Aluminum chloride (AlCl3 ), also known as aluminum trichloride , describes compounds with the formula AlCl3 (H2 O) n (n = 0 or 6). They contain aluminum and chlorine atoms in a ratio of 1:3 , and also contain six waters of hydration in one form. Both are white solids, but samples are often contaminated with iron(III) chloride , which gives a yellow colour.
Anhydrous content is commercially important. It has low melting point and boiling point. It is mainly produced and consumed in the production of aluminum metal, but is also used in large quantities 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 temperatures.
| Property | |
|---|---|
| chemical formula | AlCl 3 |
| 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 | 180 °C (356 °F; 453 K) (anhydrous, sublimes) 100 °C (212 °F; 373 K) (hexahydrate, Dec.) |
| 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 | Slightly soluble in benzene, soluble in hydrogen chloride, ethanol, chloroform, carbon tetrachloride |
| vapor pressure | 133.3 Pa (99 °C) 13.3 kPa (151 °C) |
| viscosity | 0.35 CP (197 °C) 0.26 CP (237 °C) |
| related compound | |
|---|---|
| other ions | Aluminum Fluoride Aluminum Bromide Aluminum Iodidebro |
| other quotes | Boron Trichloride Gallium Trichloride Indium(III) Chloride Magnesium Chloride |
| Related Lewis Acids | iron(III) chloride boron trifluoride |
Use
Alkylation and acylation of arenes
AlCl3 is a common Lewis-acid catalyst for Friedel–Crafts reactions, both acylation and alkylation. [8] Important products are detergents and ethylbenzene. These types of reactions are, for example, the major uses for aluminum chloride in the preparation of anthraquinone (used in dyestuffs from industry) and cyanogen. [9] In the typical Friedel–Crafts reaction, an acyl chloride or alkyl halide reacts with an aromatic system as shown:
The alkylation reaction is more widely used than the acylation reaction, although its practice is more technically demanding. For both reactions, aluminum chloride, as well as other materials and equipment, must be dry, although a trace of moisture is necessary for the reaction to proceed. [10] Detailed procedures are available for alkylation [11] and acylation [12] [13] arenes .
A common problem with the Friedel–Crafts reaction is that the aluminum chloride catalyst is sometimes required in absolute stoichiometric quantities, as it is strongly complexed with the products. This complication sometimes generates large amounts of corrosive waste. For these and similar reasons, the use of aluminum chloride has often been replaced by zeolites. [7]
Aluminum 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.
Other applications in organic and organometallic synthesis
Aluminum chloride finds a wide variety of other applications in organic chemistry. [15] For example, it can catalyze an “NE reaction”, such as the addition of 3-butene-2-one (methyl vinyl ketone) to a carvone:
It is used to induce a variety of hydrocarbon couplings and rearrangements.
Aluminum chloride combined with aluminum in the presence of arene can be used to synthesize bis(arene) metal complexes, such as bis(benzene)chromium, from certain metal halides via the so-called Fischer–Hafner synthesis. Dichlorophenylphosphine is prepared by the reaction of benzene and phosphorus trichloride catalyzed by aluminum chloride. [19]
structure
anhydrous
AlCl 3 adopts three structures depending on the temperature and state (solid, liquid, gas). Solid AlCl 3 is a sheet-like layered cubic close packed layer. In this framework, the Al centers exhibit octahedral coordination geometry. [20] Yttrium(III) chloride adopts the same structure as a range of other compounds. When aluminum trichloride is in its molten state, it exists as the dimer Al 2 Cl 6 with tetracoordinate aluminum . This change in composition is related to the lower density of the liquid phase (1.78 g/cm3 ) versus the solid aluminum trichloride (2.48 g/cm ) . al 2 cl 6Dimers are also found in the vapor phase. At higher temperatures, Al 2 Cl 6 dimers dissociate into tri-planar AlCl 3 , which is structurally analogous to Bf 3. Unlike more ionic halides such as sodium chloride, the melt conducts electricity poorly,
The aluminum chloride monomer belongs to the point group D 3h in its monomeric form and D 2h in its dimeric form .
hexahydrate
The hexahydrate has octahedral [Al( H2O ) 6 ] 3+ centers and chloride counterions. Hydrogen bonds link cations and anions. [21] The hydrated form of aluminum chloride has an octahedral molecular geometry, with the central aluminum ion surrounded by six water ligand molecules. Being coordinately saturated, the hydrate is of little value as a catalyst in the Friedel–Crafts alkylation and related reactions.
reactions
Anhydrous aluminum chloride is a potent Lewis acid, capable of forming Lewis acid-base adducts with weak Lewis bases such as benzophenone and mesitylene. [8] It forms tetrachloroaluminate (AlCl 4 – ) in the presence of chloride ions .
