Rate constants for aqueous‐phase reactions of SO₄⁻ with C₂F₅C(O)O⁻ and C₃F₇C(O)O⁻ at 298 K

Abstract

Perfluorocarboxylic acids and their anions (PFCAs), such as perfluorooctanate (C7F15C(O)O−), have been generally recognized to be global pollutants and are believed to persist in the environment. Kinetic data for reactions of sulfate anion radicals (SO4−) with PFCAs are needed to evaluate the residence times of PFCAs in the environment, but no kinetic data have been reported, except for the rate constant for the reaction of SO4− with trifluoroacetate (CF3C(O)O−) (k1). In this study, using the fact that PFCAs react with SO4− to form shorter chain PFCAs, we determined rates relative to k1 of the reactions of photolytically generated SO4− with two short‐chain PFCAs, pentafluoropropionate (C2F5C(O)O−; k2) and heptafluorobutyrate (C3F7C(O)O−; k3), along with conversion ratios for conversion of C2F5C(O)O− into CF3C(O)O− (α) and conversion of C3F7C(O)O− into C2F5C(O)O− (β) and CF3C(O)O− (γ) at 298 K. Values of k1, k2, or k3 might change over the course of reaction with increasing ionic strength. Nevertheless, if the values of k1/k2, k2/k3, α, β, and γ remain almost constant during the reaction, a simple equation involving relative rates, such as k1/k2, can be used to relate the concentrations of C3F7C(O)O−, C2F5C(O)O−, and CF3C(O)O−. We compared the relative rates, such as k1/k2, and the conversion ratios determined from various experimental runs with different initial conditions to check whether relative rates and conversion ratios remained almost constant during each experimental run. The values of k1/k2, k2/k3, α, β, and γ seemed to remain almost constant, which facilitated determination of k2/k1 = 0.89 ± 0.07, k3/k1 = 0.84 ± 0.08, α = 0.88 ± 0.05, β = 0.75 ± 0.05, and γ = 0.17 ± 0.02. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 276–288, 2007

Treatment technologies for aqueous perfluorooctanesulfonate (PFOS) and perfluorooctanoate (PFOA)

“…Advanced oxidation processes (AOPs) [88], which utilize the hydroxyl radical, such as alkaline ozonation, peroxone (i.e., a mixture of O 3 and H 2 O 2 ), or Fenton's reagent (i.e., H 2 O 2 and Fe 2+ salts), have been shown to be relatively ineffective for PFOA and PFOS destruction [89][90][91]. A number of photolytic methods such as direct photolysis [91][92][93][94][95][96], persulfate photolysis [92,[97][98][99], alkaline isopropanol photolysis [94] and photocatalysis [91,[100][101][102][103][104] have shown varying degrees of efficacy on higher concentrations of perfluorocarboxylates. Reduction by elemental iron under near super-critical water conditions has been shown to be possible for PFOS degradation.…”

The effect of oxygen in the photocatalytic oxidation pathways of perfluorooctanoic acid

“…5 -Reaction h) [68,72]; in the presence of water, the acyl fluorides hydrolyze to carboxylic acids (Fig. 5 -Reaction i) [72][73][74][75].…”

“…5 -Reaction h) [68,72]; in the presence of water, the acyl fluorides hydrolyze to carboxylic acids (Fig. 5 -Reaction i) [72][73][74][75]. The carbon-centered perfluorinated radical is redirected at the step of reaction (e), while fluorophosgene is quenched in the aqueous environment generating hydrogen fluoride and carbon dioxide [72].…”

“…5 -Reaction i) [72][73][74][75]. The carbon-centered perfluorinated radical is redirected at the step of reaction (e), while fluorophosgene is quenched in the aqueous environment generating hydrogen fluoride and carbon dioxide [72]. It is remarkable that the mechanism based on β-scissions can promote an almost complete PFOA decomposition without the formation of perfluorinated acids as intermediates.…”

Występowanie perfluorowanych związków organicznych w środowisku i fizykochemiczne metody usuwania ich z roztworów wodnych

“…Przebieg tej reakcji (rys. 7) został zaproponowany przez Kutsuna i Hori [38]. Degradacja PFOS to stopniowe eliminowanie jednostki -CF 2 , co prowadzi do otrzymywania krótszych łańcuchów PFA, które następnie ulegają utlenianiu za pomocą rodnika anionu siarczanowego aż do całkowitego rozpadu do CO 2 i HF.…”