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

A comparative theoretical study is presented on the formation and fate of α-amino-peroxyl radicals, recently proposed as important intermediates in the aerobic oxidation of amines. After radical abstraction of the weakly bonded αH-atom in the amine substrate, the α-amino-alkyl radical reacts irreversibly with O(2), forming the corresponding α-amino-peroxyl radical. HO(2)˙-elimination from various types of α-amino-peroxyl radicals (forming the corresponding imine) and the kinetically competing substrate H-abstraction (forming the α-amino-hydroperoxide) were computationally characterized. Polar solvents were found to reduce the HO(2)˙-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.