Chromium(III) chloride

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Chromium(III) chloride
Chromium(III)-chloride-purple-anhydrous-sunlight.jpg
Anhydrous
Chromium chloride.jpg
Hexahydrate
Names
IUPAC names
Chromium(III) chloride
Chromium trichloride
Other names
Chromic chloride
Identifiers
3D model (JSmol)
ChEBI
ChEMBL
ChemSpider
DrugBank
ECHA InfoCard 100.030.023 OOjs UI icon edit-ltr-progressive.svg
1890 130477 532690
PubChem CID
RTECS number
  • GB5425000
UNII
  • InChI=1S/3ClH.Cr/h3*1H;/q;;;+3/p-3 Yes check.svgY
    Key: QSWDMMVNRMROPK-UHFFFAOYSA-K Yes check.svgY
  • InChI=1/3ClH.Cr/h3*1H;/q;;;+2/p-3
    Key: HUQISNLCWMVGCG-DFZHHIFOAJ
  • InChI=1/3ClH.Cr/h3*1H;/q;;;+3/p-3
    Key: QSWDMMVNRMROPK-DFZHHIFOAF
  • Cl[Cr](Cl)Cl
Properties
CrCl3
Molar mass 158.36 g/mol (anhydrous)
266.45 g/mol (hexahydrate) [1]
Appearancepurple (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 in ethanol
insoluble in ether, acetone
Acidity (pKa)2.4 (0.2M solution)
+6890.0·10−6 cm3/mol
Structure
YCl3 structure
Octahedral
Hazards
GHS labelling:
GHS-pictogram-acid.svg GHS-pictogram-exclam.svg GHS-pictogram-pollu.svg
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)
[3]
3
0
0
Flash point Non-flammable
Lethal dose or concentration (LD, LC):
1870 mg/kg (oral, rat) [4]
NIOSH (US health exposure limits):
PEL (Permissible)
TWA 1 mg/m3 [5]
REL (Recommended)
TWA 0.5 mg/m3 [5]
IDLH (Immediate danger)
250 mg/m3 [5]
Safety data sheet (SDS) ICSC 1316 (anhydrous)
ICSC 1532 (hexahydrate)
Related compounds
Other anions
Chromium(III) fluoride
Chromium(III) bromide
Chromium(III) iodide
Other cations
Molybdenum(III) chloride
Tungsten(III) chloride
Related compounds
Chromium(II) chloride
Chromium(IV) chloride
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
X mark.svgN  verify  (what is  Yes check.svgYX mark.svgN ?)

Chromium(III) chloride (also called chromic chloride) describes any of several chemical compounds with the formula CrCl3 · x H2O , where x can be 0, 5, and 6. The anhydrous compound with the formula CrCl3 is a violet solid. The most common form of the trichloride is the dark green hexahydrate, CrCl3 · 6 H2O . Chromium chlorides find use as catalysts and as precursors to dyes for wool.

Contents

Structure

Anhydrous chromium(III) chloride adopts the YCl3 structure, with Cr3+ occupying one third of the octahedral interstices in alternating layers of a pseudo-cubic close packed lattice of Cl ions. The absence of cations in alternate layers leads to weak bonding between adjacent layers. For this reason, crystals of CrCl3 cleave easily along the planes between layers, which results in the flaky (micaceous) appearance of samples of chromium(III) chloride. [6] [7] If pressurized to 9.9 GPa it goes under a phase transition. [8]


Chromium(III) chloride hydrates

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 the water of crystallization. The different forms exist both as solids and in aqueous solutions. Several members are known of the series of [CrCl3−z(H2O)n]z+. The common hexahydrate can be more precisely described as [CrCl2(H2O)4]Cl · 2 H2O . It consists of the cation trans-[CrCl2(H2O)4]+ and additional molecules of water and a chloride anion in the lattice. [9] Two other hydrates are known, pale green [CrCl(H2O)5]Cl2 · H2O and violet [Cr(H2O)6]Cl3. Similar isomerism is seen with other chromium(III) compounds.

