Nitroxides are putative intermediates in the accepted reaction mechanisms of the diarylamine and hindered amine antioxidants that are universally added to preserve synthetic and natural hydrocarbon-based materials. New methodology which enables monitoring of hydrocarbon autoxidations at low rates of radical generation has revealed that diarylnitroxides and hindered nitroxides are far better inhibitors of unsaturated hydrocarbon autoxidation than their precursor amines, implying intervention of a different mechanism. Experimental and computational investigations suggest that the nitroxides catalyze the cross-dismutation of hydroperoxyl and alkylperoxyl radicals to yield O₂ and a hydroperoxide, thereby halting the autoxidation chain reaction. The hydroperoxyl radicals – key players in hydrocarbon combustion, but essentially unknown in autoxidation – are proposed to derive from a tunneling-enhanced intramolecular (1,4-) hydrogen-atom transfer/elimination sequence from oxygenated radical addition intermediates. These insights suggest that nitroxides are preferred additives for the protection of hydrocarbon-based materials from autoxidation since they exhibit catalytic activity under conditions where their precursor amines are less effective and/or inefficiently converted to nitroxides in situ.

中文翻译：

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通过硝基氧催化的氢过氧基和烷基过氧基自由基的交叉歧化抑制烃自氧化†

硝基氧化物是二芳基胺和受阻胺抗氧化剂公认反应机制中的假定中间体，普遍添加这些抗氧化剂来保护合成和天然烃基材料。能够以低自由基生成率监测烃自氧化的新方法表明，二芳基硝基氧和受阻硝基氧是比其前体胺更好的不饱和烃自氧化抑制剂，这意味着不同机制的干预。实验和计算研究表明，硝基氧催化氢过氧自由基和烷基过氧自由基的交叉歧化，产生O ₂和氢过氧化物，从而停止自氧化链式反应。氢过氧自由基——碳氢化合物燃烧中的关键参与者，但在自氧化中本质上是未知的——被认为源自含氧自由基加成中间体的隧道增强分子内（1,4-）氢原子转移/消除序列。这些见解表明，硝基氧是保护烃基材料免于自氧化的优选添加剂，因为它们在其前体胺不太有效和/或不能有效地原位转化为硝基氧的条件下表现出催化活性。