Generation of nitrous acid by ultrasound irradiation in the organic solution consisting of tri-n-butylphosphate, nitric acid and water

The generation of nitrous acid (HNO₂) by ultrasound was investigated for an organic solution consisting of tri-n-butylphosphate, nitric acid (HNO₃) and water under several conditions. The amount of HNO₂ was found to increase by a factor of 40 upon ultrasound irradiation, and the concentration of HNO₂ reached the steady-state after long time irradiation. Although the concentration of HNO₃ was low, the rate of generation of HNO₂ in the organic solution was higher than that in aqueous solution equilibrated with the organic solution. The formation rates of HNO₂ were greatly enhanced with an increase in concentration of HNO₃ in the organic solution. The concentration of HNO₂ was higher in the absence of a gas phase, because the HNO₂ was transferred from the solution into the gas phase as a form of NOx. In the presence of a gas phase, a higher concentration of HNO₂ was obtained at a lower temperature, due to the higher solubility of NOx in the solution. (author)