Theoretical modeling of the mechanism of aniline oxidation by singlet O2

The mechanism of aniline oxidation by singlet oxygen was studied by the DFT-PBE/L2 method. According to the calculations, aniline endoperoxide cannot participate in the reaction because of its energy instability. The addition of 1O2 to aniline proceeds with the simultaneous proton transfer to the oxygen molecule from the NH2 group (for the syn-approach of oxygen) or from the aromatic ring (for the anti-approach). For the syn-approach of the 1O2 molecule, the HNC6H4(H)OOH intermediate is formed, whose decomposition leads to aniline p-hydroperoxide (predominantly) or p-iminoquinone. In the case of the anti-approach, the 1O2 molecule is inserted at the C–H bond to form aniline p-hydroperoxide (H2NC6H4OOH). The decomposition of aniline p-hydroperoxide with the formation of p-aminophenol and H2O2 molecule proceeds via concerted mechanism.