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(N)2 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 (N-2) and water (H2O)). (C) 2003 Elsevier Ltd. All rights reserved.