Tetrachloroaluminate

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Tetrachloroaluminate [AlCl4]− is an anion formed from aluminium trichloride and chloride. The anion has a tetrahedral shape and is isoelectronic with silicon tetrachloride. 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 is used in some lithium batteries.

Quick facts Names, Identifiers ...
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
  • InChI=1S/Al.4ClH/h;4*1H/q+3;;;;/p-4
    Key: BXILREUWHCQFES-UHFFFAOYSA-J
  • InChI=1S/Al.4ClH/h;4*1H/q+3;;;;/p-4
    Key: BXILREUWHCQFES-UHFFFAOYSA-J
  • Cl[Al-](Cl)(Cl)Cl
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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Formation

structure of tetrachloroaluminate salt of trichlorocyclopropenium cation. Color code: Cl = green, mauve = Al. The Al-Cl distance is 213 picometers.[1]

Tetrachloroaluminate ions are formed as intermediates in the Friedel–Crafts reactions when aluminium chloride is used as the catalyst. In the case of the Friedel–Crafts acylation, the reaction is often broken into three steps as follows:[2][3]

  1. The acyl halide reacts with the strong Lewis acid to form an activated electrophile, tetrachloroaluminate salt of the acylium ion.
RC(O)Cl +AlCl3 → [RC≡O+][AlCl−4]
  1. The aromatic substrate reacts with the acylium cation to give a benzenium carbocation.
[RC≡O+][AlCl−4] + C6H6 → RC(=O)C6H+6][AlCl−4]
  1. The acylbenzenium carbocation releases a proton, generating the acylarene, aluminium trichloride, and hydrogen chloride (not hydrochloric acid).
[C6H6COR]+AlCl−4 → C6H5COR + AlCl3 + HCl

References

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