Oxidation of manganese

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

Fused potassium nitrate is a powerful oxidising agent (cf. the oxidation of manganese compounds, p.. IS6 ... 

However the Mn (aq) ion can be stabilised by using acid solutions or by complex formation it can be prepared by electrolytic oxidation of manganese(II) solutions. The alum CaMn(S04)2.12H2O contains... 

Sodium bismuthate (oxidation of manganese) heat 20 parts of NaOH nearly to redness in an iron or nickel crucible, and add slowly 10 parts of basic bismuth nitrate which has been previously dried. Add 2 parts of sodium peroxide, and pour the brownish-yellow fused mass on an iron plate to cool. When cold break up in a mortar, extract with water, and collect on an asbestos filter. 

The brown crystalline manganese(III) acetate dihydrate is of considerable commercial importance because it is often used as the source material for other trivalent manganese compounds. It can be made by oxidation of manganese(II) acetate using chlorine or potassium permanganate, or by reaction of manganese(II) nitrate and acetic anhydride. 

Oxidation of manganese dioxide to higher valence states takes place in the fusion process of Mn02 and KOH. A tetravalent manganese salt identified as K MnO [12142-27-7] (63) which disproportionates spontaneously is formed. 

Both ions can be removed by oxidation and subsequent filtration. Aeration is adequate for iron(II) oxidation at above pH 6, but the oxidation of manganese(II) is much too slow, even at higher pH values, for effective removal. Potassium permanganate or chlorine dioxide is frequently used for the oxidation of manganese however, their use must be foHowed by coagulation prior to filtration because of the formation of coHoidal Mn02. 

The direct electrochemical oxidation of manganese alloys was developed and commercialized at the Rustavi Chemical Combine in the Georgian Repubhc (formerly the USSR). The electrode reactions are... 

Oxides of manganese and iron are often found deposited together. Similar conditions cause oxidation of both iron and manganese ions. Exposure to oxygenated water, chlorination, and some microbiological processes causes such oxidation. Often, a few percent chlorine is found in deposits, possibly because of associated chlorination. 

The lower oxides of manganese are basic and react with aqueous acids to give salts of Mn and Mn cations. The higher oxides, on the other hand, are acidic and react with alkalis to yield oxoanion salts, but the polymerization which was such a feature of the chemistry of the preceding group is absent here. 

To prepare sabinenic acid for the identification of the terpene, Wallach operates as follows 10 grams of the crude terpene are mixed with the theoretical amount of potassium permanganate in water at ice temperature. The oxide of manganese is filtered off, the liquid rendered acid and extracted with ether, and the ethereal solution shaken with caustic soda solution. The sodium salt is very sparingly soluble, and is precipitated, collected, and decomposed with dilute sulphuric acid and purified by a further solution in ether. It must be well dried in a desiccator before its melting-point is determined. Sabinene has the following constitution —... 

The reaction of MnC03 is of particular interest because of the possibility of the formation and interconversion of the various oxides of manganese [733,1276], Westerdahl and Leader [762] identify the initial process as... 

Hastings, D. and Emerson, S. (1986). Oxidation of manganese by spores of a marine Bacillus Kinetics and thermodynamic considerations. Geochem. Cosmochim. Acta 50,1819-1824. 

Case a, i is well illustrated by the arsenite-induced oxidation of manganese(II) by chromic acid, studied by Lang and Zwerina. The overall equation of this induced reaction is... 

Considering the limiting values of the induction factor it may be postulated that in the case of iodide and bromide the induced oxidation is caused by chromium(V), whereas for induced oxidation of manganese(II) chromium(lV) is the coupling intermediate. Therefore, one has to assume that in the course of reaction between arsenic(ril) and chromium(VI) both chromium(V) and chromium(IV) intermediates are involved. The mechanism below, proposed by Westheimer seems to be in agreement with experiment. 

In the presence of manganese(II) ions the rate of oxidation of H2R by chromic acid decreases . Under favourable experimental conditions (high concentration of alcohol and low concentration of chromate) the diminution of rate is about 50 % which is in accordance with results listed in Table 6, according to which ci = 0.5. The inhibiting effect of manganese(II) on the oxidation of H2R can be explained by reaction (23) followed by step (24). Therefore the induced oxidation of manganese(II) can be described by reactions (26), (23) and (24). 

The mechanism of the induced oxidation of manganese(II) cannot be regarded as sufficiently clear. Thus, the data obtained do not make it possible to decide whether manganese(IV) is formed by interacting with the chromium(V) intermediate... 

To decide whether the reaction involves 1- or 2-electron transfers, i.e. chromium-(rv) or chromium(V) is formed first, the induced oxidation of manganese(II) was investigated. When sodium perchlorate was used to maintain a constant ionic strength, the rate of oxidation of benzaldehyde dropped to one-half of the original rate in the presence of manganese(II) ions. On the contrary, when magnesium perchlorate was used as the neutral salt, the rate was reduced to of its original value. This peculiar observation, however, has not been interpreted. 

FORMALDEHYDE-INDUCED OXIDATION OF MANGANESE(II) BY CHROMIC ACID... 

N. C. Uren, Chemical reduction of an insoluble higher oxide of manganese by plant roots. J. Plant Niitr. 4 65 (1981). 

Manganese ores are mined. On the ocean floor in the proximity of volcanoes there are so-called manganese nodules, which consist of oxides of manganese, iron and other heavy metals. They arise from deposition by microorganisms around a solid core (piece of mussel, shark tooth, etc.). 

The oxidation of manganese dioxide to manganate by solid alkafi-chlorate mixtures becomes explosive above 80-90°C at pressures above 19 kbar. 

McKenzie R.M. The adsorption of lead and other heavy metals on oxides of manganese and iron. Austral J Soil Res 1980 18 61-73. 

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