Diphenhydramine (DPH), the active ingredent in Benadryl, has been detected in streams, rivers and other surface water sources.  DPH is biologically active and can have a negative impact on human health and the environment at low concentrations. Ultrasonic irradiation of an aqueous solution of DPH with 640 KHz at 5 °C leads to the rapid degradation of DPH. The degradation follows pseudo first-order kinetics.  The degradation rates were also measured over a range of initial concentrations.  The degradation process occurs during cavitation, which produces hot spot, interfacial and bulk solvent regions. Hydroxyl radicals and elevated temperatures are generated at the hot spot and interfacial regions.  To better understand the contribution of hydroxyl and thermal degradation processes during cavitation, the Langmuir model was applied and a hydroxyl radical trap was added during the treatment. Application of the Langmuir adsorption model indicates partitioning of DPH to the interfacial region during cavitation. The Langmuir kinetic parameters obtained were K=0.624 µM<sup>-1</sup> and k = 1.509µM/min. The addition of coumarin, a hydroxyl radical trap, results in a decrease in the DPH degradation, demonstrating it plays a critical role in the degradation. Product studies using LC-MS demonstrate the formation of two major by-products from the addition of one or two hydroxyl radicals to the benzene rings to yield phenolic adducts.  Continued treatment leads to the degradation of these by-products. An analysis of the effects of water quality parameters on the degradation process is currently underway. Our resulted demonstrate ultrasonic irradiation has potential as an effective method to remove DPH from water.

Detailed product and kinetic studies of the ultrasonically induced degradation of the popular antihistamine, diphenhydramine

251st National Meeting (2016)

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