On the formation of dioxiranes and of singlet oxygen by the ketone-catalysed decomposition of Caro's acid

Measurements of the infrared phosphorescence of singlet molecular oxygen (1O2) at 1270 nm have been used to demonstrate the formation of 1O2 by the ketone-catalysed decomposition of peroxymonosulfuric acid (Caro's acid). The kinetics of the ketone-catalysed decomposition of Caro's acid have been studied by this technique and the rate law was found to be of first order for HSO5–, for ketone and for a pH-dependent factor F=KW/([H+]+ Ka2). Eleven ketones were chosen to determine kDI, the third-order rate constant for the formation of the corresponding dioxirane. The values of kDI depend on ketone structure and vary over a wide range. For both the acetone- and cyclohexanone-catalysed decomposition of Caro's acid measurements have been performed at different temperatures. The apparent activation energies Eaa were determined to be Eaa(acetone)= 47.8 kJ mol–1 and Eaa(cyclohexanone)= 36.0 kJ mol–1, respectively. For the uncatalysed self-decomposition of Caro's acid the second-order rate constant was determined to be k2= 5.9 × 10–2 dm3 mol–1 s–1.