Gas-phase oxidation of nitric oxide: Chemical kinetics and rate constant

Inhaled nitric oxide (NO) is gaining popularity as a selective pulmonary vasodilator. Because of the potential toxicity of NO and its oxidizing product nitrogen dioxide (NO₂), any system for the delivery of inhaled NO must aim at predictable and reproducible levels of NO and at as low concentrations of NO₂ as possible. This review describes the chemical kinetics and rate constant values k for the reaction 2NO + O₂ = 2NO₂. This reaction has been well established as a third-order homogeneous reaction. Published data support two equally plausible two-step mechanisms for the reaction between NO and O₂ over a wide range of temperature and pressure. The Arrhenius equation k (L² · mol^-2, · s^-1) = 1.2 x 10³ e(530/T) (=1.2 x 10³ x 10(230/T)) gives the best fit to the experimental values of the rate constant thus far reported in a temperature range of 273 to 600 K. Using the reaction mechanism and the rate constant k, one can make reliable predictions about NO₂ formation in any set of NO inhalation therapy conditions. It is also pointed out that NO₃, the intermediate of one of the two mechanisms, deserves serious attention in NO inhalation therapy.