Hydrolysis and Atmospheric Oxidation Reactions of Perfluorinated Carboxylic Acid Precursors

• Main Author: Jackson, Derek Andrew
• Other Authors: Mabury, Scott A.
• Language: en_ca
• Published: 2013
• Subjects: environmental; chemistry; analytical; transformation; fluorinated; PFCA; atmospheric; hydrolysis; 0486
• Online Access: http://hdl.handle.net/1807/35854

This dissertation explores a number of different environmentally relevant reactions that lead to the production of perfluorocarboxylic acids (PFCAs), a family of environmental pollutants that does not undergo any further degradation pathways. The compound perfluoro-2-methyl-3-pentanone (PFMP) is a new fire fighting fluid developed by 3M that is designed as a Halon replacement. The environment fate of PFMP with regards to direct photolysis, abiotic hydrolysis and hydration was determined using a combination of laboratory experiments and computational modeling. PFMP was found to undergo direct photolysis giving a lifetime of 4-14 days depending on latitude and time of year. Offline samples confirmed PFCA products and a mechanism was proposed. Polyfluorinated amides (PFAMs) are a class of chemicals produced as byproducts of polyfluorinated sulfonamide synthesis via electrochemical fluorination (ECF). Using synthesized standards of four model compounds, PFAMs were detected and quantified in a variety of legacy commercial materials synthesized by ECF. PFAMs were hypothesized to undergo biological hydrolysis reactions, suggesting their importance as historical PFOA precursors. The PFAMs were also investigated with regards to their environmental fate upon atmospheric oxidation. Using a smog chamber, the kinetics and degradation mechanisms of N-ethylperfluorobutyramide (EtFBA) were elucidated. The lifetime of EtFBA to oxidation by OH was found to be approximately 4 days. Using offline sampling, PFAMs were shown to give PFCAs upon atmospheric oxidation and a plausible mechanism was proposed involving an initial N-dealkylation step followed by loss of isocyanic acid to give a perfluorinated radical. The perfluorinated radical then produces PFCAs by a series of known atmospheric reactions. Finally, the biological hydrolysis of the polyfluoroalkyl phosphate monoesters (monoPAPs) were studied in vitro using a bovine alkaline phosphatase enzyme. Michaelis-Menten kinetic parameters were measured and compared to hexyl phosphate. It was discovered that monoPAPs hydrolyzed on average 100 times faster than hexyl phosphate due to the electron withdrawing fluorine substituents. The results were also used to rationalize the results of a previous in vivo study which suggested monoPAPs were rapidly hydrolyzed in the small intestines of rats following a high dose by oral gavage.