Tetrachloroaluminate lCl₄sup>− is an

anion An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conve ...

formed from

aluminium Aluminium (aluminum in American and Canadian English) is a chemical element with the symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately one third that of steel. I ...

and

chlorine Chlorine is a chemical element with the symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate between them. Chlorine i ...

. The anion has a

tetrahedral In geometry, a tetrahedron (plural: tetrahedra or tetrahedrons), also known as a triangular pyramid, is a polyhedron composed of four triangular faces, six straight edges, and four vertex corners. The tetrahedron is the simplest of all the ...

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 Lithium tetrachloroaluminate (LAC, lithium aluminium chloride) is an inorganic compound, a tetrachloroaluminate of lithium, with the formula LiAlCl4. Solution of lithium tetrachloroaluminate in thionyl chloride is the liquid cathode and electroly ...

is used in some

lithium batteries Lithium battery may refer to: * Lithium metal battery, a non-rechargeable battery with lithium as an anode ** Rechargeable lithium metal battery, a rechargeable counterpart to the lithium metal battery * Lithium-ion battery, a rechargeable batte ...

Formation

Tetrachloroaluminate ions are formed as intermediates in the Friedel–Crafts reactions when

aluminium chloride Aluminium chloride, also known as aluminium trichloride, is an inorganic compound with the formula . It forms hexahydrate with the formula , containing six water molecules of hydration. Both are colourless crystals, but samples are often contam ...

is used as the catalyst. In the case of the Friedel –Crafts alkylation, the reaction can be broken into three steps as follows: Step 1: The alkyl halide reacts with the strong Lewis acid to form an activated electrophile composed of the tetrachloroaluminate ion and the alkyl group. : Step 2: The aromatic ring (

benzene Benzene is an organic chemical compound with the molecular formula C6H6. The benzene molecule is composed of six carbon atoms joined in a planar ring with one hydrogen atom attached to each. Because it contains only carbon and hydrogen atoms ...

in this case) reacts with the activated electrophile forming an alkylbenzenium carbocation. : Step 3: The alkylbenzenium carbocation reacts with a tetrachloroaluminate anion, regenerating the aromatic ring and the Lewis acid and forming

hydrochloric acid Hydrochloric acid, also known as muriatic acid, is an aqueous solution of hydrogen chloride. It is a colorless solution with a distinctive pungent smell. It is classified as a strong acid Acid strength is the tendency of an acid, symbol ...

(HCl). : A similar mechanism occurs in the Friedel –Crafts acylation.Friedel-Crafts Acylation
Organic-chemistry.org. Retrieved on 2014-01-11.

References

{{reflist, refs= {{Cite web, title=electrophilic substitution - the alkylation of benzene, url=https://www.chemguide.co.uk/mechanisms/elsub/fcalkyl.html, access-date=2020-09-07, website=www.chemguide.co.uk Non-coordinating anions