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Gattermann Koch Reaction Mechanism - Overview, Structure, Properties & Uses, FAQs

Gattermann Koch Reaction Mechanism - Overview, Structure, Properties & Uses, FAQs

Edited By Team Careers360 | Updated on Jul 02, 2025 04:44 PM IST

What is Gattermann Koch reaction?

The reaction is named after two German chemists Ludwig Gattermann and Julius Arnold Koch. In the Gattermann Koch reaction, instead of using hydrogen cyanide, we use carbon monoxide. The other names of Gattermann Koch reaction are Gattermann Koch formylation reaction and Gattermann salicylaldehyde synthesis.

This Story also Contains
  1. What is Gattermann Koch reaction?
  2. Explain Gattermann Koch Reaction.
  3. Gattermann Koch Synthesis
  4. Conclusion of Gattermann Koch reaction Mechanism:
  5. Electrophilic substitution:
  6. Duff Reaction Mechanism:
  7. Vilsmeier Reaction Mechanism:
Gattermann Koch Reaction Mechanism - Overview, Structure, Properties & Uses, FAQs
Gattermann Koch Reaction Mechanism - Overview, Structure, Properties & Uses, FAQs

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Explain Gattermann Koch Reaction.

The Gattermann Koch reaction mechanism started with the formation of reactive species and those species are generally acidic in nature. In the Gattermann chemical reaction, the aromatic compounds are formylated. The formylation reaction of the Gattermann Koch reaction took place in the presence of Lewis acid and the catalyst which is being used here is Aluminium chloride. Formylation of the Gattermann reaction occurs with the mixture of hydrogen cyanide and hydrogen chloride. Gattermann Koch formylation is a type of substitution reaction.

The Gattermann Koch reaction is not at all applicable to Phenol and the substrates of Phenol ether. In such a reaction the formyl cation (formyl cation so formed is called protonated carbon monoxide) which is being formed as an intermediate product is highly unstable formyl chloride. Without any further delay, the reaction of such formyl chloride occurs with arene with no initial formation of formyl chloride. It can be noted that in place of Aluminium chloride in the Gattermann Koch reaction as a catalyst Zinc chloride is used as Lewis acid, or instead of carbon monoxide at high temperature is not used but traces of copper chloride or nickel chloride is must work as co-catalyst.

The metal used here is transition metal which serves as a “carrier” that initially reacts with carbon monoxide and produces a carbonyl complex, which is active electrophile after transformation. The Gattermann Koch reaction is being used widely for industrial purposes for the production of benzaldehyde. The main aim of the Gattermann Koch reaction is the attachment of the formal group to the aromatic system.

Gattermann Koch Synthesis

Following are the steps that are included in the Gattermann Koch reaction mechanism or the synthesis of the Gattermann Koch reaction.

Step 1: Includes the formation of formyl chloride.

In the very first step of the Gattermann Koch reaction, the reactive species are generated as they later in the mechanism react with an aromatic ring. Accepting a proton from hydrochloric acid, carbon monoxide gets protonated which works as a Lewis acid in it. In such a mechanism the molecule changes its resonance structures and becomes positively charged. Showing the reactivity of the hybrid structure formed, carbon here gets a positive charge on it. Further it reacts with aromatic rings, this happens because the species work like electrophile. As we know that in hydrochloric acid the chloride is negatively charged and works as a nucleophile, which behaves as a target of electrophile. The following reaction is shown below:

Formation of formyl chloride+

Step 2: Includes the formation of Electrophile.

In the next Gattermann Koch reaction step after getting the intermediate product adding the lewis acid which is aluminium chloride AlCl3to it, works as a catalyst and removes the chloride ion from the species. The obtained species now reverts to formyl cation which is reactive in nature. The reaction can be shown below in compiled form with the final product in the third step.

Step 3: Includes the formation of Benzaldehyde.

Gattermann Koch reaction is substitution reaction so here electrophilic aromatic substitution can be seen at the aromatic ring. The aromatic ring here behaves as a nucleophile which donates an electron pair to the intermediate formyl cation. The loss of aromaticity will no longer be there in the reaction and can be resolved by the expulsion of a proton. Such type of mechanism is called the Gatterman Koch formylation. The complete Gattermann Koch reaction is shown below where we get the final product.

