Chromium(III) bromide

Chromium(III) bromide
Names
IUPAC name
Chromium(III) bromide
Other names
  • Chromic bromide
  • Chromium bromide
  • Chromium tribromide
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.030.068 Edit this at Wikidata
EC Number
  • 233-088-6
UNII
  • InChI=1S/3BrH.Cr/h3*1H;/q;;;+3/p-3
    Key: UZDWIWGMKWZEPE-UHFFFAOYSA-K
  • [Cr+3].[Br-].[Br-].[Br-]
Properties
CrBr3
Molar mass 291.708 g·mol−1
Appearance Black lustrous crystals; green in transmitted light, reddish in reflected light[1]
Density 4.25 g/cm3[2]
Melting point 1,130 °C (2,070 °F; 1,400 K) (anhydrous)[2]
79 °C (hexahydrate)
anhydrous: insoluble in cold water, soluble with addition of Chromium(II) ion salts,[1] soluble in hot water;[2] hexahydrate: highly soluble[2]
Structure
trigonal
Hazards
NIOSH (US health exposure limits):
PEL (Permissible)
 TWA 1 mg/m3[3]
REL (Recommended)
 TWA 0.5 mg/m3[3]
IDLH (Immediate danger)
 250 mg/m3[3]
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.

Synthesis

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.[1]

2Cr + 3Br2 → 2CrBr3

The effect of bromine on a highly heated mixture of chromium(III) oxide with coal:

Cr2O3 + 3Br2 + 3C → 2CrBr3 + 3CO

Chemical properties

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.[1] The reducing agent generates chromous bromide on the surface of the solid, which dissolves and re-oxidizes to Cr(III).[citation needed]

Chromium(III) bromide is reduced by hydrogen gas at 350-400 °C to give chromium(II) bromide:[1]

2 CrBr3 + H2 → 2 CrBr2 + 2 HBr

Oxidizes when heated in air:

2 CrBr3 + 3 O2 → 2 Cr2O3 + 6 Br2

References

  1. ^ a b c d e Brauer, Georg (1965) [1962]. Handbuch Der Präparativen Anorganischen Chemie [Handbook of Preparative Inorganic Chemistry] (in German). Vol. 2. Stuttgart; New York, New York: Ferdinand Enke Verlag; Academic Press, Inc. p. 1340. ISBN 978-0-32316129-9. Retrieved 2014-01-10.
  2. ^ a b c d Perry, Dale L. (2011). Handbook of Inorganic Compounds, Second Edition. Boca Raton, Florida: CRC Press. p. 122. ISBN 978-1-43981462-8. Retrieved 2014-01-10.
  3. ^ a b c NIOSH Pocket Guide to Chemical Hazards. "#0141". National Institute for Occupational Safety and Health (NIOSH).