Aluminium monochloride, or chloridoaluminium is the metal halide with the formula AlCl. Aluminium monochloride as a molecule is thermodynamically stable at high temperature and low pressure only. This compound is produced as a step in the Alcan process to smelt aluminium from an aluminium-rich alloy.
When an aluminium alloy is placed in a reactor that is heated to 1,300 ðC and mixed with aluminium trichloride, a gas of aluminium monochloride is produced.
It then disproportionates into aluminium melt and aluminium trichloride upon cooling to 900 ðC.
The process is an instance of the general sub-halide catalytic distillation method (subhalide process) developed by Philipp Gross. It was sold to Alcan but never put into full-scale production.
This molecule has been detected in the interstellar medium, where molecules are so dilute that intermolecular collisions are unimportant.