Aluminium Chloride

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Aluminium Chloride Formula

Aluminium chloride is sometimes referred to as aluminium trichloride. Aluminium chloride (AlCl3) is a pure compound formed by the exothermic reaction of metallic aluminum and chlorine. Aluminium Chloride formula is written as AlCl3. As for physical appearance, it is usually white in color. However, due to the presence of contaminants (iron(III) chloride), it acquires a yellowish colour.

Aluminium chloride is a well-known catalyst for organic reactions. This compound is soluble in water, hydrogen chloride, ethanol, chloroform, CCl4 and is slightly soluble in benzene. It is a silvery-white powder but sometimes turns yellow if it is contaminated by ferric chloride. It tends to absorb water easily (hygroscopic) to form monohydrate or hexahydrate. Aluminium chloride is a corrosive substance and it is also very toxic. It can cause high damage to the eyes, skin, and respiratory systems if inhaled or upon contact.

Alcl3 Structure is represented as:

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Properties of Aluminium Chloride 

The chemical formula of Aluminium Chloride

AlCl3

The molecular weight of Aluminium Chloride

133.341 g/mol (anhydrous)

The density of Aluminium Chloride

2.48 g/cm3 (anhydrous)

The boiling point of Aluminium Chloride

192.6 °C

The melting point of Aluminium Chloride

180 °C


The chemical and physical properties of aluminium chloride are as follows.


Physical Properties of AlCl3

  • Aluminium chloride has a very low melting and boiling point.

  • It sublimes at a temperature of 180°C.

  • AlCl3 in a molten state is a poor conductor of electricity.

  • The colour of aluminium chloride is white, but often it is contaminated with iron trichloride, which makes it yellow in colour.

  • It is in a liquid state only at pressures above 2.5 atm and temperature above 190°C.


Chemical Properties of AlCl3

  • Aluminium chloride is a powerful Lewis acid.

  • It is a major industrial catalyst.

  • AlCl3 is anhydrous, non-explosive, non-flammable but a corrosive solid.

  • It reacts violently when it comes in contact with water.


Uses of Aluminium Chloride 

Aluminium Chloride is often regarded as a versatile chemical compound and therefore finds application in many areas. The uses of aluminium chloride are discussed below.

  1. Aluminium Chloride (AlCl3) is used mainly as a catalyst for different chemical reactions. It is used extensively in Friedel-Crafts reaction including both acylations and alkylations. It is used during the preparation of anthraquinone from phosgene and benzene.

  2. Aluminium chloride can be used to bring in or attach aldehyde groups on aromatic series or rings. 

  3. It is also used in polymerization and isomerization reactions of light molecular weight hydrocarbons. Some of the common examples include the production of ethylbenzene or the manufacture of dodecylbenzene for detergents.

  4. Aluminium chloride can be mixed with aluminium along with arene to synthesize bis(arene) metal complexes.


Industrial Uses of Aluminium Chloride (AlCl3)

  • Aluminium chloride is used widely in manufacturing rubber, lubricants, wood preservatives, and paints.

  • It is used in pesticides and pharmaceuticals.

  • As a flux in Aluminium melting.

  • It is used in antiperspirants.


Aluminium Chloride Reaction with Water

Aluminium chloride is hygroscopic, and it can absorb moisture from the air. Usually, this chemical compound fumes in air containing moisture. It creates a hissing sound when it comes in contact with water. When the reaction occurs the Cl– ions are replaced with H2O molecules and forms hexahydrate [Al(H2O)6]Cl3. The anhydrous state of AlCl3 is lost and when the heat is applied HCl also dissipates and the final product that is obtained is aluminium hydroxide.

Al(H2O)6Cl3 → Al(OH)3 + 3HCl + 3H2O

When the temperature is further increased to about 400°C, aluminium oxide is formed from the hydroxide.

2Al(OH)3 → Al2O3 + 3H2O

One distinct characteristic of the AlCl3 aqueous solution is that it is ionic. Due to this, it is a good conductor of electricity. It is also acidic and this can lead to partial hydrolysis in Al³⁺ ions. 

The reaction can be written as:

[Al(H2O)6]3+(aq) ⇌ [Al(OH)(H2O5]2+(aq) + H + (aq)

Aluminium salts that contain hydrated Al³⁺ ions are similar to the aqueous solution of aluminium chloride. They also behave in a similar manner. For example, it gives a thick precipitate of Al(OH)3 on reaction with dilute sodium hydroxide.

AlCl3 + 3NaOH → Al(OH)3 + 3NaCl

Precautions should be taken to keep anhydrous aluminium chloride away from water or bases. Aluminium chloride can explode on coming in contact with water because of the high heat of hydration. It also fumes in the air. Safety items like glasses, gloves, face guard, etc. should be worn during chemical reactions. This chemical compound should be stored in a tightly sealed container and protected from moisture.

  • When it comes in contact with moist air, AlCl3 can absorb the moisture present in the air to become highly acidic and it turns into a sticky substance.

  • It can furiously corrode materials such as stainless steel and rubber.

  • Prolonged exposure to this chemical can cause irritation to the skin, eyes, and the respiratory tract.

  • In some studies, aluminium chloride has been found to be a neurotoxin that can be destructive to nerve tissues and can cause permanent damage.


Aluminium Chloride Reactions

Anhydrous aluminium chloride is a powerful Lewis acid. It means that it is capable of forming Lewis acid-base adducts even with bases that are weak in nature. For example, mesitylene and benzophenone. Some of the common reactions are given below.

  • AlCl3 can form tetrachloroaluminate (AlCl4 -) when chloride ions are present.

  • Aluminium chloride can react with magnesium and calcium hydride in tetrahydrofuran to form tetrahydridoaluminate.

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