Gattermann Koch Reaction
The Gattermann Koch reaction is a process used to synthesize aromatic aldehydes from benzene or substituted benzenes. This reaction involves the introduction of a formyl group (CHO) onto the benzene ring. Here is a detailed explanation of the reaction:

Reaction Mechanism
1. Formation of the intermediate: The reaction starts with the formation of an intermediate complex by reacting benzene with carbon monoxide (CO) and hydrogen chloride (HCl) in the presence of a Lewis acid catalyst such as AlCl3. This intermediate complex is a chloromethyl benzene.
2. Electrophilic aromatic substitution: The chloromethyl benzene intermediate then undergoes electrophilic aromatic substitution with carbon monoxide to form a benzaldehyde derivative. The Lewis acid catalyst helps in the activation of the benzene ring towards electrophilic attack.
3. Hydrolysis: The benzaldehyde derivative is then hydrolyzed using a strong acid such as hydrochloric acid (HCl) or sulfuric acid (H2SO4) to give the final aromatic aldehyde product.

Applications
- The Gattermann Koch reaction is a useful method for the synthesis of aromatic aldehydes, which are important intermediates in organic chemistry.
- It can be used in the preparation of various aromatic aldehydes for further reactions or as key building blocks in the synthesis of more complex organic molecules.

Conclusion
The Gattermann Koch reaction provides a convenient and efficient way to introduce formyl groups onto benzene rings, allowing for the synthesis of aromatic aldehydes. Understanding the reaction mechanism and its applications can help in designing organic synthesis routes for various compounds.