Hexol
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| Names | |
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| IUPAC name
Tris[tetrammine-μ-dihydroxocobalt(III)]cobalt (III) ion
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| Properties | |
| Co4H42N12O18S3 | |
| Molar mass | 830.31 g·mol−1 |
| Sparingly soluble in water [1] | |
| Vapor pressure | {{{value}}} |
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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 | |
Hexol is the name for various salts of a coordination complex that has historical significance. The salts were the first synthetic non-carbon-containing chiral compounds.[2] The sulfate salt has the formula {[Co(NH3)4(OH)2]3Co}(SO4)3.
Contents
Preparation and optical resolution
Salts of hexol were first described by Jorgenson.[3] The salt is prepared by heating [Co(NH3)4(H2O)2]3+ with dilute base such as ammonia followed by precipitation of the sulfate salt:
- 4 [Co(NH3)4(H2O)2]3+ → {[Co(NH3)4(OH)2]3Co}6+ + 4 NH4+ + 2 H+ + 2 H2O
Depending on the conditions one obtains the 9-hydrate, the 6-hydrate, and the 4-hydrate. These salts exists as dark brownish-violet or black tabular crystals. The salts has low solubility in water. The cation can be quantitatively precipitated from its yellow-gray chromate and hexachloroplatinate salts. When treated with concentrated hydrochloric acid, hexol converts to cis-diaquotetramminecobalt(III) sulfate. In boiling dilute sulfuric acid, hexol degrades with evolution of oxygen and nitrogen.[1]
Optical resolution
In a historic set of experiments, Alfred Werner obtained chiral resolution by fractional crystallisation of the diastereomeric D-(+)-bromocamphorsulfonate salt. This ion has a high specific rotation of 2640°.[4] More efficient methods involve the bis(tartrato)diantimonate(III) salt.[5]
The "second hexol"
Werner also described a second achiral hexol (a minor byproduct from the production of Fremy's salt) that he incorrectly identified as a linear trimer. The second hexol is hexanuclear (contains six cobalt centres in each ion), not tetranuclear.[6]
References
- ↑ 1.0 1.1 Lua error in package.lua at line 80: module 'strict' not found.
- ↑ Miessler, G. L. and Tarr, D. A. Inorganic Chemistry, 3rd ed., Pearson/Prentice Hall publisher, ISBN 0-13-035471-6.
- ↑ Lua error in package.lua at line 80: module 'strict' not found.
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External links
- Hexol Molecule of the Month September 1997 Website
- National Pollutant Inventory – Cobalt fact sheet
