OH Kinetics with a Range of Nitrogen-Containing Compounds: N-Methylformamide, t-Butylamine, and N-Methyl-propane Diamine.

Abstract

Emissions of amines and amides to the atmosphere are significant from both anthropogenic and natural sources, and amides can be formed as secondary pollutants. Relatively little kinetic data exist on overall rate coefficients with OH, the most important tropospheric oxidant, and even less on site-specific data which control the product distribution. Structure-activity relationships (SARs) can be used to estimate both quantities. Rate coefficients for the reaction of OH with t-butylamine (k1), N-methyl-1,3-propanediamine (k2), and N-methylformamide (k3) have been measured using laser flash photolysis coupled with laser-induced fluorescence. Proton-transfer-reaction mass spectrometry (PTR-MS) has been used to ensure the reliable introduction of these low-vapor pressure N-containing compounds and to give qualitative information on products. Supporting ab initio calculations are presented for the t-butylamine system. The following rate coefficients have been determined: k1,298K= (1.66 ± 0.20) × 10-11 cm3 molecule-1 s-1, k(T)1 = 1.65 × 10-11 (T/300)-0.69 cm3 molecule-1 s-1, k2,293K = (7.09 ± 0.22) × 10-11 cm3 molecule-1 s-1, and k3,298K = (1.03 ± 0.23) × 10-11 cm3 molecule-1 s-1. For OH + t-butylamine, ab initio calculations predict that the fraction of N-H abstraction is 0.87. The dominance of this channel was qualitatively confirmed using end-product analysis. The reaction of OH with N-methyl-1,3-propanediamine also had a negative temperature dependence, but the reduction in the rate coefficient was complicated by reagent loss. The measured rate coefficient for reaction 3 is in good agreement with a recent relative rate study. The results of this work and the literature data are compared with the recent SAR estimates for the reaction of OH with reduced nitrogen compounds. Although the SARs reproduce the overall rate coefficients for reactions, site-specific agreement with this work and other literature studies is less strong.