Gattermann-Koch Reaction

Overall Reaction:

$$\text{C}_6\text{H}_6 + \text{CO} + \text{HCl} \xrightarrow{\text{Anhy. AlCl}_3 / \text{CuCl}} \text{C}_6\text{H}_5\text{--CHO} + \text{HCl}$$

Concept: Direct formylation of a benzene ring using carbon monoxide and hydrogen chloride gas under Lewis acid catalysis, functioning effectively as an in-situ electrophilic aromatic substitution path.

Notation:

• $$\text{Anhydrous AlCl}_3$$ = Lewis acid catalyst;
• $$\text{CO} + \text{HCl}$$ = Reagents generating the reactive formylating intermediate.