Aluminium chloride

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Aluminium chloride
Aluminium-trichloride-hexahydrate-white-and-yellow.jpg
Aluminium trichloride hexahydrate, pure (top), and contaminated with iron(III) chloride (bottom)
Aluminium trichloride dimer Aluminium-trichloride-dimer-3D-balls.png
Aluminium trichloride dimer
Aluminium trichloride unit cell Aluminium-chloride-xtal-unit-cell-3D-bs-17.png
Aluminium trichloride unit cell
Names
IUPAC name
Aluminium chloride
Other names
Aluminium(III) chloride
Aluminium trichloride
Identifiers
3D model (JSmol)
ChEBI
ChemSpider
ECHA InfoCard 100.028.371 OOjs UI icon edit-ltr-progressive.svg
EC Number
  • 231-208-1
1876
PubChem CID
RTECS number
  • BD0530000
UNII
  • InChI=1S/Al.3ClH/h;3*1H/q+3;;;/p-3 Yes check.svgY
    Key: VSCWAEJMTAWNJL-UHFFFAOYSA-K Yes check.svgY
  • InChI=1/Al.3ClH/h;3*1H/q+3;;;/p-3
    Key: VSCWAEJMTAWNJL-DFZHHIFOAR
  • monomer:Cl[Al](Cl)Cl
  • dimer:Cl[Al-]1(Cl)[Cl+][Al-]([Cl+]1)(Cl)Cl
Properties
AlCl3
Molar mass
  • 133.341 g/mol (anhydrous)
  • 241.432 g/mol (hexahydrate)
[1]
AppearanceColourless crystals, hygroscopic
Density
  • 2.48 g/cm3 (anhydrous)
  • 2.398 g/cm3 (hexahydrate)
[1]
Melting point
  • 180 °C (356 °F; 453 K) (anhydrous, sublimes) [1]
  • 100 °C (212 °F; 373 K) (hexahydrate, decomposes) [1]
  • 439 g/L (0 °C)
  • 449 g/L (10 °C)
  • 458 g/L (20 °C)
  • 466 g/L (30 °C)
  • 473 g/L (40 °C)
  • 481 g/L (60 °C)
  • 486 g/L (80 °C)
  • 490 g/L (100 °C)
Solubility
  • Soluble in hydrogen chloride, ethanol, chloroform, carbon tetrachloride
  • Slightly soluble in benzene
Vapor pressure
  • 133.3 Pa (99 °C)
  • 13.3 kPa (151 °C)
[2]
Viscosity
  • 0.35 cP (197 °C)
  • 0.26 cP (237 °C)
[2]
Structure
Monoclinic, mS16
C12/m1, No. 12 [3]
a = 0.591 nm, b = 0.591 nm, c = 1.752 nm [3]
0.52996 nm3
6
Octahedral (solid)
Tetrahedral (liquid)
Trigonal planar
(monomeric vapour)
Thermochemistry
91.1 J/(mol·K) [4]
Std molar
entropy
(S298)
109.3 J/(mol·K) [4]
−704.2 kJ/mol [4]
−628.8 kJ/mol [4]
Pharmacology
D10AX01 ( WHO )
Hazards
GHS labelling: [5]
GHS-pictogram-acid.svg
Danger
H314
P260, P280, P301+P330+P331, P303+P361+P353, P305+P351+P338+P310, P310
NFPA 704 (fire diamond)
3
0
2
Lethal dose or concentration (LD, LC):
380 mg/kg, rat (oral, anhydrous)
3311 mg/kg, rat (oral, hexahydrate)
NIOSH (US health exposure limits):
PEL (Permissible)
None [6]
REL (Recommended)
2 mg/m3 [6]
IDLH (Immediate danger)
N.D. [6]
Related compounds
Other anions
Other cations
Related Lewis acids
Supplementary data page
Aluminium chloride (data page)
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 ?)

Aluminium chloride, also known as aluminium trichloride, is an inorganic compound with the formula AlCl3. It forms hexahydrate with the formula [Al(H2O)6]Cl3, containing six water molecules of hydration. Both are colourless crystals, but samples are often contaminated with iron(III) chloride, giving a yellow color.

