Magnesium iodide

Magnesium iodide is an inorganic compound with the chemical formula MgI₂. It forms various hydrates MgI₂·xH₂O. Magnesium iodide is a salt of magnesium and hydrogen iodide. These salts are typical ionic halides, being highly soluble in water.

Magnesium iodide

Names
IUPAC name Magnesium iodide
Identifiers
CAS Number	10377-58-9 (anhydrous) Y 75535-11-4 (hexahydrate) N 7790-31-0 (octahydrate) Y
3D model (JSmol)	Interactive image Interactive image
ChemSpider	59700 N
ECHA InfoCard	100.030.738
EC Number	233-825-1
PubChem CID	66322
UNII	W74QE3H320 (anhydrous) Y 72I5H6SWMT (octahydrate) Y
CompTox Dashboard (EPA)	DTXSID6065056
InChI InChI=1S/2HI.Mg/h2*1H;/q;;+2/p-2 N Key: BLQJIBCZHWBKSL-UHFFFAOYSA-L N InChI=1/2HI.Mg/h2*1H;/q;;+2/p-2 Key: BLQJIBCZHWBKSL-NUQVWONBAV
SMILES I[Mg]I [Mg+2].[I-].[I-]
Properties
Chemical formula	MgI2 (anhydrous) MgI2·6H2O (hexahydrate) MgI2·8H2O (octahydrate)[1]
Molar mass	278.1139 g/mol (anhydrous) 386.2005 g/mol (hexahydrate) 422.236 g/mol (octahydrate)
Appearance	white crystalline solid
Odor	odorless
Density	4.43 g/cm3 (anhydrous solid) 2.353 g/cm3 (hexahydrate solid) 2.098 g/cm3 (octahydrate solid)
Melting point	637 °C (1,179 °F; 910 K) (anhydrous, decomposes) 41 °C (octahydrate, decomposes)
Solubility in water	54.7 g/(100 cm3) (anhydrous, 0 °C) 148 g/(100 cm3) (anhydrous, 18 °C)[2] 81 g/(100 cm3) (octahydrate, 20 °C)
Solubility	soluble in ether, alcohol and ammonia
Magnetic susceptibility (χ)	−111.0·10−6 cm3/mol
Structure
Crystal structure	Hexagonal (anhydrous) Monoclinic (hexahydrate) Orthorhombic (octahydrate)
Thermochemistry
Heat capacity (C)	74 J/(mol·K)
Std molar entropy (S⦵298)	134 J/(mol·K)
Std enthalpy of formation (ΔfH⦵298)	−364 kJ/mol
Hazards
GHS labelling:
Pictograms
Signal word	Warning
Hazard statements	H315, H319
NFPA 704 (fire diamond)	3 1 1 COR
Related compounds
Other anions	Magnesium fluoride Magnesium bromide Magnesium chloride
Other cations	Beryllium iodide Calcium iodide Strontium iodide Barium 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

Uses

Magnesium iodide has few commercial uses, but can be used to prepare compounds for organic synthesis.

Preparation

Magnesium iodide can be prepared from magnesium oxide, magnesium hydroxide, and magnesium carbonate by treatment with hydroiodic acid:^[3]

MgO + 2 HI → MgI₂ + H₂O

Mg(OH)₂ + 2 HI → MgI₂ + 2 H₂O

MgCO₃ + 2 HI → MgI₂ + CO₂ + H₂O

Reactions

Magnesium iodide is stable at high heat under a hydrogen atmosphere, but decomposes in air at normal temperatures, turning brown from the release of elemental iodine. When heated in air, it decomposes completely to magnesium oxide.^[4]

Another method to prepare MgI₂ is mixing powdered elemental iodine and magnesium metal. In order to obtain anhydrous MgI₂, the reaction should be conducted in a strictly anhydrous atmosphere; dry-diethyl ether can be used as a solvent.

Usage of magnesium iodide in the Baylis-Hillman reaction tends to give (Z)-vinyl compounds.^[5]

Demethylation of certain aromatic methyl ethers can be afforded using magnesium iodide in diethyl ether.^[6]

Hydrates

Two hydrates are known, the octahydrate and the nonahydrate, both verified by X-ray crystallography These hydrates feature [Mg(H₂O)₆]²⁺ ions.^[7]

References

1. Perry, Dale L.; Phillips, Sidney L. (1995), Handbook of Inorganic Compounds, CRC Press, p. 240, ISBN 0-8493-8671-3, retrieved 2007-12-09
2. Magnesium Iodide MSDS at AlfaAesar^{[permanent dead link‍]}
3. Patnaik, Pradyot (2003), Handbook of Inorganic Chemicals, McGraw-Hill Professional, pp. 527–528, ISBN 0-07-049439-8, retrieved 2007-12-09
4. Wilsmore, N. T. M. (1891). "Note on Magnesium Iodide". In James Hector (ed.). Report of the Third Meeting of the Australasian Association for the Advancement of Science. Sydney: The Association. p. 116. Retrieved 2007-12-09.
5. Tietze, Lutz-Friedjan; Brasche, Gordon; Gericke, Kersten (2006), "Domino Reactions in Organic Synthesis", Chemical Reviews, 96 (1), Wiley-VCH: 115–136, doi:10.1021/cr950027e, ISBN 3-527-29060-5, PMID 11848746, retrieved 2007-12-09
6. Yamaguchi, Seiji; Nedachi, Masahiro; Yokoyama, Hajime; Hirai, Yoshiro (October 1999). "Regioselective demethylation of 2,6-dimethoxybenzaldehydes with magnesium iodide etherate". Tetrahedron Letters. 40 (41): 7363–7365. doi:10.1016/S0040-4039(99)01411-2.
7. Hennings, Erik; Schmidt, Horst; Voigt, Wolfgang (2013). "Crystal Structures of Hydrates of Simple Inorganic Salts. I. Water-Rich Magnesium Halide Hydrates MgCl₂·8H₂O, MgCl₂·12H₂O, MgBr₂·6H₂O, MgBr₂·9H₂O, MgI₂·8H₂O and MgI₂·9H₂O". Acta Crystallographica Section C Crystal Structure Communications. 69 (11): 1292–1300. doi:10.1107/S0108270113028138. PMID 24192174.