4.4 Article

Atmospheric Oxidation of Imine Derivative of Piperazine Initiated by OH Radical

Journal

ACS EARTH AND SPACE CHEMISTRY
Volume 6, Issue 10, Pages 2453-2464

Publisher

AMER CHEMICAL SOC
DOI: 10.1021/acsearthspacechem.2c00170

Keywords

atmospheric chemistry; imine; oxidation; reaction kinetics; computational chemistry

Funding

  1. Academy of Finland
  2. Doctoral Programme in Chemistry and Molecular Sciences (CHEMS) at the University of Helsinki

Ask authors/readers for more resources

The reaction mechanism and fate of cyclic imine 1,2,3,6-tetrahydropyrazine (THPyz) upon oxidation by OH radicals were studied using quantum chemistry and theoretical kinetics methods. The major reaction steps involve H-abstraction from a carbon adjacent to the amine nitrogen, leading to the formation of a second imine function. The calculated yields of potentially hazardous products are low but non-negligible. Additionally, it was found that the aminyl radical formed from OH radical addition to the imine carbon undergoes C-C bond scission, leading to the formation of an imidic acid. These findings are important for understanding the oxidative processes of THPyz and similar compounds in the atmosphere.
The cyclic imine 1,2,3,6-tetrahydropyrazine (THPyz) has been observed to be the major atmospheric photo-oxidation product of piperazine, a widely used solvent in carbon-capture technology, yet little is known about its own fate. Very few studies have focused on the atmospheric chemistry of imines in general, despite consistently appearing as major products of amine oxidation. In this work, we explore the reaction mechanism of THPyz oxidation initiated by OH radicals, as well as the fate of the first-generation C-centered (alkyl) and N-centered (aminyl) radical products, with quantum chemistry and theoretical kinetics methods. We predict that the major initial reaction steps involve H-abstraction from a carbon adjacent to the amine nitrogen, leading to subsequent formation of a second imine function via the O2-addition/HO2-elimination pathway. Calculated yields of potentially hazardous products are low but non-negligible. Typically carcinogenic compounds, nitrosamines and nitramines, are expected to have a maximum yield of -7% and -11%, respectively, under high NOx regimes, considering the uncertainties in the obtained rates. Low yield (1-14%) of an isocyanate is also predicted, formed in a channel following initial H-abstraction from the imine carbon. The aminyl radical formed from OH radical addition to the imine carbon undergoes fast C-C bond scission, leading to an imidic acid. These pathways are minor for OH radical oxidation of THPyz but could be more competitive for other Schiff bases.

Authors

I am an author on this paper
Click your name to claim this paper and add it to your profile.

Reviews

Primary Rating

4.4
Not enough ratings

Secondary Ratings

Novelty
-
Significance
-
Scientific rigor
-
Rate this paper

Recommended

No Data Available
No Data Available