Oxygenate-Induced Tuning of Aldehyde-Amine Reactivity and Its Atmospheric Implications

Abstract

Atmospheric aerosols often contain a significant fraction of carbon-nitrogen functionality, which makes gas-phase aldehyde-amine chemistries an important source of nitrogen containing compounds in aerosols. Here we use high-level ab initio calculations to examine the key determinants of amine (ammonia, methylamine, and dimethylamine) addition onto three different aldehydes (acetaldehyde, glycolaldehyde, and 2-hydroperoxy acetaldehyde), with each reaction being catalyzed by a single water molecule. The model aldehydes reflect different degrees of oxygenation at a site adjacent to the carbonyl moiety, the α-site, and represent typical oxygenates that can arise from atmospheric oxidation especially under conditions where the concentration of NO is low. Our results show that the reaction barrier is influenced not only by the nature of the amine but also by the nature of the aldehyde. We find that, for a given amine, the reaction barrier decreases with increasing oxygenation of the aldehyde. This observed trend in barrier height can be explained through a distortion/interaction analysis, which reveals a gradual increase in internal hydrogen bonding interactions upon increased oxygenation, which, in turn, impacts the reaction barrier. Further, the calculations reveal that the reactions of methylamine and dimethylamine with the oxygenated aldehydes are barrierless under catalysis by a single water molecule. As a result, we expect these addition reactions to be energetically feasible under atmospheric conditions. The present findings have important implications for atmospheric chemistry as amine-aldehyde addition reactions can facilitate aerosol growth by providing low-energy neutral pathways for the formation of larger, less volatile compounds, from readily available smaller components.

Organic Acid Formation from the Atmospheric Oxidation of Gem Diols: Reaction Mechanism, Energetics, and Rates

“…These results are shown in Figure S3 of the Supporting Information. A similar trend arising from internal hydrogen bonding has recently been reported in studies examining the reactions of amines with oxygenated atmospheric molecules …”

A Computational Study Investigating the Energetics and Kinetics of the HNCO + (CH3)2NH Reaction Catalyzed by a Single Water Molecule

“…Further, we see that the barriers for both these reaction pathways decrease with increased methylation of the amine; so, the reaction barriers decrease along the series NH 3 , MA, and DMA. This trend in barrier heights has also been seen in other reactions involving these amines. − The trends for the present reactions are summarized in Table and schematically illustrated in Figure . The impact of water catalysis is also indicated in Table .…”

Elucidating the molecular mechanisms of Criegee-amine chemistry in the gas phase and aqueous surface environments

“…The reaction between anti-CH 3 CHOO and CH 3 NH 2 on the water droplet is favored over the reaction between anti-CH 3 CHOO and H 2 O because amines are more reactive than water. 70 The interfacial water molecules stabilize oligomers originating from the Criegeeamine reactions via hydrogen-bonding and thus, may play a role in lowering their vapor pressures and enhancing the rate of particle formation. Our viewpoint is indirectly supported by laboratory experiments demonstrating that although amines have concentrations at least an order of magnitude lower than that of NH 3 in the atmosphere, 21 they are more effective than NH 3 in enhancing particle formation.…”