Magnesium bromide

Crystal structure
__ Mg 2+      __ Br -
General
Surname	Magnesium bromide
other names	Magnesium (II) bromide Magnesium dibromide
Ratio formula	MgBr 2
Brief description	colorless solid
External identifiers / databases
CAS number 7789-48-2 13446-53-2 (hexahydrate) PubChem 82241 Wikidata Q420413
properties
Molar mass	184.11 g mol −1
Physical state	firmly
density	3.72 g cm −3 (25 ° C)
Melting point	711 ° C
solubility	good in water (1015 g l −1 at 20 ° C)
safety instructions
GHS labeling of hazardous substances Caution H and P phrases H: 315-319-335 P: 261-305 + 351 + 338
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Magnesium bromide is the magnesium salt of hydrobromic acid (HBr). It belongs to the group of bromides and has the empirical formula MgBr ₂ .

Occurrence

Magnesium bromide occurs naturally in overburden salts from potash deposits (bromides occur in potash salts in a ratio of about 1: 300 to the analogous chlorides ) and in seawater (in a concentration of about 70 g / m³).

Extraction and presentation

There are several ways to make magnesium bromide. On the one hand, magnesium bromide can be obtained by reacting a magnesium hydroxide solution (obtained from magnesium chloride ) with hydrogen bromide .

${\displaystyle \mathrm {Mg(OH)_{2}+2\ HBr+4\ H_{2}O\longrightarrow \ MgBr_{2}+6\ H_{2}O} }$

Another possibility is given by the representations from the elements . This reaction is carried out in anhydrous diethyl ether , since the direct dropwise addition of elemental bromine to metallic magnesium would cause too violent a reaction.

${\displaystyle \mathrm {Mg+Br_{2}\longrightarrow MgBr_{2}} }$

properties

Magnesium bromide is a colorless, hygroscopic powder and also occurs as a hexahydrate , which dehydrates at 165 ° C to form anhydrous magnesium bromide. It crystallizes in the trigonal polytype 2H of cadmium iodide with the lattice parameters a = 4.154 Å and c = 6.862 Å.

use

Magnesium bromide can be used to produce bromine from bromide-containing alkalis .

${\displaystyle \mathrm {MgBr_{2}+Cl_{2}\longrightarrow Br_{2}+MgCl_{2}} }$

In organic synthesis, the compound is used as a Lewis acid catalyst, with transition states being stabilized in addition reactions. Furthermore, alkyl bromides can be obtained from the tosylates of primary and secondary alcohols .

Individual evidence

1. ↑ ^{a b} Data sheet Magnesium bromide, anhydrous (PDF) from Strem, accessed on December 25, 2012.
2. ↑ ^{a b c d} data sheet Magnesium bromide from Sigma-Aldrich , accessed on April 9, 2011 ( PDF ).
3. ↑ Brom at Seilnacht .
4. ^ MA Brogan, AJ Blake, C. Wilson, DH Gregory: Magnesium diiodide, MgI ₂ . In: Acta Crystallographica , C59, 2003, pp. I136-i138, doi: 10.1107 / S0108270103025769 .
5. ↑ ^{a b} entry on magnesium bromide. In: Römpp Online . Georg Thieme Verlag, accessed on September 12, 2017.
6. ↑ Yuji Kazuta, Hiroshi Abe, Akira Matsuda, Satoshi Shuto: Highly Stereoselective Grignard Addition to Cis-Substituted C-Cyclopropylaldonitrones. The Bisected s-Trans Transition State Can Be Stabilized Effectively by the Lewis Acid-Coordination in J. Org. Chem. 69 (2004) 9143-9150, doi : 10.1021 / jo048637e .

literature

• Georg Brauer (Ed.), With the collaboration of Marianne Baudler a . a .: Handbook of Preparative Inorganic Chemistry. 3rd, revised edition. Volume II, Ferdinand Enke, Stuttgart 1978, ISBN 3-432-87813-3 , pp. 905-907.