Chromium(III) bromide

Chromium(III) bromide

Names
IUPAC name Chromium(III) bromide
Other names Chromic bromide Chromium bromide Chromium tribromide
Identifiers
CAS Number	10031-25-1  Y 13478-06-3 (hexahydrate)
3D model (JSmol)	Interactive image
ChemSpider	74280
ECHA InfoCard	100.030.068
EC Number	233-088-6
PubChem CID	5155129
UNII	WZB719DDER  Y
CompTox Dashboard (EPA)	DTXSID40905343
InChI InChI=1S/3BrH.Cr/h3*1H;/q;;;+3/p-3 Key: UZDWIWGMKWZEPE-UHFFFAOYSA-K
SMILES [Cr+3].[Br-].[Br-].[Br-]
Properties
Chemical formula	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)
Solubility in water	anhydrous insoluble in cold water soluble with addition of chromium(II) salts [1] soluble in hot water [2] hexahydrate highly soluble [2]
Structure
Crystal structure	trigonal
Hazards
GHS labelling: [3]
Pictograms
Signal word	Danger
Hazard statements	H302+H312, H314, H317, H330, H361
Precautionary statements	P203, P260, P264, P264+P265, P270, P271, P272, P280, P284, P301+P317, P301+P330+P331, P302+P352, P302+P361+P354, P304+P340, P305+P354+P338, P316, P317, P318, P320, P321, P330, P333+P317, P362+P364, P363, P403+P233, P405, P501
NIOSH (US health exposure limits):
PEL (Permissible)	TWA 1 mg/m3 [4]
REL (Recommended)	TWA 0.5 mg/m3 [4]
IDLH (Immediate danger)	250 mg/m3 [4]
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

Chromium(III) bromide is an inorganic compound with the chemical formula Cr Br ₃. 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 charcoal:^{[ citation needed ]}

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. ^[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:^{[ citation needed ]}

2 CrBr₃ + 3 O₂ → 2 Cr₂O₃ + 6 Br₂

References

1. F. Hein and S. Herzog (1963). "Chromium, Molybdenum, Tungsten, Uranium". In G. Brauer (ed.). Handbook of Preparative Inorganic Chemistry, 2nd Ed. Vol. 2. NY, NY: Academic Press. p. 1341.
2. 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. PubChem. "Chromic bromide". pubchem.ncbi.nlm.nih.gov. Retrieved 2026-02-08.
4. NIOSH Pocket Guide to Chemical Hazards. "#0141". National Institute for Occupational Safety and Health (NIOSH).