Formation of Benzaldehyde

Conclusion of Gattermann Koch reaction Mechanism:

In the last step, we see that the formyl group is attached to an aromatic ring which is done with the help of the Gattermann Koch reaction. The above example of the mechanism shows that benzaldehyde can be prepared from the treatment of benzene with carbon monoxide and of course the action of hydrochloride on it, the process occurs in the presence of a catalyst which is aluminium chloride. One of the major conclusion that can be drawn from the reaction is that the Gattermann reaction is different from the Gattermann Koch reaction.

The Gattermann reaction is named after the scientist Ludwig Gattermann whereas the Gattermann Koch reaction is named after two scientists from Germany, Ludwig Gattermann and Julius Koch In the Gattermann reaction reaction follows the substitution reaction of organic compounds in which we can formylate the aromatic compounds. In the Gattermann reaction conditions are different as in the involvement of hydrogen cyanide and hydrochloric acid can be seen here, on the other hand in the Gattermann Koch reaction, instead of using hydrogen cyanide carbon monoxide is being used. Gattermann reaction can be applied to phenol and substrates of phenol ether which can be applied in the Gattermann Koch reaction.

Example: In the presence of anhydrous aluminium chloride AlCl3 ,what are the products formed when benzene reacts with CO and HCl.

In the Gattermann – Koch reaction: In an acidic medium in presence of anhydrous aluminum chloride AlCl3, benzene is treated with carbon monoxide and produces the product benzaldehyde. Here aluminum chloride works as a catalyst, which is Lewis acid. The Gattermann Koch reaction is an electrophilic substitution reaction.

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Electrophilic substitution:

Electrophilic substitution can be seen in benzene because benzene is electron rich and undergoes such a reaction. Complete step-by-step substitution reaction can be seen here.

The reagents used in such reactions are formaldehyde and hydrochloric acid and benzene work as substrate. This type of reaction is the so-called Chloromethylation reaction of benzene. In the presence of hydrochloric acid, the benzene reacts with formaldehyde to give the product as benzene methyl chloride. This reaction is called the Electrophilic substitution reaction. The reaction may include a step wherein the first step we see the intermediated product formed is an electrophile.

Step 1: In this step, the reaction between benzene and HCHO, HCl takes place to give the species positive methyl chloride, which is an electrophile.

Step 2: Further this electrophile reacts with benzene to produce benzyl chloride, after this product reacts with AgCN to produce the final product which is benzyl isocyanide. AgCN is covalent in which C and N can both donate the electrons but reaction (attack) takes place on N as donating the electron pair gives rise to the major product formed in this reaction which is benzyl isocyanide. The reaction mechanism is shown below.

Electrophilic substitution of benzene using HCHO and HCl.

Duff Reaction Mechanism:

The Duff reaction was named after the scientist Cooper Duff. The reaction can also be called hexamine aromatic formylation which is used in organic chemistry for the mechanism procedure related to benzaldehydes. Duff reaction takes place when benzaldehyde reacts with hexamine which is the formyl carbon source. In Duff’s reaction, the electrophilic species here is the iminium ion, which is the initial product in this reaction which further hydrolyzes to the aldehyde.

Initially, we get the oxidation state of benzylamine, in addition to the aromatic ring. After this, the oxidation state of aldehyde is achieved when an intramolecular redox reaction raises the benzylic carbon. And in the final step we see that the acid hydrolysis occurs by water which gives the oxygen in the final stage of the reaction mechanism of Duff reaction.

Below are the reaction mechanism showing you the exact synthesis process that occurs in the Duff reaction:

Also known as hexamine aromatic formylation.

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Vilsmeier Reaction Mechanism:

Vilsmeier reaction is the alternative reaction mechanism of Friedel-craft reaction, which helps in avoiding the use of strong Lewis acid, that is Aluminium chloride. Vilsmeirer reaction mechanism is very specifically used for formylation. The reaction of Vilsmeier can be completed with the help of three major steps. In the first step, the formation of iminium cation occurs which is the intermediate product, which further tends to create the second step in which nucleophilic substitution occurs. And in the last final step hydrolysis of an iminium salt occur which gives us the major product. The reaction mechanism is shown below:

Alternative reaction mechanism of Friedal-Craft reaction

Example:

  1. What do you mean by the pyrrole ring?

It is defined as a ring structure consisting of four carbon atoms and one nitrogen atom of organic compounds of heterocyclic series is so-called a Pyrrole ring. Talking about the simplest member of the pyrrole family, pyrrole itself is considered as the simplest one, with molecular formula C4H5N.

