Reduction and Defluorination of Pentafluorophenol in Aqueous Solutions

Abstract

Hydrated electrons and hydrogen atoms react with pentafluorophenol (PFP) to result in fluoride ion elimination and subsequent production of the tetrafluorophenoxyl radical. Evidence for the formation of this radical was obtained from its reaction with ascorbate, which is oxidized by this species as it is oxidized by other phenoxyl radicals. Tetrafluorophenoxyl radical reacts with OH- to eliminate another fluoride ion and yield the trifluorobenzosemiquinone radical anion. Addition of OH to PFP also leads to fluoride ion elimination to yield the tetrafluorobenzosemiquinone radical anion. Oxidation of PFP by SO4 •- or N3 • yields the pentafluorophenoxyl radical.

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

“…For example, PFOS can be reduced by elemental iron, Fe(0), in water under hightemperature and high-pressure conditions (e.g., 350°C, 20 MPa) [175]. Unsaturated per-and poly-fluoroorganics (i.e., those containing aromatic, benzylic, olefinic, and tertiary functional groups) will readily reductively defluorinate [176][177][178][179][180][181]. Fluoroorganics containing only secondary and primary C-F bonds are difficult to defluorinate due to low reduction potentials (E < -2.7 V) [182,183].…”

“…Only the aqueous electron and elemental alkali and alkaline metals have lower standard reduction potentials. Reductive defluorination kinetics are influenced by a number of FC chemical properties [177,178,182,[184][185][186] and electrondonating strength of the reductant [187]. For example, branched PFOX is observed to have faster reduction kinetics than linear PFOX [94,188].…”

“…Electron tunneling leads to activation energies for reaction with halogenated organics that are invariable and small (6 to 30 kJ$mol -1 ) [206]. Reaction rates of the aqueous electron with fluorinated compounds have been reported [177,178,185,186,207]. Organic fluoro-saturation decreases aqueous electron reduction kinetics since fluorine doesn't have low-lying vacant d-orbital to accept an electron.…”

Defluorination and Mineralization of Difluorophenols in Water by Anodic Contact Glow Discharge Electrolysis

“…For the degradation of FPs, previous studies focused mainly on monofluorophenols and pentafluorophenol [1,10,11]. To the best of the authors' knowledge, this is the first report of the degradation of six difluorophenol (DFP) compounds by CGDE.…”

“…Halogenated phenols (XPs) constitute a large group of chemicals that include chlorophenols (CPs), bromophenols (BPs), and fluorophenols (FPs) [1]. Most of these compounds are extremely harmful to the environment because of their toxicity.…”