Names | |
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IUPAC name
Chromium(III) bromide
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Other names
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Identifiers | |
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3D model (
JSmol)
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ChemSpider | |
ECHA InfoCard | 100.030.068 |
EC Number |
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PubChem
CID
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UNII | |
CompTox Dashboard (
EPA)
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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)
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TWA 1 mg/m3 [3] |
REL (Recommended)
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TWA 0.5 mg/m3 [3] |
IDLH (Immediate danger)
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250 mg/m3 [3] |
Except where otherwise noted, data are given for materials in their
standard state (at 25 °C [77 °F], 100 kPa).
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Chromium(III) bromide is an inorganic compound with the chemical formula Cr Br3. 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. [1]
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]