Gattermann – Koch reaction is used for the industrial production of benzaldehyde. It is one of the very important name reactions for students. Chemists generally give names to reactions associated with either product 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 the acidic medium in presence of anhydrous aluminium chloride to give benzaldehyde. In this reaction, anhydrous aluminium chloride works as a 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 the following three steps –
Step 1. Formation of Formyl chloride
In this step, carbon monoxide reacts with HCl and forms formyl chloride. The reaction can be written as follows :
Step 2. Formation of Electrophile: H-C+=O
In this step, formyl chloride reacts with anhydrous aluminium chloride and forms an electrophile (H-C+=O). The 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 are removed. The reaction can be written as follows –
Thus, the aldehyde group gets attached to the aromatic ring by Gattermann – Koch reaction.
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