Introduction of an octyltelluro group ortho to the phenolic moiety in 3-tert-butyl-4-hydroxyanisole (BHA) was found to significantly improve the antioxidant characteristics of the material In contrast to BHA and the corresponding ortho-substituted octylthio-(9c) and octylseleno (9b) derivatives, the organotellurium 9a was regenerable when assayed for its capacity to inhibit azo-initiated peroxidation of linoleic acid in a chlorobenzene/water two-phase system containing N-acetylcysteine as a stoichiometric reducing agent, and peroxyl radicals were quenched more efficiently than with alpha-tocopherol In the homogeneous phase, inhibition of styrene autoxidation occurred with a rate constant k(inh) as large as 1 x 10(7) M-1 s(-1) but with a low (n = 0 4) stoichiometric factor Evans Polanij plots of log (k(inh)) versus BDE(O-H), which are usually linear for phenols with similar steric crowding reacting by H-atom transfer, revealed that compound 9a was more than 2 orders of magnitude more reactive than expected Although further mechanistic investigations are needed, it seems that the ortho-arrangement of an alkyltelluro group and hydroxyl should be considered a privileged structure for phenolic antioxidants
Organochalcogen Substituents in Phenolic Antioxidants
substituents and their contribution to the O−H bond dissociation enthalpy (BDE) in phenolic compounds. A series of ortho- and para-(S,Se,Te)R-substituted phenols were prepared and investigated by EPR, IR, and computational methods. Substituents lowered the O−H BDE by >3 kcal/mol in the para position, while the ortho-effect was modest due to hydrogenbonding (∼3 kcal/mol) to the O−H group.
关于有机硫属元素取代基的ED / EW特性及其对酚类化合物中O-H键离解焓(BDE)的贡献知之甚少。制备了一系列邻-和对-(S,Se,Te)R取代的酚,并通过EPR,IR和计算方法进行了研究。取代基降低了O - H BDE由> 3千卡/摩尔在对位位置,而邻-效应是氢键适度由于(〜3千卡/摩尔)向O-H基团。