Chromium(II) chloride

Chromium(II) chloride
IUPAC name

Chromium(II) chloride
Other names

Chromous chloride
Identifiers
CAS number 10049-05-5 Y
PubChem 24871
ChemSpider 23252 Y
UNII CET32HKA21 Y
RTECS number GB5250000
Jmol-3D images Image 1
Properties
Molecular formula CrCl2
Molar mass 122.902 g/mol
Density 2.9 g/cm3
Melting point

824 °C
Boiling point

1120 °C
Solubility in water soluble
Structure
Crystal structure Orthorhombic (deformed rutile), oP6
Space group Pnnm, No. 58
Coordination
geometry		 octahedral, 6-coordinate
Hazards
MSDS Oxford MSDS
EU Index Not listed
LD50 1870 mg/kg (oral, rat)
Related compounds
Other anions Chromium(II) fluoride
Chromium(II) bromide
Chromium(II) iodide
Other cations Chromium(III) chloride
Chromium(IV) chloride
Molybdenum(II) chloride
Tungsten(II) chloride
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Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Chromium(II) chloride is the inorganic compound with the formula CrCl2. This white, crystalline solid is used for the synthesis of other chromium complexes. CrCl2 is hygroscopic. It dissolves in water to give bright blue solutions that are easily oxidized by air to give Cr(III)-containing products.

Contents

Structure and synthesis

CrCl2 crystallizes with the calcium chloride structure, an orthorhombically distorted variant of that of rutile. The Cr centres are octahedral, being distorted by the Jahn-Teller Effect.[1]

CrCl2 is produced by reducing chromium(III) chloride with hydrogen at 500 °C:[2]

2 CrCl3 + H2 → 2 CrCl2 + 2 HCl

Small scale preparations can use LiAlH4, or related reagents, to reduce CrCl3

4 CrCl3 + LiAlH4 → 4 CrCl2 + LiCl + AlCl3 + 2 H2

Commonly, it is generated by reduction of CrCl3 with zinc.

2 CrCl3 + Zn → 2 CrCl2 + ZnCl2

Reactions

Chromium(II) chloride reacts with any small amount of acid in the water to form hydrogen gas:

3 CrCl2 + H2O → 2 CrCl3 + CrO + H2

The reduction potential for Cr3+ + e– ⇄ Cr2+ is −0.41. The reduction potential for water in acidic conditions is +0.00, making the reaction occur easily. The reaction in basic environments is:

CrCl2 + 2 OH– → Cr(OH)2 + 2 Cl–

This reaction forms a precipitate of chromium(II) oxide.

Organic chemistry

Chromium(II) chloride is used as precursor to other inorganic and organometallic chromium complexes. Alkyl halides and nitroaromatics are reduced by CrCl2. The moderate electronegativity of chromium and the range of substrates that CrCl2 can accommodate make organochromium reagents very synthetically versatile.[3] It is a reagent in the Nozaki-Hiyama-Kishi reaction, a useful method for preparing medium-size rings.[4]

References

  1. ^ Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Oxford: Butterworth-Heinemann. ISBN 0080379419. 
  2. ^ Burg, A. B. (1950). Audrieth, Ludwig F.. ed. "Anhydrous Chromium(II) Chloride". Inorg. Synth. 3: 150–153. doi:10.1002/9780470132340. 
  3. ^ (a) Kazuhiko Takai, K.; Loh, T.-P. "Chromium(II) Chloride" in Encyclopedia of Reagents for Organic Synthesis John Wiley & Sons: New York; 2005. doi:10.1002/047084289X.rc166. (b) Alois Fürstner, "Carbon−Carbon Bond Formations Involving Organochromium(III) Reagents" Chemical Reviews, 1999, 99 (4), 991–1046 doi:10.1021/cr9703360
  4. ^ (a) MacMillan, D. W. C.; Overman, Larry E. "Enantioselective Total Synthesis of (-)-7-Deacetoxyalcyonin Acetate. First Synthesis of a Eunicellin Diterpene" J. Am. Chem. Soc. 1995, 117 (41), 10391–10392. doi:10.1021/ja00146a028. (b) Lotesta, S. D.; Liu, J.; Yates, E. V.; Krieger, I.; Sacchettini, J. C.; Freundlich, J. S.; Sorensen, E. J. "Expanding the pleuromutilin class of antibiotics by de novo chemical synthesis" Chem. Sci. 2011, 2, 1258-1261. doi:10.1039/C1SC00116G.

External links