Preparation

Anhydrous chromium(III) chloride may be prepared by chlorination of chromium metal directly, or indirectly by carbothermic chlorination of chromium(III) oxide at 650–800 °C [10] [11]

Cr2O3 + 3 C + 3 Cl2 → 2 CrCl3 + 3 CO

The hydrated chlorides are prepared by treatment of chromate with hydrochloric acid and aqueous methanol.

Reactions

Slow reaction rates are common with chromium(III) complexes. The low reactivity of the d3 Cr3+ ion can be explained using crystal field theory. One way of opening CrCl3 up to substitution in solution is to reduce even a trace amount to CrCl2, for example using zinc in hydrochloric acid. This chromium(II) compound undergoes substitution easily, and it can exchange electrons with CrCl3 via a chloride bridge, allowing all of the CrCl3 to react quickly.

With the presence of some chromium(II), however, solid CrCl3 dissolves rapidly in water. Similarly, ligand substitution reactions of solutions of [CrCl2(H2O)4]+ are accelerated by chromium(II) catalysts.

With molten alkali metal chlorides such as potassium chloride, CrCl3 gives salts of the type M3CrCl6 and K3Cr2Cl9, which is also octahedral but where the two chromiums are linked via three chloride bridges.

The hexahydrate can also be dehydrated with thionyl chloride: [12]

CrCl3 · 6 H2O + 6 SOCl2 → CrCl3 + 6 SO2 + 12 HCl

Complexes with organic ligands

CrCl3 is a Lewis acid, classified as "hard" according to the Hard-Soft Acid-Base theory. It forms a variety of adducts of the type [CrCl3L3]z, where L is a Lewis base. For example, it reacts with pyridine (C
5
H
5
N
) to form the pyridine complex:

CrCl3 + 3 C5H5N → CrCl3(C5H5N)3

Treatment with trimethylsilylchloride in THF gives the anhydrous THF complex: [13]

CrCl3 · 6 H2O + 12 Me3SiCl → CrCl3(THF)3 + 6 (Me3Si)2O + 12 HCl

Precursor to organochromium complexes

Chromium(III) chloride is used as the precursor to many organochromium compounds, for example bis(benzene)chromium, an analogue of ferrocene:

CrCl3 dibenzenechromium.png

Phosphine complexes derived from CrCl3 catalyse the trimerization of ethylene to 1-hexene. [14] [15]

Use in organic synthesis

One niche use of CrCl3 in organic synthesis is for the in situ preparation of chromium(II) chloride, a reagent for the reduction of alkyl halides and for the synthesis of (E)-alkenyl halides. The reaction is usually performed using two moles of CrCl3 per mole of lithium aluminium hydride, although if aqueous acidic conditions are appropriate zinc and hydrochloric acid may be sufficient.

CrCl3 CrCl2.png

Chromium(III) chloride has also been used as a Lewis acid in organic reactions, for example to catalyse the nitroso Diels-Alder reaction. [16]

Dyestuffs

A number of chromium-containing dyes are used commercially for wool. Typical dyes are triarylmethanes consisting of ortho-hydroxylbenzoic acid derivatives. [17]

Precautions

Although trivalent chromium is far less poisonous than hexavalent, chromium salts are generally considered toxic.

Related Research Articles

Iron(III) chloride Inorganic compound

Iron(III) chloride is the inorganic compound with the formula FeCl3. Also called ferric chloride, it is a common compound of iron in the +3 oxidation state. The anhydrous compound is a crystalline solid with a melting point of 307.6 °C. The color depends on the viewing angle: by reflected light the crystals appear dark green, but by transmitted light they appear purple-red.

Zinc chloride Chemical compound

Zinc chloride is the name of inorganic chemical compounds with the formula ZnCl2 and its hydrates. Zinc chlorides, of which nine crystalline forms are known, are colorless or white, and are highly soluble in water. This salt is hygroscopic and even deliquescent. Zinc chloride finds wide application in textile processing, metallurgical fluxes, and chemical synthesis. No mineral with this chemical composition is known aside from the very rare mineral simonkolleite, Zn5(OH)8Cl2·H2O.

Praseodymium(III) chloride Chemical compound

Praseodymium(III) chloride is the inorganic compound with the formula PrCl3. Like other lanthanide trichlorides, it exists both in the anhydrous and hydrated forms. It is a blue-green solid that rapidly absorbs water on exposure to moist air to form a light green heptahydrate.

