Step-by-Step Mechanism and Real-World Applications of the Gattermann Reaction
It is used in the synthesis of aromatic ring compounds such as aromatic halides and aromatic aldehydes. It is similar to the Friedel-Crafts reaction. It is named after German Chemist Ludwig Gattermann. It is also known as Gattermann Formylation. In Gattermann Reaction for the formation of aromatic halide diazonium salt reacts with copper powder in presence of corresponding halogen acid. It is a substitution reaction.
Gattermann Reaction can be written as Follows -
How is Diazonium Salt Formed?
Aromatic amine reacts with nitrous acid and mineral acid to form diazonium salt and produces water as a side product. This reaction is known as Diazotization Reaction.
Reaction can be written as follows-
ArNH2 + HNO2 + HX 🡪 RN2+X- + H2O
Aromatic amine nitrous acid mineral acid Diazonium salt water
Diazotization of Aniline
It is done by treating aniline with sodium nitrate and HCl at the temperature of 273K. the reaction involved is given below –
Synthesis of Aromatic Aldehyde by Gattermann Reaction
Gattermann Reaction Mechanism
The mechanism of the Gattermann Reaction is explained for the formation of aromatic aldehydes. The reaction takes place by following four steps –
Step 1. Formation of Formimino Chloride
Hydrogen cyanide reacts with hydrogen chloride and forms chloride.
The reaction can be written as follows –
Step 2. Formation of Electrophile
Formimino chloride reacts with lewis acid catalysts (such as AlCl3) and forms cations. The reaction is given below –
Step 3. Attack of Electrophile on Benzene Ring
Formimino cation (electrophile) attacks benzene rings and forms benzylamine. The reaction is given below -
Step 4. Hydrolysis of Benzylamine
Hydrolysis of benzylamine takes place in this step. Which results in the formation of benzaldehyde. The reaction is given below –
Applications of Gattermann Reaction
It is used for the formation of chlorobenzene and bromobenzene.
It is used for the formation of benzaldehydes.
Products of Gattermann Reaction such as benzaldehydes and haloarenes etc. are used in various fields such as pharmaceuticals, agricultural, medicinal etc.
It is used in the formation of aromatic halides and aromatic aldehydes.
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Talking about the Gattermann Reaction, when the synthesis of any aromatic ring compounds like aromatic halides and aromatic aldehydes. There is one more reaction that is somewhat similar to the Gattermann Reaction, and it is known as the Friedel Crafts reaction. This reaction is named after the famous chemist, the German Ludwig Gattermann. It is sometimes also known as Gattermann Formulation. While using this reaction, when we are forming aromatic halide diazonium salt is reacted with copper powder in the presence of corresponding halogen acid. It is also a substitution reaction.
The Formation of Diazonium Salt
Only when the aromatic amine is reacted with mineral acid and nitrous acid, the diazonium salt is formed. This whole process also has a side product that is water. The whole reaction is known as Diazotization Reaction. This reaction can also be written as the following chemical equation:
ArNH2 + HNO2 + HX + RN2 +X- + H2O
The Mechanism of Gattermann Reaction
There are a certain number of steps that need to be followed in order to complete the Gattermann Reaction. This process consists of 4 steps, which are given below:
Step 1 - The forming the Formimino Chloride
The first and foremost step in order to create a Gattermann Reaction is to create a Formimino Chloride. In this, hydrogen chloride reacts with hydrogen cyanide which in turn forms Formimino chloride.
Step 2 - The forming of Electrophile
The next step is to create Electrophile. As a result, the formimino chloride is reacted with a lewis acid catalyst and helps in the formation of forming cation, which is also known as Electrophile.
Step 3 - When the Electrophile attacks on Benzene Ring
The third step explains how the Formimino cation (Electrophile) attacks benzene rings and in the result forms benzylamine.
Step 4 - When the Benzylamine is Hydrolysed
The fourth step is also one of the most interesting and important steps. In this step, the hydrolysis of Benzylamine occurs. Which in turn produces benzaldehyde.
Now, let us discuss some of the major applications of the Gattermann Reaction.
The applications are given below:
It can be used to form aromatic halides and aromatic aldehydes.
There are many products of the Gattermann Reaction, such as benzaldehydes and haloarenes, etc. These elements in turn are used in various applications or fields of agriculture, pharmaceuticals, medicine, etc.
It is also used to form benzaldehydes.
It is also used to form chlorobenzene and bromobenzene.
All these applications are also the use-cases of the Gattermann Reaction. These uses are the majority in the chemical field.
FAQs on Gattermann Reaction: Complete Guide for Chemistry Students
1. What is the Gattermann reaction in simple terms?
The Gattermann reaction is a chemical process used to add a formyl group (–CHO) to an aromatic ring, such as benzene. In essence, it converts an aromatic compound into an aromatic aldehyde. It is a type of electrophilic aromatic substitution, similar in principle to the Friedel-Crafts reaction.
2. What are the key reagents needed for the Gattermann reaction?
The primary reagents required for the Gattermann reaction are:
- A mixture of hydrogen cyanide (HCN) and hydrogen chloride (HCl), which together form the reactive species.
- A Lewis acid catalyst, most commonly anhydrous aluminium chloride (AlCl₃).
- The aromatic compound (substrate) that is to be formylated, for example, benzene.
3. How does the Gattermann reaction mechanism work?
The mechanism involves three main steps:
- Step 1: Formation of the Electrophile: Hydrogen cyanide and hydrogen chloride react in the presence of the Lewis acid catalyst (AlCl₃) to form a highly reactive electrophile, the formimino cation.
- Step 2: Electrophilic Attack: The electron-rich aromatic ring attacks this electrophile, forming an intermediate sigma complex.
- Step 3: Hydrolysis: The intermediate is then treated with water (hydrolysis) to replace the imine group with an oxygen atom, yielding the final product, an aromatic aldehyde like benzaldehyde.
4. What are the common applications or uses of the Gattermann reaction?
The main application of the Gattermann reaction is in organic synthesis. It is specifically used for the preparation of aromatic aldehydes (like benzaldehyde and its derivatives). These aldehydes are valuable intermediates in the manufacturing of pharmaceuticals, dyes, perfumes, and other specialty chemicals.
5. How is the Gattermann reaction different from the Gattermann-Koch reaction?
Although their names are similar, they use different reagents to achieve formylation. The key difference is:
- Gattermann Reaction: Uses a mixture of hydrogen cyanide (HCN) and HCl. It is more versatile and can be used with phenols and phenolic ethers.
- Gattermann-Koch Reaction: Uses carbon monoxide (CO) and HCl. This method is generally not suitable for phenols as the catalyst complexes with the hydroxyl group.
6. What is the difference between the Gattermann reaction and the Sandmeyer reaction?
Both reactions can start from an aromatic diazonium salt, but they differ in the catalyst used:
- Gattermann Reaction: Uses freshly prepared copper powder and a corresponding halogen acid (e.g., HCl or HBr) as the catalyst.
- Sandmeyer Reaction: Uses a copper(I) salt, such as copper(I) chloride (CuCl) or copper(I) bromide (CuBr), as the catalyst. The Sandmeyer reaction generally produces a better yield than the Gattermann reaction.
7. Why does the Gattermann reaction often give lower yields?
The Gattermann reaction can have lower yields because the primary reagent, hydrogen cyanide (HCN), is highly toxic, volatile, and difficult to handle safely in a laboratory setting. This can lead to procedural challenges and side reactions, impacting the overall efficiency and yield of the desired aromatic aldehyde.
