Manganese complexes formation mechanism

The rate of peroxide decomposition and the resultant rate of oxidation are markedly increased by the presence of ions of metals such as iron, copper, manganese, and cobalt [13]. This catalytic decomposition is based on a redox mechanism, as in Figure 15.2. Consequently, it is important to control and limit the amounts of metal impurities in raw rubber. The influence of antioxidants against these rubber poisons depends at least partially on a complex formation (chelation) of the damaging ion. In favor of this theory is the fact that simple chelating agents that have no aging-protective activity, like ethylene diamine tetracetic acid (EDTA), act as copper protectors. 

The Mn(II)-catalysed oxidation of glucose by peroxodisulfate ions occurs via a radical-chain mechanism.26 Kinetics of oxidation of thiodiglycollic acid by (trans-cyclohexane-l,2-diaminc-/V, N, N, /V -tetraacetatolmanganateilJI) have been investigated.27 Oxidations of ketoses and aldoses by manganese(IV) in sulfuric acid media have a first-order dependence on sugar and fractional-order dependence on oxidant.28 A mechanism has been proposed for the oxidation of L-malic acid by Mn(III) pyrophosphate in aqueous acid, involving complex formation and radicals.29... 

The mechanism of the epoxidation of alkenes by the cytochrome P450 model, sodium hypochlorite-manganese(III) tetraarylporphyrins, involves rate-determining formation of an active species 234 from a hypochlorite-manganese complex 233 (Scheme 6) pyridine or imidazole derivatives, as axial ligands, accelerate this step by electron donation, although the imidazoles are destroyed under the reaction conditions368. 

We also have attempted to inhibit these free radical reactions with 2,6-di-t-butyl-4-methylphenol and found no effect on the formation of cyclohexanol or cyclohexanone using catalyst 4. This latter result strongly suggests that peroxyl, alkoxyl, or hydroxyl radicals are not intermediates in these reactions. The intermediacy of a putative oxo-manganese complex is further strengthened by the reaction of 1-4 with cyclohexene in the presence of TBHP or iodosylbenzene to provide cyclohexene epoxide and our proposed mechanism is shown in the Equation (2). w H... 

The stepwise unwrapping of edta from its manganese(III) complex by cyanide is reflected in a variable-order dependence on the incoming ligand. The kinetically observable steps follow initial rapid reaction to [Mn(CN)3(edta)] or [Mn(CN)4(edta)] . The cyanide dependence of the reverse reaction helped in the elucidation of the overall formation mechanism. " ... 

UV irradiation of [cp Re (CO)3] (M = Mn, Re cp = rj -CsHs) in the presence of hydrogen yielded the non-classical dihydrogen complex [cp Re (CO)2 (H2)], but the classical dihydride [cpRe (CO)2 ra 5-H2]. The manganese complex possessed sufficient thermodynamic stability to arrest further oxidative addition at the metal centre. Formation of a rhenium trans-dihydhde complex must have occurred via a c/.s-intermediate. The latter is thermodynamically unstable and the researchers deduced the role of the hydrogen-rich environment in kinetically sustaining the mechanism [12]. 

Willems et al. [37] used a polarographic method to study the miconazole complexes of some trace elements. Manganese, iron, cobalt, and zinc element formed miconazole complexes with different stability constants. Polarography was used for detecting stability constants. The evolution of the respective formation constants followed the natural (Irving-Williams) order. The stepwise constant of the complexes formed increased from manganese to cobalt and decreased for zinc. The results are discussed with respect to the possible mechanism of action of miconazole. 

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