Ammoniumiodid

Ammonium iodide, with the chemical formula NH4I, is an inorganic salt composed of ammonium cations (NH4+) and iodide anions (I−). It forms a white crystalline solid that is highly soluble in water and is typically hygroscopic, tending to absorb moisture from the air.

Preparation and occurrence

Ammonium iodide can be prepared by the reaction of ammonia with hydroiodic acid: NH3 + HI → NH4I. It may also be produced by neutralization of iodide sources with ammonium salts under appropriate conditions. In aqueous solution, it behaves as a conventional salt of a weak base (ammonia) and a strong acid (hydroiodic acid).

Properties and reactions

On heating, ammonium iodide undergoes thermal decomposition to ammonia and hydrogen iodide: NH4I → NH3 + HI. Hydrogen iodide can further decompose to hydrogen and iodine at higher temperatures: 2 HI → H2 + I2. In the presence of oxidizing agents, iodide can be oxidized to iodine, releasing oxidized iodine species. In solution, NH4I remains a source of iodide ions (I−), which can participate in various iodination reactions in organic synthesis.

Applications

NH4I is used as a source of iodide in chemical synthesis and as a laboratory reagent for preparing and manipulating iodide-containing compounds. It can serve as a convenient salt for introducing iodide into reactions and for generating iodine-containing intermediates under controlled conditions.

Safety

Ammonium iodide is an irritant and should be handled with appropriate care. Heating or strong oxidation can release ammonia or iodine-containing vapors. It should be stored in a dry, well-ventilated area away from incompatible oxidizers, in properly labeled containers.