Kinetics and Products of the Aqueous Phase Oxidation of Triethylamine by OH
Ye Tao, Tengyu Liu, Xiaoying Yang, J. G. Murphy
Abstract
Low-molecular-weight alkyl amines have attracted attention for their roles in new particle formation, ultrafine particle growth, and neutralizing aerosol acidity. The major source of the low-molecular-weight aminium ions in fine particles is generally believed to be the corresponding gaseous precursors emitted to the atmosphere. Relatively little work has investigated whether larger amines can be transformed into smaller amines within the condensed phase itself. In this work, we studied the bulk aqueous phase oxidation kinetics and products of triethylamine/triethylaminium (pKa = 10.75) against OH under different values of pH. Using relative rate kinetics, we find that the oxidation rates against OH for TEA and TEAH+ are (74.3 ± 6.5) × 108 and (1.8 ± 0.2) × 108 M–1 s–1, respectively. In a dilute NaHSO4 solution with a pH of 3.2, the ionic products of TEAH+ oxidation include diethylaminium, ethylaminium, and ammonium ions, which are formed within an atmospherically relevant oxidation time scale. Under common atmospheric conditions, aqueous phase oxidation is calculated to be competitive with gas phase oxidation as a sink for TEA. This indicates that some low-molecular-weight aminium ions can also be the products of the aqueous phase oxidation of larger N-containing molecules.