Disproportionation manganese compounds

The purple permanganate ion [14333-13-2], MnOu can be obtained from lower valent manganese compounds by a wide variety of reactions, eg, from manganese metal by anodic oxidation from Mn(II) solution by oxidants such as o2one, periodate, bismuthate, and persulfate (using Ag" as catalyst), lead peroxide in acid, or chlorine in base or from MnO by disproportionation, or chemical or electrochemical oxidation. 

Although catalase cycles only between the MnIIMnII/MnIIIMn111 states, manganese compounds in other oxidation states can also catalyze the disproportionation of H202 (Scheme 3) [1 OOg]. 

The thermodynamically favored oxidation state for manganese in both acidic and basic solutions is + 2, this being the most stable oxidation state. Trivalent manganese is less stable and readily disproportionates. Penta-and hexavalent manganese compounds also tend to undergo disproportionation under the influence of H" and OH (Reidies... 

The Mn ion is so unstable that it scarcely exists in aqueous solution. In acidic aqueous solution, manganic compounds readily disproportionate to form Mn ions and hydrated manganese(IV) oxide, Mn02 2H20 in basic solution these compounds hydroly2e to hydrous manganese(III) oxide, MnO(OH). Sulfuric acid concentrations of about 400 450 g/L are required to stabilize the noncomplexed Mn ion in aqueous solutions. 

Manganese is used by nature to catalyze a number of important biological reactions that include the dismutation of superoxide radicals, the decomposition of hydrogen peroxide, and the oxidation of water to dioxygen. The dinuclear manganese centers that occur in Lactobacillus plantar-aum catalase and Thermus thermophilus catalase have attracted considerable attention and many model compounds have now been synthesized that attempt to mimic aspects of these biological systems.The catalases have at least four accessible oxidation states (Mn Mn , Mn°Mn , Mn" Mn", and Mn Mn ) it is believed that the Mn"Mn"/Mn"Mn" redox couple is effective in catalyzing the disproportionation of water. 

Manganese(III) is a strong oxidizing agent and is subject to disproportionation as well. Complexes of Mn(III) are also relatively unstable with the exception of [Mn(CN)6]3, which forms readily upon exposure of a solution of manganese(II) and cyanide to air. A few iron(IV) compounds are known. 

Manganese(VI) compounds contain the manganate(VI) MnO " anion. This is stable in alkaline solutions, and possesses a green colour. Upon neutralization a disproportionation reaction takes place manganese dioxide precipitate and manganate(VII) (permanganate) ions are formed ... 

X-ray crystal structures of the manganese(II) derivatives (PZ7 or PZ9) and of the copper(II)-PZ5 complex were determined (196-198). All manganese(II) compounds showed catalytic activity toward disproportionation of H202 in DMF at 0°C. A probable mechanism for this reaction has also been proposed. 

The activation entropy for thermal decomposition of /ra j -[MnX(CO)3(PPh3)2] indicates that manganese-phosphorus bond breaking is rate-determining. The rate law for the decomposition of CoH(CO)4 to Co2(CO)8 plus hydrogen is second-order in cobalt compound. While this decomposition has previously been studied in the gas phase, this is the first report of decomposition kinetics in the liquid phase. The first step in reaction of Co2(CO)s with organomercury halides is solvent-induced disproportionation of the dimeric carbonyl. ... 

Compounds with elements in the intermediate oxidation states tend to disproportionate, for example, Mn04 (+6). At low pH the ions will disproportionate to form manganate(vii) ions and manganese(iv) oxide. 

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