Potassium hypomanganate

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Potassium hypomanganate
Names
IUPAC names
potassium manganate(V)
potassium tetraoxidomanganate(3−)
Properties[1]
K3MnO4
Molar mass 236.23 g mol−1
Appearance bright blue solid
UV-vismax) 670 nm
(ε = 900 dm3 mol−1 cm−1)
Related compounds
Other anions
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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Infobox references

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:

MnO
4
+ SO2−
3
+ H2O → MnO3−
4
+ SO2−
4
+ 2 H+
2 MnO2−
4
+ H2O2 + 2 OH2 MnO3−
4
+ O2 + 2 H2O
  • by the reduction of potassium manganate with mandelate in 3–10 M potassium hydroxide solution;[1]
2 MnO2−
4
+ C
8
H
7
O
3
+ 2 OH2 MnO3−
4
+ C
8
H
5
O
3
+ 2 H2O
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:[2][3] estimated electrode potentials at pH 14 are[5][6][7]

MnO2−
4
+ e is in equilibrium with MnO3−
4
   E = +0.27 V
MnO3−
4
+ e + 2 H2O is in equilibrium with MnO2 + 4 OH   E = +0.96 V

The disproportionation is believed to pass through a protonated intermediate,[7] with the acid dissociation constant for the reaction HMnO2−
4
 is in equilibrium with MnO3−
4
 + H+ being estimated as pKa = 13.7 ± 0.2.[8] However, K3MnO4 has been cocrystallized with Ca2Cl(PO4), allowing the study of the UV–visible spectrum of the hypomanganate ion.[2][9]

References[edit]

  1. ^ 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 .
  2. ^ a b c d Cotton, F. Albert; Wilkinson, Geoffrey (1980), Advanced Inorganic Chemistry (4th ed.), New York: Wiley, p. 746, ISBN 0-471-02775-8 .
  3. ^ a b Greenwood, Norman N.; Earnshaw, Alan (1984). Chemistry of the Elements. Oxford: Pergamon Press. pp. 1221–22. ISBN 0-08-022057-6. .
  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 .
  5. ^ Weast, Robert C., ed. (1981). CRC Handbook of Chemistry and Physics (62nd ed.). Boca Raton, FL: CRC Press. p. D-134. ISBN 0-8493-0462-8. .
  6. ^ Manganese – compounds – standard reduction potentials, WebElements, retrieved 2010-06-26 .
  7. ^ a b Sekula-Brzezińska, K.; Wrona, P. K.; Galus, Z. (1979), "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 .
  8. ^ Rush, J. D.; Bielski, B. H. J. (1995), "Studies of Manganate(V), -(VI), and -(VII) Tetraoxyanions by Pulse Radiolysis. Optical Spectra of Protonated Forms", Inorg. Chem. 34 (23): 5832–38, doi:10.1021/ic00127a022 .
  9. ^ Carrington, A.; Symons, M. C. R. (1956), "Structure and reactivity of the oxy-anions of transition metals. Part I. The manganese oxy-anions", J. Chem. Soc.: 3373–80, doi:10.1039/JR9560003373 .