# Sodium iodide

Sodium iodide
Identifiers
3D model (JSmol)
ChEBI
ChemSpider
ECHA InfoCard 100.028.800
RTECS number WB6475000
UNII
Properties
NaI
Molar mass 149.89 g mol−1
Appearance white solid
deliquescent
Odor odorless
Density 3.67 g cm−3
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]
Acidity (pKa) 8–9.5
−57.0 × 10−6 cm3 mol−1
1.7745
Structure
Halite
Octahedral
Thermochemistry
91 J mol−1 K−1[2]
−288 kJ mol−1[2]
Hazards
Main hazards Irritant, can harm the unborn child
Safety data sheet [1]
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).
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Infobox references

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.[3]

## 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.[3]

### Organic synthesis

Monatomic NaI chains grown inside double-wall carbon nanotubes.[4]

Sodium iodide is used for conversion of an alkyl chlorides into an alkyl iodides. This method, the Finkelstein reaction,[5] relies on the insolubility of sodium chloride in acetone to drive the reaction:[6]

${\displaystyle {\ce {{R-Cl}+NaI->{R-I}+NaCl}}}$

### 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.[7]

## 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)[8]
H2O 184.2
Liquid ammonia 162
Liquid sulfur dioxide 15
Methanol 62.5–83.0
Formic acid 61.8
Acetonitrile 24.9
Acetone 50.4425
Formamide 57–85
Acetamide 32.3 (41.5 °C)
Dimethylformamide 3.7–6.4
Dichloromethane 0.009[9]