# Synthesis of the tetrachloroaluminate(III) anion

Looking for random chemicals, I found a reference on the anion and thought that it could be synthesised from common laboratory reagents:

\begin{align} \ce{2 Al + 2 NaOH + 2 H2O &-> 2 NaAlO2 + 3 H2}\\ \ce{NaAlO2 + 4 HCl &-> NaAlCl4 + 2 H2O} \end{align}

The first reaction obviously occurs at high yield at STP. Does the second reaction occur at STP or not? If not, how can the $$\ce{AlCl4^-}$$ ion be synthesised?

• You do not synthesize ions, you synthesize compounds. – Nilay Ghosh Jan 1 '20 at 6:05

Note that the first reaction would require substantial amount of heat to assure the designated product $$\ce{NaAlO2}$$ is formed (nowhere near STP):

$$\ce{2 Al(s) + 2 NaOH(l) + 2 H2O(g) ->[\pu{\approx 450 °C}] 2 NaAlO2(s) + 3 H2(g)}$$

In aqueous solution the product would be tetrahydroxoaluminate $$\ce{[Al(OH)4]-}:$$

$$\ce{2 Al(s) + 2 NaOH(aq, conc) + 6 H2O (l) ->[Δ] 2 Na[Al(OH)4](aq) + 3 H2(g)}$$

Synthetic procedure from "common laboratory reagents" is described in Brauer's Handbook of Preparative Inorganic Chemistry [1, p. 816]:

### Sodium Tetrachloroaluminate

$$\ce{NaAlCl4}$$

$$\ce{\underset{58.4}{NaCl} + \underset{133.4}{AlCl3} = \underset{191.8}{NaAlCl4}}$$

The reaction is carried out in a Pyrex vessel (Fig. 245), which should be as compact as possible. The stoichiometric amounts of C.P. $$\ce{NaCl}$$ and freshly sublimed $$\ce{AlCl3}$$ are introduced into the pear-shaped part of the reaction vessel.

Fig. 245. Preparation of sodium tetrachloroaluminate.

The filling is done under nitrogen and the vessel should be very clean and dry. A melting point capillary is then affixed underneath the ground joint; the apparatus is evacuated to a high vacuum and torch-sealed. It is then immersed as deeply as possible in an oil bath at 200–240 °C. The $$\ce{AlCl3},$$ which tends to sublime onto the cool parts of the wall, is driven back by passing a luminous flame over the condensate spots. When the flask contents have become a nearly clear melt, they are poured hot into the side flask of the vessel. The product solidifies on cooling.

### References

1. Handbook of Preparative Inorganic Chemistry, 2nd ed.; Brauer, G., Ed.; Academic Press: New York; London, 1963; Vol. 1.