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Frequently Asked Questions (FAQs)

1. What are the different types of organic compounds prepared by the Gattermann-Koch reaction?

The Gattermann reaction or the Gattermann formylation is an organic chemical reaction in which aromatic compounds are formylated with the help of a mixture of hydrogen cyanide (HCN) and hydrogen chloride (HCl) in the presence of a catalyst. The Gattermann reaction is also called Gattermann salicylaldehyde synthesis, the catalyst used in the reaction is Lewis acid i.e.aluminium chloride.

2. The electrophile used in the Vilsmeier-Haack reaction is?

A chloro-iminium salt is found as a weak electrophile which works great in this reaction. Because of chloro-iminium salt, the Vilsmeier–Haack reaction works better with electron-rich carbocycles and also heterocycles.

3. What is Duff's reaction?

The reaction between hexamethylenetetramine and boric acid in the presence of glycerol, and phenol is heated salicylaldehyde is formed. This reaction is termed a Duff reaction.

4. Does benzene show electrophilic substitution? If so, why?

Delocalized electrons are present in the planar molecular geometry of benzene above and below the plane of the ring. Therefore, it is an electron-rich species. Due to this, it is more attractive to electron-deficient species. So we can say that yes, it shows electrophilic substitution reactions very easily.

5. What is the beginning of mechanism of gattermann Koch reaction?
Gattermann Koch's reaction mechanism begins with the formation of the reactive species with the help of the acid.
6. Which catalyst is used in gattermann Koch reaction?
Anhydrous aluminium chloride works as a catalyst is used in gattermann Koch reaction
7. Which product is formed after gatterman reaction?
When benzene is treated with carbon monoxide in an acidic medium in presence of anhydrous aluminium chloride, it results in the production of benzaldehyde. This reaction is a name reaction, popularly known as Gattermann-Koch reaction.
8. What type of aromatic compounds work best in the Gattermann-Koch reaction?
The Gattermann-Koch reaction works best with electron-rich aromatic compounds, such as phenols, ethers, and aromatic amines. These compounds are more reactive towards electrophilic aromatic substitution, which is a key step in the mechanism.
9. Why doesn't the Gattermann-Koch reaction work well with strongly deactivated aromatic compounds?
Strongly deactivated aromatic compounds, such as nitrobenzene or benzoic acid, have electron-withdrawing groups that make the aromatic ring less nucleophilic. This reduces the ring's ability to undergo electrophilic aromatic substitution, which is a crucial step in the Gattermann-Koch reaction.
10. What is the role of the Lewis acid catalyst in the Gattermann-Koch reaction?
The Lewis acid catalyst (typically AlCl3 or CuCl) serves two main purposes:
11. What is the significance of regioselectivity in the Gattermann-Koch reaction?
Regioselectivity in the Gattermann-Koch reaction determines where the aldehyde group will be introduced on the aromatic ring. It is important because it affects the structure of the final product and can influence subsequent reactions or the compound's properties.
12. How does the electronic nature of substituents on the aromatic ring affect the Gattermann-Koch reaction?
The electronic nature of substituents greatly influences the Gattermann-Koch reaction:
13. What is the first step in the Gattermann-Koch reaction mechanism?
The first step in the Gattermann-Koch reaction mechanism is the formation of the electrophile. Carbon monoxide reacts with hydrogen chloride in the presence of the Lewis acid catalyst to form a reactive formyl chloride species (HC(O)Cl).
14. Can you explain the concept of chemoselectivity in the context of the Gattermann-Koch reaction?
Chemoselectivity in the Gattermann-Koch reaction refers to the preferential formation of aldehydes over other possible products. The reaction is chemoselective because it specifically introduces an aldehyde group without affecting other functional groups present in the molecule, such as ethers or amines.
15. What is the role of hydrogen chloride in the Gattermann-Koch reaction?
Hydrogen chloride serves multiple roles in the Gattermann-Koch reaction:
16. Can the Gattermann-Koch reaction be used to introduce multiple aldehyde groups on a single aromatic ring?
While it is theoretically possible to introduce multiple aldehyde groups using the Gattermann-Koch reaction, it is generally challenging and not commonly done. The presence of one aldehyde group tends to deactivate the ring towards further substitution. Multiple formylations would require harsh conditions and often result in low yields and complex mixtures of products.
17. What are some limitations of the Gattermann-Koch reaction?
