Potassium osmate
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| Names | |
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| Other names
Potassium osmate(VI) dihydrate
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| Identifiers | |
3D model (JSmol)
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| ChemSpider | |
| ECHA InfoCard | 100.157.189 |
| EC Number |
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PubChem CID
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| UNII | |
CompTox Dashboard (EPA)
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| Properties | |
| K2[OsO2(OH)4] | |
| Molar mass | 368.42 g/mol |
| Appearance | Garnet red[1] |
| Soluble[2] | |
| Solubility | Insoluble in alcohol or ether |
| Hazards | |
| GHS labelling: | |
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| Danger | |
| H301, H311, H330, H331 | |
| P260, P261, P264, P270, P271, P280, P284, P301+P310, P302+P352, P304+P340, P310, P311, P312, P320, P321, P322, P330, P361, P363, P403+P233, P405, P501 | |
| NFPA 704 (fire diamond) | |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Potassium osmate is the inorganic compound with the formula K2[OsO2(OH)4]. This diamagnetic purple salt contains osmium in the VI (6+) oxidation state.[4] When dissolved in water a red solution is formed. When dissolved in dilute alcohols, the salt gives a pink solution, and it gives a blue solution when dissolved in methanol.[1][4][5] The salt gained attention as a catalyst for the asymmetric dihydroxylation of olefins.[6]
Structure
[edit]The complex anion is octahedral. Like related d2 dioxo complexes, the oxo ligands are trans.[7] The Os=O and Os-OH distances are 1.75(2) and 1.99(2) Å, respectively. It is a relatively rare example of a metal oxo complex that obeys the 18e rule.
Preparation
[edit]The compound was first reported by Edmond Frémy in 1844.[8] Potassium osmate is prepared by reducing osmium tetroxide with ethanol:[9]
- 2 OsO4 + C2H5OH + 5 KOH → CH3CO2K + 2 K2[OsO2(OH)4]
Alkaline oxidative fusion of osmium metal also affords this salt.[4]
Properties
[edit]Potassium osmate slowly decomposes in aqueous solution, producing osmium tetroxide.[10][3] It is more stable in cold water under alkaline conditions, but hot water or acid accelerates decomposition. When exposed to sunlight for prolonged periods of time, it decomposes and produces a sooty powder along with the odor of the tetroxide.[1][11][5] It does not dissolve in alcohol or ether, but in aqueous solution it forms a complex with alcohol, producing a pink color.[11][5][12]
Reactions
[edit]Potassium osmate reacts with acids to produce osmyl salts, such as potassium osmyl chloride and the osmyl bromide. It reacts with oxalic acid to produce potassium osmyl oxalate.[5][1]
- K2[OsO2(OH)4] + 4HCl → K2(OsO2)Cl4 + 4H2O
- K2[OsO2(OH)4] + 2H2C2O4 → K2(OsO2)(C2O4)2 + 4H2O
It also reacts with potassium nitrite to yield potassium osmyl nitrite,[5] and it reacts with ammonium salts to produce osmyl tetra-ammine compounds such as [OsO2(NH3)4]Cl2.[1] [5]
Potassium osmate can be reduced to osmium dioxide with alcohol.[1][5]
- K2[OsO2(OH)4] + C2H5OH → OsO2•2H2O + 2KOH + CH3CHO
Potassium osmate can be used to be prepare many other compounds. If potassium osmate is refluxed with HCl, it can be reduced to hexachloroosmic acid.[13] It reacts with hydrogen sulfide to produce osmium disulfide, OsS2, and with sulfurous acid to form potassium osmium sulfite.[5][11]
Applications
[edit]Potassium osmate is used for the oxidative hydroxylation of organic compounds, notably the Sharpless dihydroxylation of olefins, as well as a catalyst for other asymmetric syntheses, such as carboranylated diols. It is also used for the synthesis of active pharmaceutical ingredients.[14][15]
Other uses include the stereoselective synthesis of β-N-glycopyranosides, and the preparation of osmium complexes for the voltammetric analysis of polysaccharides.[15]
Related compounds
[edit]Other osmates are known, such as the highly water soluble sodium osmate, and insoluble osmates such as those of barium, strontium, calcium, and lead.[5][11]
When osmium tetroxide is treated with an alkali hydroxide, or even when potassium osmate is oxidized in alkaline medium, the perosmate anion is formed, [OsO4(OH)2]²⁻. When treated with alcohol or heating, perosmates are reduced to osmates, [OsO2(OH)4]²⁻[5][12][16] Perosmate salts share the same valency as osmium tetroxide, as opposed to perruthenates.[16] Unlike the tetroxide however, they are not volatile.[12] The perosmates of sodium, potassium, rubidium, cesium, and barium are known.[12][17]
When osmium tetroxide is dissolved in anhydrous methanol containing potassium hydroxide, a blue solution of dipotassium tetramethyl osmate (DTMO) is obtained. DTMO was used as a staining agent for electron microscopy.[18]
Images
[edit]-
Osmate dissolved in water -
Osmate complexed with alcohol -
Color comparison between osmate and perosmate
See also
[edit]References
[edit]- ^ a b c d e f J. Newton Friend (1920). "Osmium and its compounds". A textbook of inorganic chemistry, vol.IX Part I Cobalt, Nickel, and The Elements of The Platinum Group (PDF). London: Charles Griffin and Company, Limited. pp. 219–225, 231. Retrieved 3 July 2025.