The anhydrous material is important commercially. It has a low melting and boiling point. It is mainly produced and consumed in the production of aluminium metal, but large amounts are also used in other areas of the chemical industry. [7] The compound is often cited as a Lewis acid. It is an example of an inorganic compound that reversibly changes from a polymer to a monomer at mild temperature.

Structure

Anhydrous

AlCl3 adopts three structures, depending on the temperature and the state (solid, liquid, gas). Solid AlCl3 has a sheet-like layered structure with cubic close-packed chloride ions. In this framework, the Al centres exhibit octahedral coordination geometry. [8] Yttrium(III) chloride adopts the same structure, as do a range of other compounds. When aluminium trichloride is in its melted state, it exists as the dimer Al2Cl6, with tetracoordinate aluminium. This change in structure is related to the lower density of the liquid phase (1.78 g/cm3) versus solid aluminium trichloride (2.48 g/cm3). Al2Cl6 dimers are also found in the vapour phase. At higher temperatures, the Al2Cl6 dimers dissociate into trigonal planar AlCl3 monomer, which is structurally analogous to BF3. The melt conducts electricity poorly, [9] unlike more ionic halides such as sodium chloride.

Aluminium chloride monomer belongs to the point group D3h in its monomeric form and D2h in its dimeric form.

Hexahydrate

Aluminium-trichloride-3D-structures.png

The hexahydrate consists of octahedral [Al(H2O)6]3+ cation centers and chloride anions (Cl) as counterions. Hydrogen bonds link the cation and anions. [10] The hydrated form of aluminium chloride has an octahedral molecular geometry, with the central aluminium ion surrounded by six water ligand molecules. Being coordinatively saturated, the hydrate is of little value as a catalyst in Friedel-Crafts alkylation and related reactions.

Uses

Alkylation and acylation of arenes

AlCl3 is a common Lewis-acid catalyst for Friedel-Crafts reactions, both acylations and alkylations. [11] Important products are detergents and ethylbenzene. These types of reactions are the major use for aluminium chloride, for example, in the preparation of anthraquinone (used in the dyestuffs industry) from benzene and phosgene. [9] In the general Friedel-Crafts reaction, an acyl chloride or alkyl halide reacts with an aromatic system as shown: [11]

Benzene Friedel-Crafts alkylation-diagram.svg

The alkylation reaction is more widely used than the acylation reaction, although its practice is more technically demanding. For both reactions, the aluminium chloride, as well as other materials and the equipment, should be dry, although a trace of moisture is necessary for the reaction to proceed. [12] Detailed procedures are available for alkylation [13] and acylation [14] [15] of arenes.

A general problem with the Friedel-Crafts reaction is that the aluminium chloride catalyst sometimes is required in full stoichiometric quantities, because it complexes strongly with the products. This complication sometimes generates a large amount of corrosive waste. For these and similar reasons, the use of aluminium chloride has often been displaced by zeolites. [7]

Aluminium chloride can also be used to introduce aldehyde groups onto aromatic rings, for example via the Gattermann-Koch reaction which uses carbon monoxide, hydrogen chloride and a copper(I) chloride co-catalyst. [16]

AlCl3 formylation.gif

Other applications in organic and organometallic synthesis

Aluminium chloride finds a wide variety of other applications in organic chemistry. [17] For example, it can catalyse the "ene reaction", such as the addition of 3-buten-2-one (methyl vinyl ketone) to carvone: [18]

AlCl3 ene rxn.gif

It is used to induce a variety of hydrocarbon couplings and rearrangements. [19] [20]

Aluminium chloride combined with aluminium in the presence of an arene can be used to synthesize bis(arene) metal complexes, e.g. bis(benzene)chromium, from certain metal halides via the so-called Fischer-Hafner synthesis. Dichlorophenylphosphine is prepared by reaction of benzene and phosphorus trichloride catalyzed by aluminium chloride. [21]

Reactions

Anhydrous aluminium chloride is a powerful Lewis acid, capable of forming Lewis acid-base adducts with even weak Lewis bases such as benzophenone and mesitylene. [11] It forms tetrachloroaluminate ([AlCl4]) in the presence of chloride ions.

Aluminium chloride reacts with calcium and magnesium hydrides in tetrahydrofuran forming tetrahydroaluminates.

