Oxidation catalyzed by Fe

As a contribution to a subproject of CMD of EUROTRAC-2, scientists from ICHF studied experimentally the effect of a-pinene and cis-verbenol on the rate of S(IV) oxidation catalyzed by Fe, as well as the ozone-affected autoxidation of aqueous SO2 in the presence of calcium. The investigations were aimed at clarifying the mechanism of the aqueous phase oxidation of SO(IV) simultaneously by O3 and O2, calcium acting as condensation nuclei. Inhibition of the S(IV) autoxidation in the atmosphere by secondary terpenic compounds was also studied... 

Participation of Catalysts Active Forms in Elementary Stages of Radical-chain Ethylbenzene Oxidation Catalyzed by Fe(II,III)(acac)n+R4NBr ... 

The reaction (I) and interaction of the resulting Fe(II) complex with dioxygen appear to be responsible for chain initiation in the ethylbenzene oxidation, catalyzed by Fe(III)(acac)3 or Fe(III)(acac)3+ + R4NBr. ... 

Table 1. Cyclohexene oxidations by various oxidants catalyzed by Fe (cyclam)(OTf)2 ... 

Propanol inhibits benzaldehyde oxidation catalyzed by Fe(acac), ... 

At The American University, Isbell s major interest in research turned to the study of the oxidation of saccharides with hydrogen peroxide. In collaboration with Dr. Frush, he published some forty papers on the subject. A number of major discoveries were made, including that of a stepwise degradative peroxidation, which is catalyzed by base or by such metals as iron(II). It starts at the anomeric carbon of an aldose, either in the acyclic or the cyclic form, and affords the lower aldose and formic acid (see Fig. 8). Two mechanisms were recognized an ionic one prevalent in strong alkali, and a free-radical process catalyzed by Fe(II) (see Fig. 9). 

Table I. Oxidation of Adamantane with Dioxygen Catalyzed by Fe(Salen)20, 1...

Figure 19 Structureofbicyclo[2,l,0]pentaneanditsuseasaradical clock for C-H bond oxidation catalyzed by P450 enzymes. The radical intermediate can undergo the rebound step with the Fe -OH species before and after ring-opening rearrangement...

Cobalt is mostly incorporated into the iron phase of manganese nodules. However, theoretically, it would suit much better in the manganese phase which has experimentally been confirmed by Giovanoli and Brutsch There is a theory, not yet proved by experiments, staling that Co is oxidized to Co in sea-water. This process should be catalyzed by Fe(OH)3, The final product of oxidation, Co(OH)3, forms a solid solution with Fe(OH)3 The theory does not include a discussion about the possibilities of diadochic incorporation of cobalt after cristalliza-tion of iron hydroxide. 

A key observation supporting the Fe(III)-Fe(V) mechanistic scheme presented above was the low-temperature trapping of iron(III)-peroxo species for 6, 9, 11, and 12 [46,49,54,57,58]. Since the olefin oxidations catalyzed by these complexes are highly stereoselective, it is unlikely that Fe "-OOH species proposed to form in the course of catalysis would imdergo 0-0 homolysis to produce HO. Instead, it has been argued that the Fe -OOH species must undergo 0-0 heterolytic... 

At the National Institute of Chemistry (NIC), in the frame of CMD subproject of EUROTRAC-2, experimental studies of the role of soluble constituents of atmospheric aerosols in the aqueous-phase autoxidation mechanisms of S(IV) was studied. The research focused on atmospheric water droplets (clouds, fog), where soluble constituents of atmospheric particles may be important in aqueous SO2 oxidation under non-photochemical conditions. In the frame of CMD project laboratory experiments in a semi-batch continuous stirred tank reactor under controlled conditions (T, air flow rate, stirring), were made in order to study the autoxidation of S(IV)-oxides catalyzed by transition metal ions (Fe(III), Fe(II), Co(II), Cu(II), Ni(II), Mn(II)). These studies were carried out at the National Institute of Chemistry. 

Bacterial oxidation of ferrous ion in Acidithiobacillus ferrooxidans occurs by the catalysis of a system consisted of several enzymes and proteins. In the oxidation of ferrous ion by A. ferrooxidans Fel (JCM 7811), electrons are first pulled out of the ion by the catalysis of Fe(II)-cytochrome c oxidoreductase. Then, electrons are transferred to ferricytochrome c-552 (native cytochrome c of the bacterium), fer-rocytochrome c-552 formed is oxidized with oxygen by the catalysis of cytochrome c oxidase (Yamanaka and Fukumori, 1995). However, the mechanism of the oxidation of ferrous ion appears to be a little different between the strains of A. ferrooxidans. Thus, in certain strains of the bacterium the oxidation of ferrous ion is catalyzed by Fe(II)-rusticyanin oxidoreductase (Blake and Shute, 1994). However, as will be pointed out below, the enzyme should be carefully checked. Moreover, in a moderately thermophilic iron-oxidizing bacterium, the oxidation of ferrous ion is reported to be catalyzed by an iron oxidase containing heme A (Takai et al., 1999, 2001). 

On the addition of 3,7-10"3 mol/l H20 into the ethylbenzene oxidation, catalyzed with Fe(III)(acac)3 and R4NBr (R4NBr = (C2H5)4NBr, Me4NBr) the effectivity of catalytic systems, estimated by the values of parameters >S PEHmax (and S-C) decreases (Figure 1, a-c). 

The changes in parameters Speh, C (S C), and w° and w observed in the reactions catalyzed by Fe(III)(acac)3 in the presence of R4NBr and H20 additives, and also obtained kinetics of catalytic ethylbenzene oxidation are evidently caused with the formation of catalytic active complexes of (Fe(II)(acae)2)x(R4NBr)y(H20)n and products of their transformation in the course of ethylbenzene oxidation. [11,13], The decrease in intermediate products of the (Fe(II)(acac)2)x(R4NBr)y(H20)n transformation to the end products as a consequence of coordination of H20 molecules with iron complexes. As result, the decrease in steady-state concentrations of selective catalysts Fe(II)x(acac)y(0Ac)z(L2)n(H20)m, took place. 

---