Efficient oxygen-induced decomposition of triphenylsulfonium trifluoromethanesulfonate to fluoride ions in subcritical water

• CF3SO3− in [(C6H5)3S][CF3SO3] showed low reactivity in pure subcritical water under argon.
• Zerovalent iron enhanced decomposition of CF3SO3− in [(C6H5)3S][CF3SO3] to F−.
• O2 further increased the decomposition of CF3SO3− to F− at temperature close to the critical point.
• The maximum F− yield reached 93.6% by use of O2.
• Decomposition of CF3SO3− in [(C6H5)3S][CF3SO3] proceeded more efficiently than that in CF3SO3K.

Decomposition of [(C6H5)3S][CF3SO3] in subcritical water, specifically, in the presence of either an iron-based reducing agent (zerovalent iron or FeO) or an oxidizing agent (O2), was investigated with the aim of developing a technique to recover the fluorine component from the liquid waste. This is the first report on the decomposition of salts consisting of perfluoroalkanesulfonates and organic cations, which are widely used in the electronics industry as photoacid generators. The highest F− yield was achieved by the reaction in the presence of O2 at a temperature close to the critical point: when the reaction was carried out at 372 °C for 6 h, the F− yield reached 93.6%, indicating that almost all the fluorine atoms in the anionic moiety, CF3SO3−, were transformed into F− ions. In addition, the formation of CHF3 and benzene was suppressed by the use of O2. Whereas the CF3SO3− in [(C6H5)3S][CF3SO3] was efficiently decomposed to F− ions in the presence of O2, the CF3SO3− in the corresponding potassium salt, CF3SO3K, was less reactive: the F− yield of the reaction in the presence of O2 at 373 °C for 6 h was only 57.1%, indicating that the cation in these salts affects the reactivity of the anion.

CF3SO3− in [(C6H5)3S][CF3SO3] can be almost completely decomposed to F− ions in subcritical water in the presence of O2.Figure optionsDownload as PowerPoint slide