Sodium iodide

Crystal structure
__ Na +      __ I -
Crystal system	cubic
Space group	Fm 3 m (No. 225)
Coordination numbers	Na [6], I [6]
General
Surname	Sodium iodide
other names	SODIUM IODIDE ( INCI )
Ratio formula	NaI
Brief description	colorless solid
External identifiers / databases
CAS number 7681-82-5 EC number 231-679-3 ECHA InfoCard 100,028,800 PubChem 5238 ChemSpider 5048 DrugBank DB11119 Wikidata Q390305
Drug information
ATC code	V09 FX02 , V10 XA01
properties
Molar mass	149.89 g mol −1
Physical state	firmly
density	3.67 g cm −3 (20 ° C) (anhydrate) 2.45 g cm −3 (dihydrate)
Melting point	662 ° C
boiling point	1304 ° C
solubility	very good in water (1793 g l −1 at 20 ° C) good in DMSO (300 g l −1 at 25 ° C)
Refractive index	1,774
safety instructions
Please note the exemption from the labeling requirement for drugs, medical devices, cosmetics, food and animal feed GHS labeling of hazardous substances Caution H and P phrases H: 400 P: 273
Toxicological data	4340 mg kg −1 ( LD 50 ,  rat ,  oral )
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions . Refractive index: Na-D line , 20 ° C

Sodium iodide (outdated sodium iodide) is a white, crystalline salt with the empirical formula Na I , which is used for the detection of ionizing radiation , for the treatment of iodine deficiency and for the production of iodine alkanes in the Finkelstein reaction .

Extraction and presentation

It can be obtained by reacting sodium carbonate with iron iodide . It is obtained as a dihydrate.

${\displaystyle \mathrm {4\ Na_{2}CO_{3}+Fe_{3}I_{8}+16\ H_{2}O\longrightarrow 8\ NaI*2H_{2}O+Fe_{3}O_{4}+4\ CO_{2}} }$

properties

The salt can be present as an anhydrous compound ( anhydrate ), di- or pentahydrate. Above 65 ° C the anhydrate crystallizes from aqueous solutions. Crystallization at room temperature gives the dihydrate. The pentahydrate can be obtained at lower temperatures between −13.5 ° C and −31.5 ° C.

solubility

solvent	Solubility of NaI g NaI / 100 g solvent at 25 ° C
water	184
ammonia	162
Sulfur dioxide (liquid)	15th
Methanol	62.5-83.0
Formic acid	61.8
Acetonitrile	24.9
acetone	28.0
Formamide	57-85
Dimethylformamide	3.7-6.4

The standard enthalpy of formation of sodium iodide is ΔH _f ⁰  = −288 kJ / mol.

use

Sodium iodide is widely used to treat and prevent iodine deficiency . The radioactive isotopes ¹²³ iodine and ¹³¹ iodine are used as sodium iodide for nuclear medicine diagnostics - especially for thyroid scintigraphy . ¹³¹ Iodine is used in the form of sodium iodide in radioiodine therapy as a therapeutic agent.

Another area of ​​application is the Finkelstein reaction . An alkyl chloride or bromide is treated with sodium iodide in acetone.

${\displaystyle \mathrm {R-Cl+NaI\longrightarrow R-I+NaCl} }$

The better leaving group iodide displaces the worse leaving group chloride. The driving force behind the reaction is the low solubility of sodium chloride in acetone , which shifts the equilibrium to the side of the alkyl iodide. In addition to acetone, THF and acetonitrile can also be used as solvents.

There are also numerous reactions analogous to the Finkelstein reaction, such as B. the representation of trimethylsilyl iodide from trimethylsilyl chloride , acetyl iodide from acetyl chloride and much more

In crystals that are doped with thallium on part of the sodium positions (NaI: Tl ⁺ ), photons are generated by ionizing radiation and can thus be used as scintillation detectors , traditionally in nuclear medicine , geophysics , nuclear physics , etc. NaI: Tl ⁺ is the most widely used scintillation material as it produces the most light. The crystals are usually coupled with a photomultiplier and hermetically sealed because NaI is hygroscopic . Some parameters ( radiation hardness, afterglow, transparency) can be influenced by controlling the conditions under which the crystal grows. Crystals with higher doping are used as X-ray detectors with high spectroscopic quality. Sodium iodide can be used as a single crystal or polycrystalline .

Individual evidence

1. ↑ entry to SODIUM IODIDE in the CosIng database of the European Commission, accessed on 17 April 2020th
2. ↑ ^{a b c d e f g} Entry on sodium iodide in the GESTIS substance database of the IFA , accessed on February 1, 2016(JavaScript required) .
3. ↑ ^{a b c} Brockhaus ABC Chemie, FA Brockhausverlag Leipzig 1971, p. 924.
4. ↑ Dimethyl Sulfoxide (DMSO) Solubility Data. Gaylord Chemical Company, LLC; Bulletin 102, June 2014, p. 14. (PDF)
5. ↑ David R. Lide (Ed.): CRC Handbook of Chemistry and Physics . 90th edition. (Internet version: 2010), CRC Press / Taylor and Francis, Boca Raton, FL, Index of Refraction of Inorganic Crystals, pp. 10-247.
6. ↑ Entry on sodium iodide in the ChemIDplus database of the United States National Library of Medicine (NLM) .
7. ^ Burgess, J. Metal Ions in Solution (Ellis Horwood, New York, 1978) ISBN 0-85312-027-7 .
8. ^ AF Holleman , E. Wiberg , N. Wiberg : Textbook of Inorganic Chemistry . 101st edition. Walter de Gruyter, Berlin 1995, ISBN 3-11-012641-9 , p. 1170.