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 (O-1(2)) at 1270 nm have been used to demonstrate the formation of O-1(2) by the ketone-catalysed decomposition of peroxymonosulfuric acid (Care'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 = K-W/([H+] + K-a2). Eleven ketones were chosen to determine k(DI), the third-order rate constant for the formation of the corresponding dioxirane. The values of k(DI) 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 E(aa) were determined to be E(aa)(acetone) = 47.8 kJ mol(-1) and E(aa)(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 k(2) = 5.9 x 10(-2) dm(3) mol(-1) s(-1).