次錳酸鉀

次錳酸鉀
	IUPAC名; potassium manganate(V); potassium tetraoxidomanganate(3−)
性質
化學式	K3MnO4
莫耳質量	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; 過錳酸鉀
	若非註明，所有數據均出自標準狀態（25 ℃，100 kPa）下。

次錳酸鉀（K₃MnO₄）是一種淡藍色的鹽，它是很少見的次錳酸鹽。

製備

最早製得的次錳酸鹽是Na₃MnO₄·10H₂O，但後來發現它實際上是Na₃MnO₄·0.25NaOH·10H₂O。^[2]

用過量的亞硫酸鉀還原過錳酸鉀：^[3]^[4]

MnO−
4 + SO2−
3 + H₂O → MnO3−
4 + SO2−
4 + 2 H⁺

錳酸鉀與過氧化氫在10mol/L的氫氧化鉀溶液中反應：^[5]

2 MnO2−
4 + H₂O₂ + 2 OH⁻ → 2 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
8H
7O−
3 + 2 OH⁻ → 2 MnO3−
4 + C
8H
5O−
3 + 2 H₂O

二氧化錳在濃氫氧化鉀溶液中歧化：^[3]

2 MnO₂ + 3 OH⁻ → MnO3−
4 + MnO(OH) + H₂O

性質

次錳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⁺的酸度係數的負對數，即pK_a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]

用過錳酸鉀或錳酸鉀氧化有機化合物時，次錳酸根離子經常作為中間體出現。^[2]

參考資料

^ ^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 .
^ ^2.0 ^2.1 《无机化学丛书》第九卷：锰分族、铁系、铂系. 北京: 科學出版社. : P46–47. ISBN 7-03-002238-6.
^ ^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 .
^ ^4.0 ^4.1 Greenwood, Norman N.; Earnshaw, A. Chemistry of the Elements. Oxford: Pergamon. 1984: 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 .
^ Weast, Robert C. (編). CRC Handbook of Chemistry and Physics 62nd. Boca Raton, FL: CRC Press. 1981: D-134. ISBN 0-8493-0462-8. .
^ Manganese – compounds – standard reduction potentials, WebElements, [2010-06-26], （原始內容存檔於2021-01-17） .
^ ^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 .
^ 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 .

[Mandelate-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 .

[wc-2] 2.0 ^2.1 《无机化学丛书》第九卷：锰分族、铁系、铂系. 北京: 科學出版社. : P46–47. ISBN 7-03-002238-6.

[C&W-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 .

[G&E-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], （原始內容存檔於2021-01-17） .

[Epot-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

IUPAC名 potassium manganate(V) potassium tetraoxidomanganate(3−)
性質^[1]
化學式	K₃MnO₄
莫耳質量	236.23 g·mol⁻¹
外觀	淡藍色固體
λ_max	670 nm (ε = 900 dm³ mol⁻¹ cm⁻¹) nm
相關物質
其他陰離子	錳酸鉀過錳酸鉀
若非註明，所有數據均出自標準狀態（25 ℃，100 kPa）下。