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
SMILES Cl[Cr]Cl
InChI InChI=1S/2ClH.Cr/h2*1H;/q;;+2/p-2 Y Key: XBWRJSSJWDOUSJ-UHFFFAOYSA-L Y InChI=1/2ClH.Cr/h2*1H;/q;;+2/p-2 Key: XBWRJSSJWDOUSJ-NUQVWONBAQ
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
Y (verify) (what is: Y/N?) 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 chemical 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. CrCl₂ crystallizes with the calcium chloride structure, an orthorhombically distorted variant of that of rutile.

Synthesis

CrCl₂ is produced by reducing chromium(III) chloride with hydrogen at 500 °C:^[1]

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.

Uses

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.^[2] It is a reagent in the Nozaki-Hiyama-Kishi reaction.

References

1. ^ Burg, A. B. (1950). Audrieth, Ludwig F.. ed. "Anhydrous Chromium(II) Chloride". Inorg. Synth. 3: 150–153. doi:10.1002/9780470132340. 
2. ^ 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.

• Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Oxford: Butterworth-Heinemann. ISBN 0080379419. 

External links

• http://www.osha.gov/SLTC/healthguidelines/chromium2/recognition.html