Chromium tribromide, Chromium bromide, Chromic bromide
3D model (JSmol)
CompTox Dashboard (EPA)
|Molar mass||291.71 g/mol|
|Appearance||Black lustrous crystals; green in transmitted light, reddish in reflected light|
|Melting point|| 1,130 °C (2,070 °F; 1,400 K) (anhydrous) |
79 °C (hexahydrate)
|insoluble in cold water, soluble with addition of Chromium(II) ion salts, soluble in hot water|
|NIOSH (US health exposure limits):|
|TWA 1 mg/m3|
|TWA 0.5 mg/m3|
IDLH (Immediate danger)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Chromium(III) bromide is an inorganic compound with the chemical formula CrBr3. It is a dark colored solid that appears green in transmitted light but red with reflected light. It is used as a precursor to catalysts for the oligomerization of ethylene.
The compound is prepared in a tube furnace by the reaction of bromine vapor and chromium powder at 1000 °C. It is purified by extracting with absolute diethyl ether to remove any CrBr2, and is subsequently washed with absolute diethyl ether and absolute ethanol.
Analogous to the behavior of related chromium(III) halides, the tribromide dissolves in water to give CrBr3(H2O)3 only upon the addition of catalytic amounts of a reducing agent, which generates CrBr2. The reducing agent generates chromous bromide on the surface of the solid, which dissolves and re-oxidizes to Cr(III).