Trihaloaluminums

Trihaloaluminums are a class of chemical compounds with the general formula AlX3, where X represents a halogen atom (fluorine, chlorine, bromine, or iodine). Aluminum is in the +3 oxidation state in these compounds. The most common and widely studied trihaloaluminum is aluminum chloride (AlCl3). Others include aluminum fluoride (AlF3), aluminum bromide (AlBr3), and aluminum iodide (AlI3).

These compounds typically exist as solids at room temperature, with melting and boiling points that vary depending on the specific halogen. Aluminum chloride, for instance, sublimes at 177.8 °C. In the solid state, trihaloaluminums often form polymeric structures. However, in the melt or in the gas phase, they tend to exist as discrete, monomeric AlX3 molecules.

Trihaloaluminums are Lewis acids, meaning they can accept electron pairs. This property makes them potent catalysts in various organic reactions, such as Friedel-Crafts alkylation and acylation. They are also reactive towards Lewis bases, forming adducts. For example, AlCl3 readily reacts with ethers and amines.

The reactivity of trihaloaluminums with water is significant. They undergo hydrolysis, often vigorously, producing aluminum hydroxide and the corresponding hydrohalic acid. This necessitates careful handling and storage under anhydrous conditions. Trihaloaluminums are important industrial chemicals, primarily used as catalysts, but also in the production of aluminum metal and other chemical processes.