Potassium hypomanganate is the inorganic compound with the formula K3MnO4. 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.[2]
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| IUPAC names
potassium manganate(V)
potassium tetraoxidomanganate(3−) | |
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3D model (JSmol)
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CompTox Dashboard (EPA)
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| Properties[1] | |
| K3MnO4 | |
| Molar mass | 236.229 g·mol−1 |
| Appearance | bright blue solid |
| Density | 2.78 g/cm3 |
| Melting point | 900 °C (1,650 °F; 1,170 K) (decomposes) |
| UV-vis (λmax) | 670 nm (ε = 900 dm3 mol−1 cm−1) |
| Related compounds | |
Other anions
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Potassium manganate Potassium permanganate |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Properties
editPotassium hypomanganate is oxidized in water to potassium manganate:[3]
- 2 K3MnO4 + H2O + 0.5 O2 → 2 KOH + 2 K2MnO4
However, it undergoes disproportionation in acidic solutions producing manganese dioxide and potassium permanganate.[3]
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.[4]
Preparative routes
editThe solid salt can be produced by the reaction of potassium carbonate and manganese carbonate in the presence of oxygen at 800 °C.[3] 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.[2]
A solution of potassium hypomanganate is produced:
- by two-electron reduction of potassium permanganate with excess potassium sulfite;[5][6]
- MnO−4 + SO2−3 + H2O → MnO3−4 + SO2−4 + 2 H+
- by the single-electron reduction of potassium manganate with hydrogen peroxide in 10 M potassium hydroxide solution;[7]
- 2 MnO2−4 + H2O2 + 2 OH− → 2 MnO3−4 + O2 + 2 H2O
- by the single-electron reduction of potassium manganate with mandelate in 3–10 M potassium hydroxide solution;[1]
- 2 MnO2−4 + C8H7O−3 + 2 OH− → 2 MnO3−4 + C8H5O−3 + 2 H2O
- by disproportionation when manganese dioxide is dissolved in a concentrated solution of potassium hydroxide;[5]
- 2 MnO2 + 3 OH− → MnO3−4 + MnOOH + H2O
The compound is unstable due to the tendency of the hypomanganate anion to disproportionate in all but the most alkaline solutions.[5][6]
References
edit- ^ a b Lee, Donald G.; Chen, Tao (1993), "Reduction of manganate(VI) by mandelic acid and its significance for development of a general mechanism of oxidation of organic compounds by high-valent transition metal oxides", J. Am. Chem. Soc., 115 (24): 11231–36, doi:10.1021/ja00077a023.
- ^ a b Kenneth Pisarczyk (2005). "Manganese Compounds". Kirk-Othmer Encyclopedia of Chemical Technology. doi:10.1002/0471238961.1301140716091901.a01.pub2.
- ^ a b c Tupec, Josef (2001). Interoperational analytical control during the production of potassium permanganate (PDF) (Diploma thesis).
- ^ H. Peters; K.-H. Radeke; L. Till (1966). "Über das thermische Verhalten von Kaliummanganat(V), -(VI) und -(VII)" [About the thermal behavior of potassium manganate(V), -(VI) and -(VII)]. Zeitschrift für anorganische und allgemeine Chemie (in German). 346 (1–2): 1–11. doi:10.1002/zaac.19663460102.
- ^ a b c Cotton, F. Albert; Wilkinson, Geoffrey (1980), Advanced Inorganic Chemistry (4th ed.), New York: Wiley, p. 746, ISBN 0-471-02775-8.
- ^ a b Greenwood, Norman N.; Earnshaw, Alan (1984). Chemistry of the Elements. Oxford: Pergamon Press. pp. 1221–22. ISBN 978-0-08-022057-4..
- ^ Lee, Donald G.; Chen, Tao (1989), "Oxidation of hydrocarbons. 18. Mechanism of the reaction between permanganate and carbon-carbon double bonds", J. Am. Chem. Soc., 111 (19): 7534–38, doi:10.1021/ja00201a039.