Reactivities of chlorine atoms and peroxyl radicals formed in the radiolysis of dichloromethane

Abstract

Radiolysis of dichloromethane (DCM) leads to formation of primary oxidizing radicals and carbon-centered radicals. The latter react with oxygen to yield peroxyl radicals. The yields and chemical behavior of these intermediates were studied by pulse radiolysis of DCM solutions containing various solutes: phenols, anilines, dimethoxybenzene, hexamethylbenzene, cyclohexene, dimethyl sulfoxide, and zinc tetratolylporphyrin. At low concentrations, some of these solutes were found to be oxidized by two peroxyl radicals, CH2C102* and CHC1202', with different rate constants. At higher concentrations, the solutes react also with the primary radicals: Cl atoms and the radical cations CH2C12+", with diffusion-controlled rate constants.The rates of these reactions were determined by competition kinetics because of the very short lifetimes of the species. Cl atoms were found to have a half-life of about 5 ns in DCM, reacting predominantly with the solvent by hydrogen abstraction. The radical cations decay within a fraction of a nanosecond. The total yield of these primary radicals was determined to be G = 3.6 and appears to be divided about equally between Cl and the radical cations. The total yield of oxidation, by the primary and the peroxyl radicals, was found to be G = 7.5. Cl atoms were found to be very reactive in electron transfer as well as addition and hydrogen abstraction reactions.

Solvent effects on the photochemistry of dimethyl sulfoxide–Cl complexes studied by combined pulse radiolysis and laser flash photolysis

“…1b). In CCl 4 and other halocarbons, the Cl atoms initially produced react with DMSO to yield DMSO _ Cl complexes Alfassi et al, 1989):…”

Synthesis of 2,4-dihalogenofluorobenzenes and their antimicrobial and antifungal activity studies

“…Similarly many other haloagens are important environmental pollutants (Lu et al, 2000). Halogenated organic compounds are frequently employed as solvents, pesticides, and refrigerants and for the study of electron transfer reactions in radiation and electrochemical investigations (Alfassi et al, 1989;Emmi et al, 1989;Lal et al, 1986, Grodkowski andNeta, 1984). Many of these compounds are toxic in nature if metabolized in living species (Mönig et al, 1983;Reynolds et al, 1980;Slater et al, 1982).…”

Tetrabenzoporphyrins: Metal Incorporation and Exchange Kinetics, Ligational Equilibria and Pulse Radiolysis Studies

“…In aerated CH 2 Cl 2 , the porphyrins are oxidized mainly by the two peroxyl radicals, CH 2 ClOO• and CHCl 2 OO•, formed in the radiolysis of this solvent [55]. Direct oxidation by the solvent radical cation and by chlorine atoms is probably unimportant since these species are very short lived and the porphyrin concentration is relatively low.…”