Symmetrical and unsymmetrical peroxides can be obtained by the oxidation of isopropyl arenes with tertiary hydroperoxides in the presence of copper salt-crown ether as catalysts. The efficiency of the investigated catalytic system enhances markedly in the presence of some alkali metal salts, with a cation diameter corresponding to the inner diameter of the crown ether. The oxidation of isopropyl arenes with hydroperoxides in the presence of a copper salt-crown ether-alkali metal salt catalytic system proved to be a simple and efficient method for the synthesis of ditertiary peroxides. A possible mechanism of this phenomenon is discussed. The results obtained confirm strongly that phase transfer catalysis operates in the investigated reaction.