Periodic acid (HIO4, H5IO6) — properties, reactions and uses

Properties and forms

Orthoperiodic acid (H5IO6) is a hydrated form in which iodine is surrounded by oxygen atoms and bound to hydrogen through hydroxyl groups; heating or dehydration can produce the anhydrous metaperiodic form HIO4. Periodic acids and periodate salts are usually colorless and crystalline, soluble to varying degrees in water, and tend to be hygroscopic. In solution they can equilibrate between different protonation and hydration states depending on pH.

Reactions and uses

Periodic acid is best known for its ability to cleave vicinal diols (adjacent two‑carbon hydroxyl groups) to give carbonyl compounds — a transformation widely used in organic synthesis called periodate oxidation or the Malaprade reaction. In biological and histological applications, periodic acid is used to oxidize sugar residues to aldehydes prior to staining, as in the periodic acid–Schiff (PAS) technique for detecting polysaccharides and glycoproteins. Analytical chemists also use periodate reagents to probe carbohydrate structure and to selectively modify biomolecules.

• Oxidative cleavage of vicinal diols
• Preparation of aldehydes and ketones from glycols
• Histological staining methods (e.g., periodic acid–Schiff)
• Chemical modification and analysis of carbohydrates

Preparation, related compounds and distinctions

Laboratory and industrial routes to periodic acid typically proceed by oxidation of iodate compounds or by controlled electrochemical methods; numerous periodate salts (sodium, potassium, etc.) are more convenient to handle than the free acid. Periodic acids differ from iodic acid (HIO3) by their higher oxygen content and stronger oxidizing behavior. Salts of periodate (for example sodium periodate) retain many of the oxidative properties useful in synthesis.

Safety and handling

Periodic acid is a corrosive oxidizer and should be handled with appropriate protective equipment and under controlled conditions. It can attack organic material and is incompatible with reducing agents and combustibles. Consult material safety data and institutional guidance when storing, diluting, or disposing of periodate reagents.

Further reading and references: general overview at reference page, reagent specifications at technical datasheet, synthetic applications at organic methods, histology protocols at laboratory guide, and safety guidance at safety resource.