Sodium iodide

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.[4]

Sodium iodide
3D model (JSmol)
ECHA InfoCard 100.028.800
RTECS number
  • WB6475000
Molar mass 149.89 g mol1
Appearance white solid
Odor odorless
Density 3.67 g cm3
Melting point 661 °C (1,222 °F; 934 K)
Boiling point 1,304 °C (2,379 °F; 1,577 K)
158.7 g/100 mL (0 °C)
184.2 g/100 mL (25 °C)
227.8 g/100 mL (50 °C)
294 g/100 mL (70 °C)
302 g/100 mL (100 °C)[1]
57.0 × 10−6 cm3 mol1
91 J mol−1 K−1[2]
−288 kJ mol−1[2]
Main hazards Irritant, can harm the unborn child
Safety data sheet
GHS pictograms
GHS Signal word Danger
H315, H319, H400
P273, P305+351+338[3]
NFPA 704 (fire diamond)
Flash point Non-flammable
Related compounds
Other anions
Sodium fluoride
Sodium chloride
Sodium bromide
Sodium astatide
Other cations
Lithium iodide
Potassium iodide
Rubidium iodide
Caesium iodide
Francium iodide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N verify (what is YN ?)
Infobox references


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.[4]

Organic synthesis

Sodium iodide is used for conversion of alkyl chlorides into alkyl iodides. This method, the Finkelstein reaction,[6] relies on the insolubility of sodium chloride in acetone to drive the reaction:[7]

RCl + NaI → RI + NaCl

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 (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.[8]

Solubility data

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

Solvent Solubility of NaI (g NaI/100 g of solvent at 25 °C)[9]
Liquid ammonia162
Liquid sulfur dioxide15
Formic acid61.8
Acetamide32.3 (41.5 °C)

See also


  1. Seidell, Atherton (1919). Solubilities of inorganic and organic compounds c. 2. D. Van Nostrand Company. p. 655.
  2. Zumdahl, Steven S. (2009). Chemical Principles (6th ed.). Houghton Mifflin. p. A23. ISBN 978-0-618-94690-7.
  3. "Sodium iodide 383112". NaI.
  4. Lyday, Phyllis A. (2005). "Iodine and Iodine Compounds". Ullmann's Encyclopedia of Industrial Chemistry. A14. Weinheim: Wiley-VCH. pp. 382–390. doi:10.1002/14356007.a14_381. ISBN 978-3-527-30673-2.
  5. Senga, Ryosuke; Suenaga, Kazu (2015). "Single-atom electron energy loss spectroscopy of light elements". Nature Communications. 6: 7943. Bibcode:2015NatCo...6.7943S. doi:10.1038/ncomms8943. PMC 4532884. PMID 26228378.
  6. Finkelstein, Hank (1910). "Darstellung organischer Jodide aus den entsprechenden Bromiden und Chloriden". Ber. Dtsch. Chem. Ges. (in German). 43 (2): 1528–1532. doi:10.1002/cber.19100430257.
  7. Streitwieser, Andrew (1956). "Solvolytic Displacement Reactions At Saturated Carbon Atoms". Chemical Reviews. 56 (4): 571–752. doi:10.1021/cr50010a001.
  8. "Scintillation Materials and Assemblies" (PDF). Saint-Gobain Crystals. 2016. Retrieved June 21, 2017.
  9. Burgess, John (1978). Metal Ions in Solution. Ellis Horwood Series in Chemical Sciences. New York: Ellis Horwood. ISBN 9780470262931.
  10. De Namor, Angela F. Danil; Traboulssi, Rafic; Salazar, Franz Fernández; De Acosta, Vilma Dianderas; De Vizcardo, Yboni Fernández; Portugal, Jaime Munoz (1989). "Transfer and partition free energies of 1:1 electrolytes in the water–dichloromethane solvent system at 298.15 K". Journal of the Chemical Society, Faraday Transactions 1. 85 (9): 2705–2712. doi:10.1039/F19898502705.
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