Periodic acid

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Periodic acid
Names
IUPAC name
Periodic acid
Other names
Hydrogen periodate
Iodic(VII) acid
Paraperiodic acid
Periodic acid dihydrate (ortho)
Properties
HIO4 (metaperiodic)
H5IO6 (orthoperiodic)
Molar mass 227.941 g/mol (H5IO6)
190.91 g/mol (HIO4)
Appearance Colorless crystals
Odor Odorless
Melting point 128.5 °C (263.3 °F; 401.6 K)
Soluble
Solubility Soluble in alcohols
Hazards
Safety data sheet Sigma-Aldrich (ortho)
Flash point Non-flammable
Related compounds
Related compounds
Perchloric acid
Perbromic acid
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Periodic acid is the highest oxoacid of iodine, in which the iodine exists in oxidation state +7. Like all periodates it can exist in two forms: orthoperiodic acid, with the chemical formula H5IO6 and metaperiodic acid, which has the formula HIO4.

Properties

Chemical

Heating metaperiodic acid to around 150 °C gives iodine pentoxide (I2O5) rather than the expected anhydride diiodine heptoxide (I2O7), while releasing oxygen as byproduct.[1]

2 HIO4 → I2O5 + H2O + O2

Like all periodates periodic acid can be used to cleave various 1,2-difunctional compounds. Most notably periodic acid will cleave vicinal diols into two aldehyde or ketone fragments (Malaprade reaction).

This can be useful in determining the structure of carbohydrates as periodic acid can be used to open saccharide rings. This process is often used in labeling saccharides with fluorescent molecules or other tags such as biotin.

Periodic acid is also used as an oxidising agent of moderate strength.

Physical

Both orthoperiodic and metaperiodic acid are white colorless crystalline solids, very soluble in water.

Availability

Periodic acid, both the ortho- and the meta- forms can be bought from chemical suppliers.

Preparation

Modern industrial scale production involves the oxidation of a solution of sodium iodate under alkaline conditions, either electrochemically on a PbO2 anode, or by treatment with chlorine:[2]

IO
3
+ 6 HO
− 2 eIO5−
6
+ 3 H2O (counter ions omitted for clarity) E° = ;-1.6 V[3]
IO
3
+ 6 HO
+ Cl2IO5−
6
+ 2 Cl + 3 H2O

Orthoperiodic acid can be dehydrated to give metaperiodic acid by heating to 100 °C under reduced pressure.

H5IO6 ⇌ HIO4 + 2 H2O

Metaperiodic acid can also be prepared from various orthoperiodates by treatment with dilute nitric acid.[4]

H5IO6 → HIO4 + 2 H2O

Projects

Handling

Safety

Periodic acid is irritant, corrosive and mildly oxidizer. Proper protection should be worn when handling the compound.

Storage

In closed airtight bottles, away from moisture and reducing agents.

Disposal

Should be neutralized with a base to the safer periodate salts.

References

  1. https://www.bionity.com/en/encyclopedia/Periodic_acid.html
  2. https://www.sciencedirect.com/book/9780750633659/chemistry-of-the-elements?via=ihub=
  3. https://archive.org/details/ost-chemistry-parsons-handbookofelectrochemicalconstants/page/n41/mode/2up
  4. Riley, edited by Georg Brauer; translated by Scripta Technica, Inc. Translation editor Reed F. (1963). Handbook of preparative inorganic chemistry. Volume 1 (2nd ed.). New York, N.Y.: Academic Press. pp. 323–324

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