Nitrate radical reactions: interactions with alkynes

Abstract

The kinetics of the reaction between NO₃ radicals and hex-2-yne has been investigated in discharge-flow experiments. The main motivation for this study was to determine whether secondary reactions enter into the determination of the rate constant. The optical and mass-spectrometric detection methods employed yielded essentially the identical result that the stoicheiometry –Δ[NO₃]/–Δ[2-C₆H₁₀] departs little from unity under the conditions of the experiments. Optical absorption studies were conducted with prolonged contact times to enhance deliberately potential contributions from secondary reactions. At low concentrations of added 2-C₆H₁₀, losses of NO₃ are practically equal to the amount of the alkyne added. At higher hex-2-yne concentrations, the consumption of NO₃ is virtually complete and the shape of the titration curve is also consistent with unity stoicheiometry.

The rate constant obtained in the mass-spectrometric experiments for the reaction of NO₃ with 2-C₆H₁₀ at room temperature is (2.8 ± 0.1)× 10^–14 cm³ molecule^–1 s^–1.