Cobalt(II) bromide


Cobalt bromide is an inorganic compound. In its anhydrous form, it is a green solid that is soluble in water, used primarily as a catalyst in some processes.

Properties

When anhydrous, cobalt bromide appears as green crystals, while the hexahydrate appears as red-purple crystals. The hexahydrate loses four waters of crystallization molecules at 100 °C forming the dihydrate:
Further heating to 130 °C produces the anhydrous form:
The anhydrous form melts at 678 °C. At higher temperatures, cobalt bromide reacts with oxygen, forming cobalt oxide and bromine vapor.

Preparation

Cobalt bromide can be prepared as a hydrate by the reaction of cobalt hydroxide with hydrobromic acid:
Anhydrous cobalt bromide may be prepared through the direct reaction of elemental cobalt and liquid bromine.

Reactions and uses

The classical coordination compound bromopentaamminecobalt bromide is prepared by oxidation of a solution of cobalt bromide in aqueous ammonia.
Triphenylphosphine complexes of cobalt bromide have been used as a catalysts in organic synthesis.

Safety

Exposure to large amounts of cobalt can cause cobalt poisoning. Bromide is also mildly toxic.