Degradation mechanisms of simple aliphatic amines under ozonation: a DFT study

Abstract

Aliphatic amines as common constituents of dissolved organic nitrogen (DON) exhibit high reactivity during ozonation, however, our understanding of their degradation mechanisms is very limited. In this study, methylamine (MA)...

Rapid Gas-Phase Autoxidation of Nicotine in the Atmosphere

“…Because calculations of ozone suffer from orbital instability (singlet–triplet instability); therefore O 3 , intermediates, and transition states are treated as diradical with unrestricted UM06-2X calculations . It is noticed that the ozonolysis of amines in the gas phase is different from that in the aqueous phase where formation of N -oxide dominates by transferring an O atom from ozone to nicotine forming amine- N ′-oxide. − …”

Computational studies of rubber ozonation explain the effectiveness of 6PPD as an antidegradant and the mechanism of its quinone formation

“…51 Amines. The reactivity between amines and O 3 is generally understood as a nucleophilic attack of N toward O 3 , [52][53][54] and this pathway is particularly important in tertiary amines. 55,56 Depending on the substitution pattern of the parent amine, reaction products may include N -oxides, nitrones, hydroxylamines, nitrosoalkanes, and nitroalkanes, and dealkylated amines.…”

“…55,56 Depending on the substitution pattern of the parent amine, reaction products may include N -oxides, nitrones, hydroxylamines, nitrosoalkanes, and nitroalkanes, and dealkylated amines. 54,[56][57][58] Amines may also react with ozone through insertion into the N−H bond. 59 The N lone pair plays a critical role in amine reactivity towards O 3 , such that more highly substituted aliphatic amines exhibit increased O 3 reactivity.…”

“…59 The N lone pair plays a critical role in amine reactivity towards O 3 , such that more highly substituted aliphatic amines exhibit increased O 3 reactivity. 54 By the same token, these reactions are highly sensitive to pH, as amine protonation eliminates the reaction channel. 56,60 Even in the most favorable systems and conditions, high barrier heights for N−O bond formations 59 can limit these reactions relative to other available ozonation pathways.…”

“…For each of the classes of reactions discussed above, a number of authors argue that ozonation reactions are initiated by one-electron charge transfer (CT) to form biradical, zwitterionic pre-reaction complexes (Figure 1). Examples for alkenes, [74][75][76][77] amines, [52][53][54]56,78 aromatics, 64,66 and PPDs 70,71,79,80 can be found at the indicated references. Such proposals are defended on the basis of a strong correlation between substrate ionization potential and O 3 reaction rates, 71,74 electron spin resonance (ESR) spectra that presence of radicals in the reaction mixture, 70 or details of product distributions.…”