Differences in the isomer composition of perfluoroctanesulfonyl (PFOS) derivatives

Abstract

Perfluorooctanesulfonyl (PFOS)-based materials and related compounds are an emerging group of environmental pollutants. Perfluorooctanesulfonyl fluoride, the key intermediate for the production of these materials, was manufactured by an electrochemical fluorination process that resulted in complex mixtures containing linear and branched PFOS derivatives and other perfluorinated compounds. This study uses ¹⁹F-NMR spectroscopy to investigate differences in the composition between commercial samples of PFOS and PFBS (perfluorobutanesulfonyl) derivatives. While PFBS derivatives, which are under evaluation as substitutes for PFOS-based materials, contained no detectable levels of branched impurities, all PFOS derivatives contained significant levels of branched and other impurities. Analysis of the NMR data reveals that PFOS fluorides typically have a higher content of internally branched and similar levels of isopropyl branched PFOS isomers compared to PFOS potassium salts. Furthermore, the isomer distribution of PFOS derivatives may vary depending on their source. These findings suggest that it is important to determine the isomer composition of PFOS samples used in both environmental and toxicological studies.

Keywords:

• Fluorinated surfactants
• perfluorooctanesulfonyl fluoride
• perfluorooctanesulfonic acid
• PFOS
• ¹⁹F-NMR analysis

Acknowledgments

The authors would like to thank Mr. John A. Snyder for help with the ¹⁹F NMR experiments. This work was supported by grants from the National Institutes of Health (ES12475 and EB02748) and the National Science Foundation (NIRT 0210517). Its contents are solely the responsibility of the authors and do not necessarily represent the official views of the funding agencies.

Notes

^a Determined for each experiment as the average percentage calculated based on the signals at −81.8 (CF₃) and −127.0 (CF₂) ppm;

^b determined for each experiment as the average percentage calculated based on the signals at −72.8 (CF₃) and −187.0 (CF) ppm;

^c calculated based on the integration of all signals between −70 and −72 ppm;

^d calculated using a characteristic multiplet at -62.5 ppm;

^e calculated using a characteristic broad singlet at −171 ppm;

^f Alfa Aesar;

^g Across;

^h Aldrich;

ⁱ Oakwood Products;

^j Fluka Chemie GmbH;

^k synthesized from perfluorooctanesulfonyl fluoride AF;

^l synthesized from perfluorooctanesulfonyl fluoride AAF;

^m synthesized from perfluorooctanesulfonyl fluoride ALF;

ⁿ synthesized from perfluorooctanesulfonic acid OWH.