in the production of polytetrafluoroethylene (Teflon) and related fluoropolymers.
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Production
These compounds are typically prepared by electrochemical fluorination of the carboxylic acid fluorides followed by hydrolysis:
- CnH(2n+1)COF + (2n+1) HF → CnF(2n+1)COF + (2n+1) H2
- CnF(2n+1)COF + H2O → CnF(2n+1)CO2H + HF
Environmental concerns
Long-chain PFCAs such as perfluorooctanoic acid (PFOA) are either banned or under scrutiny because they are extremely persistent and bioaccumulative. In 2019, PFOA, its salts, and PFOA-related compounds were added to Annex A of the Stockholm Convention on Persistent Organic Pollutants, requiring treaty members to take measures to eliminate their production and use. In 2025, C9–C21 long-chain PFCAs (CnF2n+1COOH, 8 ≤ n ≤ 20), their salts, and related compounds were added to Annex A.
Short-chain PFCAs (scPFCAs) are formed from atmospheric oxidation of fluorotelomer compounds and chlorofluorocarbon (CFC) replacements introduced as a result of the Montreal Protocol.
Side-chain fluorinated polymers (SCFPs), in which fluorotelomers are attached to a polymer backbone, may release fluorotelomer alcohols through hydrolysis. The latter are then degraded to PFCAs.