Chromium(III) bromide

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Chromium(III) bromide
Kristallstruktur Bismut(III)-iodid.png
Names
IUPAC name
Chromium(III) bromide
Other names
  • Chromic bromide
  • Chromium bromide
  • Chromium tribromide
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.030.068 OOjs UI icon edit-ltr-progressive.svg
EC Number
  • 233-088-6
PubChem CID
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
AppearanceBlack 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 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.

Contents

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

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<span class="mw-page-title-main">Hydrogen bromide</span> Chemical compound

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2
O
3
. It is one of the principal oxides of chromium and is used as a pigment. In nature, it occurs as the rare mineral eskolaite.

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<span class="mw-page-title-main">Vanadium(III) bromide</span> Chemical compound

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Chromium(II) sulfate is an inorganic compound with the chemical formula CrSO4. It often comes as hydrates CrSO4·nH2O. Several hydrated salts are known. The pentahydrate CrSO4·5H2O is a blue solid that dissolves readily in water. Solutions of chromium(II) are easily oxidized by air to Cr(III) species. Solutions of Cr(II) are used as specialized reducing agents of value in organic synthesis.

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References

  1. 1 2 3 4 5 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. 1 2 3 4 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. 1 2 3 NIOSH Pocket Guide to Chemical Hazards. "#0141". National Institute for Occupational Safety and Health (NIOSH).