Aluminum chloride reacts with calcium and magnesium hydrides in tetrahydrofuran to form tetrahydroaluminates.
react with water
Anhydrous aluminum chloride is hygroscopic, with a very pronounced affinity for water. It fumes in moist air and puffs when mixed with liquid water as the Cl – ligands displace with the H 2 O molecules to form the hexahydrate [Al(H 2 O) 6 ]Cl 3 . The anhydrous phase cannot be recovered upon heating the hexahydrate. HCl is lost instead, leaving aluminum hydroxide or alumina (aluminum oxide):
Al (H 2 O) 6 Cl 3 → Al (OH) 3 + 3 HCl + 3 H 2 O
Like metal aquo complexes, aqueous AlCl 3 is acidic due to ionization of aquo ligands:
[Al (H 2 O) 6 ] 3+ [Al (OH) (H 2 O) 5 ] 2+ + H +
Aqueous solutions behave similarly to other aluminum salts containing hydrated Al 3+ ions, which upon reaction with dilute sodium hydroxide give a gelatinous precipitate of aluminum hydroxide:
AlCl 3 + 3 NaOH → [Al(OH) 3 ] + 3 NaCl
synthesis
Aluminum chloride is produced largely by the exothermic reaction of aluminum metal with chlorine or hydrogen chloride at temperatures between 650 to 750 °C (1,202 to 1,382 °F).
2 Al + 3 Cl 2 → 2 AlCl 3
2Al + 6HCl → 2AlCl 3 + 3H 2
Aluminum chloride can be formed through a single displacement reaction between copper chloride and aluminum metal.
2 Al + 3 CuCl 2 → 2 AlCl 3 + 3 Cu
In the US in 1993, approximately 21,000 tonnes were produced, not counting the quantity consumed in the production of aluminum.
Hydrated aluminum trichloride is prepared by dissolving aluminum oxide in hydrochloric acid. Metallic aluminum also dissolves readily in hydrochloric acid – releasing hydrogen gas and producing considerable heat. Heating this solid does not form anhydrous aluminum trichloride, the hexahydrate on heating decomposes into aluminum hydroxide:
Al (H 2 O) 6 Cl 3 → Al (OH) 3 + 3 HCl + 3 H 2 O
Aluminum also forms a lower chloride, aluminum(I) chloride (AlCl), but it is very unstable and is known to exist only in the vapor phase.
natural phenomena
The anhydrous compound is now unknown among minerals. However, the hexahydrate is known as the rare mineral chloraluminite. [22] A more complex, basic and hydrated mineral is cadwalderite.
Security
Anhydrous AlCl 3 reacts vigorously with bases, so appropriate precautions are required. It can cause eye, skin and respiratory tract irritation when inhaled or in contact.
Observation
Aluminum chloride (AlCl3), also known as aluminum trichloride, is the main compound of aluminum and chlorine . It is white, but samples are often contaminated with iron(III) chloride, which gives it a yellow colour. Solids have low melting and boiling points. It is mainly produced and consumed in the production of aluminum metal, but is also used in large quantities in other areas of the chemical industry . The compound is often cited as a Lewis acid. It is an example of an inorganic compound that changes from a polymer to a monomer at mild temperatures.
The chemical formula is AlCl 3 . Anhydrides and crystals are hydrates with 6 molecules of water, and they have different properties in different ways.
anhydrous aluminum chloride
White solid, usually yellow due to impurities. Melting point 182.7 °C (755mmHg). It is highly volatile and sublimes above 180 °C. Specific gravity 2.44 (25 °C). It is made by reacting aluminum metal with chlorine or hydrogen chloride gas . It is highly deliquescent and hydrolyzes in humid air to produce white hydrogen chloride fumes . The solid has a macromolecular structure as shown in the figure , with 6Cl bonded to Al and 2Cl bonded to Al. The gas is a dimer represented by Al 2 Cl 6 , and four Cl bonds to Al in the tetrahedral form. However, it becomes monomeric AlCl 3 at 800 °C or more. electrical conductivity of liquidis very low, indicating that the Al–Cl bond is covalent. It has been used as a catalyst for the Friedel–Crafts reaction. It exhibits strong activity in various other reactions such as polymerization and isomerization , and is used as a catalyst.
aluminum chloride hexahydrate
The chemical formula is AlCl 3 6H 2 O. It can be obtained by dissolving aluminum hydroxide in hydrochloric acid and saturating it with hydrogen chloride. In the crystal, 6 water molecules are coordinated to Al 3 . Very soluble in water, soluble in water up to 47.3g of AlCl 3 at 20 °C . In aqueous solution, it hydrolyzes to form hydroxide and the solution becomes acidic. Used as a brine-out agent in the soap industry, and for preserving, dyeing, fixing photographs and degreasing wood.
polyaluminum chloride
When aluminum hydroxide Al (OH) 3 is dissolved in hydrochloric acid , the original polyaluminum chloride is polymerized to aluminum chloride [Al 2 (OH) n Cl 6 – n] m (n, 3, m 10). Colorless or pale yellow liquid. Due to its high potting power, it is used as a water purifier.
kunihiko mizumachi
