Efficient photochemical decomposition of trifluoroacetic acid and its analogues with electrolyzed sulfuric acid

Electrolyzed sulfuric acid is a new chemical reagent prepared by electrolysis of aqueous sulfuric acid. In the present work, the concentrations of the oxidizing species (S2O82-, HSO5−, and H2O2) present in electrolyzed sulfuric acid were quantified, and photochemical decomposition of trifluoroacetic acid (CF3COOH, TFA), pentafluoropropionic acid (C2F5COOH, PFPA), and heptafluorobutyric acid (C3F7COOH, HFBA) in water with electrolyzed sulfuric acid was investigated. TFA was efficiently decomposed to F− and CO2 with electrolyzed sulfuric acid under irradiation with UV-visible light (220-460 nm), and the quantum yield for TFA decomposition under irradiation with 254-nm monochromatic light was measured to be 0.20. Among the oxidizing species present in the electrolyzed sulfuric acid, S2O82- played the dominant role in the photochemical reactions, and the combination of S2O82− and highly acidic conditions (pH ∼1.0) resulting from the coexistence of H2SO4 was the main reason for the high reactivity. PFPA and HFBA were also efficiently decomposed with electrolyzed sulfuric acid. The pseudo-first-order rate constants for the decrease in the amounts of these substrates were 1.6-1.9 times as high as those for conventional decomposition reactions with the potassium salt of S2O82−.