Phenolic Acids Ozonation: QSAR Analysis and pH Influence on the Selectivity of Ozone
AbstractOzone reacts selectively with ortho-, meta- and para- substituted phenolic acids in aqueous solution. Analysis of second-order rate constants for correlations reveals quantitative structure-activity relationships (QSARs). The kinetic rate constants for oxidation of these phenolic acids were correlated to Hammett-substituent-electronic constant. The values of Hammett parameter ρ varying between -2.9 and -0.3 were found for different pH conditions. The pH influence on this parameter reveals the expected change in the ozonation mechanism due to the decomposition of ozone generating hydroxyl radicals. Contrarily, hydroxyl radicals are non-selective and the substituent-electronic effects are small. This Hammett’s study reflects the progressive change in the selectivity of the oxidation system when the pH increases from 2 up to 9.