Sodium iodide


Sodium iodide is an ionic compound formed from the chemical reaction of sodium metal and iodine. Under standard conditions, it is a white, water-soluble solid comprising a 1:1 mix of sodium cations and iodide anions in a crystal lattice. It is used mainly as a nutritional supplement and in organic chemistry. It is produced industrially as the salt formed when acidic iodides react with sodium hydroxide. It is a chaotropic salt.

Uses

Food supplement

Sodium iodide, as well as potassium iodide, is commonly used to treat and prevent iodine deficiency. Iodized table salt contains 10 ppm iodide.

Organic synthesis

Sodium iodide is used for conversion of alkyl chlorides into alkyl iodides. This method, the Finkelstein reaction, relies on the insolubility of sodium chloride in acetone to drive the reaction:

Nuclear medicine

Some radioactive iodide salts of sodium, including Na125I and Na131I, have radiopharmaceutical uses, such as in the treatment of thyroid cancer and hyperthyroidism or as radiolabeling tracers in imaging.

Thallium-doped NaI(Tl) scintillators

Sodium iodide activated with thallium, NaI, when subjected to ionizing radiation, emits photons and is used in scintillation detectors, traditionally in nuclear medicine, geophysics, nuclear physics, and environmental measurements. NaI is the most widely used scintillation material. The crystals are usually coupled with a photomultiplier tube, in a hermetically sealed assembly, as sodium iodide is hygroscopic. Fine-tuning of some parameters can be achieved by varying the conditions of the crystal growth. Crystals with a higher level of are used in X-ray detectors with high spectrometric quality. Sodium iodide can be used both as single crystals and as polycrystals for this purpose. The wavelength of maximum emission is 415 nm.

Solubility data

Sodium iodide exhibits high solubility in some organic solvents, unlike sodium chloride or even bromide:
SolventSolubility of NaI
H2O1842
Liquid ammonia1620
Liquid sulfur dioxide150
Methanol625–830
Formic acid618
Acetonitrile249
Acetone504
Formamide570–850
Acetamide323
Dimethylformamide37–64
Dichloromethane0.09

Stability

Iodides are detectably oxidized by atmospheric oxygen to molecular iodine. I2 and I− complex to form the triiodide complex, which has a yellow color, unlike the white color of sodium iodide. Water accelerates the oxidation process, and iodide can also produce I2 by photooxidation, therefore for maximum stability sodium iodide should be stored under dark, low temperature, low humidity conditions.

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