Some limitations of the Gattermann-Koch reaction include:
18. What are the main reactants in the Gattermann-Koch reaction?
The main reactants in the Gattermann-Koch reaction are:
19. Can the Gattermann-Koch reaction be used to synthesize ketones?
No, the Gattermann-Koch reaction specifically produces aldehydes. It cannot be used to synthesize ketones directly. For ketone synthesis, other methods like Friedel-Crafts acylation are more appropriate.
20. How does the Gattermann-Koch reaction differ from the traditional Gattermann reaction?
The main difference is that the Gattermann-Koch reaction uses carbon monoxide as the source of the aldehyde group, while the traditional Gattermann reaction uses hydrogen cyanide (HCN). The Gattermann-Koch reaction is often preferred due to the lower toxicity of carbon monoxide compared to hydrogen cyanide.
21. How does the reactivity of different aromatic compounds compare in the Gattermann-Koch reaction?
The reactivity of aromatic compounds in the Gattermann-Koch reaction generally follows this order:
22. Why is the Gattermann-Koch reaction important in organic synthesis?
The Gattermann-Koch reaction is important because it provides a direct method for introducing an aldehyde group onto an aromatic ring. This is particularly useful when other formylation methods are not suitable or when specific substitution patterns are desired.
23. How does the Gattermann-Koch reaction compare to the Vilsmeier-Haack reaction in terms of substrate scope and conditions?
Comparing the Gattermann-Koch and Vilsmeier-Haack reactions:
24. How does the Gattermann-Koch reaction compare to other formylation methods?
The Gattermann-Koch reaction offers several advantages over other formylation methods:
25. What are some modern variations or improvements to the classic Gattermann-Koch reaction?
Modern variations and improvements to the Gattermann-Koch reaction include:
26. What is the Gattermann-Koch reaction?
The Gattermann-Koch reaction is an organic synthesis method used to produce aromatic aldehydes from aromatic compounds. It involves the reaction of an aromatic compound with carbon monoxide and hydrogen chloride in the presence of a Lewis acid catalyst, typically aluminum chloride or copper(I) chloride.
27. How does the Gattermann-Koch reaction compare to the Reimer-Tiemann reaction for aldehyde synthesis?
The Gattermann-Koch reaction and Reimer-Tiemann reaction are both used for aldehyde synthesis, but they differ in several ways:
28. How does the Gattermann-Koch reaction fit into the broader context of C-C bond forming reactions?
The Gattermann-Koch reaction is an important C-C bond forming reaction because:
29. How does the reactivity of heteroaromatic compounds compare to carbocyclic aromatics in the Gattermann-Koch reaction?
Heteroaromatic compounds generally show different reactivity in the Gattermann-Koch reaction:
30. How does temperature affect the Gattermann-Koch reaction?
Temperature plays a crucial role in the Gattermann-Koch reaction:
31. How can the Gattermann-Koch reaction be monitored and when is it considered complete?
The Gattermann-Koch reaction can be monitored and considered complete as follows:
32. What are the environmental considerations when performing the Gattermann-Koch reaction?
Environmental considerations for the Gattermann-Koch reaction include:
33. What safety precautions should be taken when performing the Gattermann-Koch reaction?
Important safety precautions for the Gattermann-Koch reaction include:
34. What is the significance of using anhydrous conditions in the Gattermann-Koch reaction?
Anhydrous conditions are crucial in the Gattermann-Koch reaction because:
35. How does the choice of Lewis acid catalyst affect the Gattermann-Koch reaction?
The choice of Lewis acid catalyst can significantly impact the Gattermann-Koch reaction:
36. What are some industrial applications of the Gattermann-Koch reaction?
The Gattermann-Koch reaction has several industrial applications:
37. How does the presence of ortho-para directing groups affect the outcome of the Gattermann-Koch reaction?
Ortho-para directing groups (e.g., -OH, -NH2, -NHR, -OR) in the Gattermann-Koch reaction:
38. What are some common side reactions in the Gattermann-Koch reaction?
Common side reactions in the Gattermann-Koch reaction include:
39. What is the role of solvent in the Gattermann-Koch reaction?
The solvent plays several important roles in the Gattermann-Koch reaction:
40. What is the significance of the formyl chloride intermediate in the Gattermann-Koch reaction mechanism?
The formyl chloride intermediate is crucial in the Gattermann-Koch reaction because:
41. How does the presence of a halogen substituent on the aromatic ring affect the Gattermann-Koch reaction?
The presence of a halogen substituent affects the Gattermann-Koch reaction as follows:

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