Abstract
The reaction of peroxynitrite/peroxynitrous acid with morpholine as a model compound for secondary amines is reinvestigated in the absence and presence of carbon dioxide. The concentration‐ and pH‐dependent formation of N‐nitrosomorpholine and N‐nitromorpholine as reported in three previous papers ([25] [26] [14]) is basically confirmed. However, ^13^C‐NMR spectroscopic product analysis shows that, in the absence of CO~2~, N‐hydroxymorpholine is, at pH ≥ 7, the major product of this reaction, even under anaerobic conditions. The formation of N‐hydroxymorpholine has been overlooked in the three cited papers. Additional (ring‐opened) oxidation products of morpholine are also detected. The data account for radical pathways for the formation of these products via intermediate morpholine‐derived aminyl and α‐aminoalkyl radicals. This is further supported by EPR‐spectrometric detection of morpholine‐derived nitroxide radicals, i.e., morpholin‐4‐yloxy radicals. N‐Nitrosomorpholine, however, is very likely formed by electrophilic attack of peroxynitrite‐derived N~2~O~4~. ^15^N‐CIDNP Experiments establish that, in the presence of CO~2~, N‐nitro‐ and C‐nitromorpholine are generated by radical recombination. The present results are in full accord with a fractional (28 ± 2%) homolytic decay of peroxynitrite/peroxynitrous acid with release of free hydroxyl and nitrogen dioxide radicals.