Tetrachloroaluminate

Tetrachloroaluminate [AlCl4]− is an anion formed from aluminium and chlorine. The anion has a tetrahedral 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. E.g. lithium tetrachloroaluminate is used in some lithium batteries.

Tetrachloroaluminate
Names
IUPAC name
Tetrachloroaluminate(1–)
Systematic IUPAC name
Tetrachloroaluminate(1-)
Other names
 
  • Aluminate(1-), tetrachloro
  • tetrachloridoaluminate(1-)
  • tetrachloridoaluminate(1-); tetrachloroalumanuide
  • tetrachloroalumanuide
Identifiers
3D model (JSmol)
ChEBI
ChemSpider
2297
Properties
AlCl4−
Molar mass 168.78 g·mol−1
Structure
Td
Tetrahedral
Hybridisation sp3
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Formation

Tetrachloroaluminate ions are formed as intermediaries in the Friedel–Crafts alkylation reaction, in which Aluminium chloride is used as a catalyst. The Friedel-Crafts alkylation reaction can be broken into three steps, as follows:[1]

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 in this case) reacts with the activated electrophile forming an alkyl-benzenonium carbocation.

Step 3: The alkyl-benzenonium carbocation reacts with a tetrachloroaluminate anion, regenerating the aromatic ring and the Lewis acid and forming hydrochloric acid (HCl).

References
  1. "Electrophilic substitution - the alkylation of benzene". chemguide. Retrieved 28 July 2020.
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