Radical transformations of some N-alkylanilines by their oxidation with different agents: an EPR study

Oxidation of quinolones with peracids (an in situ EPR study)

“…2b), characterized by the spin Hamiltonian parameters a N = 0.691 mT, a H = 0.303 mT, 0.340 mT, 0.206 mT, 0.261 mT and g = 2.0036 typical for aminyl radicals. [19] Comparing the primary formed radical Q 1 -a with the consecutive radical Q 1 -b, the dominant β-hydrogen with a β H ¼ 1:200 mT from Q 1 -a is missing in Q 1 -b. Additionally, the g-value (g = 2.0036) and the value of nitrogen hyperfine coupling (a N = 0.691 mT) of the radical Q 1 -b are below those characteristic for nitroxide radicals (g~2.0057) indicating that the radical Q 1 -b most likely represents an aminyl intermediate of the oxidative degradation of quinolone Q 1 . The unspecified substituents (R) in the suggested radical structures represent reactive species generated in the oxidation system by the interaction of peracids with quinolones, solvent and nitrones, most probably carbon-centered or oxygen-centered radicals.…”

“…The unspecified substituents (R) in the suggested radical structures represent reactive species generated in the oxidation system by the interaction of peracids with quinolones, solvent and nitrones, most probably carbon-centered or oxygen-centered radicals. [19,28] However, their reaction routes are very complex, frequently exhibiting various consecutive rearrangements. So it is very difficult to specify hypothetical structures that would correspond to the real system.…”

“…[19,38] A continuing oxidation process results in the elimination of the last β-hydrogen; however, an EPR spectrum corresponding to C 6 H 5 NO [39] was observed, produced in a complex peracid-mediated mechanism coupled with the generation and trapping of phenyl radicals from the solvent.…”

“…N-methylaniline, [33] which is oxidized to nitroxide radical. [19] Further data on the radical products generated upon the progressive oxidation are not found in the literature. The EPR spectrum of the primary observed radical species in the oxidation of DMA is shown in Fig.…”

“…[17] The oxidative reaction mechanisms are not fully explained, and the generation of oxygen-centered or nitrogen-centered radicals possessing different stabilities is often involved. [19][20][21][22] Here, electron paramagnetic resonance (EPR) spectroscopy plays a unique role among experimental techniques, because it enables the direct identification of radical intermediates. [23] Our EPR study is focused on the detailed investigation of paramagnetic species produced by the oxidation of 4-oxoquinoline and its derivatives ( Fig.…”