In the mechanism for the acetylation of bromobenzene, how is $\ce{HCl}$ gas produced?
The reactants are acetic anhydride, bromobenzene, $\ce{AlCl3}$ and dichloromethane.
Initially, 4-bromoacetophenone is made, accompanied with (as far as I know) acetic acid and the regeneration of $\ce{AlCl3}$.
How then is $\ce{HCl}$ produced?
To remove the $\ce{AlCl3}$ at the end, 3 $\ce{H2O}$ are added and $\ce{HCl}$ gas is produced then.
I'm trying to think of ways that $\ce{HCl}$ gas is produced prior to that, however. Could a chlorine of the aluminate ion deprotonate the arenium ion?
Could dichloromethane (solvent) donate a $\ce{Cl-}$ to $\ce{AlCl3}$?