Functional model oxygenations by nonheme iron complexes - Advances in Catalytic Activation of Dioxygen by Metal Complexes - page 197

The selective oxygenation of methane and light alkanes by the
Fenton system was performed in the three-phase catalytic membrane
reactor, enabling simultaneous reaction and product separation. Frusteri et al.
reported that Nafion-based catalytic membranes catalyze the selective oxidation of
methane to methanol, 341 ethane to ethanol and acetaldehyde, 342 and propane to
acetone, propionic aldehyde, isopropanol, and n-propanol. 343 The partial oxidation
proceeds according to a radical mechanism which involves the activation of paraffin
on superacid sites and the subsequent reaction of activated paraffins with OH
radicals generated according to the Fenton reaction. Bianchi et al. developed a
biphasic system (water/acetonitrile) for the selective oxidation of benzene to phenol,
with the pyrazinecarboxylic acid derivatives as a ligand to

in the presence of

trifluoroacetic acid. 344
Tert -butyl hydroperoxide (TBHP) is no doubt an important and useful
oxidant for monooxygenation of various hydrocarbons. Barton et al. developed
oxidation systems which oxidizes cyclohexane and various hydrocarbons by TBHP
with Fe(III) salts such as or a cyclohexane soluble iron complex,
(TMA: trimethylacetate) in the absence or presence of picolinic acid. 345-
347 A pathway, alkane alkyl hydroperoxide ketone or alcohol, was proposed.
Schuchard et al. extended the reaction system to that under 15 bar of oxygen at 70
°C and found the increase in the conversion from 5% to 9% but the decrease in the
selectivity. 348 Oxidations of cyclohexadienes to aromatic products, anthracene to
anthraquinone, 349 and alcohols and allylic methylene groups to ketones even in the
absence of pyridine/acetic acid 350, 351 were reported. Nguyen et al. used
a model ligand that mimics the metal-binding domain
of the bleomycin for oxidation of cyclohexane to cyclohexanol and
cyclohexanone (1 : 1 ratio, 1700% yield on the basis of catalyst concentration) and
adamantane and 3-methylpentane. No oxidation of an aromatic C-H bond was
observed. 352 Low-spin species and were

detected by ESR in the reaction of with TBHP and
respectively. Formation of a perferryl intermediate from the
Fe(III)-peroxo species were thought unlikely. The homolytic cleavage of the O-O
bond in to form was thought to take part in
the catalytic process by forming cyclohexyl and t -butoxy radicals. Spectroscopic
properties and electronic structure, and reactivity for the homolysis of the O-O bond
of low-spin (x = 1 or 2) have been studied in detail. 353,
354 The role of and manifolds in the oxidation systems were
studied by ionic trapping with chloride, azide, and other anions. 351, 355, 356 However,
since Minisci et al. have established that TBHP chemistry was best interpreted as