Gattermann-Koch Reaction: Aromatic Aldehyde Synthesis
by Yuvi K - December 17, 2023
Gattermann-Koch Reaction: Aromatic Aldehyde Synthesis
Gattermann-Koch reaction or Gattermann-Koch Aldol condensation is an important starting material in organic chemistry for generating an aromatic aldehyde or ketone from an aromatic acid halide.
This reaction was first introduced in 1895 by the German chemists Gattermann and Koch who proposed this reaction as a synthetic method for the preparatory synthesis of aromatic aldehydes or ketones.
The Gattermann-Koch reaction is an aldol condensation reaction that is catalyzed by copper (I) chloride or Cuprous chloride (केप्रस च्लोराइड)(CuCl) in the presence of chloroform.
The Gattermann-Koch reaction is a useful technology to efficiently generate highly functionalised aldehydes or ketones from dihalobenzenes and other aromatic acid halides. It is often used in synthesizing various molecules, including pharmaceuticals, pesticides, and industrial compounds. The Gattermann-Koch reaction is one of the most well-known methods for the synthesis of aromatic aldehydes.
Reaction Mechanism
The Gattermann-Koch reaction proceeds in a two steps mechanism. In the first step, a strongly acidic medium is formed due to the presence of copper (I) chloride and the protonation of the aromatic ring.
The protonated aromatics are then modified by an electrophilic addition of chloroform. This results in an intermediate that is a reactive nucleophile having an aromaticity of two additionally activated by a metallic cation, creating a strongly activated complex.
In the second step, the activated complex reacts spontaneously at room temperature to produce the desired aromatic aldehyde or ketone. This type of reaction is known as the Aldol condensation. The overall reaction of the Gattermann-Koch reaction is shown below:
Advantages of Gattermann-Koch Reaction
The Gattermann-Koch reaction has many advantages when compared to other methods for synthesizing aromatic aldehydes. Firstly, it produces an aromatic aldehyde or ketone in a single synthesis step, eliminating the need to use a two-step process and perform an additional reaction. This makes the reaction highly efficient and simple.
Another advantage of this reaction is that it is compatible with a wide range of aromatics, including monosubstituted, disubstituted, and trisubstituted aromatics. Moreover, the Gattermann-Koch reaction is easy to control and the reaction conditions can easily be changed to give different results.
Moreover, the reaction is highly regio- and stereoselective and the yields are usually high. The reaction is also environmentally friendly as there are no hazardous products and a low amount of by-products.
Limitations of Gattermann-Koch Reaction
Though the Gattermann-Koch reaction is highly efficient and useful, there are still some limitations. Firstly, this reaction is only applicable to halogen substituted aromatics and is not suitable for other cases. Moreover, it can only be used at low temperatures (10-15°C) and highly acidic mediums. This reaction is also not applicable to some kinds of unsaturated aromatics.
Furthermore, the Gattermann-Koch reaction produces toxic and hazardous byproducts such as chloroform, hydrochloric acid, and copper chloride, which can be harmful if not disposed off properly.
Conclusion
In conclusion, the Gattermann-Koch reaction is an important tool in organic synthesis for the synthesis of highly functionalized aldehydes or ketones from dihalobenzenes and other aromatic acid halides. This reaction is easy to control, highly efficient, and produces high yields. Though there are some limitations, the Gattermann-Koch reaction is still a useful technology for the preparation of aromatic aldehydes.
