Atmospheric Oxidation of Piperazine Initiated by ·Cl: Unexpected High Nitrosamine Yield

Abstract

Chlorine radicals (·Cl) initiated amine oxidation plays an important role for the formation of carcinogenic nitrosamine in the atmosphere. Piperazine (PZ) is considered as a potential atmospheric pollutant since it is an alternative solvent to monoethanolamine (MEA), a benchmark solvent in a leading CO capture technology. Here, we employed quantum chemical methods and kinetics modeling to investigate ·Cl-initiated atmospheric oxidation of PZ, particularly concerning the potential of PZ to form nitrosamine compared to MEA. Results showed that the ·Cl-initiated PZ reaction exclusively leads to N-center radicals (PZ-N) that mainly react with NO to produce nitrosamine in their further reaction with O/NO. Together with the PZ + ·OH reaction, the PZ-N yield from PZ oxidation is still lower than that of the corresponding MEA reactions. However, the nitrosamine yield of PZ is higher than the reported value for MEA when [NO] is <5 ppb, a concentration commonly encountered in a polluted urban atmosphere. The unexpected high nitrosamine yield from PZ compared to MEA results from a more favorable reaction of N-center radicals with NO compared to O. These findings show that the yield of N-center radicals cannot directly be used as a metric for the yield of the corresponding carcinogenic nitrosamine.

Nitramine and nitrosamine formation is a minor pathway in the atmospheric oxidation of methylamine: A theoretical kinetic study of the CH3NH + O2 reaction

“…However, given a tropospheric O 2 concentration of 5.2 × 10 18 molecule cm −3 , the half‐life for CH 3 N • H consumption is still short, at 3.7 ms. Under the same conditions, reaction of aminyl radicals with • NO and NO 2 • proceeds with a much faster rate coefficient, around 2 × 10 −11 cm 3 molecule −1 s −1 . However, given the significantly higher concentration of O 2 than NO x , we predict that reaction with O 2 to form CH 2 NH + HO 2 • will be the dominant fate under all but the most polluted conditions.…”

“…Abstraction from N–H sites produces nitrogen‐centered aminyl radicals of the form RN • H, which are thought to react slowly with O 2 . Instead, these radicals can associate with NO x (NO 2 and NO ), to form nitramines and nitrosamines, with rate coefficients on the order of 10 −11 cm 3 molecule −1 s −1 …”

Computational study on atmospheric transformationmechanisms and kinetics of volatile amines

“…Ma等人 [98] 采用CCSD(T)/aug-cc-pVTZ//MP2/6-31+ ; the black values represent branching ratios of products for •OH-initiated reaction [93,94] ( . 此外, 一些低分子量叔胺如TMA和三乙胺(TEA) 也是目前大气中最常见的烷基胺 [14] .…”

“…Proposed atmospheric oxidation reaction scheme of piperazine initiated by •OH and •Cl. The red values represent branching ratios of products for •Cl-initiated reaction[98] …”

Atmospheric Oxidation of Piperazine Initiated by OH: A Theoretical Kinetics Investigation

“…The extent of branching to the PzN radical is of particular interest, as aminyl radicals can react with NO and NO2 to generate toxic nitrosamines and nitramines, respectively. [20][21][22][23][24][25][26][27] On the other hand, -aminoalkyl radicals such as PzC have been shown to predominantly react with O2 to produce imines. 28,29 Experimentally, Pz has been shown to react with • OH mainly via C-H abstraction, although there is limited information on the further reaction products under atmospheric conditions.…”