Chromium(II) chloride
| 3D model of chromium(II) chloride, green atom is chloride | |
| Sample of chromium(II) chloride | |
| Names | |
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| IUPAC name
Chromium(II) chloride
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| Other names
Chromous chloride
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| Identifiers | |
10049-05-5  |
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| ChemSpider | 23252  |
| Jmol 3D model | Interactive image |
| PubChem | 24871 |
| RTECS number | GB5250000 |
| UNII | CET32HKA21 |
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| Properties | |
| Cl2Cr | |
| Molar mass | 122.90 g·mol−1 |
| Appearance | White to grey/green powder (anhydrous), very hygroscopic |
| 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 |
| 7.23·10−3 cm3/mol[1] | |
| Structure | |
| Orthorhombic (deformed rutile, anhydrous), oP6[2] Monoclinic (tetrahydrate)[3] |
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| Pnnm, No. 58 (anhydrous)[2] P21/c, No. 14 (tetrahydrate)[3] |
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| 2/m 2/m 2/m (anhydrous)[2] 2/m (tetrahydrate)[3] |
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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 | |
| 71.2 J/mol·K[1] | |
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Std molar
entropy (S |
115.3 J/mol·K[1] |
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Std enthalpy of
formation (ΔfH |
−395.4 kJ/mol[1] |
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Gibbs free energy (ΔfG˚)
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−356 kJ/mol[1] |
| Vapor pressure | {{{value}}} |
| Related compounds | |
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Other anions
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Chromium(II) fluoride Chromium(II) bromide Chromium(II) iodide |
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Other cations
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Chromium(III) chloride Chromium(IV) chloride Molybdenum(II) chloride Tungsten(II) chloride |
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Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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 verify (what is ?) |
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| Infobox references | |
Chromium(II) chloride is an inorganic compound with the formula CrCl2. This crystalline 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 [Cr(H2O)4]Cl2. Chromium(II) chloride has no industrial uses but is used on a laboratory-scale for the synthesis of other chromium complexes.
Synthesis
CrCl2 is produced by reducing chromium(III) chloride with hydrogen at 500 °C:[4]
- 2 CrCl3 + H2 → 2 CrCl2 + 2 HCl
Small scale preparations can use LiAlH4, Zinc or related reagents, to reduce CrCl3
- 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.[5]
- Cr2(OAc)4 + 4 HCl → 2 CrCl2 + 4 AcOH
Structure and Properties
Anhydrous CrCl2 is white[5] 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.[6]
The hydrated derivative, CrCl2(H2O)4, forms monoclinic crystals with the P21/c space group. The molecular geometry is approximately square planar with Cr—O distances of 2.078 Å and two Cr—Cl distances of 2.758 Å.[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 ions 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.[7] It is a reagent in the Nozaki-Hiyama-Kishi reaction, a useful method for preparing medium-size rings.[8] It is also used in the Takai olefination to form vinyl iodides from aldehydes in the presence of iodoform.[9]
References
- ↑ 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 Lua error in package.lua at line 80: module 'strict' not found.
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- ↑ 3.0 3.1 3.2 3.3 Lua error in package.lua at line 80: module 'strict' not found.
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- ↑ 5.0 5.1 Lua error in package.lua at line 80: module 'strict' not found.
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- ↑ (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.
