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 for introducing a formyl group (\( -CHO \)) to aromatic compounds, yielding aromatic aldehydes. This reaction is valuable in organic synthesis.The general reaction is:\[\text{Aromatic compound} + \text{CO} + \text{HCl} \xrightarrow{\text{AlCl}_3 \, \text{or} \, \text{CuCl}} \text{Aromatic aldehyde}.\]It utilizes carbon monoxide (CO) and hydrogen chloride (HCl) with a Lewis acid catalyst, such as AlCl\(_3\) or CuCl.Step 1: Reaction Mechanism.
The catalyst facilitates the reaction between carbon monoxide and hydrogen chloride to form an electrophilic species, \( \text{COCl}^+ \). This species then attacks the aromatic ring, adding the formyl group (\( -CHO \)).Step 2: Example Reaction.
For example, benzene (\( \text{C}_6\text{H}_6 \)) reacts with carbon monoxide and hydrogen chloride in the presence of AlCl\(_3\) to produce 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:The Gattermann-Koch reaction is a formylation process that introduces a formyl group (\( -CHO \)) to an aromatic ring, corresponding to option \( \mathbf{(A)} \).Therefore, the correct answer is \( \mathbf{(A)} \).