A highly effective method to synthesise dialkyl peroxides from alkyl hydroperoxides and alkyl bromides in a liquid–liquid–liquid system using tetraalkylammonium salts as phase-transfer catalysts is reported. This process was conducted in the presence of highly concentrated aqueous KOH solutions and cyclohexane as an organic solvent. In a liquid–liquid–liquid system, the phase-transfer catalyst forms an insoluble third-liquid phase between the organic and aqueous phases that enables the catalyst to be recycled multiple times. Dialkyl peroxides were obtained in high yields and with 100% selectivity.