Question

Which of the following represents the Gattermann-Koch reaction?

• A. \( \text{Introduction of a formyl group (-CHO) to an aromatic compound using CO and HCl in the presence of AlCl}_3 \text{ or CuCl.} \)
• B. \( \text{Reduction of a nitro group to an amine group.} \)
• C. \( \text{Introduction of an acyl group (-COCH}_3) \text{ to an aromatic ring.} \)
• D. \( \text{Halogenation of an aromatic compound in the presence of a Lewis acid.} \)

Hint:

The Gattermann-Koch reaction is a useful method for introducing a formyl group to aromatic compounds. The reaction requires CO, HCl, and a Lewis acid catalyst such as \( \text{AlCl}_3 \) or \( \text{CuCl} \).

Answer 1

The Correct Option is A

The Gattermann-Koch reaction is a method used for the formylation of aromatic compounds, meaning the introduction of a formyl group (\( -CHO \)) to an aromatic ring. This reaction is particularly useful in organic synthesis for the preparation of aromatic aldehydes. The general reaction is as follows: \[ \text{Aromatic compound} + \text{CO} + \text{HCl} \xrightarrow{\text{AlCl}_3 \, \text{or} \, \text{CuCl}} \text{Aromatic aldehyde}. \] This reaction uses carbon monoxide (CO) and hydrogen chloride (HCl) in the presence of a Lewis acid catalyst such as AlCl\(_3\) or CuCl. Step 1: Reaction Mechanism.
In the presence of the catalyst, carbon monoxide and hydrogen chloride react to form a reactive electrophilic species, \( \text{COCl}^+ \), which then attacks the aromatic ring to introduce the formyl group (\( -CHO \)). Step 2: Example Reaction.
For instance, when benzene (\( \text{C}_6\text{H}_6 \)) reacts with carbon monoxide and hydrogen chloride in the presence of AlCl\(_3\) (a common Lewis acid), the product formed is benzaldehyde (\( \text{C}_6\text{H}_5\text{CHO} \)): \[ \text{C}_6\text{H}_6 + \text{CO} + \text{HCl} \xrightarrow{\text{AlCl}_3} \text{C}_6\text{H}_5\text{CHO}. \] Conclusion: Thus, the Gattermann-Koch reaction is a formylation reaction where a **formyl group** (\( -CHO \)) is introduced to an aromatic ring, as described in option \( \mathbf{(A)} \). Thus, the correct answer is \( \mathbf{(A)} \).