Chromium(III) bromide
Chemical compound From Wikipedia, the free encyclopedia
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.
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| Names | |
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| IUPAC name
Chromium(III) bromide | |
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) |
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).
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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
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