Reactions with water

Anhydrous aluminium chloride is hygroscopic, having a very pronounced affinity for water. It fumes in moist air and hisses when mixed with liquid water as the Cl ligands are displaced with H2O molecules to form the hexahydrate [Al(H2O)6]Cl3. The anhydrous phase cannot be regained on heating the hexahydrate. Instead HCl is lost leaving aluminium hydroxide or alumina (aluminium oxide):

[Al(H2O)6]Cl3 → Al(OH)3 + 3 HCl + 3 H2O

Like metal aquo complexes, aqueous AlCl3 is acidic owing to the ionization of the aquo ligands:

[Al(H2O)6]3+[Al(OH)(H2O)5]2+ + H+

Aqueous solutions behave similarly to other aluminium salts containing hydrated Al3+ ions, giving a gelatinous precipitate of aluminium hydroxide upon reaction with dilute sodium hydroxide:

AlCl3 + 3 NaOH → Al(OH)3 + 3 NaCl

Synthesis

Aluminium chloride is manufactured on a large scale by the exothermic reaction of aluminium metal with chlorine or hydrogen chloride at temperatures between 650 to 750 °C (1,202 to 1,382 °F). [9]

2 Al + 3 Cl2 → 2 AlCl3
2 Al + 6 HCl → 2 AlCl3 + 3 H2

Aluminium chloride may be formed via a single displacement reaction between copper(II) chloride and aluminium metal.

2 Al + 3 CuCl2 → 2 AlCl3 + 3 Cu

In the US in 1993, approximately 21,000 tons were produced, not counting the amounts consumed in the production of aluminium. [7]

Hydrated aluminium trichloride is prepared by dissolving aluminium oxides in hydrochloric acid. Metallic aluminium also readily dissolves in hydrochloric acid ─ releasing hydrogen gas and generating considerable heat. Heating this solid does not produce anhydrous aluminium trichloride, the hexahydrate decomposes to aluminium hydroxide when heated:

[Al(H2O)6]Cl3 → Al(OH)3 + 3 HCl + 3 H2O

Aluminium also forms a lower chloride, aluminium(I) chloride (AlCl), but this is very unstable and only known in the vapour phase. [9]

Natural occurrence

Anhydrous aluminium chloride is not found as a mineral. The hexahydrate, however, is known as the rare mineral chloraluminite. [22] A more complex, basic and hydrated aluminium chloride mineral is cadwaladerite. [23] [22]

Safety

Anhydrous AlCl3 reacts vigorously with bases, so suitable precautions are required. It can cause irritation to the eyes, skin, and the respiratory system if inhaled or on contact. [24]

See also

Related Research Articles

<span class="mw-page-title-main">Iron(III) chloride</span> 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.

The Friedel–Crafts reactions are a set of reactions developed by Charles Friedel and James Crafts in 1877 to attach substituents to an aromatic ring. Friedel–Crafts reactions are of two main types: alkylation reactions and acylation reactions. Both proceed by electrophilic aromatic substitution.

In organic chemistry, an acyl chloride is an organic compound with the functional group −C(=O)Cl. Their formula is usually written R−COCl, where R is a side chain. They are reactive derivatives of carboxylic acids. A specific example of an acyl chloride is acetyl chloride, CH3COCl. Acyl chlorides are the most important subset of acyl halides.

<span class="mw-page-title-main">Acyl halide</span> Oxoacid compound with an –OH group replaced by a halogen

In organic chemistry, an acyl halide is a chemical compound derived from an oxoacid by replacing a hydroxyl group with a halide group.

<span class="mw-page-title-main">Zinc chloride</span> 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.

<span class="mw-page-title-main">Triphenylmethane</span> Chemical compound

Triphenylmethane, or triphenyl methane, is the hydrocarbon with the formula (C6H5)3CH. This colorless solid is soluble in nonpolar organic solvents and not in water. Triphenylmethane is the basic skeleton of many synthetic dyes called triarylmethane dyes, many of them are pH indicators, and some display fluorescence. A trityl group in organic chemistry is a triphenylmethyl group Ph3C, e.g. triphenylmethyl chloride (trityl chloride) and the triphenylmethyl radical (trityl radical).

