Difference between revisions of "Potassium hypomanganate"
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'''Potassium hypomanganate''', K<sub>3</sub>MnO<sub>4</sub>, also known as '''potassium manganate(V)''', is a bright blue salt and a rare example of a manganese(V) compound. It is formed: | '''Potassium hypomanganate''', K<sub>3</sub>MnO<sub>4</sub>, 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]];<ref name="C&W">{{Cotton&Wilkinson4th|page=746}}.</ref><ref name="G&E">{{Greenwood&Earnshaw1st|pages=1221–22}}.</ref> | + | *by the [[reduction]] of [[potassium permanganate]] with excess [[potassium sulfite]];<ref name="C&W">{{Cotton&Wilkinson4th|page=746}}.</ref><ref name="G&E">{{Greenwood&Earnshaw1st|pages=1221–22}}.</ref> |
::MnO{{su|b=4|p=−}} + SO{{su|b=3|p=2−}} + H<sub>2</sub>O → MnO{{su|b=4|p=3−}} + SO{{su|b=4|p=2−}} + {{nowrap|2 H<sup>+</sup>}} | ::MnO{{su|b=4|p=−}} + SO{{su|b=3|p=2−}} + H<sub>2</sub>O → MnO{{su|b=4|p=3−}} + SO{{su|b=4|p=2−}} + {{nowrap|2 H<sup>+</sup>}} | ||
*by the reduction of [[potassium manganate]] with [[hydrogen peroxide]] in 10 M [[potassium hydroxide]] solution;<ref>{{citation | title = Oxidation of hydrocarbons. 18. Mechanism of the reaction between permanganate and carbon-carbon double bonds | first1 = Donald G. | last1 = Lee | first2 = Tao | last2 = Chen | journal = J. Am. Chem. Soc. | year = 1989 | volume = 111 | issue = 19 | pages = 7534–38 | doi = 10.1021/ja00201a039}}.</ref> | *by the reduction of [[potassium manganate]] with [[hydrogen peroxide]] in 10 M [[potassium hydroxide]] solution;<ref>{{citation | title = Oxidation of hydrocarbons. 18. Mechanism of the reaction between permanganate and carbon-carbon double bonds | first1 = Donald G. | last1 = Lee | first2 = Tao | last2 = Chen | journal = J. Am. Chem. Soc. | year = 1989 | volume = 111 | issue = 19 | pages = 7534–38 | doi = 10.1021/ja00201a039}}.</ref> | ||
::{{nowrap|2 MnO{{su|b=4|p=2−}}}} + H<sub>2</sub>O<sub>2</sub> + {{nowrap|2 OH<sup>−</sup>}} → {{nowrap|2 MnO{{su|b=4|p=3−}}}} + O<sub>2</sub> + {{nowrap|2 H<sub>2</sub>O}} | ::{{nowrap|2 MnO{{su|b=4|p=2−}}}} + H<sub>2</sub>O<sub>2</sub> + {{nowrap|2 OH<sup>−</sup>}} → {{nowrap|2 MnO{{su|b=4|p=3−}}}} + O<sub>2</sub> + {{nowrap|2 H<sub>2</sub>O}} | ||
| − | *by [[disproportionation]] when [[manganese dioxide]] is dissolved in a concentrated solution of | + | *by [[disproportionation]] when [[manganese dioxide]] is dissolved in a concentrated solution of potassium hydroxide;<ref name="C&W"/> |
::{{nowrap|2 MnO<sub>2</sub>}} + {{nowrap|3 OH<sup>−</sup>}} → MnO{{su|b=4|p=3−}} + MnO(OH) + H<sub>2</sub>O | ::{{nowrap|2 MnO<sub>2</sub>}} + {{nowrap|3 OH<sup>−</sup>}} → MnO{{su|b=4|p=3−}} + MnO(OH) + H<sub>2</sub>O | ||
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:MnO{{su|b=4|p=2−}} + e<sup>−</sup> {{eqm}} MnO{{su|b=4|p=3−}} ''E'' = +0.27 V | :MnO{{su|b=4|p=2−}} + e<sup>−</sup> {{eqm}} MnO{{su|b=4|p=3−}} ''E'' = +0.27 V | ||
:MnO{{su|b=4|p=3−}} + e<sup>−</sup> + {{nowrap|4 H<sub>2</sub>O}} {{eqm}} MnO<sub>2</sub> + {{nowrap|6 OH<sup>−</sup>}} ''E'' = +0.96 V | :MnO{{su|b=4|p=3−}} + e<sup>−</sup> + {{nowrap|4 H<sub>2</sub>O}} {{eqm}} MnO<sub>2</sub> + {{nowrap|6 OH<sup>−</sup>}} ''E'' = +0.96 V | ||
| − | The | + | The disproportionation is believed to pass through a protonated intermediate, with the [[acid dissociation constant]] for the reaction HMnO{{su|b=4|p=2−}} {{eqm}} MnO{{su|b=4|p=3−}} + H<sup>+</sup> being estimated as p''K''<sub>a</sub> = 13.7(2).<ref>{{citation | title = Studies of Manganate(V), -(VI), and -(VII) Tetraoxyanions by Pulse Radiolysis. Optical Spectra of Protonated Forms | first1 = J. D. | last1 = Rush | first2 = B. H. J. | last2 = Bielski | journal = Inorg. Chem. | year = 1995 | volume = 34 | issue = 23 | pages = 5832–38 | doi = 10.1021/ic00127a022}}.</ref> However, K<sub>3</sub>MnO<sub>4</sub> has been cocrystallized with Ca<sub>2</sub>Cl(PO<sub>4</sub>), allowing the study of the [[Ultraviolet–visible spectroscopy|UV–visible spectrum]] of the hypomanganate ion.<ref name="C&W"/><ref>{{citation | journal = J. Chem. Soc. | year = 1956 | pages = 3373–80 | doi = 10.1039/JR9560003373 | title = Structure and reactivity of the oxy-anions of transition metals. Part I. The manganese oxy-anions | first1 = A. | last1 = Carrington | first2 = M. C. R. | last2 = Symons}}.</ref> |
==References== | ==References== | ||
Revision as of 09:58, 26 June 2010
| 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][4][5]
- 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, with the acid dissociation constant for the reaction HMnO2−4 ⇌ MnO3−4 + H+ being estimated as pKa = 13.7(2).[6] However, K3MnO4 has been cocrystallized with Ca2Cl(PO4), allowing the study of the UV–visible spectrum of the hypomanganate ion.[1][7]
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).
- ↑ 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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