Mechanistic Investigations of Thermal Decomposition of Perfluoroalkyl Ether Carboxylic Acids and Short-Chain Perfluoroalkyl Carboxylic Acids

Environ Sci Technol. 2023 Jun 13;57(23):8796-8807. doi: 10.1021/acs.est.3c00294. Epub 2023 May 17.


In this study, we investigated the thermal decomposition mechanisms of perfluoroalkyl ether carboxylic acids (PFECAs) and short-chain perfluoroalkyl carboxylic acids (PFCAs) that have been manufactured as replacements for phased-out per- and polyfluoroalkyl substances (PFAS). C-C, C-F, C-O, O-H, and C═C bond dissociation energies were calculated at the M06-2X/Def2-TZVP level of theory. The α-C and carboxyl-C bond dissociation energy of PFECAs declines with increasing chain length and the attachment of an electron-withdrawing trifluoromethyl (-CF3) group to the α-C. Experimental and computational results show that the thermal transformation of hexafluoropropylene oxide dimer acid to trifluoroacetic acid (TFA) occurs due to the preferential cleavage of the C-O ether bond close to the carboxyl group. This pathway produces precursors of perfluoropropionic acid (PFPeA) and TFA and is supplemented by a minor pathway (CF3CF2CF2OCFCF3COOH → CF3CF2CF2· + ·OCFCF3COOH) through which perfluorobutanoic acid (PFBA) is formed. The weakest C-C bond in PFPeA and PFBA is the one connecting the α-C and the β-C. The results support (1) the C-C scission in the perfluorinated backbone as an effective PFCA thermal decomposition mechanism and (2) the thermal recombination of radicals through which intermediates are formed. Additionally, we detected a few novel thermal decomposition products of studied PFAS.

Keywords: GC−MS; PFAS; density functional theory; high-resolution mass spectrometry; spent media; thermal transformation.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, U.S. Gov't, Non-P.H.S.
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Carboxylic Acids / chemistry
  • Ether
  • Ethers
  • Fluorocarbons* / analysis
  • Water Pollutants, Chemical* / analysis


  • Ether
  • Carboxylic Acids
  • Water Pollutants, Chemical
  • Ethers
  • perfluoropropionic acid
  • Fluorocarbons
  • perfluorobutyric acid