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次錳酸鉀

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次錳酸鉀
IUPAC名
potassium manganate(V)
potassium tetraoxidomanganate(3−)
性質[1]
化學式 K3MnO4
摩爾質量 236.23 g·mol⁻¹
外觀 淡藍色固體
λmax 670 nm
(ε = 900 dm3 mol−1 cm−1) nm
相關物質
其他陰離子 錳酸鉀
高錳酸鉀
若非註明,所有數據均出自一般條件(25 ℃,100 kPa)下。

錳(V)酸鉀(K3MnO4)是一種淡藍色的鹽,它是很少見的Mn(V)的含氧酸鹽。

製備

最早製得的錳(V)酸鹽是Na3MnO4·10H2O,但後來發現它實際上是Na3MnO4·0.25NaOH·10H2O。[2]

MnO
4
+ SO2−
3
+ H2O → MnO3−
4
+ SO2−
4
+ 2 H+
2 MnO2−
4
+ H2O2 + 2 OH2 MnO3−
4
+ O2 + 2 H2O
  • 在3-10mol/L的氫氧化鉀溶液中用扁桃酸還原錳酸鉀:[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

性質

錳(V)酸鹽在無水和無二氧化碳的條件下能穩定存在。在水溶液中因歧化而不穩定,尤其是在鹼性溶液中。[3][4]估計pH=14的水溶液中它的標準電極電勢如下所示:[6][7][8]

MnO2−
4
+ e ⇌ MnO3−
4
   E = +0.27 V
MnO3−
4
+ e + 4 H2O ⇌ MnO2 + 6 OH   E = +0.96 V

歧化反應被認為經過質子化的中間體,[8]因為HMnO2−
4
 ⇌ MnO3−
4
 + H+酸度係數的負對數,即pKa約為13.7 ± 0.2[9]然而,K3MnO4能與Ca2Cl(PO4)共結晶並析出,使得人們可以用紫外可見吸收光譜來研究錳(V)酸根離子。[3][10]

用高錳酸鉀或錳酸鉀氧化有機化合物時,錳(V)酸根離子經常作為中間體出現。[2]

參考資料

  1. ^ 1.0 1.1 Lee, Donald G.; Chen, Tao, 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., 1993, 115 (24): 11231–36, doi:10.1021/ja00077a023 .
  2. ^ 2.0 2.1 《無機化學叢書》第九卷:錳分族、鐵系、鉑系. 北京: 科學出版社. : P46–47. ISBN 7-03-002238-6. 
  3. ^ 3.0 3.1 3.2 3.3 Cotton, F. Albert; Wilkinson, Geoffrey, Advanced Inorganic Chemistry 4th, New York: Wiley: 746, 1980, ISBN 0-471-02775-8 .
  4. ^ 4.0 4.1 Greenwood, Norman N.; Earnshaw, A. Chemistry of the Elements. Oxford: Pergamon. 1984: 1221–22. ISBN 0-08-022057-6. .
  5. ^ 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 .
  6. ^ Weast, Robert C. (編). CRC Handbook of Chemistry and Physics 62nd. Boca Raton, FL: CRC Press. 1981: D-134. ISBN 0-8493-0462-8. .
  7. ^ Manganese – compounds – standard reduction potentials, WebElements, [2010-06-26] .
  8. ^ 8.0 8.1 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, 1979, 24 (5): 555–63, doi:10.1016/0013-4686(79)85032-X .
  9. ^ 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 .
  10. ^ 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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次錳酸鉀
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