Iodine pentoxide is the chemical compound with the formula I<sub>2</sub>O<sub>5</sub>. This iodine oxide is the anhydride of iodic acid, and one of the few iodine oxides that is stable. It is produced by dehydrating iodic acid at 200 ðC in a stream of dry air:
This dehydration proceeds through the hydrogen bonded adduct (HI<sub>3</sub>O<sub>8</sub>), which is present in commercial "HIO<sub>3</sub>."
I<sub>2</sub>O<sub>5</sub> is bent with an IâÂÂOâÂÂI angle of 139.2ð, but the molecule has no mirror plane so its symmetry is C<sub>2</sub> rather than C<sub>2v</sub>. The terminal IâÂÂO distances are around 1.80 àand the bridging IâÂÂO distances are around 1.95 à.
Iodine pentoxide easily oxidises carbon monoxide to carbon dioxide at room temperature:
This reaction can be used to analyze the concentration of CO in a gaseous sample.
I<sub>2</sub>O<sub>5</sub> forms iodyl salts, [IO<sub>2</sub><sup>+</sup>], with SO<sub>3</sub> and S<sub>2</sub>O<sub>6</sub>F<sub>2</sub>, but iodosyl salts, [IO<sup>+</sup>], with concentrated sulfuric acid.
Iodine pentoxide decomposes to iodine (vapor) and oxygen when heated to about 350 ðC.