| Iron-based systems for oxidizing hydrocarbons have received detailed attention, but the nature of the active oxidants involved and their mode of action are topics of debate. This work clearly demonstrates that for Gif-type systems which are supported by hydrogen peroxide, hydrocarbon oxidation occurs agent under argon, coupled to a more selective substrate-centered oxidant under increasing partial pressures of dioxygen.; The structural and functional features of iron complexes of trifluoroacetic acid and the picolinic acid anion are described. These catalysts were employed to mediate oxidation of adamantane by H2O2 to reveal that both tert- and sec-adamantyl radicals are generated in Gif solutions. In Gif systems, product profile is entirely dictated by trapping of the diffusively free adamantyl radicals, since authentic tert- and sec-adamantyl radicals are shown to partition between dioxygen and protonated pyridine or TEMPO, in a manner analogous to that observed in Gif oxygenations of adamantane. Gif oxygenation of DMSO by H2O2, provides pyridine-trapped methyl radicals under argon, as expected for the addition reaction of hydroxyl radicals to DMSO. Quantification of the DMSO-versus EtOH-derived alky1 radicals affords an estimate of kEtOH/kDMSO in reasonable agreement with the kinetics of radiolytically produced hydroxyl radicals. We conclude that Gif/H2O2 systems perform Fenton chemistry. |
