-chloride-purple-anhydrous-sunlight.jpg) Anhydrous | |
 Hexahydrate | |
| Names | |
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IUPAC name
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| Other names Chromic chloride | |
| Identifiers | |
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3D model (JSmol) |
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| ChEBI | |
| ChEMBL | |
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| DrugBank | |
| ECHA InfoCard | 100.030.023 |
| 1890 130477 532690 | |
| RTECS number |
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| Properties | |
| CrCl3 | |
| Molar mass | 158.36 g/mol (anhydrous) 266.45 g/mol (hexahydrate)[1] |
| Appearance | Purple (anhydrous), dark green (hexahydrate) |
| Density | 2.87 g/cm3 (anhydrous) 1.760 g/cm3 (hexahydrate) |
| Melting point | 1,152 °C (2,106 °F; 1,425 K) (anhydrous) 81 °C (hexahydrate)[2] |
| Boiling point | 1,300 °C (2,370 °F; 1,570 K) decomposes |
| slightly soluble (anhydrous) 585 g/L (hexahydrate) | |
| Solubility | insoluble inethanol insoluble inether,acetone |
| Acidity (pKa) | 2.4 (0.2M solution) |
| +6890.0·10−6 cm3/mol | |
| Structure | |
| YCl3 structure | |
| Octahedral | |
| Hazards | |
| GHS labelling: | |
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| Danger | |
| H302,H314,H411 | |
| P260,P264,P270,P273,P280,P301+P312,P301+P330+P331,P303+P361+P353,P304+P340,P305+P351+P338,P310,P321,P330,P363,P391,P405,P501 | |
| NFPA 704 (fire diamond) | |
| Flash point | Non-flammable |
| Lethal dose or concentration (LD, LC): | |
LD50 (median dose) | 1870 mg/kg (oral, rat)[4] |
| NIOSH (US health exposure limits): | |
PEL (Permissible) | TWA 1 mg/m3[3] |
REL (Recommended) | TWA 0.5 mg/m3[3] |
IDLH (Immediate danger) | 250 mg/m3[3] |
| Safety data sheet (SDS) | ICSC 1316 (anhydrous) ICSC 1532 (hexahydrate) |
| Related compounds | |
Otheranions | |
Othercations | |
Related compounds | |
Except where otherwise noted, data are given for materials in theirstandard state (at 25 °C [77 °F], 100 kPa). | |
Chromium(III) chloride (also calledchromic chloride) is aninorganic chemical compound with thechemical formulaCrCl3. This crystalline salt forms severalhydrates with the formulaCrCl3·nH2O, among which are hydrates wheren can be 5 (chromium(III) chloride pentahydrateCrCl3·5H2O) or 6 (chromium(III) chloride hexahydrateCrCl3·6H2O). Theanhydrous compound with the formulaCrCl3 are violetcrystals, while the most common form of the chromium(III) chloride are the dark green crystals of hexahydrate,CrCl3·6H2O. Chromium chlorides find use ascatalysts and as precursors to dyes for wool.
Anhydrous chromium(III) chloride adopts theYCl3 structure,[6] withCr3+ occupying one third of theoctahedral interstices in alternating layers of a pseudo-cubic close packed lattice ofCl− ions. The absence of cations in alternate layers leads to weak bonding between adjacent layers. For this reason, crystals ofCrCl3cleave easily along the planes between layers, which results in the flaky (micaceous) appearance of samples of chromium(III) chloride.[7][8] The anhydrousCrCl3 is exfoliable down to the monolayer limit.[6] If pressurized to 9.9GPa it goes under a phase transition.[9]
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The hydrated chromium(III) chlorides display the somewhat unusual property of existing in a number of distinct chemical forms (isomers), which differ in terms of the number of chloride anions that are coordinated to Cr(III) and thewater of crystallization. The different forms exist both as solids and inaqueous solutions. Several members are known of the series of[CrCl3−q(H2O)n]q+. The common hexahydrate can be more precisely described as[CrCl2(H2O)4]Cl·2H2O. It consists of the cationtrans-[CrCl2(H2O)4]+ and additional molecules of water and a chloride anion in the lattice.[10] Two other hydrates are known, pale green[CrCl(H2O)5]Cl2·H2O and violet[Cr(H2O)6]Cl3. Similarhydration isomerism is seen with other chromium(III) compounds.[citation needed]
Anhydrous chromium(III) chloride may be prepared bychlorination ofchromium metal directly, or indirectly bycarbothermic chlorination ofchromium(III) oxide at 650–800 °C[11][12]
The hydrated chlorides are prepared by treatment of chromate with hydrochloric acid and aqueous methanol.
Slow reaction rates are common with chromium(III) complexes. The low reactivity of the d3Cr3+ ion can be explained usingcrystal field theory. One way of openingCrCl3 up to substitution in solution is to reduce even a trace amount toCrCl2, for example usingzinc inhydrochloric acid. This chromium(II) compound undergoes substitution easily, and it can exchange electrons withCrCl3 via achloride bridge, allowing all of theCrCl3 to react quickly. With the presence of some chromium(II), solidCrCl3 dissolves rapidly in water. Similarly,ligand substitution reactions of solutions of[CrCl2(H2O)4]+ are accelerated by chromium(II) catalysts.
With moltenalkali metalchlorides such aspotassium chloride,CrCl3 gives salts of the typeM3[CrCl6] andK3[Cr2Cl9], which is also octahedral but where the two chromiums are linked via three chloride bridges.
The hexahydrate can also be dehydrated withthionyl chloride:[13]
CrCl3 is aLewis acid, classified as "hard" according to theHard-Soft Acid-Base theory. It forms a variety of adducts of the type[CrCl3L3]q+, where L is aLewis base. For example, it reacts withpyridine (C5H5N) to form thepyridine complex:
Treatment withtrimethylsilylchloride inTHF gives the anhydrous THF complex:[14]
Chromium(III) chloride is used as the precursor to manyorganochromium compounds, for examplebis(benzene)chromium, an analogue offerrocene:
Phosphine complexes derived fromCrCl3 catalyse the trimerization ofethylene to1-hexene.[15][16]
One niche use ofCrCl3 inorganic synthesis is for thein situ preparation ofchromium(II) chloride, a reagent for the reduction ofalkyl halides and for the synthesis of (E)-alkenyl halides. The reaction is usually performed using twomoles ofCrCl3 per mole oflithium aluminium hydride, although if aqueous acidic conditions are appropriatezinc andhydrochloric acid may be sufficient.
Chromium(III) chloride has also been used as a Lewis acid in organic reactions, for example to catalyse the nitrosoDiels-Alder reaction.[17]
A number of chromium-containing dyes are used commercially for wool. Typical dyes aretriarylmethanes consisting of ortho-hydroxylbenzoic acid derivatives.[18]
Althoughtrivalent chromium is far less poisonous thanhexavalent, chromium salts are generally considered toxic.
