Amorati Riccardo, Lucarini Marco, Mugnaini Veronica, Pedulli Gian Franco
Dipartimento di Chimica Organica A. Mangini, Università di Bologna, Via S. Donato 15, I-40127 Bologna, Italy.
J Org Chem. 2003 Jun 27;68(13):5198-204. doi: 10.1021/jo0342931.
A kinetic and thermodynamic investigation on the antioxidant activity of 2,2'-methylenebis(6-tert-butyl-4-methylphenol) (2), 2,2'-ethylidenebis(4,6-di-tert-butylphenol) (3), and 4,4'-methylenebis(2,6-di-tert-butylphenol) (4) are reported. EPR studies of the equilibration between 3 or 4 and a reference phenol, and the corresponding phenoxyl radicals, allowed us to determine the O-H bond dissociation enthalpy (BDE) of the O-H bond as 81.2 and 81.1 kcal/mol in 3 and 4, respectively. Despite this similarity, the absolute rate constants for the reaction with peroxyl radicals, determined by autoxidation studies under controlled conditions, indicate that the o-bisphenols 2 and 3 behave as excellent antioxidants while the p-bisphenol 4 is less effective by a factor of 64 and 22, respectively. FT-IR spectroscopy and product studies suggest that the very good antioxidant activity of the o-bisphenols largely arises from both the reduced steric crowding about the hydroxyl group and the stabilization of the aroxyl radical due to the formation of an intramolecular hydrogen bond between the residual OH and the oxygen radical center.
报道了对2,2'-亚甲基双(6-叔丁基-4-甲基苯酚)(2)、2,2'-亚乙基双(4,6-二叔丁基苯酚)(3)和4,4'-亚甲基双(2,6-二叔丁基苯酚)(4)抗氧化活性的动力学和热力学研究。通过对3或4与一种参比酚以及相应酚氧基自由基之间平衡的电子顺磁共振（EPR）研究，我们得以确定3和4中O-H键的O-H键解离焓（BDE）分别为81.2和81.1 kcal/mol。尽管存在这种相似性，但在可控条件下通过自动氧化研究确定的与过氧自由基反应的绝对速率常数表明，邻位双酚2和3表现为优异的抗氧化剂，而对位双酚4的效果分别差64倍和22倍。傅里叶变换红外光谱（FT-IR）和产物研究表明，邻位双酚非常好的抗氧化活性很大程度上源于羟基周围空间位阻的减小以及由于残留OH与氧自由基中心之间形成分子内氢键而导致的芳氧基自由基的稳定化。
