Manganese redox

The following redox potentials are given for the oxidation of manganese(II) to manganese(III) in acid and alkaline solution. 

Another unique redox system used for extending gel times consists of cumene hydroperoxide and manganese naphthenate, which provides consistent gel times of between two and four hours over a temperature range of 25—50°C. 

In addition to effects on the concentration of anions, the redox potential can affect the oxidation state and solubility of the metal ion directly. The most important examples of this are the dissolution of iron and manganese under reducing conditions. The oxidized forms of these elements (Fe(III) and Mn(IV)) form very insoluble oxides and hydroxides, while the reduced forms (Fe(II) and Mn(II)) are orders of magnitude more soluble (in the absence of S( — II)). The oxidation or reduction of the metals, which can occur fairly rapidly at oxic-anoxic interfaces, has an important "domino" effect on the distribution of many other metals in the system due to the importance of iron and manganese oxides in adsorption reactions. In an interesting example of this, it has been suggested that arsenate accumulates in the upper, oxidized layers of some sediments by diffusion of As(III), Fe(II), and Mn(II) from the deeper, reduced zones. In the aerobic zone, the cations are oxidized by oxygen, and precipitate. The solids can then oxidize, as As(III) to As(V), which is subsequently immobilized by sorption onto other Fe or Mn oxyhydroxide particles (Takamatsu et al, 1985). 

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. 

One-electron reduction or oxidation of organic compounds provides a useful method for the generation of anion radicals or cation radicals, respectively. These methods are used as key processes in radical reactions. Redox properties of transition metals can be utilized for the efficient one-electron reduction or oxidation (Scheme 1). In particular, the redox function of early transition metals including titanium, vanadium, and manganese has been of synthetic potential from this point of view [1-8]. The synthetic limitation exists in the use of a stoichiometric or excess amount of metallic reductants or oxidants to complete the reaction. Generally, the construction of a catalytic redox cycle for one-electron reduction is difficult to achieve. A catalytic system should be constructed to avoid the use of such amounts of expensive and/or toxic metallic reagents. 

Species may differ by oxidation state for example, manganese(II) and (IV) iron(II) and (III) and chromium(III) and (VI). Oxidation state is influenced by the redox potential. Mobility is affected because oxidation state influences precipitation-dissolution reactions and also toxicity in the case of heavy metals. 

Sithambaram, S., Garces, H.F. and Suib, S.L. (2009) Controlled synthesis of self-assembled metal oxide hollow spheres via tuning redox potentials versatile nanostructured cobalt and cobalt manganese oxides. Advanced Materials, 20, 1205-1209. 

Scheme 7.18. Chromium-manganese redox couple-mediated domino process for the synthesis of benzoxazoles.

Figure 6.23. Changes of the redox parameter (pe + pH) in two Israeli arid soils during saturated paste incubation (after Han and Banin, 1996. Reprinted from Soil Sci Soc Am J, 60, Han F.X., Banin A., Solid-phase manganese fractionation changes in saturated arid-zone soils Pathways and kinetics, p 1076, Copyright (1996), with permission from Soil Sci Soc Am)...

Sajwan K.S., Lindsay W.L. Effect of redox, zinc fertilization and incubation time on DTPA-extractable zinc, iron and manganese. Commun Soil Sci PlantAnal 1988 19 1-11. 

Schwab A.P., Lindsay W.L. The effect of redox on the solubility and availability of manganese in a calcareous soil Rice plants. Soil Sci Soc Am J 1983 47 217-220. 

Aime et al. took advantage of the different redox states of manganese and of the difference in the related relaxation properties to design a p02 responsive contrast agent. The adducts formed between Mn /Mnn tpps complexes and poly-P-cyclodex-trin have considerably different relaxivities depending on the redox state of the metal, itself determined by the partial oxygen pressure of the solution (tpps — 5,10,15,20-tetrakis-(p-sulfonato-phenyl porphinate) (243). 

Manganese Redox Enzymes and Model Systems Properties, Structures, and Reactivity... 

Estuaries, in contrast, appear to be important sites for manganese redox reactions. Manganese maxima have been observed in several estuaries [421-423]... 

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