Oxidation of Urea with Nitrous Acid in Nitric Acid Solutions

Abstract

The kinetics of the reaction between urea and HNO2 in nitric acid solution was studied spectrophotometrically. It was found that, at a constant ionic strength of the solution μ = 2, in the range of the initial concentrations of urea from 0.01 to 0.1 M, HNO2, from 0.003 to 0.012 M, and hydrogen ions, from 0.1 to 1.5 M, the rate constant of the reaction is described by the equation -d[HNO2]/dt = k[HNO2][CO(NH2)2][H+] · K([H+]K +1)−1, where the rate constant k = 15.6±0.3 l mol−1 min−1 and the protonation constant of urea K = 1.38 l mol−1 at 15°C. From the temperature dependence of the reaction rate in the range of 15–35°C, the activation energy was determined to be 61±5 kJ mol−1. The reaction mechanism involving the reaction of nondissociated HNO2 molecules and protonated urea species NH2CONH 3 + was suggested.