Antioxidant efficiency of triterpenoids in radical chain oxidation of organic compounds

The kinetics of the antioxidant action of a number of triterpenoids—derivatives of betulinic acid have been studied. The rate constants of the oxidation chain termination reaction were found within the framework of the model reaction of the initiated oxidation of ethylbenzene. It has been found that when a mixture of antioxidants comprising a triterpenoid molecule and a spatially hindered phenol is used, a synergistic effect is observed, which significantly increases the antioxidant efficiency of the mixture. Disclosed is a mechanism which enhances the inhibitory effect of a mixture of antioxidants. According to this mechanism, the reduction of the original structure of the terpenoid from its radical occurs due to the transfer of the hydrogen atom from the weak O–H phenol bond to the terpenoid radical. Thus, the synergistic effect reflects the effect of the antioxidant mixture on the rate of oxidation reaction. Based on the comparison of the results of this work with those obtained earlier, it was concluded that it is possible to regenerate the terpenoid molecule by two fundamentally different mechanisms: (1) by using a mixture of antioxidants with different bond strengths in active sites that determine the inhibition effect, which manifests itself in a significant decrease in the oxidation rate—a synergistic effect; (2) due to the reaction in solvents, the peroxyl radicals of which have dual reactivity: the property of an oxidizing agent in the reaction of chain continuation by reaction with a substrate molecule and a reducing agent in its reaction with a terpenoid radical. In this case, the inhibitor is reconstituted in the cleavage act, which results in an increase in the effective chain break rate constant by increasing the stoichiometric inhibition coefficient.