Sodium iodide

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Sodium iodide
Chemical compound

Sodium iodide (chemical formula NaI) 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 (Na⁺) and iodide anions (I⁻) 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.¹¹ It is a chaotropic salt.

"NaI" redirects here. For other uses, see Nai.

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.¹¹

Organic synthesis

Sodium iodide is used for conversion of alkyl chlorides into alkyl iodides. This method, the Finkelstein reaction,¹³ relies on the insolubility of sodium chloride in acetone to drive the reaction:¹⁴

R–Cl + NaI → R–I + NaCl

Nuclear medicine

Some radioactive iodide salts of sodium, including Na¹²⁵I and Na¹³¹I, have radiopharmaceutical uses for thyroid cancer and hyperthyroidism or as radioactive tracer in imaging (see Isotopes of iodine > Radioiodines I-123, I-124, I-125, and I-131 in medicine and biology).

Thallium-doped NaI(Tl) scintillators

Sodium iodide activated with thallium, NaI(Tl), when subjected to ionizing radiation, emits photons (i.e., scintillate) and is used in scintillation detectors, traditionally in nuclear medicine, geophysics, nuclear physics, and environmental measurements. NaI(Tl) 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 (i.e., radiation hardness, afterglow, transparency) can be achieved by varying the conditions of the crystal growth. Crystals with a higher level of doping 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.

Radiocontrast

António Egas Moniz searched for a radiocontrast agent for cerebral angiography.¹⁶ After experiments on rabbits and dogs he settled upon sodium iodide as the best medium.¹⁶

Solubility data

Sodium iodide exhibits high solubility in some organic solvents, unlike sodium chloride or even bromide:

Solvent	Solubility of NaI (g NaI/kg of solvent at 25 °C)¹⁷
H₂O	1842
Liquid ammonia	1620
Liquid sulfur dioxide	150
Methanol	625–830
Formic acid	618
Acetonitrile	249
Acetone	504¹⁸
Formamide	570–850
Acetamide	323 (41.5 °C)
Dimethylformamide	37–64
Dichloromethane	0.09¹⁹

Stability

Iodides (including sodium iodide) are detectably oxidized by atmospheric oxygen (O₂) to molecular iodine (I₂). 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.

References

1Haynes, p. 4.86
2Seidell, Atherton (1919). Solubilities of inorganic and organic compounds c. 2. D. Van Nostrand Company. p. 655.
3Haynes, p. 5.171
4Miyata, Takeo (1969). "Exciton Structure of NaI and NaBr". Journal of the Physical Society of Japan. 27 (1): 266. Bibcode:1969JPSJ...27..266M. doi:10.1143/JPSJ.27.266.
5Guizzetti, G.; Nosenzo, L.; Reguzzoni, E. (1977). "Optical properties and electronic structure of alkali halides by thermoreflectivity". Physical Review B. 15 (12): 5921–5926. Bibcode:1977PhRvB..15.5921G. doi:10.1103/PhysRevB.15.5921.
6Haynes, p. 4.130
7Haynes, p. 10.250

Cited sources

Haynes, William M., ed. (2016). CRC Handbook of Chemistry and Physics (97th ed.). CRC Press. p. 4.49. ISBN 9781498754293.

External links

"ICSC 1009 – Sodium Iodide (Anhydrous)". International Chemical Safety Card. April 20, 2005. Retrieved June 21, 2017.
"Material Safety Data Sheet (MSDS) – Safety data for sodium iodide". ScienceLab.com. May 21, 2013. Archived from the original on June 3, 2018. Retrieved June 21, 2017.
"Sodium iodide (Oral route, Injection route, Intravenous route)". Drugs.com. 2017. Retrieved June 21, 2017.
"Safety Data Sheet – Sodium iodide" (PDF). Global Safety Management. January 23, 2015. Retrieved October 16, 2019.

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