Selenium dioxide

Selenium dioxide
	Selenium dioxide
	Ball-and-stick model of a chain in crystalline selenium dioxide
	Crystals of selenium dioxide
Names
	Other names Selenium(IV) oxide; Selenous anhydride
Identifiers
CAS Number	7446-08-4 ;
3D model (JSmol)	monomer: Interactive image; polymer: Interactive image;
ChEMBL	ChEMBL3183452;
ChemSpider	22440 ;
ECHA InfoCard	100.028.358
EC Number	231-194-7;
PubChem CID	24007;
RTECS number	VS8575000;
UNII	9N3UK29E57 ;
UN number	3283
CompTox Dashboard (EPA)	DTXSID4021264 ;
	InChI InChI=1S/O2Se/c1-3-2 Key: JPJALAQPGMAKDF-UHFFFAOYSA-N ; InChI=1/O2Se/c1-3-2 Key: JPJALAQPGMAKDF-UHFFFAOYAQ;
	SMILES monomer: O=[Se]=O; polymer: O[Se](=O)O[Se](=O)O[Se](=O)O[Se](=O)O[Se](=O)O[Se](=O)O[Se](=O)O[Se](=O)O[Se](=O)O[Se](=O)O[Se](=O)O[Se](=O)O[Se](=O)O[Se](=O)O[Se](=O)O;
Properties
Chemical formula	SeO2
Molar mass	110.96 g/mol
Appearance	White crystals, turn slightly pink with trace decomposition
Odor	rotten radishes
Density	3.954 g/cm3, solid
Melting point	340 °C (644 °F; 613 K) (sealed tube)
Boiling point	350 °C (662 °F; 623 K) subl.
Solubility in water	38.4 g/100 mL (20 °C) ; 39.5 g/100 ml (25 °C) ; 82.5 g/100 mL (65 °C)
Solubility	soluble in benzene
Solubility in ethanol	6.7 g/100 mL (15 °C)
Solubility in acetone	4.4 g/100 mL (15 °C)
Solubility in acetic acid	1.11 g/100 mL (14 °C)
Solubility in methanol	10.16 g/100 mL (12 °C)
Vapor pressure	1.65 kPa (70 °C)
Acidity (pKa)	2.62; 8.32
Magnetic susceptibility (χ)	−27.2·10−6 cm3/mol
Refractive index (nD)	> 1.76
Structure
Crystal structure	see text
Coordination geometry	trigonal (Se)
Hazards
	Occupational safety and health (OHS/OSH):
Main hazards	Toxic by ingestion and inhalation
	GHS labelling:
Pictograms
Signal word	Danger
Hazard statements	H301, H331, H373, H410
Precautionary statements	P260, P261, P264, P270, P271, P273, P301+P310, P304+P340, P311, P314, P321, P330, P391, P403+P233, P405, P501
NFPA 704 (fire diamond)	3 0 0
Flash point	Non-flammable
	Lethal dose or concentration (LD, LC):
LCLo (lowest published)	5890 mg/m3 (rabbit, 20 min); 6590 mg/m3 (goat, 10 min); 6590 mg/m3 (sheep, 10 min)
Safety data sheet (SDS)	ICSC 0946
Related compounds
Other anions	Selenium disulfide
Other cations	Ozone; Sulfur dioxide; Tellurium dioxide
Related selenium oxides	Selenium trioxide
Related compounds	Selenous acid
	Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). verify (what is ?) Infobox references

Selenium dioxide is the chemical compound with the formula SeO₂. This colorless solid is one of the most frequently encountered compounds of selenium. It is used in making specialized glasses as well as a reagent in organic chemistry.^[4]

Properties

Solid SeO₂ is a one-dimensional polymer, the chain consisting of alternating selenium and oxygen atoms. Each Se atom is pyramidal and bears a terminal oxide group. The bridging Se-O bond lengths are 179 pm and the terminal Se-O distance is 162 pm.^[5] The relative stereochemistry at Se alternates along the polymer chain (syndiotactic). In the gas phase selenium dioxide is present as dimers and other oligomeric species, at higher temperatures it is monomeric.^[6] The monomeric form adopts a bent structure very similar to that of sulfur dioxide with a bond length of 161 pm.^[6] The dimeric form has been isolated in a low temperature argon matrix and vibrational spectra indicate that it has a centrosymmetric chair form.^[5] Dissolution of SeO₂ in selenium oxydichloride give the trimer [Se(O)O]₃.^[6] Monomeric SeO₂ is a polar molecule, with the dipole moment of 2.62 D ^[7] pointed from the midpoint of the two oxygen atoms to the selenium atom.

