Tetrachloroaluminate

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.

Formation

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:

1. The acyl halide reacts with the strong Lewis acid to form an activated electrophile, tetrachloroaluminate salt of the acylium ion.

1. The aromatic substrate reacts with the acylium cation to give a benzenium carbocation.

1. The acylbenzenium carbocation releases a proton, generating the acylarene, aluminium trichloride, and hydrogen chloride (not hydrochloric acid).

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