Question

Why does potassium cyanide give a nitrile while silver cyanide an isonitrile when treated with an alkyl halide?

Answer 1

When treated with an alkyl halide, potassium cyanide (KCN) gives a nitrile (R – C ≡ N), while silver cyanide (AgCN) gives an isonitrile (R – N ≡ C). This happens because of the difference in the bonding nature of the cyanide ion in each compound.

Potassium Cyanide (KCN): KCN gives a nitrile (R – C ≡ N) because it is ionic, and the free carbon end of the cyanide ion attacks the alkyl halide.

R – X + KCN → R – C ≡ N (nitrile)

Silver Cyanide (AgCN): AgCN gives an isonitrile (R – N ≡ C) because the carbon is bonded to silver, so the free nitrogen end attacks instead.

R – X + AgCN → R – N ≡ C (isonitrile)