Perfluoroalkyl carboxylic acids
Perfluoroalkyl carboxylic acids, or perfluorocarboxylic acids are compounds of the formula CnFCO2H that belong to the class of per- and [polyfluoroalkyl substances]. The simplest example is trifluoroacetic acid. These compounds are organofluorine analogues of ordinary carboxylic acids, but they are stronger by several pKa units and they exhibit great hydrophobic character. Perfluoroalkyl dicarboxylic acids are also known, e.g. C2F42.
Applications
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 and related fluoropolymers.
Production
These compounds are typically prepared by electrochemical fluorination of the carboxylic acid fluorides followed by hydrolysis:Environmental concerns
Long-chain PFCAs such as perfluorooctanoic acid 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, their salts, and related compounds were added to Annex A.Short-chain PFCAs are formed from atmospheric oxidation of fluorotelomer compounds and chlorofluorocarbon replacements introduced as a result of the Montreal Protocol.
Side-chain fluorinated polymers, in which fluorotelomers are attached to a polymer backbone, may release fluorotelomer alcohols through hydrolysis. The latter are then degraded to PFCAs.
File:Urethane SCFP hydrolysis simplified.svg|center|thumb|500x500px|Simplified degradation pathway of urethane side-chain fluorinated polymers: hydrolysis yields fluorotelomer alcohols that are then degraded to PFCAs of different chain lengths.