Question

Explain why:

Alkyl halides form nitroalkanes on treatment with silver nitrite but form alkyl nitrites on treatment with potassium nitrite.

Answer 1

Alkyl halides give different products with potassium nitrite (KNO₂) and silver nitrite (AgNO₂) due to the different bonding and reactivity of the nitrite ion in each case.

1. With Potassium Nitrite (KNO₂): The more ionic and less coordinating potassium ion (K⁺) does not strongly interact with the halide ion. Here, the nitrite ion prefers to attack through the oxygen atom, causing the reaction to produce alkyl nitrites (R–ONO). This is because the oxygen end of \[\ce{NO^-_2}\] is more nucleophilic in this environment.
   \[\ce{R - X + KNO2 ->R – O – NO + KX}\]
2. With Silver Nitrite (AgNO₂): The silver ion (Ag⁺) binds strongly to the halide ion (X⁻), precipitating out as silver halide (AgX), and helps favor nucleophilic attack via the nitrogen atom of the \[\ce{NO^-_2}\] ion. This leads to the formation of nitroalkanes. The coordination of silver ions facilitates a direct nucleophilic substitution with the nitrite ion attacking through nitrogen.
   \[\ce{R - X + AgNO2 ->R-NO2 + AgX}\]