Question

Which from following reagents is used in Gatterman-Koch formylation of arene?

Options

• AlH(i-Bu)₂

• CO, HCl (anhyd. AICl₃)

• CrO₂Cl₂(CS₂)

• DIBAI -H

Answer 1

CO, HCl (anhyd. AICl₃)

Explanation:

Gattermann-Koch Formylation

It introduces a –CHO group onto an arene via electrophilic aromatic substitution.

Reagents: CO + HCl + anhydrous AlCl₃ + CuCl

\[\mathrm{ArH}+\mathrm{CO}+\mathrm{HCl}\xrightarrow{\mathrm{AlCl}_3}\mathrm{Ar-CHO}\]

AlCl₃ generates the formyl carbocation [CHO]⁺ (electrophile) which attacks the benzene ring to give an aromatic aldehyde.