The solid sublimes readily. At very low concentrations the vapour has a revolting odour, resembling decayed horseradishes. At higher concentrations the vapour has an odour resembling horseradish sauce and can burn the nose and throat on inhalation. Whereas SO₂ tends to be molecular and SeO₂ is a one-dimensional chain, TeO₂ is a cross-linked polymer.^[5]

SeO₂ is considered an acidic oxide: it dissolves in water to form selenous acid.^[6] Often the terms selenous acid and selenium dioxide are used interchangeably. It reacts with base to form selenite salts containing the SeO²⁻
₃ anion. For example, reaction with sodium hydroxide produces sodium selenite:

SeO₂ + 2 NaOH → Na₂SeO₃ + H₂O

Preparation

Selenium dioxide is prepared by oxidation of selenium by burning in air or by reaction with nitric acid or hydrogen peroxide, but perhaps the most convenient preparation is by the dehydration of selenous acid.

2 H₂O₂ + Se → SeO₂ + 2 H₂O

3 Se + 4 HNO₃ + H₂O → 3 H₂SeO₃ + 4 NO

H₂SeO₃ ⇌ SeO₂ + H₂O

Occurrence

The natural form of selenium dioxide, downeyite, is a very rare mineral. It is only found at a small number of burning coal banks, where it forms around vents created from escaping gasses.^[8]

Uses

Organic synthesis

SeO₂ is an important reagent in organic synthesis. Oxidation of paraldehyde (acetaldehyde trimer) with SeO₂ gives glyoxal^[9] and the oxidation of cyclohexanone gives 1,2-cyclohexanedione.^[10] The selenium starting material is reduced to selenium, and precipitates as a red amorphous solid which can easily be filtered off.^[10] This type of reaction is called a Riley oxidation. It is also renowned as a reagent for allylic oxidation,^[11] a reaction that entails the following conversion

This can be described more generally as;

R₂C=CR'-CHR"₂ + [O] → R₂C=CR'-C(OH)R"₂

where R, R', R" may be alkyl or aryl substituents.

Selenium dioxide can also be used to synthesize 1,2,3-selenadiazoles from acylated hydrazone derivatives.^[12]

As a colorant

Selenium dioxide imparts a red colour to glass. It is used in small quantities to counteract the colour due to iron 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 cold-bluing solutions.

It was also used as a toner in photographic developing.

Safety

Selenium is an essential element, but ingestion of more than 5 mg/day leads to nonspecific symptoms.^[13]

References

^ "Safety data sheet: Selenium dioxide" (PDF). integrachem.com. 27 March 2015. Retrieved 2022-12-02.
^ "Selenium dioxide safety and hazards". pubchem.ncbi.nlm.nih.gov. Retrieved 2022-12-02.
^ "Selenium compounds (as Se)". Immediately Dangerous to Life or Health Concentrations (IDLH). National Institute for Occupational Safety and Health (NIOSH).
^ Hoekstra, William J.; Fairlamb, Ian J. S.; Giroux, Simon; Chen, Yuzhong (2017). "Selenium(IV) Oxide". Encyclopedia of Reagents for Organic Synthesis. pp. 1–12. doi:10.1002/047084289X.rs008.pub3. ISBN 978-0-470-84289-8.
^ ^a ^b ^c Handbook of Chalcogen Chemistry: New Perspectives in Sulfur, Selenium and Tellurium, Franceso A. Devillanova, Royal Society of Chemistry, 2007, ISBN 9780854043668
^ ^a ^b ^c ^d Holleman, Arnold Frederik; Wiberg, Egon (2001), Wiberg, Nils (ed.), Inorganic Chemistry, translated by Eagleson, Mary; Brewer, William, San Diego/Berlin: Academic Press/De Gruyter, ISBN 0-12-352651-5
^ Takeo, Harutoshi; Hirota, Eizi; Morino, Yonezo (1972). "Third-order potential constants and dipole moment of SeO2 by microwave spectroscopy". Journal of Molecular Spectroscopy. 41 (2): 420–422. Bibcode:1972JMoSp..41..420T. doi:10.1016/0022-2852(72)90216-0. ISSN 0022-2852.
^ Finkelman, Robert B.; Mrose, Mary E. (1977). "Downeyite, the first verified natural occurrence of SeO₂" (PDF). American Mineralogist. 62: 316–320.
^ Ronzio, A. R.; Waugh, T. D. (1955). "Glyoxal Bisulfite". Organic Syntheses{{cite journal}}: CS1 maint: multiple names: authors list (link); Collected Volumes, vol. 3, p. 438.
^ ^a ^b Hach, C. C. Banks, C. V.; Diehl, H. (1963). "1,2-Cyclohexanedione Dioxime". Organic Syntheses{{cite journal}}: CS1 maint: multiple names: authors list (link); Collected Volumes, vol. 4, p. 229.
^ Coxon, J. M.; Dansted, E.; Hartshorn, M. P. (1977). "Allylic Oxidation with Hydrogen Peroxide–Selenium Dioxide: trans-Pinocarveol". Organic Syntheses. 56: 25. doi:10.15227/orgsyn.056.0025{{cite journal}}: CS1 maint: multiple names: authors list (link).
^ Lalezari, Iraj; Shafiee, Abbas; Yalpani, Mohamed (1969). "A novel synthesis of selenium heterocycles: substituted 1,2,3-selenadiazoles". Tetrahedron Letters. 10 (58): 5105–5106. doi:10.1016/S0040-4039(01)88895-X.
^ Bernd E. Langner "Selenium and Selenium Compounds" in Ullmann's Encyclopedia of Industrial Chemistry, 2005, Wiley-VCH, Weinheim. doi:10.1002/14356007.a23_525

