Amorati Riccardo, Fumo Maria Grazia, Menichetti Stefano, Mugnaini Veronica, Pedulli Gian Franco
Dipartimento di Chimica Organica A. Mangini, Università di Bologna, Via S. Donato 11, 40126 Bologna, Italy.
J Org Chem. 2006 Aug 18;71(17):6325-32. doi: 10.1021/jo060281e.
A kinetic and thermodynamic investigation of phenols para-substituted with thiyl (SR), sulfinyl (SOR), and sulfonyl (SO(2)R) groups and ortho-substituted with thiyl groups is reported. The effect of the sulfur substituents on the O-H bond dissociation enthalpy values, BDE(O-H), was measured by means of the EPR radical equilibration technique and the reactivity toward peroxyl radicals, k(inh), of these phenolic antioxidants was determined by inhibited autoxidation studies. An inverse correlation between these two parameters was found. A p-SMe substituent decreased the BDE(O-H) value to a lesser extent than a p-OMe group (-3.6 vs -4.4 kcal/mol), whereas the effect of the same groups in an ortho position showed an opposite trend (-0.85 vs -0.2 kcal/mol). The latter result is explained in terms of the different strength of the intramolecular hydrogen bond between the OH proton and the sulfur or oxygen substituents in ortho derivatives. ESI-MS analysis of the products formed by reacting the sulfides with peroxyl radicals from the azoinitiator AIBN revealed the formation of a complex mixture of products, which may play an important role in determining the overall antioxidant activity of the parent compounds.
本文报道了对酚类化合物的动力学和热力学研究，这些酚类化合物在对位被硫基（SR）、亚磺酰基（SOR）和磺酰基（SO₂R）取代，在邻位被硫基取代。通过电子顺磁共振自由基平衡技术测量了硫取代基对O-H键解离焓值（BDE(O-H)）的影响，并通过抑制自氧化研究确定了这些酚类抗氧化剂对过氧自由基的反应活性（k(inh)）。发现这两个参数之间呈负相关。对甲硫基取代基使BDE(O-H)值降低的程度小于对甲氧基取代基（-3.6对-4.4 kcal/mol），而相同基团在邻位的影响则呈现相反趋势（-0.85对-0.2 kcal/mol）。后一结果可根据邻位衍生物中OH质子与硫或氧取代基之间分子内氢键强度的差异来解释。对硫化物与偶氮引发剂AIBN产生的过氧自由基反应形成的产物进行电喷雾电离质谱（ESI-MS）分析，揭示了产物形成的复杂混合物，这可能在决定母体化合物的整体抗氧化活性中起重要作用。
