Antimony trioxide

Antimony trioxide
IUPAC name Antimony(III) oxide
Other names Antimony sesquioxide Antimonous oxide Flowers of Antimony oxo-oxostibanyloxystibane
Identifiers
CAS number	1309-64-4 Y
ChemSpider	25727 Y
UNII	P217481X5E Y
KEGG	C19192 Y
RTECS number	CC5650000
Jmol-3D images	Image 1
SMILES O=[Sb]O[Sb]=O
InChI InChI=1S/3O.2Sb Y Key: ADCOVFLJGNWWNZ-UHFFFAOYSA-N Y InChI=1/3O.2Sb/rO3Sb2/c1-4-3-5-2 Key: ADCOVFLJGNWWNZ-VTKDZCJOAA
Properties
Molecular formula	Sb2O3
Molar mass	291.52 g/mol
Appearance	white solid
Density	5.2 g/cm3, α-form
Melting point	656 °C
Boiling point	1425 °C (sublimes)
Solubility in water	1.21 mg/100 mL (0 °C) 1.80 mg/100 mL (20 °C) 8.20 mg/100 mL (100 °C), with hydrolysis
Solubility	insoluble
Refractive index (nD)	2.087
Structure
Crystal structure	cubic (α)<570 °C orthorhombic (β) >570 °C
Coordination geometry	pyramidal
Dipole moment	zero
Hazards
MSDS	External MSDS
EU classification	Harmful (Xn) Carc. Cat. 3
R-phrases	R40
S-phrases	(S2), S22, S36/37
NFPA 704	0 2 0
LD50	7000 mg/kg, oral (rat)
Related compounds
Other anions	Antimony trisulfide
Other cations	Arsenic trioxide Bismuth trioxide
Related compounds	Diantimony tetraoxide Antimony pentoxide
Supplementary data page
Structure and properties	n, εr, etc.
Thermodynamic data	Phase behaviour Solid, liquid, gas
Spectral data	UV, IR, NMR, MS
Y (verify) (what is: Y/N?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Antimony trioxide is the inorganic compound with the formula Sb₂O₃. It is the most important commercial compound of antimony. It is found in nature as the minerals valentinite and senarmontite.^[1] Like most polymeric oxides, Sb₂O₃ dissolves in aqueous solutions only with hydrolysis.

Production and properties

Global production of antimony trioxide in 2005 was 120,000 tonnes, an increase from 112,600 tonnes in 2002. China produces the largest share (47 %) followed by US/Mexico (22 %), Europe (17 %), Japan (10 %) and South Africa (2 %) and other countries (2%).^[2]

Antimony trioxide is mainly produced via the smelting of stibnite ore, which is oxidised to crude Sb₂O₃ using furnaces operating at approximately 850 to 1,000 °C. The transformation is described as follows:

2 Sb₂S₃ + 9 O₂ → 2 Sb₂O₃ + 6 SO₂

Crude Sb₂O₃ is purified by sublimation, which allows it to be separated from the more volatile arsenic trioxide. This step is relevant because antimony ores commonly contain significant amounts of arsenic.

Antimony oxide is also obtained via antimony trichloride, which can be obtained from stibnite.

2 Sb₂S₃ + 3 CaCl₂ + 6 O₂ → 4 SbCl₃ + 3 CaSO₄

After fractional distillation to separate it from arsenic trichloride, SbCl₃ can be hydrolyzed to the oxide:

2 SbCl₃ + 3 H₂O → Sb₂O₃ + 6 HCl

Intermediates in the hydrolysis include the oxychlorides SbOCl and Sb₄O₅Cl₂.

Although impractical for commercial purposes, Sb₂O₃ can be prepared by burning elemental antimony in air:

4 Sb + 3 O₂ → 2 Sb₂O₃

Properties

Antimony trioxide is an amphoteric oxide, dissolving in alkaline solution to give antimonites and in acid solution to given a range of polyantimonous acids. It can be readily oxidized to antimony pentoxide and related antimony(V) compounds, but it is also easily reduced to antimony, sometimes with production of stibine.