External links

International Chemical Safety Card 0946

[msds-1] "Safety data sheet: Selenium dioxide" (PDF). integrachem.com. 27 March 2015. Retrieved 2022-12-02.

[2] "Selenium dioxide safety and hazards". pubchem.ncbi.nlm.nih.gov. Retrieved 2022-12-02.

[3] "Selenium compounds (as Se)". Immediately Dangerous to Life or Health Concentrations (IDLH). National Institute for Occupational Safety and Health (NIOSH).

[4] Hoekstra, William J.; Fairlamb, Ian J. S.; Giroux, Simon; Chen, Yuzhong (2017). "Selenium(IV) Oxide". Encyclopedia of Reagents for Organic Synthesis. pp. 1–12. doi:10.1002/047084289X.rs008.pub3. ISBN 978-0-470-84289-8.

[Devillanova-5] Handbook of Chalcogen Chemistry: New Perspectives in Sulfur, Selenium and Tellurium, Franceso A. Devillanova, Royal Society of Chemistry, 2007, ISBN 9780854043668

[Holl&Wib-6] Holleman, Arnold Frederik; Wiberg, Egon (2001), Wiberg, Nils (ed.), Inorganic Chemistry, translated by Eagleson, Mary; Brewer, William, San Diego/Berlin: Academic Press/De Gruyter, ISBN 0-12-352651-5

[TakeoHirota1972-7] Takeo, Harutoshi; Hirota, Eizi; Morino, Yonezo (1972). "Third-order potential constants and dipole moment of SeO2 by microwave spectroscopy". Journal of Molecular Spectroscopy. 41 (2): 420–422. Bibcode:1972JMoSp..41..420T. doi:10.1016/0022-2852(72)90216-0. ISSN 0022-2852.

[8] Finkelman, Robert B.; Mrose, Mary E. (1977). "Downeyite, the first verified natural occurrence of SeO₂" (PDF). American Mineralogist. 62: 316–320.

[9] Ronzio, A. R.; Waugh, T. D. (1955). "Glyoxal Bisulfite". Organic Syntheses{{cite journal}}: CS1 maint: multiple names: authors list (link); Collected Volumes, vol. 3, p. 438.

[Hachorgsyn-10] Hach, C. C. Banks, C. V.; Diehl, H. (1963). "1,2-Cyclohexanedione Dioxime". Organic Syntheses{{cite journal}}: CS1 maint: multiple names: authors list (link); Collected Volumes, vol. 4, p. 229.

[11] Coxon, J. M.; Dansted, E.; Hartshorn, M. P. (1977). "Allylic Oxidation with Hydrogen Peroxide–Selenium Dioxide: trans-Pinocarveol". Organic Syntheses. 56: 25. doi:10.15227/orgsyn.056.0025{{cite journal}}: CS1 maint: multiple names: authors list (link).

[12] Lalezari, Iraj; Shafiee, Abbas; Yalpani, Mohamed (1969). "A novel synthesis of selenium heterocycles: substituted 1,2,3-selenadiazoles". Tetrahedron Letters. 10 (58): 5105–5106. doi:10.1016/S0040-4039(01)88895-X.

[13] Bernd E. Langner "Selenium and Selenium Compounds" in Ullmann's Encyclopedia of Industrial Chemistry, 2005, Wiley-VCH, Weinheim. doi:10.1002/14356007.a23_525

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