Samarium(III) chloride Chemical compound

Samarium(III) chloride, also known as samarium trichloride, is an inorganic compound of samarium and chloride. It is a pale yellow salt that rapidly absorbs water to form a hexahydrate, SmCl3.6H2O. The compound has few practical applications but is used in laboratories for research on new compounds of samarium.

Europium(III) chloride Chemical compound

Europium(III) chloride is an inorganic compound with the formula EuCl3. The anhydrous compound is a yellow solid. Being hygroscopic it rapidly absorbs water to form a white crystalline hexahydrate, EuCl3·6H2O, which is colourless. The compound is used in research.

Aluminium chloride Chemical compound

Aluminium chloride (AlCl3), also known as aluminium trichloride, describe compounds with the formula AlCl3(H2O)n (n = 0 or 6). They consist of aluminium and chlorine atoms in a 1:3 ratio, and one form also contains six waters of hydration. Both are white solids, but samples are often contaminated with iron(III) chloride, giving a yellow color.

Manganese(II) chloride Chemical compound

Manganese(II) chloride is the dichloride salt of manganese, MnCl2. This inorganic chemical exists in the anhydrous form, as well as the dihydrate (MnCl2·2H2O) and tetrahydrate (MnCl2·4H2O), with the tetrahydrate being the most common form. Like many Mn(II) species, these salts are pink, with the paleness of the color being characteristic of transition metal complexes with high spin d5 configurations. It is a paramagnetic salt.

Cobalt(II) chloride Chemical compound

Cobalt(II) chloride is an inorganic compound of cobalt and chlorine, with the formula CoCl
2
. The compound forms several hydrates CoCl
2
nH
2
O
, for n = 1, 2, 6, and 9. Claims of the formation of tri- and tetrahydrates have not been confirmed. The anhydrous form is a blue crystalline solid; the dihydrate is purple and the hexahydrate is pink. Commercial samples are usually the hexahydrate, which is one of the most commonly used cobalt compounds in the lab.

Copper(II) chloride Chemical compound

Copper(II) chloride is the chemical compound with the chemical formula CuCl2. The anhydrous form is yellowish brown but slowly absorbs moisture to form a blue-green dihydrate.

Nickel(II) chloride Chemical compound

Nickel(II) chloride (or just nickel chloride) is the chemical compound NiCl2. The anhydrous salt is yellow, but the more familiar hydrate NiCl2·6H2O is green. Nickel(II) chloride, in various forms, is the most important source of nickel for chemical synthesis. The nickel chlorides are deliquescent, absorbing moisture from the air to form a solution. Nickel salts have been shown to be carcinogenic to the lungs and nasal passages in cases of long-term inhalation exposure.

Iron(II) chloride Chemical compound

Iron(II) chloride, also known as ferrous chloride, is the chemical compound of formula FeCl2. It is a paramagnetic solid with a high melting point. The compound is white, but typical samples are often off-white. FeCl2 crystallizes from water as the greenish tetrahydrate, which is the form that is most commonly encountered in commerce and the laboratory. There is also a dihydrate. The compound is highly soluble in water, giving pale green solutions.

Thionyl chloride Chemical compound

Thionyl chloride is an inorganic compound with the chemical formula SOCl
2
. It is a moderately volatile colourless liquid with an unpleasant acrid odour. Thionyl chloride is primarily used as a chlorinating reagent, with approximately 45,000 tonnes per year being produced during the early 1990s, but is occasionally also used as a solvent. It is toxic, reacts with water, and is also listed under the Chemical Weapons Convention as it may be used for the production of chemical weapons.

Tin(II) chloride Chemical compound

Tin(II) chloride, also known as stannous chloride, is a white crystalline solid with the formula SnCl2. It forms a stable dihydrate, but aqueous solutions tend to undergo hydrolysis, particularly if hot. SnCl2 is widely used as a reducing agent (in acid solution), and in electrolytic baths for tin-plating. Tin(II) chloride should not be confused with the other chloride of tin; tin(IV) chloride or stannic chloride (SnCl4).

