One of the successful means in formylating aromatic ring is afforded by gattermann reaction. Reaction formylation affected by HCN & HCl mixture in the presence of a suitable catalyst is called Gattermann Reaction.
The Gattermann reaction is a chemical reaction in which aromatic compounds reacts with hydrogen cyanide (HCN) and hydrogen chloride (HCl) in presence of lewis acid catalyst (AlCl3). The reaction is carried out by passing a mixture of HCN and HCl into the solution of the aromatic compound having aluminium chloride as the suspended catalyst.
The reaction is shown below.
The toxic HCN can be substituted by Zn(CN)2.