Sandmeyer's Reaction

Sandmeyer's reaction is a chemical reaction used to convert an aromatic diazonium salt into a new functional group. In this reaction, the diazonium salt is decomposed and replaced with a new functional group.

Decomposition of Benzene Diazonium Chloride

In the given question, the benzene diazonium chloride is decomposed using Cu2Cl2/HCl to form chlorobenzene. Let's understand the reaction step by step:

1. Formation of Benzene Diazonium Chloride:
- The diazonium ion (N2+) is formed by the reaction of an amine with nitrous acid (HNO2).
- In this case, benzene reacts with nitrous acid to form benzene diazonium chloride (C6H5N2Cl).

2. Decomposition of Benzene Diazonium Chloride:
- Benzene diazonium chloride is a highly reactive compound and can easily decompose.
- In the presence of a copper(I) chloride catalyst (Cu2Cl2) and hydrochloric acid (HCl), the diazonium salt decomposes to form chlorobenzene.
- The reaction proceeds as follows:
C6H5N2Cl + Cu2Cl2/HCl → C6H5Cl + N2 + CuCl2

Explanation of the Reaction

1. Copper(I) Chloride Catalyst (Cu2Cl2):
- Copper(I) chloride (Cu2Cl2) acts as a catalyst in this reaction.
- It helps in the decomposition of the diazonium salt and promotes the formation of the desired product.

2. Hydrochloric Acid (HCl):
- Hydrochloric acid (HCl) provides the necessary acidic conditions for the reaction.
- It helps in the protonation of the diazonium ion, making it more reactive and prone to decomposition.

3. Formation of Chlorobenzene:
- In the reaction, the diazonium chloride is decomposed, resulting in the formation of chlorobenzene (C6H5Cl).
- The nitrogen gas (N2) and copper(II) chloride (CuCl2) are also produced as byproducts of the reaction.

Conclusion

The decomposition of benzene diazonium chloride using Cu2Cl2/HCl to form chlorobenzene is an example of Sandmeyer's reaction. This reaction is commonly used to replace the diazonium group with a new functional group, in this case, the chlorine atom. The presence of a copper(I) chloride catalyst and hydrochloric acid helps in the decomposition and formation of the desired product.