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

Abstract

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=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 k₂= 5.9 × 10^–2 dm³ mol^–1 s^–1.