Kinetics of Aqueous Persulfate-Induced Oxidative Degradation of Heptafluorobutanoate, Pentafluoropropionate, and Trifluoroacetate

Abstract

The kinetics of reaction of three fluorinated carboxylates (heptafluorobutanoate, pentafluoropropionate, and trifluoroacetate) with ammonium persulfate were studied by in situ 19F nuclear magnetic resonance and Raman spectroscopies in acidic aqueous solutions at temperatures between 323 and 363 K. Oxidative decarboxylation of the carboxylates yields a terminal perfluoroalkyl radical intermediate; the dominant reaction of this intermediate is recombination with hydroxyl radical followed by rearrangement to the acid fluoride and then hydrolysis, but other minor recombination products are observed. Arrhenius parameters for the initial decomposition of ammonium persulfate and the reaction of sulfate radical with the fluorinated carboxylates were derived. Heptafluorobutanoate and pentafluoropropionate were found to have similar reaction rates with sulfate radical, while the reaction with trifluoroacetate was 30–50% slower. Reaction rates did not show a strong dependence on pH in the range of 2 – 7.