Chromium(II) chloride

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Chromium(II) chloride
Systematic name	Chromium(II) Chloride
Molecular formula	CrCl₂
Formula Weight	122.901 g/mol
CAS number	[10049-05-5]
Density	2.9 g/cm³
Solubility (water)	Soluble
Melting point	824°C
Boiling point	1120°C
Disclaimer and references

1 Introduction
2 Synthesis
3 Uses
4 References
5 See also
6 External links

[edit] Introduction

Chromium(II) chloride is Cr Cl₂. ^[1] It is a white, crystalline solid at standard temperature and pressure with strong reducing properties. CrCl₂ is also extremely hygroscopic. It dissolves in water to give bright blue solutions.

[edit] Synthesis

CrCl₂ is produced by reducing chromium(III) chloride with hydrogen. This reaction affords white needle-like crystals.

CrCl₃ + 1/2H₂ → CrCl₂ + HCl

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

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

[edit] Uses

Chromium(II) Chloride is used as a catalyst in the synthesis of many organic compounds and as a reagent in the synthesis of inorganic and organometallic chromium complexes.

The reduction of alkyl halides is easily accomplished by CrCl₂ by addition of CrCl₃, HCl, and Zn to the alkyl halide. (CrCl₃ with HCl and Zn is used to generate CrCl₂ in situ.)

Carbon-carbon unsaturated bonds are also reducible by Chromium(II) Chloride. In a 2:1 mixture of tetrahydrofuran and water, an unsaturated C-C bond is reduced by CrCl₂ in good to excellent yield.

CrCl₂ can also reduce other functional groups. Nitrobenzene can be reduced to anilines and aliphatic nitro componds can be reduced to aldehydes by reflux with CrCl₂ in alcohol.

In another reaction, chromium(II) chloride is used to protect alcohol groups during synthesis by forming tetrahydrofuranal ethers.

Lastly, CrCl₂ is used to create alkyl chromium reagents that add selectively to aldehydes. The moderate electronegativity of chromium and the range of substrates that CrCl₂ can accommodate make organochromium reagents very synthetically powerful.