Kinetics and mechanism of the reaction between ammonium and nitrite ions: experimental and theoretical studies

The kinetics of the reaction between ammonium ion (NH₄⁺) and nitrite ion (NO₂⁻) in aqueous solutions was studied as a function of pH, temperature, and activities of the reactants. This reaction belongs to a class of fused chemical reactions that can be used to remediate paraffin and asphaltene deposition problems in oil pipelines. The reaction rate was found to be first-order with respect to the total concentration of ammonium species and second-order with respect to the total concentration of nitrite species. The reaction is strongly dependent on the pH of the solution, increasing the rate by a factor of 4000 as pH decreased from 7 to 3. The activity of hydrogen ion catalyzes the reaction by changing the concentrations of the two true reactants (ammonia (NH₃) and nitrogen trioxide (N₂O₃)), not by changing the reaction pathway. Reaction mechanisms were developed. A mechanism involving the S_N2 reaction in which the nucleophile NH₃ reacts with the electrophile N₂O₃ in the rate-limiting step was found to fit all experimental observations. This reaction mechanism releases the nitrite ion (NO₂⁻) to produce an intermediate (nitrosamine (H₂NNO)) which dissociates very rapidly to form the final products (nitrogen (N₂) and water (H₂O)).