Chromium(III) bromide is an inorganic compound with the

chemical formula In chemistry, a chemical formula is a way of presenting information about the chemical proportions of atoms that constitute a particular chemical compound or molecule, using chemical element symbols, numbers, and sometimes also other symbol ...

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

catalyst Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recyc ...

s for the

oligomerization In chemistry and biochemistry, an oligomer () is a molecule that consists of a few repeating units which could be derived, actually or conceptually, from smaller molecules, monomers.Quote: ''Oligomer molecule: A molecule of intermediate relativ ...

of ethylene.

Synthesis

The compound is prepared in a tube furnace by the reaction of

bromine Bromine is a chemical element with the symbol Br and atomic number 35. It is the third-lightest element in group 17 of the periodic table ( halogens) and is a volatile red-brown liquid at room temperature that evaporates readily to form a simi ...

vapor and chromium powder at 1000 °C. It is purified by extracting with absolute

diethyl ether Diethyl ether, or simply ether, is an organic compound in the ether class with the formula , sometimes abbreviated as (see Pseudoelement symbols). It is a colourless, highly volatile, sweet-smelling ("ethereal odour"), extremely flammable li ...

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).

Reactions

Chromium(III) bromide is reduced by

hydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic ...

gas at 350-400 °C to give chromium(II) bromide: :2CrBr₃ + H₂ → 2CrBr₂ + 2HBr

References

Chromium(III) compounds Bromides Metal halides {{Inorganic-compound-stub