Write Gatterman Koch reaction

Explanation

Gatterman Koch reaction : In their reaction benzene or its derivatives react with a mixture of CO and HCl in the presence of anhydrous aluminium chloride to give benzenaldehyde or its derivative. In this reaction CO + HCl acts as formyl chloride, which is unstable.
For example
`CO + HCl rarr [H -overset(C)(||)-Cl]`

Thus it can be considered as a modification of Friedel Crafts acylation.