# Gattermann-Koch reaction - Role of cuprous chloride

I am unable to figure out what the role of $\ce{CuCl}$ in Gatterman-Koch reaction is. Does it provide $\ce{Cl-}$ ions by dissociating into $\ce{CuCl2}$ and $\ce{2Cl-}$, but that can also be achieved by using more $\ce{HCl}$? So why do we add $\ce{CuCl}$ in the reaction?

The formylation of aromatic compound can be accomplished by treatment with $\ce{CO}$ and $\ce{HCl}$ in the presence of Lewis acid. The reaction is performed either under pressure or using copper(I) chloride or anhydrous aluminum chloride whose role may be to aid the reaction between $\ce{CO}$ and $\ce{HCl}$ via the complex which it forms with $\ce{CO}$.
As you can see, it does not involve in the mechanism (provide $\ce{Cl-}$ via dissociation of $\ce{CuCl}$) but act as a promoter to speed up the reaction.