Potassium hypomanganate
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| Potassium hypomanganate | |
|---|---|
| IUPAC name | potassium manganate(V) potassium tetraoxidomanganate(3−) |
| Properties | |
| Chemical formula | K3MnO4 |
| Molar mass | 236.23 g mol−1 |
| Related compounds | |
| Other anions | Potassium manganate Potassium permanganate |
| Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) | |
Potassium hypomanganate, K3MnO4, also known as potassium manganate(V), is a bright blue salt and a rare example of a manganese(V) compound. It is formed:
- by the reduction of potassium permanganate with excess potassium sulfite;[1][2]
- MnO−4 + SO2−3 + H2O → MnO3−4 + SO2−4 + 2 H+
- by the reduction of potassium manganate with hydrogen peroxide in 10 M potassium hydroxide solution;[3]
- 2 MnO2−4 + H2O2 + 2 OH− → 2 MnO3−4 + O2 + 2 H2O
- by disproportionation when manganese dioxide is dissolved in a concentrated solution of potassium hydroxide;[1]
- 2 MnO2 + 3 OH− → MnO3−4 + MnO(OH) + H2O
The hypomanganate anion is unstable with respect to disproportionation in all but the most alkaline of solutions:[1][2] estimated electrode potentials at pH 14 are[4][5][6]
- MnO2−4 + e− ⇌ MnO3−4 E = +0.27 V
- MnO3−4 + e− + 4 H2O ⇌ MnO2 + 6 OH− E = +0.96 V
The disproportionation is believed to pass through a protonated intermediate,[6] with the acid dissociation constant for the reaction HMnO2−4 ⇌ MnO3−4 + H+ being estimated as pKa = 13.7 ± 0.2.[7] However, K3MnO4 has been cocrystallized with Ca2Cl(PO4), allowing the study of the UV–visible spectrum of the hypomanganate ion.[1][8]
References
- ↑ 1.0 1.1 1.2 1.3 Cotton, F. Albert; Wilkinson, Geoffrey Advanced Inorganic Chemistry, 4th ed.; Wiley: New York, 1980; p 746. ISBN 0-471-02775-8.
- ↑ 2.0 2.1 Greenwood, Norman N.; Earnshaw, A. Chemistry of the Elements; Pergamon: Oxford, 1984; pp 1221–22. ISBN 0-08-022057-6.
- ↑ Lee, Donald G.; Chen, Tao Oxidation of hydrocarbons. 18. Mechanism of the reaction between permanganate and carbon-carbon double bonds. J. Am. Chem. Soc. 1989, 111 (19), 7534–38. DOI: 10.1021/ja00201a039.
- ↑ CRC Handbook of Chemistry and Physics, 62nd ed.; Weast, Robert C., Ed.; CRC Press: Boca Raton, FL, 1981; p D-134. ISBN 0-8493-0462-8.
- ↑ Manganese – compounds – standard reduction potentials; WebElements, <http://www.webelements.com/manganese/compounds.html>. (accessed 26 June 2010).
- ↑ 6.0 6.1 Sekula-Brzezińska, K.; Wrona, P. K.; Galus, Z. Rate of the MnO4−/MnO42− and MnO42−/MnO43− electrode reactions in alkaline solutions at solid electrodes. Electrochim. Acta, 24 (5), 555–63. DOI: 10.1016/0013-4686(79)85032-X.
- ↑ Rush, J. D.; Bielski, B. H. J. Studies of Manganate(V), -(VI), and -(VII) Tetraoxyanions by Pulse Radiolysis. Optical Spectra of Protonated Forms. Inorg. Chem. 1995, 34 (23), 5832–38. DOI: 10.1021/ic00127a022.
- ↑ Carrington, A.; Symons, M. C. R. Structure and reactivity of the oxy-anions of transition metals. Part I. The manganese oxy-anions. J. Chem. Soc. 1956, 3373–80. DOI: 10.1039/JR9560003373.
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