Structure

The structure of Sb₂O₃ depends on the temperature of the sample. Dimeric Sb₄O₆ is the high temperature (1560 °C) gas.^[3] Sb₄O₆ molecules are bicyclic cages, similar to the related oxide of phosphorus(III), phosphorus trioxide.^[4] The cage structure is retained in a solid that crystallizes in a cubic habit. The Sb-O distance is 197.7 pm and the O-Sb-O angle of 95.6°.^[5] This form exists in nature as the mineral senarmontite.^[4] Below 606 °C, the more stable form is orthorhombic, consisting of pairs -Sb-O-Sb-O- chains that are linked by oxide bridges between the Sb centers. This form exists in nature as the mineral valentinite.^[4]

Sb4O6	senarmontite	valentinite

Uses

The annual consumption of antimony trioxide in the United States and Europe is approximately 10,000 and 25,000 tonnes, respectively. The main application is for flame retardants in combination with halogenated materials. The combination of the halides and the antimony being key to the flame-retardant action for polymers, helping to form less flammable chars. Such flame retardants are found in electrical apparatus, textiles, leather, and coatings.^[6]

Other applications:

• Antimony trioxide is an opacifying agent for glasses, ceramics and enamels.
• Some specialty pigments contain antimony.
• Antimony trioxide is a useful catalyst in the production of polyethylene terephthalate (PET plastic) and the vulcanization of rubber.
• Flame retardant for textiles, leather, polymers, and coatings.

Safety

The toxicity of Sb₂O₃ is topical because it is a likely byproduct of the combustion of some materials "fireproofed" with antimony compounds. The oxides of arsenic, antimony, and bismuth are comparable in their toxicity, but their volatilities differ widely. Antimony trioxide has suspected carcinogenic potential for humans.^[6] Its TLV is 0.5 mg/m³, as for most antimony compounds.^[7]

References

1. ^ Greenwood, N. N.; & Earnshaw, A. (1997). Chemistry of the Elements (2nd Edn.), Oxford:Butterworth-Heinemann. ISBN 0-7506-3365-4.
2. ^ http://ecb.jrc.ec.europa.eu/DOCUMENTS/Existing-Chemicals/RISK_ASSESSMENT/REPORT/datreport415.pdf Risk Assessment of Diantimony Trioxide
3. ^ Egon Wiberg, Arnold Frederick Holleman (2001) Inorganic Chemistry, Elsevier ISBN 0123526515
4. ^ ^{a b c} Wells, A.F. (1984) Structural Inorganic Chemistry, Oxford: Clarendon Press. ISBN 0-19-855370-6.
5. ^ C. Svensson “Refinement of the crystal structure of cubic antimony trioxide, Sb₂O₃” Acta Crystographica, 1975, volume B31, pp. 2016-2018. doi:10.1107/S0567740875006759
6. ^ ^{a b} Sabina C. Grund, Kunibert Hanusch, Hans J. Breunig, Hans Uwe Wolf “Antimony and Antimony Compounds” in Ullmann's Encyclopedia of Industrial Chemistry 2006, Wiley-VCH, Weinheim. doi: 10.1002/14356007.a03_055.pub2
7. ^ Inhalation Developmental Toxicity Studies In Rats With Antimony Trioxide (Sb2O3). Newton PE; Schroeder RE; Zwick L; Serex T; Toxicologist 2004 Mar;78(1-S):38

Further reading

• Institut national de recherche et de sécurité (INRS), Fiche toxicologique nº 198 : Trioxyde de diantimoine, 1992.
• The Oxide Handbook, G.V. Samsonov, 1981, 2nd ed. IFI/Plenum, ISBN 0-306-65177-7

External links

• International Chemical Safety Card 0012
• ESIS: European chemical Substances Information System
• Antimony Market And Price
• Société industrielle et chimique de l'Aisne