- ^ Comey, Arthur Messinger (1896). A Dictionary of Chemical Solubilities: Inorganic. Macmillan and Company. p. 275. Retrieved 6 July 2025.
- ^ a b "Potassium osmate(VI) dihydrate". Chemical Book. Retrieved 6 July 2025.
- ^ a b c F. Albert Cotton; Geoffrey Wilkinson (1966). Advanced Inorganic Chemistry: A Comprehensive Treatise. New York, Interscience Publishers. p. 1007.
- ^ a b c d e f g h i j Prakash Satya (2013). "Platinum Metals-IV:Osmium". Advanced Chemistry of Rare Elements, 5th Ed. India: S Chand and Company Limited. pp. 611–622.
- ^ Li, Guigen; Chang, Han-Ting; Sharpless, K. Barry (1996). "Catalytic Asymmetric Aminohydroxylation (AA) of Olefins". Angew. Chem. Int. Ed. Engl. 35 (4): 451–4. doi:10.1002/anie.199604511.
- ^ R. K. Murmann, C. L. Barnes "Redetermination of the crystal structure of potassium trans-(dioxo)-tetra(hydroxo)osmate(VI), K2[Os(OH)4(O)2]" Z. Kristallogr. NCS 217, 2002, pp. 303–304. doi:10.1524/ncrs.2002.217.jg.303
- ^ Frémy, E. "Ueber das Osmium" Journal für Praktische Chemie 1844 vol.33, 406-416. doi:10.1002/prac.18440330160
- ^ John M. Malin (1980). "Potassium Tetrahydroxodioxoosmate(VI) and trans ‐Bis(Ethylenediamine)Dioxoosmium(VI) Chloride". Potassium Tetrahydroxodioxoosmate(VI) and trans-Bis(Ethylenediamine)Dioxoosmium(VI) Chloride. Inorganic Syntheses. Vol. 20. pp. 61–63. doi:10.1002/9780470132517.ch18. ISBN 9780470132517.
- ^ "Potassium Osmate(VI) Dihydrate". Wiley Online Library. Retrieved 6 July 2025.
- ^ a b c d J.W. Mellor (May 1936). "Osmium". A comprehensive treatise on inorganic and theoretical chemistry, Volume 15. London: Longmans, Green and Co. p. 706. Retrieved 22 June 2025.
- ^ a b c d McFadzean, Belinda (December 2007). The Kinetics and Associated Equilibra of High Oxidation State Osmium Complexes (PDF) (PhD thesis). Port Elizabeth, South Africa: Nelson Mandela Metropolitan University. Retrieved 3 July 2025.
- ^ Chiririwa, Haleden; Muzenda, Edison (November 2014). "The Preparation and Characterisation of Osmium (IV), Osmium (II), and Osmium (0) Complexes from Refinery Materials" (PDF). International Conference on Chemical Engineering & Advanced Computational Technologies (ICCEACT): 32–33. Retrieved 19 June 2025.
- ^ "Potassium osmate". Heraeus Precious Metals. Retrieved 5 July 2025.
- ^ a b "Potassium osmate(VI) dihydrate". Sigma Aldrich. Retrieved 5 July 2025.
- ^ a b Stopinski, Orin (September 1977). "Platinum-Group Metals" (PDF). Environmental Health Effects Research Series. Washington, DC: Environmental Protection Agency: 85–87. Retrieved 19 June 2025.
- ^ Williamson, J.; Savage, J. (January 1965). "The Determination of Osmiridium in Witwatersrand Ores". Journal of the South African Institute of Mining and Metallurgy: 350. Retrieved 7 July 2025.
- ^ Hinckley, C.; Murphy, Judith (13 August 1974). "Dipotassium Tetramethyl Osmate: A Stain for Electron Microscopy". Journal of Histochemistry and Cytochemistry. 23 (2): 123–127. Retrieved 6 July 2025.