Formation of Aryl Nitrile from Diazonium Salts

Diazonium salts are compounds containing a positively charged nitrogen atom that is linked to an aromatic ring. These salts are often used in organic synthesis as a source of the aryl group. When treated with cuprous cyanide or KCN and copper powder, diazonium salts undergo a reaction known as Sandmeyer reaction, which forms aryl nitriles.

Reaction Mechanism

The reaction mechanism involves several steps:

1. Formation of Copper(I) Salt

First, cuprous cyanide or KCN is added to the diazonium salt solution to form a copper(I) salt. The copper(I) salt plays a crucial role in the reaction by catalyzing the formation of the aryl nitrile.

2. Formation of Aryl Copper(I) Intermediate

Next, copper powder is added to the reaction mixture, which reduces the copper(I) salt to copper metal. The copper metal then reacts with the diazonium salt to form an aryl copper(I) intermediate.

3. Formation of Aryl Cyanide

The aryl copper(I) intermediate then reacts with the cyanide ion from the cuprous cyanide or KCN to form the aryl cyanide. The reaction releases copper metal, which can then react with more diazonium salt to form more aryl copper(I) intermediate.

Overall Reaction

The overall reaction can be represented as follows:

ArN2+X- + CuCN/KCN → [CuX] + N2 + ArCu + HX
ArCu + CN- → ArCN + Cu

Where Ar represents the aryl group, X represents the anion of the diazonium salt, and HX represents the acid formed in the reaction.

Conclusion

In conclusion, the treatment of diazonium salts with cuprous cyanide or KCN and copper powder forms aryl nitriles through the Sandmeyer reaction. This reaction is an important method for the synthesis of aryl nitriles, which have a variety of applications in organic synthesis and industry.