TY - JOUR
T1 - Reactions of pyrrole, imidazole, and pyrazole with ozone
T2 - Kinetics and mechanisms
AU - Tekle-Röttering, Agnes
AU - Lim, Sungeun
AU - Reisz, Erika
AU - Lutze, Holger
AU - Abdighahroudi, Mohammad Sajjad
AU - Willach, Sarah
AU - Schmidt, Winfried
AU - Tentscher, Peter Rudolf
AU - Rentsch, Daniel
AU - McArdell, Christa S.
AU - Schmidt, Thorsten C.
AU - von Gunten, Urs
PY - 2020/1/31
Y1 - 2020/1/31
N2 - Five-membered nitrogen-containing heterocyclic compounds (azoles) belong to potential moieties in complex structures where transformations during ozonation can occur. This study focused on the azole-ozone chemistry of pyrrole, imidazole, and pyrazole as model compounds. Reaction kinetics and ozonation products were determined by kinetic and analytical methods including NMR, LC-HRMS/MS, HPLC-UV, and IC-MS. Analyses of reactive oxygen species (
1O
2, OH, H
2O
2), quantum chemical computations (Gibbs energies), and kinetic simulations were used to further support the proposed reaction mechanisms. The species-specific second-order rate constants for the reactions of ozone with pyrrole and imidazole were (1.4 ± 1.1) × 10
6 M
-1 s
-1 and (2.3 ± 0.1) × 10
5 M
-1 s
-1, respectively. Pyrazole reacted more slowly with ozone at pH 7 (k
app = (5.6 ± 0.9) × 10
1 M
-1 s
-1). Maleimide was an identified product of pyrrole with a 34% yield. Together with other products, formate, formamide, and glyoxal, C and N mass balances of ∼50% were achieved. Imidazole reacted with ozone to cyanate, formamide, and formate (∼100% yields per transformed imidazole, respectively) with a closed mass balance. For pyrazole, a high ozone:pyrazole molar stoichiometry of 4.6 was found, suggesting that the transformation products contributed to the over-stoichiometric consumption of ozone (e.g., hydroxypyrazoles). Glyoxal and formate were the only identified transformation products (C mass balance of 65%). Overall, the identified major products are suspected to hydrolyze and/or be biodegraded and thereby abated by a biological post-treatment typically following ozonation. However, as substructures of more complex compounds (e.g., micropollutants), they might be more persistent during biological post-treatment.
AB - Five-membered nitrogen-containing heterocyclic compounds (azoles) belong to potential moieties in complex structures where transformations during ozonation can occur. This study focused on the azole-ozone chemistry of pyrrole, imidazole, and pyrazole as model compounds. Reaction kinetics and ozonation products were determined by kinetic and analytical methods including NMR, LC-HRMS/MS, HPLC-UV, and IC-MS. Analyses of reactive oxygen species (
1O
2, OH, H
2O
2), quantum chemical computations (Gibbs energies), and kinetic simulations were used to further support the proposed reaction mechanisms. The species-specific second-order rate constants for the reactions of ozone with pyrrole and imidazole were (1.4 ± 1.1) × 10
6 M
-1 s
-1 and (2.3 ± 0.1) × 10
5 M
-1 s
-1, respectively. Pyrazole reacted more slowly with ozone at pH 7 (k
app = (5.6 ± 0.9) × 10
1 M
-1 s
-1). Maleimide was an identified product of pyrrole with a 34% yield. Together with other products, formate, formamide, and glyoxal, C and N mass balances of ∼50% were achieved. Imidazole reacted with ozone to cyanate, formamide, and formate (∼100% yields per transformed imidazole, respectively) with a closed mass balance. For pyrazole, a high ozone:pyrazole molar stoichiometry of 4.6 was found, suggesting that the transformation products contributed to the over-stoichiometric consumption of ozone (e.g., hydroxypyrazoles). Glyoxal and formate were the only identified transformation products (C mass balance of 65%). Overall, the identified major products are suspected to hydrolyze and/or be biodegraded and thereby abated by a biological post-treatment typically following ozonation. However, as substructures of more complex compounds (e.g., micropollutants), they might be more persistent during biological post-treatment.
UR - http://www.scopus.com/inward/record.url?scp=85083118469&partnerID=8YFLogxK
U2 - 10.1039/C9EW01078E
DO - 10.1039/C9EW01078E
M3 - Journal article
SN - 2053-1400
VL - 6
SP - 976
EP - 992
JO - Environmental Science: Water Research and Technology
JF - Environmental Science: Water Research and Technology
IS - 4
ER -