Question

The reagent used in Gatterman-Koch formylation of arene is

• A. $\text{CO}_2$, HCl
• B. $\text{CrO}_2\text{Cl}_2$
• C. CO, HCl
• D. DiBAl-H

Hint:

Associate the keywords "Koch" and "Formylation" directly with Carbon Monoxide (CO). The "C" and "O" letters in "Koch" can serve as a simple memory anchor for $\text{CO} + \text{HCl}$!

Answer 1

The Correct Option is C

Step 1: Name the reaction.
The Gatterman Koch reaction puts a $-CHO$ group onto benzene. It is a kind of Friedel Crafts type formylation.

Step 2: Recall the reagents.
The arene is treated with carbon monoxide and hydrogen chloride under pressure, with $AlCl_3$ or CuCl as catalyst.

Step 3: What forms.
CO and HCl together act like formyl chloride and deliver the $CHO$ group to the ring, giving benzaldehyde. So the reagent is CO with HCl.
\[ \boxed{\text{CO, HCl, option 3}} \]