ENTROPY AND ENTHALPY EFFECTS OF 4-(PHENYLTHIO)-SUBSTITUTED PHENOLS

Electron paramagnetic monitoring of free phenoxyl radicals in benzene- toluene (1 : 1) solution has been used to study the temperature depend ence of the equilibrium (a), for which the equilibrium constant, K-1 i s [GRAPHICS] 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 a bout each of the C-S bonds in the thiobis(phenol) 1, thus denoting the enhancement by solute-solvent interactions. As well as using the enth alpy change to account for the stability of the generated phenoxyls, a nd/or the ability of hydrogen cession by phenols, the entropy change m ust 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.