Hindered Amine Light Stabilizers (HALS) are effective antioxidants, used to protect organic materials against oxidative degradation. Despite their widespread use, the mechanism underlying their activation and regeneration, and the nature of the side-reactions that disrupt this process, is hotly debated. Not only is the commonly accepted Klemchuk's pathway kinetically unfeasible under service conditions, but it also fails to explain the experimentally detected formation of secondary piperidine analogues. There appears to be an important gap in our knowledge of the reactions of nitroxide radicals with organic materials, vital not only for designing effective HALS, but also NMP control agents, biological antioxidants and markers, etc. In this presentation we introduce a new catalytic cycle that relies on abstraction of a �-hydrogen atom from an alkoxyamine; our results suggest that this cycle is energetically feasible for a range of substrates and provides an explanation for previously misinterpreted or unexplained experimental results.

New insights into the catalytic cycle of nitroxide activation and regeneration

244th National Meeting (2012)

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