Reactivity of α-amino-peroxyl radicals and consequences for amine oxidation chemistry

A comparative theoretical study is presented on the formation and fate of alpha-amino-peroxyl radicals, recently proposed as important intermediates in the aerobic oxidation of amines. After radical abstraction of the weakly bonded alpha H-atom in the amine substrate, the alpha-amino-alkyl radical reacts irreversibly with O-2, forming the corresponding alpha-amino-peroxyl radical. HO2 center dot-elimination from various types of alpha-amino-peroxyl radicals (forming the corresponding imine) and the kinetically competing substrate H-abstraction (forming the alpha-amino-hydroperoxide) were computationally characterized. Polar solvents were found to reduce the HO2 center dot-elimination barrier, but increase the barrier for H-abstraction. Depending on the reaction conditions (gas or liquid phase, amine concentration, nature of the solvent, and temperature), either of the two mechanisms is favored. The consequences for aerobic amine oxidation chemistry are discussed.