Chemistry:Chromium(II) chloride
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_chloride.JPG)
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| Names | |
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| IUPAC name
Chromium(II) chloride
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| Other names
Chromous chloride
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| Identifiers | |
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3D model (JSmol)
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| ChemSpider | |
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PubChem CID
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| UNII |
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| UN number | 3077 |
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| Properties | |
| Cl2Cr | |
| Molar mass | 122.90 g·mol−1 |
| Appearance | White to grey/green powder (anhydrous) blue solid (tetrahydrate) |
| Odor | Odorless |
| Density | 2.88 g/cm3 (24 °C)[1] |
| Melting point | 824 °C (1,515 °F; 1,097 K) anhydrous 51 °C (124 °F; 324 K) tetrahydrate, decomposes[1] |
| Boiling point | 1,302 °C (2,376 °F; 1,575 K) anhydrous[1] |
| Soluble[1] | |
| Solubility | Insoluble in alcohol, ether |
| Acidity (pKa) | 2 |
| +7230·10−6 cm3/mol | |
| Structure | |
| Orthorhombic (deformed rutile, anhydrous), oP6[2] Monoclinic (tetrahydrate)[3] | |
| Pnnm, No. 58 (anhydrous)[2] P21/c, No. 14 (tetrahydrate)[3] | |
| 2/m 2/m 2/m (anhydrous)[2] 2/m (tetrahydrate)[3] | |
a = 6.64 Å, b = 5.98 Å, c = 3.48 Å (anhydrous)[2] α = 90°, β = 90°, γ = 90°
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| Octahedral (Cr2+, anhydrous)[2] | |
| Thermochemistry | |
Heat capacity (C)
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71.2 J/mol·K[1] |
Std molar
entropy (S |
115.3 J/mol·K[1] |
Std enthalpy of
formation (ΔfH⦵298) |
−395.4 kJ/mol[1] |
Gibbs free energy (ΔfG˚)
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−356 kJ/mol[1] |
| Hazards | |
| Safety data sheet | Oxford MSDS |
| GHS pictograms |  [4]
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| GHS Signal word | Warning |
| H302, H315, H319, H335[4] | |
| P261, P305+351+338[4] | |
| NFPA 704 (fire diamond) | |
| Lethal dose or concentration (LD, LC): | |
LD50 (median dose)
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1870 mg/kg (rats, oral)[5] |
| Related compounds | |
Other anions
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Chromium(II) fluoride Chromium(II) bromide Chromium(II) iodide |
Other cations
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Chromium(III) chloride Chromium(IV) chloride Molybdenum(II) chloride Tungsten(II) chloride |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). | |
 verify (what is   ?)
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| Infobox references | |
Chromium(II) chloride describes inorganic compounds with the formula CrCl2(H2O)n. The anhydrous solid is white when pure, however commercial samples are often grey or green; it is hygroscopic and readily dissolves in water to give bright blue air-sensitive solutions of the tetrahydrate Cr(H2O)4Cl2. Chromium(II) chloride has no commercial uses but is used on a laboratory-scale for the synthesis of other chromium complexes.
Synthesis
CrCl2 is produced by reducing chromium(III) chloride either with hydrogen at 500 °C:
- 2 CrCl3 + H2 → 2 CrCl2 + 2 HCl
or by electrolysis.
On the laboratory scale, LiAlH4, zinc, and related reductants produce chromous chloride from chromium(III) precursors:
- 4 CrCl3 + LiAlH4 → 4 CrCl2 + LiCl + AlCl3 + 2 H2
- 2 CrCl3 + Zn → 2 CrCl2 + ZnCl2
CrCl2 can also be prepared by treating a solution of chromium(II) acetate with hydrogen chloride:[6]
- Cr2(OAc)4 + 4 HCl → 2 CrCl2 + 4 AcOH
Treatment of chromium powder with concentrated hydrochloric acid gives a blue hydrated chromium(II) chloride, which can be converted to a related acetonitrile complex.[7]
- Cr + n H2O + 2 HCl → CrCl2(H2O)n + H2
Structure and properties
Anhydrous CrCl2 is white[6] however commercial samples are often grey or green. It crystallizes in the Pnnm space group, which is an orthorhombically distorted variant of the rutile structure; making it isostructural to calcium chloride. The Cr centres are octahedral, being distorted by the Jahn-Teller Effect.[8]
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The hydrated derivative, CrCl2(H2O)4, forms monoclinic crystals with the P21/c space group. The molecular geometry is approximately octahedral consisting of four short Cr—O bonds (2.078 Å) arranged in a square planar configuration and two longer Cr—Cl bonds (2.758 Å) in a trans configuration.[3]
Reactions
The reduction potential for Cr3+ + e− ⇄ Cr2+ is −0.41. Since the reduction potential of H+ to H2 in acidic conditions is +0.00, the chromous ion has sufficient potential to reduce acids to hydrogen, although this reaction does not occur without a catalyst.
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.[9] It is a reagent in the Nozaki-Hiyama-Kishi reaction, a useful method for preparing medium-size rings.[10] It is also used in the Takai olefination to form vinyl iodides from aldehydes in the presence of iodoform.[11]
References
- ↑ 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 Lide, David R., ed (2009). CRC Handbook of Chemistry and Physics (90th ed.). Boca Raton, Florida: CRC Press. ISBN 978-1-4200-9084-0.
- ↑ 2.0 2.1 2.2 2.3 2.4 Tracy, Joseph W.; Gregory, N.W.; Lingafelter, E.C.; Dunitz, J.D.; Mez, H.-C.; Rundle, R.E.; Scheringer, Christian; Yakel, H.L. et al. (1961). "The crystal structure of chromium(II) chloride". Acta Crystallographica 4 (9): 927–929. doi:10.1107/S0365110X61002710.
- ↑ 3.0 3.1 3.2 3.3 Schnering, H.G. von; Brand, B.-H. (1973). "Struktur und Eigenschaften des blauen Chrom(II)-chlorid-tetrahydrats CrCl2.4H2O". Zeitschrift für anorganische und allgemeine Chemie 402 (2): 159–168. doi:10.1002/zaac.19734020206.
- ↑ 4.0 4.1 4.2 Sigma-Aldrich Co., Chromium(II) chloride. Retrieved on 2014-07-04.
- ↑ 5.0 5.1 "MSDS of Chromium(II) chloride". Fisher Scientific. https://www.fishersci.ca/viewmsds.do?catNo=AC315190250.
- ↑ 6.0 6.1 Riley, edited by Georg Brauer ; translated by Scripta Technica, Inc. Translation editor Reed F. (1963). Handbook of Preparative Inorganic Chemistry. Volume 1 (2nd ed.). New York, N.Y.: Academic Press. p. 1337. ISBN 978-0121266011.
- ↑ Holah, David G.; Fackler, John P. (1967). "Chromium(II) Salts and Complexes". Inorganic Syntheses. Inorganic Syntheses. 10. pp. 26–35. doi:10.1002/9780470132418.ch4. ISBN 9780470132418.
- ↑ Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. pp. 1021–1022. ISBN 978-0-08-037941-8.
- ↑ (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.
- ↑ Simple and selective method for aldehydes (RCHO) -> (E)-haloalkenes (RCH:CHX) conversion by means of a haloform-chromous chloride system K. Takai, K. Nitta, K. Utimoto J. Am. Chem. Soc.; 1986; 108(23); 7408-7410. doi:10.1021/ja00283a046.
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