Friedel–Crafts catalyst

Aluminium chloride

Names
IUPAC name aluminium chloride
Other names aluminium(III) chloride aluminum trichloride
Identifiers
CAS Number	7446-70-0 (anhydrous) Y 10124-27-3 (hydrate) N 7784-13-6 (hexahydrate) N
3D model (JSmol)	Interactive image Interactive image
ChEBI	CHEBI:30114 Y
ChemSpider	22445 Y
ECHA InfoCard	100.028.371
Gmelin Reference	1876
PubChem CID	24012
RTECS number	BD0530000
UNII	LIF1N9568Y Y
InChI InChI=1S/Al.3ClH/h;3*1H/q+3;;;/p-3 Y Key: VSCWAEJMTAWNJL-UHFFFAOYSA-K Y InChI=1/Al.3ClH/h;3*1H/q+3;;;/p-3 Key: VSCWAEJMTAWNJL-DFZHHIFOAR
SMILES Cl[Al](Cl)Cl [Al](Cl)(Cl)Cl
Properties
Chemical formula	AlCl3
Molar mass	133.341 g/mol (anhydrous) 241.432 g/mol (hexahydrate)
Appearance	white or pale yellow solid, hygroscopic
Density	2.48 g/cm3 (anhydrous) 2.398 g/cm3 (hexahydrate)
Melting point	192.6 °C (378.7 °F; 465.8 K) (anhydrous) 100 °C (212 °F; 373 K) (hexahydrate, dec.)
Boiling point	180 °C (356 °F; 453 K) (sublimates)
Solubility in water	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)
Viscosity	0.35 cP (197 °C) 0.26 cP (237 °C)
Structure
Crystal structure	Monoclinic, mS16
Space group	C12/m1, No. 12
Lattice constant	a = 0.591 nm, b = 0.591 nm, c = 1.752 nm
Lattice volume (V)	0.52996 nm3
Formula units (Z)	6
Coordination geometry	Octahedral (solid) Tetrahedral (liquid)
Molecular shape	Trigonal planar (monomeric vapour)
Thermochemistry
Specific heat capacity (C)	91.1 J/mol·K
Std molar entropy (So298)	109.3 J/mol·K
Std enthalpy of formation (ΔfHo298)	−704.2 kJ/mol
Gibbs free energy (ΔfG˚)	-628.8 kJ/mol
Pharmacology
ATC code	D10AX01 (WHO)
Hazards
Safety data sheet	See: data page
GHS pictograms
GHS signal word	Danger
GHS hazard statements	H314
GHS precautionary statements	P280, P310, P305+351+338
NFPA 704	0 3 2
Lethal dose or concentration (LD, LC):
LD50 (median dose)	anhydrous: 380 mg/kg, rat (oral) hexahydrate: 3311 mg/kg, rat (oral)
US health exposure limits (NIOSH):
PEL (Permissible)	none
REL (Recommended)	2 mg/m3
IDLH (Immediate danger)	N.D.
Related compounds
Other anions	Aluminium fluoride Aluminium bromide Aluminium iodide
Other cations	Boron trichloride Gallium trichloride Indium(III) chloride Magnesium chloride
Related Lewis acids	Iron(III) chloride Boron trifluoride
Supplementary data page
Structure and properties	Refractive index (n), Dielectric constant (εr), etc.
Thermodynamic data	Phase behaviour solid–liquid–gas
Spectral data	UV, IR, NMR, MS
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N  (what is YN ?)
Infobox references

Aluminium chloride (AlCl₃) is the main compound of aluminium and chlorine. It is white, but samples are often contaminated with iron(III) chloride, giving it a yellow color. The solid 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 chemical industry. The compound is often cited as a Lewis acid. It is an example of an inorganic compound that "cracks" at mild temperature, reversibly changing from a polymer to a monomer.

AlCl₃ adopts three different structures, depending on the temperature and the state (solid, liquid, gas). Solid AlCl₃ is a sheet-like layered cubic close packed layers. In this framework, the Al centres exhibit octahedral coordination geometry. In the melt, aluminium trichloride 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) vs 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, which is structurally analogous to BF₃. The melt conducts electricity poorly, unlike more ionic halides such as sodium chloride.

The hexahydrate consists of octahedral [Al(H₂O)₆]³⁺ centers and chloride counterions. Hydrogen bonds link the cation and anions. The hydrated form of aluminium chloride has an octahedral molecular geometry, with the central aluminum ion surrounded by six water ligand molecules. This means that the hydrated form cannot act as a Lewis acid since it cannot accept electron pairs, and thus this cannot be used as a catalyst in Friedel-Crafts alkylation of aromatic compounds.