Ruthenium tetroxide
4449147
224309888
2008-07-08T07:47:57Z
Benbest
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/* Preparation */ wording, spelling, grammar
{{Chembox new
| Name = Ruthenium tetroxide
| ImageFile = RuO4.png
<!-- | ImageSize = 100px -->
| ImageName = Ruthenium tetroxide
| IUPACName = Ruthenium tetroxide<!--
| Synonum
| Ruthenium(VIII) Oxide
|-
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| Section1 = {{Chembox Identifiers
| CASNo = 20427-56-9
}}
| Section2 = {{Chembox Properties
| Formula = RuO<sub>4</sub>
| MolarMass = 165.07 g/mol
| Appearance = colorless liquid
| Density = 3.29 g/cm<sup>3</sup>
| Solubility = 2% w/v at 20°C
| Solvent = other solvents
| SolubleOther = Soluble in<br />[[Carbon Tetrachloride]]<br />[[Chloroform]]
| MeltingPt = 25.4 °C
| BoilingPt = 40.0 °C
}}
| Section3 = {{Chembox Structure
| MolShape = tetrahedral
| Dipole = zero
}}
| Section7 = {{Chembox Hazards
| ExternalMSDS = [http://www.polysciences.com/shop/assets/datasheets/320.pdf external MSDS sheet]
| NFPA-H = 2
| NFPA-F =
| NFPA-R =
}}
| Section8 = {{Chembox Related
| OtherCpds = '''RuO<sub>2</sub>'''<br />'''RuCl<sub>3</sub>'''
}}
}}
'''Ruthenium tetroxide''' (RuO<sub>4</sub>) is a yellow, [[diamagnetism|diamagnetic]] [[tetrahedral molecular geometry|tetrahedral]] [[ruthenium]] compound. As expected for a charge-neutral symmetrical [[oxide]], it is quite volatile. The analogous [[osmium tetroxide|OsO<sub>4</sub>]] is more widely used and better known. One of the few solvents in which it forms stable solutions is [[carbon tetrachloride|CCl<sub>4</sub>]].
==Preparation==
RuO<sub>4</sub> is prepared by oxidation of [[ruthenium(III) chloride]] with [[sodium periodate|NaIO<sub>4</sub>]].
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In a typical reactions featuring RuO<sub>4</sub> as the oxidant, many forms of ruthenium usefully serve as precursors to RuO<sub>4</sub>, e.g. oxides hydrates or hydrated [[Ruthenium trichloride|chloride]].
Because RuO<sub>4</sub> will readily decompose explosively at slightly elevated temperatures, most laboratories do not synthesize it directly, nor is it commercially available through major chemical vendors such as [[Sigma-Aldrich]]. Most laboratories instead use an anionic derivative from a salt of "TPAP", or [[tetrapropylammonium perruthenate]] (Pr<sub>4</sub>N<sup>+</sup> RuO<sub>4</sub><sup><nowiki>−</nowiki></sup>). TPAP is synthesized by oxidizing RuCl<sub>3</sub> to RuO<sub>4</sub><sup><nowiki>−</nowiki></sup> by NaBrO<sub>3</sub> and countering it with the tetrapropylamine cation.
==Properties and uses==
RuO<sub>4</sub> oxidizes virtually any hydrocarbon. For example, it will oxidize [[adamantane]] to 1-adamantanol. It is used in [[organic synthesis]] to oxidize [[alkynes]] to 1,2-di[[ketone]]s and primary [[alcohols]] to [[carboxylic acids]]. When used in this fashion, the ruthenium tetroxide is used in catalytic amounts and regenerated by the addition of [[sodium periodate]] to [[ruthenium(III) chloride]] and a [[solvent]] mixture of [[acetonitrile]], [[water]] and [[carbon tetrachloride]].
