Potassium hypomanganate
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| Template:Longitem | Template:Chembox Elements/molecular formula |
| Molar mass | Template:Chem molar mass |
| Appearance | bright blue solid |
| Density | 2.78 g/cm3 |
| Melting point | Template:Chembox CalcTemperatures |
| UV-vis (λmax) | 670 nm (ε = 900 dm3 mol−1 cm−1) |
| Template:Longitem | Potassium manganate Potassium permanganate |
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Potassium hypomanganate is the inorganic compound with the formula Template:Chem2. Also known as potassium manganate(V), this bright blue solid is a rare example of a salt with the hypomanganate or manganate(V) anion, where the manganese atom is in the +5 oxidation state. It is an intermediate in the production of potassium permanganate and the industrially most important Mn(V) compound.[1]
Properties
Potassium hypomanganate is oxidized in water to potassium manganate:[2]
- 2 K3MnO4 + H2O + 0.5 O2 → 2 KOH + 2 K2MnO4
However, it undergoes disproportionation in acidic solutions producing manganese dioxide and potassium permanganate.[2]
In the absence of moisture, it is stable up to 900 °C. Above that temperature, it decomposes to potassium oxide, manganese(II,III) oxide, and oxygen.[3]
Preparative routes
The solid salt can be produced by the reaction of potassium carbonate and manganese carbonate in the presence of oxygen at 800 °C.[2] However, in the industrial process of producing potassium permanganate, it is produced by fusing manganese dioxide and potassium hydroxide. The resulting hypomanganate further reacts with water to produce manganate.[1]
A solution of potassium hypomanganate is produced:
- by two-electron reduction of potassium permanganate with excess potassium sulfite;[4][5]
- by the single-electron reduction of potassium manganate with hydrogen peroxide in 10 M potassium hydroxide solution;[6]
- by the single-electron reduction of potassium manganate with mandelate in 3–10 M potassium hydroxide solution;[7]
- by disproportionation when manganese dioxide is dissolved in a concentrated solution of potassium hydroxide;[4]
The compound is unstable due to the tendency of the hypomanganate anion to disproportionate in all but the most alkaline solutions.[4][5]
References
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