HOI - Hypoiodous Acid

What is Hypoiodous Acid?

Hypoiodous acid is a greenish-yellow solution with the chemical formula HOI. Hypoiodous Acid is an aqueous inorganic compound. Iodine acts as a catalyst reacts with hydroxyoxidanium ion to form hypoiodous acid. It is also formed along with iodide ions by dissolving iodine in dilute alkali or by action of mercuric oxide upon iodine and water. Hypoiodous Acid is a volatile iodine species neither elemental nor organic, which has been found in steam/air atmospheres.

Other names – Oxidoiodine


Hypoiodous Acid

Conjugate base


Molecular Weight/ Molar Mass

143.89 g/mol

Hydrogen Bond Donor


Hydrogen Bond Acceptor


Chemical Formula


Hypoiodous Acid Synthesis – HOI

When iodine reacts with cold and dilute sodium hydroxide solution sodium hypoiodite is formed which undergoes hydrolysis to give hypoiodous acid.

  • 2NaOH + I2 → NaIO + NaI + H2O
  • NaIO + H2O → NaOH + HOI

Another reaction possible is

  • NaOH + I2 → HOI + NaI

Hypoiodous Acid Structure – HOI

Hypoiodous Acid Structure

Physical Properties of Hypoiodous Acid – HOI


No odour


Greenish-yellow solution

Covalently-Bonded Unit


Heavy Atom Count




Solubility in water

Soluble in water

Uses of Hypoiodous Acid – HOI

  • Used as a strong oxidizing agent and is used in rocket fuels and as an insulator.
  • Used as an active agents in microbial destruction and the major iodine compounds used for sanitizing are iodophors, alcohol-iodine solutions, and aqueous iodine solutions.
  • Used in atmospheric samplers so as to explain the abnormally high organic fractions reported by other investigators.
  • Used as a source of ‘OH radicals.
  • Used to eliminate chloramines from swimming pool water to avoid the build up of eye irritants.

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