Calcium bromide

Calcium bromide is the name for compounds with the chemical formula CaBr2(H2O)x. Individual compounds include the anhydrous material (x = 0), the hexahydrate (x = 6), and the rare dihydrate (x = 2). All are white powders that dissolve in water, and from these solutions crystallizes the hexahydrate. The hydrated form is mainly used in some drilling fluids.

Synthesis, structure, and reactions
It is produced by the reaction of calcium oxide, calcium carbonate with bromine in the presence of a reducing agent such as formic acid or formaldehyde:
 * CaO + Br2  +  HCO2H  ->  CaBr2  +  H2O  +  CO2

Solid calcium bromide adopts the rutile structure, featuring octahedral Ca2+ centres bound to six bromide anions, which also bridge to other Ca2+ centres.

When strongly heated in air, calcium bromide reacts with oxygen to produce calcium oxide and bromine:
 * 2 CaBr2 + O2 → 2 CaO + 2 Br2

Uses
It is mainly used as dense aqueous solutions for drilling fluids. It is also used in neuroses medication, freezing mixtures, food preservatives, photography and fire retardants.

It minimizes the emission of gaseous mercury in the combustion of coal.

In the laboratory
Calcium bromide forms complexes with triphenylphosphine oxide, allowing for removal of triphenylphosphine oxide from reaction mixtures without the use of chromatography.