<span class="mw-page-title-main">Cerium(III) chloride</span> Chemical compound

Cerium(III) chloride (CeCl3), also known as cerous chloride or cerium trichloride, is a compound of cerium and chlorine. It is a white hygroscopic salt; it rapidly absorbs water on exposure to moist air to form a hydrate, which appears to be of variable composition, though the heptahydrate CeCl3·7H2O is known. It is highly soluble in water, and (when anhydrous) it is soluble in ethanol and acetone.

<span class="mw-page-title-main">Manganese(II) chloride</span> 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.

<span class="mw-page-title-main">Chromium(III) chloride</span> Chemical compound

Chromium(III) chloride (also called chromic chloride) describes any of several chemical compounds with the formula CrCl3 · xH2O, 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.

<span class="mw-page-title-main">Nickel(II) chloride</span> 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.

<span class="mw-page-title-main">Iron(II) chloride</span> 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.

<span class="mw-page-title-main">Benzoyl chloride</span> Organochlorine compound (C7H5ClO)

Benzoyl chloride, also known as benzenecarbonyl chloride, is an organochlorine compound with the formula C7H5ClO. It is a colourless, fuming liquid with an irritating odour, and consists of a benzene ring with an acyl chloride substituent. It is mainly useful for the production of peroxides but is generally useful in other areas such as in the preparation of dyes, perfumes, pharmaceuticals, and resins.

<span class="mw-page-title-main">Trimethylsilyl chloride</span> 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.

<span class="mw-page-title-main">Diphenylmethane</span> Chemical compound

Diphenylmethane is an organic compound with the formula (C6H5)2CH2 (often abbreviated CH
2
Ph
2
). The compound consists of methane wherein two hydrogen atoms are replaced by two phenyl groups. It is a white solid.

The Blanc chloromethylation is the chemical reaction of aromatic rings with formaldehyde and hydrogen chloride to form chloromethyl arenes. The reaction is catalyzed by Lewis acids such as zinc chloride. The reaction was discovered by Gustave Louis Blanc (1872-1927) in 1923

<span class="mw-page-title-main">Tetrachloroaluminate</span> Ion

Tetrachloroaluminate [AlCl4] is an anion formed from aluminium and chlorine. The anion has a tetrahedral shape, similar to carbon tetrachloride where carbon is replaced with aluminium. Some tetrachloroaluminates are soluble in organic solvents, creating an ionic non-aqueous solution, making them suitable as component of electrolytes for batteries. For example, lithium tetrachloroaluminate is used in some lithium batteries.

<span class="mw-page-title-main">Sulfenyl chloride</span> Chemical group (R–S–Cl)

In organosulfur chemistry, a sulfenyl chloride is a functional group with the connectivity R−S−Cl, where R is alkyl or aryl. Sulfenyl chlorides are reactive compounds that behave as sources of RS+. They are used in the formation of RS−N and RS−O bonds. According to IUPAC nomenclature they are named as alkyl thiohypochlorites, i.e. esters of thiohypochlorous acid.

<span class="mw-page-title-main">Imidoyl chloride</span>

Imidoyl chlorides are organic compounds that contain the functional group RC(NR')Cl. A double bond exist between the R'N and the carbon centre. These compounds are analogues of acyl chloride. Imidoyl chlorides tend to be highly reactive and are more commonly found as intermediates in a wide variety of synthetic procedures. Such procedures include Gattermann aldehyde synthesis, Houben-Hoesch ketone synthesis, and the Beckmann rearrangement. Their chemistry is related to that of enamines and their tautomers when the α hydrogen is next to the C=N bond. Many chlorinated N-heterocycles are formally imidoyl chlorides, e.g. 2-chloropyridine, 2, 4, and 6-chloropyrimidines.

In organophosphorus chemistry, an aminophosphine is a compound with the formula R3−nP(NR2)n where R = H or an organic substituent, and n = 0, 1, 2. At one extreme, the parent H2PNH2 is lightly studied and fragile, but at the other extreme tris(dimethylamino)phosphine (P(NMe2)3) is commonly available. Intermediate members are known, such as Ph2PN(H)Ph. These compounds are typically colorless and reactive toward oxygen. They have pyramidal geometry at phosphorus.

Lanthanide trichlorides are a family of inorganic compound with the formula LnCl3, where Ln stands for a lanthanide metal. The trichlorides are standard reagents in applied and academic chemistry of the lanthanides. They exist as anhydrous solids and as hydrates.

References

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