Iodine pentoxide

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Iodine pentoxide
IUPAC name
Iodine pentoxide
Preferred IUPAC name
Iodine pentoxide
Systematic IUPAC name
Iodine pentoxide
Other names
Diiodine pentoxide
Iodic anhydride
Iodine pentaoxide
Iodine(V) oxide
Iodyl iodate
Molar mass 333.81 g/mol
Appearance White solid
Odor Odorless (pure)
Iodine (impure)
Density 5.08 g/cm3 (20 °C)
Melting point 350 °C (662 °F; 623 K) (decomposes)
Boiling point Decomposes
187 g/100 ml (hydrolysis)
Solubility Soluble in nitric acid
Insoluble in acetonitrile, carbon disulfide, chloroform, diethyl ether, ethanol
Vapor pressure ~0 mmHg
Safety data sheet Sigma-Aldrich
Flash point Non-flammable
Related compounds
Related compounds
Dichlorine heptoxide
Dibromine pentoxide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

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.



Iodine pentoxide hydrolyzes in water to form iodic acid.[1]

I2O5 + H2O → 2 HIO3

Iodine pentoxide easily oxidizes carbon monoxide to carbon dioxide at room temperature. Conc. sulfuric acid may be needed to activate the reaction.

5 CO + I2O5 → I2 + 5 CO2

This reaction, called Ditte's reaction, can be used to analyze the concentration of CO in a gaseous sample.

Iodine pentoxide will react with hydrogen sulfide, forming sulfur dioxide:

3 I2O5 + 5 H2S → 3 I2 + 5 SO2 + 5 H2O

Elemental sulfur will also oxidize to sulfur dioxide, though strong heat is required to initiate the reaction.

2 I2O5 + 5 S → 5 I2 + 2 SO2

A mixture of carbon and iodine pentoxide will ignite with a drop of conc. sulfuric acid is added to it.

Iodine pentoxide reacts violently with hydrazine at standard conditions, producing HI.[2]

Mixing iodine pentoxide with lithium borohydride is sufficient to ignite said mixture.

Iodine pentoxide will oxidize hydrogen chloride aka hydrochloric acid to chlorine, while forming tetrachloroiodic acid.

I2O5 + 12 HCl → 2 HICl4 + 2 Cl2 + 5 H2O

I2O5 forms iodyl salts, [IO2+], with sulfur trioxide and bis(fluorosulfuryl)peroxide, but iodosyl salts, [IO+], with concentrated sulfuric acid.


Iodine pentoxide is a white dense solid, that readily hydrolyzes in water. The pure compound is odorless, but exposure to impurities will release minute amounts of elemental iodine, giving the sample a faint iodine-like odor.


Iodine pentoxide can be bought from chemical suppliers.


Iodine pentoxide is produced by dehydrating iodic acid at 200 °C in a stream of dry air:

2 HIO3 → I2O5 + H2O

Heating metaperiodic acid to around 150 °C gives iodine pentoxide (I2O5) rather than the expected anhydride diiodine heptoxide (I2O7), while releasing oxygen as byproduct.[3]

2 HIO4 → I2O5 + H2O + O2


  • Detection of carbon monoxide
  • Make Al-I2O5 thermite



Iodine pentoxide is a powerful oxidizer and may ignite combustible materials on contact.


In closed airtight bottles.


Should be reduced with sodium thiosulfate or some other reducing agent.


  1. IODINE Its Properties and Technical Applications, CHILEAN IODINE EDUCATIONAL BUREAU, INC., 120 Broadway, New York 5, New York, 1951

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