Selenium dioxide 2696797 223215650 2008-07-03T02:30:48Z 206.192.172.22 /* Preparation */ {{Chembox new | Name = Selenium dioxide | ImageFile = Selenium dioxide.png <!-- | ImageSize = 200px --> | ImageName = Selenium dioxide | ImageFile1 = Selenium-dioxide-chain-3D-balls.png <!-- | ImageSize1 = 300px --> | ImageName1 = Ball-and-stick model of a chain in crystalline selenium dioxide | OtherNames = Selenium(IV) oxide<br />Selenium dioxide | Section1 = {{Chembox Identifiers | CASNo = 7446-08-4 | RTECS = WS4550000 }} | Section2 = {{Chembox Properties | Formula = [[Selenium|Se]][[Oxygen|O]]<sub>2</sub> | MolarMass = 110.96 g/mol | Appearance = White crystalline solid | Density = 3.95 g/cm<sup>3</sup>, solid | Solubility = 3.950 g/100 ml (25 °C) | BoilingPt = 315 °C ''sublimes'' | pKa = 2.62 (H<sub>2</sub>SeO<sub>3</sub> {{unicode|⇌}} HSeO<sub>3</sub><sup>&minus;</sup> + H<sup>+</sup>)<br />8.32 (HSeO<sub>3</sub><sup>&minus;</sup> {{unicode|⇌}} SeO<sub>3</sub><sup>2&minus;</sup> + H<sup>+</sup>) }} | Section3 = {{Chembox Structure | Coordination = trigonal | CrystalStruct = chain structure }} | Section7 = {{Chembox Hazards | EUClass = Toxic ('''T''')<br />Dangerous for<br />the environment ('''N''') | NFPA-H = 3 | NFPA-F = | NFPA-R = | RPhrases = {{R23/25}}, {{R33}}, {{R50/53}} | SPhrases = {{S1/2}}, {{S20/21}}, {{S28}}<br />{{S45}}, {{S60}}, {{S61}} | FlashPt = non-flammable }} | Section8 = {{Chembox Related | OtherCations = [[Sulfur dioxide]]<br />[[Tellurium dioxide]] | OtherCpds = [[Selenium trioxide]]<br />[[Selenous acid]] }} }} '''Selenium dioxide''' is the [[chemical compound]] with the [[chemical formula|formula]] SeO<sub>2</sub>. This colorless solid is one of the most frequently encountered compounds of [[selenium]]. ==Properties== Solid SeO<sub>2</sub> is a one-dimensional [[polymer]], the chain consisting of alternating Se and [[oxygen]] atoms. Each Se atom, which is pyramidal, bears a terminal oxide group. The relative [[stereochemistry]] at Se alternates along the polymer chain ([[syndiotactic]]). The solid sublimes readily. Gaseous selenium dioxide adopts a bent structure very similar to that of [[sulfur dioxide]]. Dissolution of SeO<sub>2</sub> in [[selenium oxydichloride]] give the trimer [Se(O)O]<sub>3</sub>.<ref>Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. ISBN 0-12-352651-5.</ref> Whereas SO<sub>2</sub> tends to be molecular and SeO<sub>2</sub> is a one-dimensional chain, [[Tellurium dioxide|TeO<sub>2</sub>]] is a cross-linked polymer. SeO<sub>2</sub> is considered an [[acidic oxide]]: it dissolves in water to form selenous (selenious) acid. Often the term selenous (selenious) acid and selenium dioxide are used interchangeably. It reacts with base to form selenite SeO<sub>3</sub><sup>2-</sup>: :SeO<sub>2</sub> + 2 NaOH → [[sodium selenite|Na<sub>2</sub>SeO<sub>3</sub>]] + H<sub>2</sub>O ==Preparation== Selenium dioxide is prepared by oxidation of [[selenium]] by burning in air, nitric acid or by reaction with [[hydrogen peroxide]], but perhaps the most convenient preparation is by the dehydration of [[selenous acid]]. :3Se + 4HNO<sub>3</sub> + H<sub>2</sub>O → 3H<sub>2</sub>SeO<sub>3</sub> + 4NO :H<sub>2</sub>O<sub>2</sub> + Se → SeO<sub>2</sub> + H<sub>2</sub> United States Patent #2,616,791 :H<sub>2</sub>SeO<sub>3</sub> {{unicode|⇌}} SeO<sub>2</sub> + H<sub>2</sub>O ==Uses== ====Organic synthesis==== SeO<sub>2</sub> is an important reagent in [[organic synthesis]]. Oxidation of [[paraldehyde]] (acetaldehyde trimer) with SeO<sub>2</sub> gives [[glyoxal]]<ref>{{OrgSynth | author = Ronzio, A. R.; Waugh, T. D. | title = Glyoxal Bisulfite | collvol = 3 | collvolpages = 438 | year = 1955| prep = CV3P0438}}</ref> and the oxidation of [[cyclohexanone]] gives cyclohexane-1,2-dione.<ref>{{OrgSynth | author = Hach, C. C. Banks, C. V.; Diehl, H. | title = 1,2-Cyclohexanedione Dioxime | collvol = 4 | collvolpages = 229 | year = 1963 | prep = CV4P0229}}</ref>. This type of reaction is called a [[Riley oxidation]]. It is also renown as a reagent for "allylic" oxidation,<ref>{{OrgSynth | author = Coxon, J. M.; Dansted, E.; Hartshorn, M. P. | title = Allylic Oxidation with Hydrogen Peroxide–Selenium Dioxide: trans-Pinocarveol | collvol = 6 | collvolpages = 946 | year = 1988 | prep = CV6P0946}}</ref> a reaction that entails the conversion :R<sub>2</sub>C=CR'-CHR"<sub>2</sub> + [O] → R<sub>2</sub>C=CR'-C(OH)R"<sub>2</sub> (where R, R', R" are [[alkyl]] or [[aryl]]). ====As a colorant==== Selenium dioxide imparts a red colour to [[glass]]: it is used in small quantities to counteract the blue colour due to [[cobalt]] impurities and so to create (apparently) colourless glass. In larger quantities, it gives a deep ruby red colour. Selenium dioxide is the active ingredient in some [[Bluing (steel)|cold-blueing]] solutions. It is also used as a toner in [[photographic developing]]. {{commonscat|selenium dioxide}} ==References== {{reflist}} ==Further reading== *{{Cotton&Wilkinson6th}} *{{RubberBible83rd}} ==External links== *{{ICSC|0946|09}} [[Category:Selenium compounds]] [[Category:Oxides]] [[Category:Photographic chemicals]] [[Category:Acidic oxides]] [[de:Selendioxid]] [[ko:이산화 셀레늄]] [[it:Diossido di selenio]] [[ja:二酸化セレン]] [[fi:Seleenidioksidi]] [[zh:二氧化硒]]