Because it is such an aggressive oxidant, reaction conditions are mild, generally room temperature. Although a strong oxidant, RuO<sub>4</sub> oxidations do not perturb [[stereocenter]]s that are not oxidized. Illustrative is the oxidation of the following diol to a [[carboxylic acid]]:
[[Image:RuO4oxidation.png|450px]]
Oxidation of [[epoxide|epoxy]] alcohols also occurs without degradation of the epoxide ring:
[[Image:RuO4epoxy.png|450px]]
Under milder condition, oxidative reaction yields [[aldehydes]] instead.
RuO<sub>4</sub> readily converts secondary alcohols into [[ketones]]. Although similar results can be achieved with other cheaper [[oxidants]] such as [[pyridinium chlorochromate|chromium(VI)]] based compounds or [[dimethyl sulfoxide|DMSO]]-based oxidants, RuO<sub>4</sub> is ideal when a very vigorous oxidant is needed but a mild conditions must be maintained.
RuO<sub>4</sub> readily cleaves double bonds to yield [[carbonyl]] products. [[Osmium tetroxide]], a more familiar oxidant that is structurally similar to RuO<sub>4</sub>, does not cleave double bonds.
In terms of practical details, the substrate to be oxidized is typically dissolved in solvent such as [[carbon tetrachloride|CCl<sub>4</sub>]], and [[acetonitrile]] is added as an aiding [[ligand]] to the catalytic cycle. [[diethyl ether|Ether]] can then be added to precipitate and recover the ruthenium pre-catalyst.
==Oxidative catalyst and mechanism==
Although used as an [[oxidant]], RuO<sub>4</sub> is occasionally used as a [[catalyst|catalytic]] for other oxidant. For an oxidation of cyclic [[alcohols]] with RuO<sub>4</sub> as a catalyst and [[bromate]] as a [[base (chemistry)|base]], RuO<sub>4</sub> first takes up an extra O and H:
:RuO<sub>4</sub> + OH<sup>-</sup> → HRuO<sub>5</sub><sup>-</sup>
Then HRuO<sub>5</sub><sup>-</sup> complexes with the cyclic alcohol and form a metal coordination complex (denoted C<sub>1</sub> here):
:HRuO<sub>5</sub><sup>-</sup> + (CH<sub>2</sub>CH<sub>2</sub>)<sub>n</sub>CHOH → C<sub>1</sub> + OH<sup>-</sup>
The Ru complex is then attracted by a bromate in which the oxidation of the coordinated alcohol take place:
:C<sub>1</sub> + BrO<sub>3</sub><sup>-</sup> → (CH<sub>2</sub>CH<sub>2</sub>)<sub>n</sub>C=O + HRuO<sub>5</sub><sup>-</sup>
In which HRuO<sub>5</sub><sup>-</sup> is reformed as the [[catalyst]], and the cyclic alcohol is oxidized into a cyclic [[ketone]].
==References==
{{Citationstyle|date=September 2007}}
{{reflist}}
* Cotton, S. A. "Chemistry of Precious Metals," Chapman and Hall (London): 1997. ISBN 0-7514-0413-6
* Martin, V. S., Palazón, J. M., 'Ruthenium(VIII) Oxide', ''Encyclopedia of Reagents for Organic Synthesis'' '''2001'''. ([http://www.mrw.interscience.wiley.com/eros/articles/rp288/frame.html Article])
*Farmer, V., Welton, T., The oxidation of alcohols in substituted imidazolium ionic liquids using ruthenium catalysts ''Royal Society of Chemistry'', '''2002'''.
*Singh, B., Srivastava, S., Kinetics and Mechanism of Ruthenium tetroxide Catalysed Oxidation of Cyclic Alcohols by Bromate in a Base ''Transition Met. Chem.'', '''1991''', 16, 466-468.
*Courtney, JL., Swansbor, KF. Ruthenium tetroxide Oxidation ''Reviews of Pure and Applied Chemistry '''1972''', 22, 47-
[[Category:Ruthenium compounds]]
[[Category:Oxides]]
[[nl:Rutheniumtetraoxide]]