[7784-16-9] · AlCl4Na · Sodium Tetrachloroaluminate · (MW 191.77)
(dehydrating and dehydrogenating agent; Friedel-Crafts acylating agent)
Alternate Name: sodium aluminum chloride.
Physical Data: mp 100-150 °C, depending on composition. The initial melting point depends on the ratio of NaCl to AlCl3 and on the coarseness of the mixture. Once the mixture has melted, the temperature may be lowered, with solidification beginning about 100 °C. The 1:2 (NaCl-AlCl3) mixture is a strong Lewis acid because it contains excess AlCl3. The 1:1 mixture is much less acidic.
Solubility: used as a solvent itself; appears to dissolve compounds with nucleophilic groups (carbonyl, hydroxyl); incompatible with water.
Form Supplied in: not supplied commercially, but easily formed from NaCl and AlCl3 in the heated reaction vessel. The reagent can be prepared in advance and stored.2
Analysis of Reagent Purity: can be done electrochemically,1 but this is rarely necessary. The purity of the reagent depends entirely on the purity of the NaCl and AlCl3 used. In the 1:1 melt, excess AlCl3 markedly changes the acidity of the reagent, but excess NaCl has little effect on the acidity. The properties of the 1:2 reagent (excess AlCl3) do not change greatly with small differences in composition.
Handling, Storage, and Precautions: similar to Aluminum Chloride, except that the molten salt is capable of producing thermal burns, as well as severe burns from AlCl3. The melt may spatter when organic reagents are added, and spattering is common when the reaction mixture is poured over ice. HCl fumes are evolved during most reactions, and large amounts of HCl are evolved when the mixture is poured over ice. Use in a fume hood.
In the presence of sodium tetrachloroaluminate, acids acylate activated aromatic rings (eq 1).3 Yields of ketones from these acylations are often best with intramolecular reactions (eq 2).3,4 Anhydrides also can be used as acylating reagents (eq 3).5,6
Acylation can also take place via the Fries rearrangement (eq 4).3 A seven-membered ring can be formed by cyclodehydration (eq 5).3,7 Aryl vinyl ketones may isomerize to give products resulting from aromatic substitution (eq 6).3
The reagent promotes the cyclization of N,N´-diphenylmalonamide by a cyclodeamination that may proceed via a ketene intermediate (eq 7).8,9 Sodium tetrachloroaluminate dehydrates simple amides to nitriles (eq 8).2
The Scholl reaction, an aromatic cyclodehydrogenation known to take place with aluminum chloride,10 also takes place with sodium tetrachloroaluminate. Examples are known using polynuclear aromatics (eq 9),11 benzophenones (eq 10),12 quinazolines,13 and benzothiophene-based heterohelicenes.14
Leroy G. Wade, Jr.
Whitman College, Walla Walla, WA, USA