Chromium(II) chloride
| Chromium(II) chloride | |
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Chromium(II) chloride |
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Other names
Chromous chloride |
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| Identifiers | |
| CAS number | 10049-05-5  |
| PubChem | 24871 |
| ChemSpider | 23252 |
| UNII | CET32HKA21 |
| RTECS number | GB5250000 |
| Jmol-3D images | Image 1 |
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| Properties | |
| Molecular formula | CrCl2 |
| Molar mass | 122.9021 g/mol |
| Exact mass | 121.878217 |
| Appearance | white crystalline solid very hygroscopic |
| Odor | odorless |
| Density | 2.9 g/cm3 |
| Melting point |
824 °C |
| Boiling point |
1120 °C |
| Solubility in water | very soluble |
| Solubility | insoluble in alcohol, ether |
| Acidity (pKa) | 2+ |
| 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 |
 (verify) (what is:  / ?)Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) |
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| 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.
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[edit] 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
[edit] 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.
[edit] 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]
[edit] References
- ^ Greenwood, N. N.; Earnshaw, A. (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 0080379419.
- ^ Burg, A. B. (1950). Audrieth, Ludwig F.. ed. "Anhydrous Chromium(II) Chloride". Inorg. Synth. 3: 150–153. doi:10.1002/9780470132340.
- ^ (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
- ^ (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.
[edit] External links
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