The synergistic effect due to the interaction between the components in mixtures of heavy metal chelates with tertiary aromatic diamines was revealed in the model reaction of initiated ethylbenzene oxidation. It was shown that the magnitude of the synergistic effect calculated from the initial rates of oxidation and the duration of the inhibitory action of the mixtures depended on the electron-donating properties of tertiary amines and increased with a decrease in the half-wave potential of electrochemical oxidation of tertiary amines. The parameter characterizing the antiradical activity was determined for two amines.