Inhibition of hydrocarbon autoxidation by nitroxide-catalyzed cross-dismutation of hydroperoxyl and alkylperoxyl radicals
Inhibition of hydrocarbon autoxidation by nitroxide-catalyzed cross-dismutation of hydroperoxyl and alkylperoxyl radicals
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DOI：
10.1039/c8sc01575a
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发表时间：
2018-07-28
期刊：
影响因子：
8.4
通讯作者：
Pratt, Derek A.
中科院分区：
文献类型：
--
作者：
Harrison, Kareem A.;Haidasz, Evan A.;Pratt, Derek A.
氮氧自由基是公认的二芳基胺和受阻胺抗氧化剂的反应机制中的假定中间体，其普遍添加以保护合成和天然烃基材料。新的方法，使监测烃自动氧化在低速率的自由基生成已显示，二芳基氮氧自由基和受阻氮氧自由基是更好的抑制剂的不饱和烃自动氧化比其前体胺，这意味着干预不同的机制。实验和计算研究表明，氮氧自由基催化交叉歧化氢过氧和烷基过氧自由基产生O-2和氢过氧化物，从而停止自氧化链反应。过氧化氢自由基-烃燃烧中的关键球员，但基本上是未知的自氧化-提出来自隧道增强的分子内（1，4-）氢原子转移/消除序列从含氧自由基加成中间体。这些见解表明，氮氧自由基是用于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较不有效和/或低效地原位转化为氮氧自由基的条件下表现出催化活性。
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 O-2 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.