Iron-catalyzed oxidation

Abstract In this review, recent developments of iron-catalyzed oxidations of olefins (epoxidation), alkanes, arenes, and alcohols are summarized. Special focus is given on the ligand systems and the catalytic performance of the iron complexes. In addition, the mechanistic involvement of high-valent iron-oxo species is discussed. 

Scheme 3 Proposed mechanism of iron-catalyzed oxidation by Que and coworkers...

Recently, Nam, Fukuzumi, and coworkers succeed in an iron-catalyzed oxidation of alkanes using Ce(IV) and water. Here, the generation of the reactive nonheme iron (IV) 0x0 complex is proposed, which subsequently oxidized the respective alkane (Scheme 16) [104]. With the corresponding iron(II) complex of the pentadentate ligand 31, it was possible to achieve oxidation of ethylbenzene to acetophenone (9 TON). 0 labeling studies indicated that water is the oxygen source. 

Oszmianski, J., Cheynier, C., and Moutounet, M., Iron-catalyzed oxidation of (+)-catechin in wine-like model solutions. J. Agric. Food Chem. 44, 1972, 1996. 

At pH > 4, the oxidation is inhibited by organics, suggesting a free radical mechanism. One proposed mechanism, which originates in the work of Backstrom (1934), is shown in Table 8.7. The inhibition occurs when the organics react with the sulfate radical ion, S04". This inhibition has also been seen in laboratory experiments using fogwater collected in Diibendorf, Switzerland, where oxidation rates for S(IV) were less than expected based on the kinetics of the iron-catalyzed oxidation (Kotronarou and Sigg, 1993). 

Neta P, Eluie RE, Mosseri S, Shastri LV, Mittal JP, Maruthamuthu P, Steenken S (1989) Rate constants for reduction of substituted methylperoxyl radicals by ascorbate ions and N,N,N, Al -tetrameth-yl-p-phenylenediamine. J Phys Chem 93 4099-4104 Netto LES, Stadtman ER (1996) The iron-catalyzed oxidation of dithiothreitol is a biphasic process hyudrogen peroxide is involved in the initiation of a free-radical chain of reactions. Arch Biochem Biophys 333 233-242... 

Hug, S.J. and Leupin, O. (2003) Iron-catalyzed oxidation of arsenic(in) by oxygen and by hydrogen peroxide pH-dependent formation of oxidants in the fenton reaction. Environmental Science and Technology, 37(12), 2734-42. 

Isatin and derivatives display diverse pharmacological activities. A summary of these activities can be found in the Supplementary Material 1 and a review on the biological properties of isatin was published some years ago641. The detection of isatin in mammalian tissues, formed probably from heme-protein bound trypthophan in an iron catalyzed oxidation reaction642, led to the development of a HRGC-MS technique for its detection in biological samples10. 

Among the first reports was the investigation of an iron-catalyzed oxidation system in 1997. ESI-MS was used to characterize the intermediate [Fe "-TPA(OOH)]2 in the stereospecific hydroxylation of alkanes by hydrogen peroxide (TPA, tris(2-pyridyl-methyl)amine) [35]. It is unique among oxidation reactions studied by ESI-MS in that all other reports address manganese- or vanadium-catalyzed systems. 

Fig. 1. Relative importance of various urban sulphate aerosol production mechanisms T = total sulfate A = H2SO4 condensation H = HjOj oxidation O = uncatalyzed oxygen oxidation Q = O3 oxidation F = iron catalyzed oxidation M = manganese catalyzed oxidation C = soot catalyzed oxidation.

---