Magnesium bromide is a chemical compound of magnesium and bromine, with the chemical formula MgBr2. It is white and deliquescent crystalline solid. It is often used as a mild sedative and as an anticonvulsant for treatment of nervous disorders.[2] It is water-soluble and somewhat soluble in alcohol. It can be found naturally in small amounts in some minerals such as: bischofite and carnallite, and in sea water, such as that of the Dead Sea.[3][4]

Magnesium bromide[1]
3D model (JSmol)
ECHA InfoCard 100.029.246 Edit this at Wikidata
  • InChI=1S/2BrH.Mg/h2*1H;/q;;+2/p-2 checkY
  • InChI=1/2BrH.Mg/h2*1H;/q;;+2/p-2
  • [Mg+2].[Br-].[Br-]
  • MgBr2 (anhydrous)
  • MgBr2·6H2O (hexahydrate)
Molar mass 184.113 g/mol (anhydrous)
292.204 g/mol (hexahydrate)
Appearance white hygroscopic hexagonal crystals (anhydrous)
colorless monoclinic crystals (hexahydrate)
Density 3.72 g/cm3 (anhydrous)
2.07 g/cm3 (hexahydrate)
Melting point 711 °C (1,312 °F; 984 K) 172.4 °C, decomposes (hexahydrate)
Boiling point 1,250 °C (2,280 °F; 1,520 K)
102 g/(100 mL) (anhydrous)
316 g/(100 mL) (0 °C, hexahydrate)
Solubility ethanol: 6.9 g/(100 mL)
methanol: 21.8 g/(100 mL)
−72.0·10−6 cm3/mol
Rhombohedral, hP3
P-3m1, No. 164
70 J/(mol·K)
117.2 J·mol−1·K−1
−524.3 kJ·mol−1
NFPA 704 (fire diamond)
NFPA 704 four-colored diamondHealth 1: Exposure would cause irritation but only minor residual injury. E.g. turpentineFlammability 0: Will not burn. E.g. waterInstability 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g. liquid nitrogenSpecial hazards (white): no code
Safety data sheet (SDS) External SDS
Related compounds
Other anions
Other cations
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Synthesis edit

Magnesium bromide can be synthesized by treating with magnesium oxide (and related basic salts) with hydrobromic acid.[4] It can also be made by reacting magnesium carbonate and hydrobromic acids, and collecting the solid left after evaporation.[3]

As suggested by its easy conversion to various hydrates, anhydrous MgBr2 is a Lewis acid. In the coordination polymer with the formula MgBr2(dioxane)2, Mg2+ adopts an octahedral geometry.[5]

Uses edit

Magnesium bromide is used as a Lewis acid catalyst in some organic synthesis, e.g., in aldol reaction.[6] In organosilicon chemistry, magnesium bromide forms adducts R2SiXMgBr2.[7]

Magnesium bromide also has been used as a tranquilizer.[3]

Magnesium bromide modifies the catalytic properties of palladium on charcoal.[8]

Magnesium bromide hexahydrate has properties as a flame retardant. It was found that if 0.125 mol/L of magnesium bromide hexahydrate was added to a cotton material it acted as a flame retardant.[9]

References edit

  1. ^ Lide, David R. (1998). Handbook of Chemistry and Physics (87 ed.). Boca Raton, Florida: CRC Press. pp. 4–67. ISBN 0-8493-0594-2.
  2. ^ Pradyot Patnaik. Handbook of Inorganic Chemicals. McGraw-Hill, 2002, ISBN 0-07-049439-8
  3. ^ a b c Gruyter, W. Concise Encyclopedia Chemistry, Walter de Gruyter & Company: Berlin, 1993; 612
  4. ^ a b Lewis, R.J. Hawley’s Condensed Chemical Dictionary, 15th ed.; John Wiley &Sons Inc.:New York, 2007; 777
  5. ^ Fischer, Reinald; Görls, Helmar; Meisinger, Philippe R.; Suxdorf, Regina; Westerhausen, Matthias (2019). "Structure–Solubility Relationship of 1,4‐Dioxane Complexes of Di(hydrocarbyl)magnesium". Chemistry – A European Journal. 25 (55): 12830–12841. doi:10.1002/chem.201903120. PMC 7027550. PMID 31328293.
  6. ^ Evans, David A.; Tedrow, Jason S.; Shaw, Jared T.; Downey, C. Wade (2002). "Diastereoselective Magnesium Halide-Catalyzed anti-Aldol Reactions of Chiral N-Acyloxazolidinones". Journal of the American Chemical Society. 124 (3): 392–393. doi:10.1021/ja0119548. PMID 11792206.
  7. ^ Lim, Young Mook; Cho, Hyeon Mo; Lee, Myong Euy; Baeck, Kyoung Koo (2006). "A Stable Magnesium Bromosilylenoid: Transmetalation of a Lithium Bromosilylenoid by Magnesium Bromide". Organometallics. 25 (21): 4960. doi:10.1021/om060589w.
  8. ^ Bouzide, Abderrahim (2002). "Magnesium Bromide Mediated Highly Diastereoselective Heterogeneous Hydrogenation of Olefins". Organic Letters. 4 (8): 1347–50. doi:10.1021/ol020032m. PMID 11950359.
  9. ^ Mostashari, S. M.; Fayyaz, F. (2008). "XRD characterization of the ashes from a burned cellulosic fabric impregnated with magnesium bromide hexahydrate as flame-retardant". Journal of Thermal Analysis and Calorimetry. 92 (3): 845. doi:10.1007/s10973-007-8928-4. S2CID 94416902.