Scandium chloride Chemical compound

Scandium(III) chloride is the inorganic compound with the formula ScCl3. It is a white, high-melting ionic compound, which is deliquescent and highly water-soluble. This salt is mainly of interest in the research laboratory. Both the anhydrous form and hexahydrate (ScCl3•6H2O) are commercially available.

Chromium(III) fluoride Chemical compound

Chromium(III) fluoride is the name for the inorganic compounds with the chemical formula CrF3 as well as several related hydrates. The compound CrF3 is a green crystalline solid that is insoluble in common solvents, but the coloured hydrates [Cr(H2O)6]F3 and [Cr(H2O)6]F3•3H2O are soluble in water. The trihydrate is green, and the hexahydrate is violet. The anhydrous form sublimes at 1100–1200 °C.

Trimethylsilyl chloride Chemical compound

Trimethylsilyl chloride, also known as chlorotrimethylsilane is an organosilicon compound (silyl halide), with the formula (CH3)3SiCl, often abbreviated Me3SiCl or TMSCl. It is a colourless volatile liquid that is stable in the absence of water. It is widely used in organic chemistry.

Chromium(II) chloride Chemical compound

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.

Uranyl chloride Chemical compound

Uranyl chloride refers to inorganic compounds with the formula UO2Cl2(H2O)n where n = 0, 1, or 3. These are yellow-colored solids.

Chromyl chloride Chemical compound

Chromyl chloride is the inorganic compound with the formula CrO2Cl2. It is a reddish brown compound that is a volatile liquid at room temperature, which is unusual for transition metal complexes.

Chromium(III) sulfate Chemical compound

Chromium(III) sulfate usually refers to the inorganic compounds with the formula Cr2(SO4)3.x(H2O), where x can range from 0 to 18. Additionally, ill-defined but commercially important "basic chromium sulfates" are known. These salts are usually either violet or green solids that are soluble in water. It is commonly used in tanning leather.

References

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  2. "Chromium(III) chloride hexahydrate Technipur™ | Sigma-Aldrich" . Retrieved 2022-08-16.
  3. Cameo Chemicals MSDS
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  5. 1 2 3 NIOSH Pocket Guide to Chemical Hazards. "#0141". National Institute for Occupational Safety and Health (NIOSH).
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  8. Meiling Hong (2022). "Pressure-Induced Structural Phase Transition and Metallization of CrCl3 under Different Hydrostatic Environments up to 50.0 GPa". Inorg. Chem. 61 (12): 4852–4864. doi:10.1021/acs.inorgchem.1c03486. PMID   35289613. S2CID   247452267.
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  13. Philip Boudjouk, Jeung-Ho So (1992). "Solvated and Unsolvated Anhydrous Metal Chlorides from Metal Chloride Hydrates". Inorganic Syntheses. Inorganic Syntheses. Vol. 29. pp. 108–111. doi:10.1002/9780470132609.ch26. ISBN   9780470132609.{{cite book}}: CS1 maint: uses authors parameter (link)
  14. John T. Dixon, Mike J. Green, Fiona M. Hess, David H. Morgan "Advances in selective ethylene trimerisation – a critical overview" Journal of Organometallic Chemistry 2004, Volume 689, pp 3641-3668. doi : 10.1016/j.jorganchem.2004.06.008
  15. Feng Zheng, Akella Sivaramakrishna, John R. Moss "Thermal studies on metallacycloalkanes" Coordination Chemistry Reviews 2007, Volume 251, 2056-2071. doi : 10.1016/j.ccr.2007.04.008
  16. Calvet, G.; Dussaussois, M.; Blanchard, N.; Kouklovsky, C. (2004). "Lewis Acid-Promoted Hetero Diels-Alder Cycloaddition of α-Acetoxynitroso Dienophiles". Organic Letters . 6 (14): 2449–2451. doi:10.1021/ol0491336. PMID   15228301.
  17. Thomas Gessner and Udo Mayer "Triarylmethane and Diarylmethane Dyes" in Ullmann's Encyclopedia of Industrial Chemistry 2002, Wiley-VCH, Weinheim. doi : 10.1002/14356007.a27_179

Further reading