Iodine pentoxide

Iodine pentoxide is the chemical compound with the formula I₂O₅. This iodine oxide is the anhydride of iodic acid, and the only stable oxide of iodine. It is produced by dehydrating iodic acid at 200 °C in a stream of dry air:[1]

2HIO₃ → I₂O₅ + H₂O

Iodine pentoxide

Names
IUPAC name Iodine pentoxide
Other names Iodine(V) oxide Iodic anhydride
Identifiers
CAS Number	12029-98-0
3D model (JSmol)	Interactive image
ChEBI	CHEBI:29914
ChemSpider	140179
ECHA InfoCard	100.031.569
PubChem CID	159402
UNII	UPU35C0Q0N
CompTox Dashboard (EPA)	DTXSID40923305
InChI InChI=1S/I2O5/c3-1(4)7-2(5)6 Key: BIZCJSDBWZTASZ-UHFFFAOYSA-N InChI=1/I2O5/c3-1(4)7-2(5)6 Key: BIZCJSDBWZTASZ-UHFFFAOYAR
SMILES O=I(=O)OI(=O)=O
Properties
Chemical formula	I 2O 5
Molar mass	333.81 g/mol
Appearance	white crystalline solid[1] hygroscopic
Density	4.980 g/cm^3[1]
Melting point	300 °C (572 °F; 573 K)[2] (decomposes)
Solubility	soluble in water and nitric acid; insoluble in ethanol, ether and CS2
Magnetic susceptibility (χ)	−79.4·10^−6 cm^3/mol
Hazards
Main hazards	oxidizer
NFPA 704 (fire diamond)	0 3 0 OX
Related compounds
Other anions	iodine pentafluoride
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Structure

I₂O₅ is bent with an I–O–I angle of 139.2°, but the molecule has no mirror plane so its symmetry is C₂ rather than C_2v. The terminal I–O distances are around 1.80 Å and the bridging I–O distances are around 1.95 Å.[3]

Reactions

Iodine pentoxide easily oxidises carbon monoxide to carbon dioxide at room temperature:

5 CO + I₂O₅ → I₂ + 5 CO₂

This reaction can be used to analyze the concentration of CO in a gaseous sample.

I₂O₅ forms iodyl salts, [IO₂⁺], with SO₃ and S₂O₆F₂, but iodosyl salts, [IO⁺], with concentrated sulfuric acid.

Iodine pentoxide decomposes to iodine (vapor) and oxygen when heated to about 350 °C.[4]

References

1. Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. pp. 851–852. ISBN 978-0-08-037941-8.
2. Patnaik, P. (2002). Handbook of Inorganic Chemicals. McGraw-Hill. ISBN 0-07-049439-8.
3. Selte, K.; Kjekshus, A. (1970). "Iodine Oxides: Part III. The Crystal Structure of I₂O₅" (pdf). Acta Chemica Scandinavica. 24 (6): 1912–1924. doi:10.3891/acta.chem.scand.24-1912.
4. G. Baxter and G. Tilley, "A Revision of the Atomic Weights of Iodine and Silver," The Chemical News and Journal of Industrial Science; Volumes 99-100, Royal Society Anniversary Meeting, December 3, 1909, p. 276. (Google Books)