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Updated on 02nd March, 2023 , 3 min read
The formation of reactive species with the help of the acid is the first step in Gattermann Koch's reaction mechanism. The reaction's overall goal is to attach a formyl group (-CHO group) to an aromatic system. The Gattermann - Koch reaction is illustrated below.
The Gattermann - Koch reaction does not work on phenol or phenol ether substrates. When using zinc chloride as a catalyst in the Gattermann - Koch reaction, traces of copper(I) chloride are frequently required because it acts as a co-catalyst.
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Gattermann Formylation |
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Named After |
Ludwig Gattermann |
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Reaction Type |
Substitution Reaction |
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Step 1 - The generation of reactive species that can later be used to react on the aromatic ring is the first step in the Gattermann Koch reaction mechanism. Carbon monoxide can accept a proton from hydrochloric acid because it is a Lewis base. This produces a positively charged molecule with various resonance structures. One such resonance structure has a positive charge on the carbon, which explains the hybrid's reactivity. While reacting with the aromatic ring, this species can act as an electrophile. It is more likely, however, to be the target of a nucleophilic attack by the chloride ion in hydrochloric acid.
Step 2 - When a Lewis acid (Aluminium Chloride) is added, a chloride ion is easily removed from the species. The species has now degenerated into the reactive formyl cation.
Step 3 - At the aromatic ring, an electrophilic aromatic substitution occurs. As a nucleophile, the aromatic ring donates an electron pair to the formyl cation. A proton expulsion quickly resolves the temporary loss of aromaticity.
As a result of the Gattermann - Koch reaction, the formyl group is attached to the aromatic ring. In the above example, benzaldehyde is formed by treating benzene with carbon monoxide and hydrochloric acid in the presence of Aluminium Chloride.
Due to a lack of suitable substrates, the Gattermann-Koch reaction is limited to alkylbenzenes; therefore, Gattermann devised a modification that allowed for the formylation of phenols, phenolic ethers, and heteroaromatic compounds such as pyrroles and indoles.
The Gattermann reaction had one major flaw: anhydrous hydrogen cyanide was required (HCN). To avoid handling HCN, R. Adams created it in-situ from zinc cyanide and hydrochloric acid; this method became known as the Adams modification, and it is now more commonly used in organic synthesis.
The Gattermann-Koch Formylation method is used to produce substituted benzaldehydes. The formyl cation is the key intermediate in this process, and once formed, it interacts similarly to the other acyl cations in Friedel-Crafts processes.
The uses of Gattermann Koch Reaction are as follows:
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The Gattermann Koch reaction is defined as a mechanism that begins with the formation of the reactive species with the usage of an Acid. The main objective of the reaction is the attachment of a formyl group (-CHO group) to an aromatic system.
Gattermann Koch Reaction Example – For instance, when Benzene or any of its derivatives is treated with Carbon Monoxide (CO) and Hydrogen Chloride (HCl) in the presence of Anhydrous Aluminimum Chloride or Cuprous Chloride, it produces Benzaldehyde or Substituted Benzaldehyde as the products. This can be considered Gattermann Koch Reaction Example – BenzeneCO + HCl.
Carbon Monoxide, Hydrogen Chloride, and Aluminium Chloride are used as the reagents in the Gattermann Koch Reaction.
The Gattermann Koch Reaction stands inapplicable in case of Phenols, or Phenol Ethers. The reason is that Phenol can not be formylated at atmospheric pressure in benzene as a solvent as the catalyst used in the reaction, CuCl remains insoluble in the solvent.
The catalyst used in the Gattermann Reaction is Aluminium Chloride.
The Gattermann Koch Reaction is different from the Gattermann Reaction as Gattermann Koch Reaction used HCl + CO, while the Gattermann Reaction uses HCN + HCl. Besides, the Gattermann Koch Reaction is not applicable when it comes to Phenols and Phenol ethers whereas the Gattermann Reaction can be used for Phenols.
The Gattermann Koch Reaction is an example of Electrophilic Substitution Reaction.
The electrophile used in the Gattermann Koch Reaction is Acylium ion.
The final product of Gattermann Koch Reaction is Benzaldehyde. When Benzene is treated with Carbon Monoxide in the presence of anhydrous aluminium chloride and acidic medium, the production of Benzaldehyde takes place.
Ludwig Gattermann was the first to discover the Gattermann Koch Reaction in 1890. He was a German Chemist.
It is a variation of the Gattermann reaction that uses CO (carbon monoxide) in the place of hydrogen cyanide. The reaction has been named after German Scientists Lugwig Gattermann and Julius Arnold Koch.
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