NEW INSIGHTS INTO N-TERT-BUTYL-ALPHA-PHENYLNITRONE (PBN) AS A SPIN TRAP .2. THE REACTIVITY OF PBN AND 5,5-DIMETHYL-4,5-DIHYDROPYRROLE N-OXIDE (DMPO) TOWARD N-HETEROAROMATIC BASES

The reactions of N-tert-butyl-alpha-phenylnitrone (PEN) and 5,5-dimeth yl-4,5-dihydropyrroline N-oxide (DMPO) with a series of N-heteroaromat ic bases have been studied in different solvents (benzene, dichloromet hane, acetonitrile) in the presence of such oxidants as PbO2, chlorani l and tetrabutylammonium dodecatungstocobalt(III)ate. In all cases spi n adducts were formed and their corresponding EPR signals were recorde d, The formation of the spin adducts, which mostly involves nucleophil ic addition of a base to the nitrone and subsequent oxidation (Forrest er-Hepburn mechanism) is also discussed and compared to conventional s pin trapping and to 'inverted spin trapping', In order to obtain furth er evidence for the mechanism involved some reactions were carried out using other oxidants, such as galvinoxyl and 2,2-diphenyl-1-picrylhyd razyl (DPPH), The reaction mechanisms are discussed on the basis of th e redox potentials of the studied nucleophiles, Particular attention i s given to the benzotriazolyl-DMPO. spin adduct, whose generation and decay rates were determined in the presence of some benzoquinones havi ng different redox potentials.