The fragmentation behavior of N, N-diethylamino-substituted azobenzene derivatives is investigated by high-resolving mass spectrometry using a Fourier transform ion cyclotron resonance mass spectrometer. Former investigations by photodissociation as well as collision-induced dissociation experiments used to induce a loss of C3H8 from the diethylamino group. The position of the additional proton in [M + H]+ ions is important due to the sequences of radical fragmentation reactions. Two possibilities arise. First, a charge is located at the azo group leading to a methyl radical loss. The second possibility is that the charge has been located on the aniline nitrogen of the molecule resulting in an ethyl radical loss. Only o-ethyl red has shown the overall loss of C3H8 in a two-step radical reaction mechanism. Nevertheless, p-ethyl red and ethyl yellow have shown systematic fragmentation reactions as well. Loss of C3H8 has not been likely regarding both these molecules. All experimental findings together with quantum chemical calculations as well as kinetic calculations support the proposed fragmentation mechanisms of the three azo dyes.
Phosphoranyl Radical Fragmentation Reactions Driven by Photoredox Catalysis