Hydriodic Acid (57%) TCI H1221

Hydriodic Acid (57%) is a solution of hydrogen iodide in water, recognized as one of the strongest mineral acids and, at the same time, a highly effective reducing agent. The combination of these two properties makes it a specialist reagent in organic synthesis laboratories, particularly when a stubborn ether linkage must be cleaved or a functional group reduced that other reagents cannot handle easily. In practice, HI also serves as a source of highly concentrated iodide ion for the preparation of alkyl iodides, which are subsequently employed as alkylating agents in later synthetic steps.

The principal characteristics behind its selection are an acid strength that surpasses both HBr and HCl, together with a reducing power of the iodide ion that is far greater than that of the other halides. The relatively weak H–I bond allows the proton to be released readily, while iodide is the best nucleophile among the halides, so substitution reactions proceed rapidly. As a consequence, this solution is sensitive to air and light: slow oxidation liberates free iodine, which darkens the liquid. The 57% preparation is the azeotropic concentration commonly traded and makes stoichiometric calculation at the bench straightforward.

In Indonesia, this reagent is used in a limited way, primarily within organic synthesis and research settings where its specific reactivity is genuinely required. Laboratories that select it typically do so for demethylation and reduction work that cannot be accomplished with milder acids. Because the material darkens on exposure to air and light, Indonesian users generally plan their consumption around the working life of an opened bottle rather than holding large quantities in reserve.

• Ether cleavage and demethylation — the strong acidity combined with the high nucleophilicity of iodide breaks stubborn ether linkages that resist HBr and HCl under comparable conditions.
• Preparation of alkyl iodides — as a concentrated source of iodide ion, HI converts alcohols and related substrates into alkyl iodides for use as alkylating agents in subsequent synthetic steps.
• Reduction of resistant functional groups — the reducing power of the iodide ion greatly exceeds that of other halides, allowing reductions that are not easily achieved with alternative reagents.
• Nucleophilic substitution chemistry — because iodide is the best nucleophile among the halides, substitution reactions run rapidly, making this reagent useful where reaction rate is limiting.
• Strong-acid applications in synthesis — the weak H–I bond releases the proton readily, giving an acid strength beyond that of HBr and HCl for demanding acid-catalysed transformations.

• Concentration: 57% aqueous solution (azeotropic composition)

Store the bottle tightly closed, protected from light and air, since slow oxidation liberates free iodine and progressively darkens the solution. Amber or otherwise light-shielded glass containers with acid-resistant closures are appropriate; keep the container upright in a ventilated cabinet designated for corrosive liquids and away from oxidising agents and incompatible bases. Handle and dispense inside a fume hood while wearing chemical splash goggles, acid-resistant gloves, and a laboratory coat. Because the material is both a strong acid and a strong reducing agent, avoid skin and eye contact, prepare spill neutralisation materials before opening, and follow the manufacturer's safety data sheet for the specific batch in use.

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