N-nitrosation of amines by NO2 and NO: a theoretical study.
Gas-phase nitrosation of amines implies a nonionic pathway different from the nitrosonium nitrosation via acidification of nitrite. Electronic structure calculations discussed in this work suggest a free radical mechanism, in which NO2 abstracts a hydrogen atom from the nitrogen in primary and secondary amines to form an intermediate complex of an aminyl radical and nitrous acid. The aminyl radical intermediate is then quenched by nitric oxide, leading to the formation of nitrosamine. High-level calculations (CBS-QB3) show that alkyl substitutions on amines can activate the H-abstraction reaction. Thus, while H-abstraction from NH3 was found to exhibit a reaction barrier (DeltaH) of 106 kJ/mol, similar calculations indicate that the corresponding barriers decrease to 72 and 45 kJ/mol for methylamine and dimethylamine, respectively. Heterocyclic secondary amines have also been investigated in a similar manner. The five-membered-ring (5-m-r) amine appears to be the most reactive: pyrrolidine (DeltaH=30 kJ/mol), azetidine (DeltaH=44 kJ/mol), piperidine (DeltaH=44 kJ/mol), and aziridine (DeltaH=74 kJ/mol). The reaction barrier for 1H-pyrrole, an aromatic 5-m-r secondary amine, was found to be 59 kJ/mol. The origin of the high activity for the 5-m-r alkylamine stems from a hydrogen-bond-like interaction between the aminyl radical and the nascent nitrous acid molecule. This theoretical study suggests that, in the presence of nitrogen oxides, the gas-phase nitrosation of secondary amines is feasible.
Zhao
Yi-Lei
YL
NIST Center for Theoretical and Computational Nanosciences, National Institute of Standards and Technology, 100 Bureau Drive MS 8380, Gaithersburg, Maryland 20899, USA. yilei.zhao@nist.gov
Garrison
Stephen L
SL
Gonzalez
Carlos
C
Thweatt
William David
WD
Marquez
Manuel
M
D000588:Amines / Q000737:chemistry*; D019277:Entropy; D006571:Heterocyclic Compounds / Q000737:chemistry; D006860:Hydrogen Bonding; D008956:Models, Chemical; D008958:Models, Molecular; D008968:Molecular Conformation; D009569:Nitric Oxide / Q000737:chemistry*; D009585:Nitrogen Dioxide / Q000737:chemistry*; D015538:Nitrosation; D009603:Nitroso Compounds / Q000737:chemistry; D011758:Pyrroles / Q000737:chemistry; D011759:Pyrrolidines / Q000737:chemistry
D000588:Amines; D006571:Heterocyclic Compounds; D009603:Nitroso Compounds; D011758:Pyrroles; D011759:Pyrrolidines; D009569:Nitric Oxide; C032519:pyrrolidine; D009585:Nitrogen Dioxide