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.
Dioxiranes: from oxidative transformations to chemiluminescence
Experimental data on the chemistry of a new class of highly effective oxidation reagents, dioxiranes, are summarised. The main methods used to generate dioxiranes and reactions in which dioxiranes are proposed as intermediates are considered. The full notion about an important property of dioxiranes, i.e. the ability to oxidise rapidly, selectively and under mild conditions various classes of organic compounds (alkanes, alkenes, compounds containing heteroatoms, organometallic substrates, etc.) is given. Various aspects and mechanisms of these reactions are discussed. The attention is focused on the analysis of mechanisms of dioxiranes decomposition in the absence of oxidisable substrates. One of the most attractive aspects of the dioxirane chemistry, chemiluminescence, is considered (the mechanisms of the generation of excited products during both thermal and catalytic decomposition and upon photochemical activation are discussed). The bibliography includes 401 references.
Sterol metabolism. XLI. Cholesterol A-ring autoxidations
Abstract Chromatographic and spectral evidence is adduced for the presence of cholest-5-en-3-one, cholest-4-en-3-one, and cholest-4-ene-3,6-dione in samples of cholesterol aged naturally in air or subjected to irradiation in air by 60 Co gamma radiation. These findings establish an additional mode of air oxidation of cholesterol to A-ring 3-ketones. Moreover, the oxidation by air of cholest-5-en-3-one induced by 60 Co gamma radiation yielded cholest-4-en-3-one, cholest-4-ene-3,6-dione, and the epimeric 3-oxocholest-4-ene-6-hydroperoxides. Cholest-4-en-3-one was not altered by irradiation in air, nor was cholesterol isomerized to cholest-4-en-3β-ol upon irradiation. From these observations it is deduced that the radiation-induced A-ring dehydrogenation of cholesterol yields initially cholest-5-en-3-one which upon isomerization yields cholest-4-en-3-one not further oxidized and which by a second oxidation yields the epimeric 3-oxocholest-4-ene-6-hydroperoxides which decompose to cholest-4-ene-3,6-dione.