Chromium(III) bromide is an inorganic compound with the chemical formula . 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.
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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 , and is subsequently washed with absolute diethyl ether and absolute ethanol.
The effect of bromine on a highly heated mixture of chromium(III) oxide with coal:
Analogous to the behavior of related chromium(III) halides, the tribromide dissolves in water to give only upon the addition of catalytic amounts of a reducing agent, which generates . The reducing agent generates chromous bromide on the surface of the solid, which dissolves and re-oxidizes to Cr(III).
Chromium(III) bromide is reduced by hydrogen gas at 350-400 °C to give chromium(II) bromide:
Oxidizes when heated in air: