Ruthenium tetroxide 4449147 224309888 2008-07-08T07:47:57Z Benbest 167797 /* Preparation */ wording, spelling, grammar {{Chembox new | Name = Ruthenium tetroxide | ImageFile = RuO4.png <!-- | ImageSize = 100px --> | ImageName = Ruthenium tetroxide | IUPACName = Ruthenium tetroxide<!-- | Synonum | Ruthenium(VIII) Oxide |- --> | 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>]]. <!--need equation--> 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>&minus;</nowiki></sup>). TPAP is synthesized by oxidizing RuCl<sub>3</sub> to RuO<sub>4</sub><sup><nowiki>&minus;</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]]