Question

The Gattermann-Koch reaction is used in the industrial preparation of benzaldehyde. The electrophile involved in this reaction is

• A. HCO+
• B. HCl + CO$_2$ + anhydrous AlCl$_3$
• C. CO+
• D. CO + anhydrous AlCl$_3$

Answer 1

The Correct Option is A

The Gattermann-Koch reaction is a method used to introduce an aldehyde group (-CHO) directly into an aromatic ring. It involves reacting benzene or a substituted benzene with carbon monoxide (CO) and hydrochloric acid (HCl) in the presence of anhydrous aluminum chloride (AlCl₃) as a catalyst.

The electrophile generated in this reaction is the formyl cation (HCO⁺), which is formed through the interaction of CO and HCl with AlCl₃.

Here's a breakdown of the electrophile formation:

CO + HCl + AlCl₃ → HCO⁺[AlCl₄]^-

The formyl cation (HCO⁺) is the electrophile that attacks the aromatic ring.

Let's analyze the given options:

• Option 1: CO⁺: This is not the correct electrophile.
• Option 2: HCl + CO₂ + anhydrous AlCl₃: CO₂ is not involved in the Gattermann-Koch reaction.
• Option 3: HCO⁺: This is the correct electrophile, the formyl cation.
• Option 4: CO + anhydrous AlCl₃: This combination does not directly form the electrophile; HCl is also required.

Therefore, the correct answer is:

Option 1: HCO⁺