Question

Pick the reaction that shows the Gattermann-Koch process:

• A. Benzene + methyl chloride → ethylbenzene (AlCl\(_3\) catalyst)
• B. Benzene + CO + HCl → benzaldehyde (AlCl\(_3\), CuCl catalysts)
• C. Benzene + bromine → bromobenzene (FeBr\(_3\) catalyst)
• D. Benzene + acetyl chloride → acetophenone (AlCl\(_3\) catalyst)

Hint:

The Gattermann-Koch process is a method for synthesizing benzaldehyde from benzene using CO and HCl in the presence of AlCl\(_3\) and CuCl catalysts.

Answer 1

The Correct Option is B

Step 1: Understanding the Gattermann-Koch process.
The Gattermann-Koch process is used for the formylation of benzene. In this process, benzene reacts with carbon monoxide (CO) and hydrochloric acid (HCl) in the presence of AlCl\(_3\) and CuCl catalysts to form benzaldehyde.
Step 2: Conclusion.
Thus, the correct reaction for the Gattermann-Koch process is: \[ \text{Benzene} + \text{CO} + \text{HCl} \rightarrow \text{Benzaldehyde} \] which corresponds to option (B).

Answer 2

Step 1: The Gattermann-Koch reaction adds a −CHO (aldehyde) group onto benzene.

Step 2: It uses carbon monoxide and HCl gas, with AlCl₃ and CuCl as catalysts.

Step 3: The product formed is benzaldehyde.

Step 4: So the reaction matching the Gattermann-Koch process is Benzene + CO + HCl → Benzaldehyde — option (B).

Answer 3

Mechanism-based check.
In the Gattermann-Koch reaction, CO and HCl combine in the presence of AlCl\(_3\) (with CuCl as a catalyst) to generate a formyl cation-type electrophile, \(\text{HC}^{+}=\text{O}\), which then attacks the benzene ring in an electrophilic aromatic substitution, installing a \(-\text{CHO}\) group.
The other listed reactions are different named processes: benzene with methyl chloride/AlCl\(_3\) is a Friedel-Crafts alkylation, benzene with bromine/FeBr\(_3\) is a halogenation, and benzene with acetyl chloride/AlCl\(_3\) is a Friedel-Crafts acylation giving a ketone, not an aldehyde.
Only the CO + HCl route produces the aldehyde that defines the Gattermann-Koch process, so the answer is option (B).