Kinetic characteristics for reactions of 2,2-diphenyl-1-picrylhydrazyl with some natural phenolic antioxidants in ethanol

Abstract

A relationship between the reaction rates of some natural phenolic antioxidants (AOs) with stable radical 2,2-diphenyl-1-picrylhydrazyl (DPPH) and the hydrogen chloride concentration in an ethanol medium was studied. The character of this relationship is determined by a change in the ratio of contributions from different mechanisms of this reaction. The range of hydrogen chloride concentrations corresponding to the minimum reaction rate was revealed. The parallel existence of two ionic mechanisms proceeding through the phenolate anion and radical cation of the antioxidant, respectively, was confirmed. The rate constants for the reaction of DPPH with some phenolic antioxidants in a 0.1 mM solution of hydrogen chloride in ethanol were determined. Correlations of the structure and activity of natural phenolic AOs with respect to the stable DPPH radical are similar to those for the reaction of these AOs with alkyl peroxide radicals leading liquid-phase peroxide oxidation chains. The possibility of using the kinetic parameters that characterize the reactions of DPPH with natural phenolic AOs for the evaluation of their antioxidant activity was concluded.