Gattermann – Koch Reaction Mechanism

Gattermann – Koch reaction is used for industrial production of benzaldehyde. It is one of the very important name reactions for students. Chemists generally give names to reactions associated to either products of reactions or discoverers of the reactions. Gattermann – Koch reaction was given by Ludwig Gattermann and Julius Arnold Koch. 

Gattermann – Koch Reaction 

In Gattermann – Koch reaction, benzene is treated with carbon monoxide in acidic medium in presence of anhydrous aluminum chloride to give benzaldehyde. In this reaction anhydrous aluminum chloride works as catalyst. It is an electrophilic substitution reaction. 

Gattermann – Koch Reaction can be written as follows –

Phenol and phenol ether substrates are not applicable for Gattermann – Koch Reaction. 

Gattermann – Koch Reaction Mechanism 

Gattermann – Koch reaction mechanism can be explained in following three steps – 

Step 1. Formation of Formyl chloride 

In this step carbon monoxide reacts with HCl and forms formyl chloride. Reaction can be written as follows – 

Step 2. Formation of Electrophile: H-C+=O

In this step formyl chloride reacts with anhydrous aluminum chloride and forms an electrophile (H-C+=O). Reaction can be written as follows – 

Step 3. Formation of benzaldehyde 

In this step H-C+=O (electrophile) reacts with benzene and forms benzaldehyde. During the reaction in this step AlCl3 and HCl is removed. Reaction can be written as follows – 

Thus, aldehyde group get attached to the aromatic ring by Gattermann – Koch reaction.

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