Singlet-oxygen generation in the catalytic reaction of dioxiranes with nucleophilic anions.
Nucleophilic anions such as Cl(-), I(-), Br(-), t-BuO(-), O(2)(-) and OH(-) efficiently catalyze the decomposition of dimethyldioxirane (DMD) and methyl(trifluoromethyl)dioxirane (TFD). Singlet oxygen ((1)O(2)) is formed in these catalytic reactions, as demonstrated by the characteristic infrared chemiluminescence (IR-CL) at 1268 nm. The yield of (1)O(2) generation, measured by the IR-CL method, lies in the range between 2 and 98%, which depends on the particular anion employed. For the bromide ion, the catalytic decomposition of the dioxirane is in competition with the oxidation of Br(-) to elemental bromine.
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.
Epoxidation by dimethyldioxirane. Electronic and steric effects
Etude de l'epoxydation d'une serie de styrenes substitues et d'alcenes di- et monosubstitues par le dimethyldioxiranne dans l'acetone. La presence d'eau accroit la vitesse de l'epoxydation