Introduction
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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FAQs on Gattermann – Koch Reaction Mechanism
1.What is the Gattermann reaction?
The Gattermann reaction (also called Gattermann formylation or Gattermann salicylaldehyde synthesis) is a chemical process in which aromatic compounds are formulated by a combination of hydrogen cyanide (HCN) and hydrogen chloride (HCl) in the presence of a Lewis acid catalyst such as AlCl3. It is analogous to the Friedel–Crafts reaction and is named after German chemist Ludwig Gattermann.
By substituting zinc cyanide for the HCN/AlCl3 combination, the process can be simplified. Zn(CN)2 is a solid that is safer to work with than gaseous HCN, even though it is likewise highly poisonous. In-situ, Zn(CN)2 combines with HCl to produce the crucial HCN reactant and Zn(Cl)2, which works as a Lewis-acid catalyst. The synthesis of metaldehyde from mesitylene is an example of the Zn(CN)2 technique.
2.What is the Gattermann - Koch reaction mechanism?
The Gattermann–Koch reaction is a version of the Gattermann reaction that uses carbon monoxide (CO) instead of hydrogen cyanide. It is named after German chemists Ludwig Gattermann and Julius Arnold Koch.
This reaction does not apply to phenol and phenol ether substrates, unlike the Gattermann reaction. Although formyl chloride, a highly unstable intermediate, was first proposed, the formyl cation (i.e., protonated carbon monoxide), [HCO]+, is now expected to react directly with the arene without first forming formyl chloride. Additionally, traces of copper(I) chloride or nickel(II) chloride co-catalyst are frequently required when zinc chloride is employed as the Lewis acid instead of aluminium chloride, or when carbon monoxide is not used at high pressure. By first interacting with CO to generate a carbonyl complex, which is then converted into the active electrophile, the transition metal co-catalyst can serve as a "carrier."
3.What is electrophilic substitution?
Electrophilic substitution is visible in benzene because it is an electron-rich compound that undergoes this reaction. Here is a complete step-by-step substitution reaction.
Formaldehyde and hydrochloric acid are utilised as reagents, with benzene serving as the substrate. The Chloromethylation reaction of benzene is an example of this type of reaction. When benzene interacts with formaldehyde in the presence of hydrochloric acid, the result is benzene methyl chloride. The Electrophilic Substitution Reaction is the name given to this process. The reaction may comprise a step in which the intermediated product generated is an electrophile in the first step.
4.What is the duff reaction mechanism?
Cooper Duff, a physicist, was the inspiration for the Duff response. Hexamine aromatic formylation is another name for the reaction, which is employed in organic chemistry for benzaldehyde mechanism procedures. When benzaldehyde combines with hexamine, the formyl carbon source, the Duff reaction occurs. The electrophilic species in Duff's reaction is the iminium ion, which is the first product in the process and thereafter hydrolyzes to the aldehyde. The oxidation state of benzylamine is obtained first, followed by the aromatic ring. After that, an intramolecular redox reaction boosts the benzylic carbon, resulting in the oxidation state of aldehyde.
