DIMERIC PRODUCTS OF RADICAL OXIDATION OF HYDROXYBENZOIC ACIDS
The research has shown that during the oxidation of mono- and dihydroxybenzoic acids with 2,2'-diphenyl-1-picrylhydrazyl the order of the reaction for the radical increases from 1 up to 4 due to the formation of secondary oxidation products of acids. These products are able to show anti-radical properties. Using the semi-empirical PM6 method it has been found that the dimerization of 2-, 4-, or 6-unsubstituted hydroxybenzoic acids phenoxyls is an spontaneous and exothermic process. The analysis of the calculated values of the Gibbs energy change of the HOOC - PhO• dimerization reaction has shown that the most stable dimeric phenols are ortho- and para-CC dimers. Using IR-Fourier transform spectroscopy it has confirmed that phenolic compounds of the dimeric type are exist in the reaction system.