作者:Daniela E. Paulon、Marta E. J. Coronel
DOI:10.1039/a707856k
日期:——
Electron paramagnetic monitoring of free phenoxyl radicals in benzene–toluene (1∶1) solution has been used to study the temperature dependence of the equilibrium (a), for which the equilibrium constant, K1 is given by eqn. (b).The fit of experimental data to eqn. (c) yields ΔH1 = 28.80 ± 3.39 kJ mol–1 and ΔS1 = 116.9 ± 12.7 J K–1 mol–1. The entropy change value is about 30 J K–1 mol–1 in excess of the absolute entropy of the molecular rotor evolving about each of the C–S bonds in the thiobis(phenol) 1, thus denoting the enhancement by solute–solvent interactions. As well as using the enthalpy change to account for the stability of the generated phenoxyls, and/or the ability of hydrogen cession by phenols, the entropy change must also be measured when evaluating the antioxidant behaviour of this type of molecule, as its influence on the Gibbs free energy change is shown to be relevant.
利用电子顺磁监测苯-甲苯(1∶1)溶液中的游离苯氧自由基来研究平衡 (a) 的温度依赖性,其平衡常数 K1 由式 (b) 给出,将实验数据拟合到式 (c) 得到 ΔH1 = 28.80 ± 3.39 kJ mol-1 和 ΔS1 = 116.9 ± 12.7 J K-1 mol-1。熵变值比硫代双(苯酚)1 中围绕每个 C-S 键演化的分子转子的绝对熵多出约 30 J K-1 mol-1,因此表示溶质-溶剂相互作用的增强。除了利用焓变来解释生成的苯氧基的稳定性和/或苯酚的氢俘获能力外,在评估这类分子的抗氧化行为时还必须测量熵变,因为它对吉布斯自由能变化的影响是相关的。