What is Gattermann Reaction Definition Mechanism Reagents and Examples
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 in Aromatic Formylation
1. What is the Gattermann reaction?
The Gattermann reaction is a chemical reaction used to introduce a formyl group (–CHO) into an aromatic ring using hydrogen cyanide (HCN) and hydrogen chloride (HCl) in the presence of a Lewis acid catalyst. It is mainly applied to activated aromatic compounds such as phenols and aromatic amines. In this reaction:
- HCN + HCl generate a formylating species in situ.
- A Lewis acid catalyst like AlCl3 or ZnCl2 is used.
- The product is an aromatic aldehyde after hydrolysis.
2. What is the mechanism of the Gattermann reaction?
The mechanism of the Gattermann reaction involves electrophilic aromatic substitution through a formylating electrophile. The steps are:
- Generation of an electrophile from HCN and HCl in the presence of a Lewis acid.
- Attack of the aromatic ring on the electrophile to form a sigma complex (arenium ion).
- Deprotonation to restore aromaticity.
- Hydrolysis to give the aromatic aldehyde (–CHO).
3. What are the reagents used in the Gattermann reaction?
The reagents used in the Gattermann reaction are hydrogen cyanide (HCN), hydrogen chloride (HCl), and a Lewis acid catalyst such as AlCl3 or ZnCl2. The main components are:
- HCN – provides the carbon for the formyl group.
- HCl – helps generate the active electrophile.
- AlCl3 or ZnCl2 – act as Lewis acid catalysts.
4. What is the difference between Gattermann and Gattermann–Koch reaction?
The key difference is that the Gattermann reaction uses HCN and HCl, while the Gattermann–Koch reaction uses CO and HCl for formylation of aromatic rings. Major differences include:
- Gattermann reaction: HCN + HCl with AlCl3/ZnCl2.
- Gattermann–Koch reaction: CO + HCl with AlCl3 and CuCl.
- Gattermann–Koch is commonly used for simple aromatics like benzene.
5. Can you give an example of the Gattermann reaction?
An example of the Gattermann reaction is the formylation of phenol to give salicylaldehyde. The simplified reaction is:
C6H5OH + HCN + HCl → o-HOC6H4CHO (after hydrolysis, in presence of AlCl3).
- The –OH group activates the ring.
- Formylation occurs mainly at the ortho position.
- The final product is an aromatic aldehyde.
6. Why is the Gattermann reaction considered an electrophilic aromatic substitution?
The Gattermann reaction is considered an electrophilic aromatic substitution because an electrophile replaces a hydrogen atom on the aromatic ring. In this reaction:
- A formylating electrophile is generated from HCN and HCl.
- The aromatic π electrons attack this electrophile.
- A proton is lost to restore aromaticity.
7. What type of compounds undergo the Gattermann reaction?
The Gattermann reaction mainly occurs with activated aromatic compounds such as phenols and aromatic amines. Suitable substrates include:
- Phenol (C6H5OH)
- Aniline (C6H5NH2)
- Other rings with electron-donating groups
8. What is the role of AlCl3 in the Gattermann reaction?
In the Gattermann reaction, AlCl3 acts as a Lewis acid catalyst that helps generate the active formylating electrophile. Its functions include:
- Coordinating with reactants to increase electrophilicity.
- Stabilizing reaction intermediates.
- Facilitating electrophilic attack on the aromatic ring.
9. What is the product of the Gattermann reaction?
The product of the Gattermann reaction is an aromatic aldehyde formed by introducing a –CHO group into the benzene ring. For example:
- Phenol gives salicylaldehyde (o-hydroxybenzaldehyde).
- Aniline gives p-aminobenzaldehyde (major product).
10. What are the limitations of the Gattermann reaction?
The main limitations of the Gattermann reaction are its restricted substrate scope and the use of toxic reagents like HCN. Important limitations include:
- Not suitable for strongly deactivated aromatic rings.
- Requires careful handling of hydrogen cyanide (HCN), which is highly toxic.
- Sometimes gives lower yields compared to the Gattermann–Koch reaction.
