Rapid transformation of H1-antihistamines cetirizine (CET) and diphenhydramine (DPH) by direct peroxymonosulfate (PMS) oxidation

With growing interest in advanced oxidation processes (AOPs), the number of research studies on peroxymonosulfate (PMS) mediated pollutant degradation has increased significantly due to its high radical generation potential upon activation. However, rare studies have focused on the non-radical based PMS reactions. In this study, degradation of model H-1-antihistamines cetirizine (CET) and diphenhydramine (DPH) by unactivated PMS was investigated. Addition of scavengers to the reaction mixture ruled out the involvement of hydroxyl radical ((OH)-O-center dot), sulfate radical (SO4 center dot-), singlet oxygen (O-1(2)) and superoxide anion radical (O-2(center dot-)), indicating direct PMS oxidation as the predominant reaction path. Such a mechanism was further supported by the N-oxide products identified by mass spectrometry and nuclear magnetic resonance (NMR) analyses. Solution pH had a pronounced influence on the degradation kinetics regardless the presence or absence of transition metal Fe(II). The highest species dependent second order rate constants were k(HSO5-/DPH0) of 175 +/- 15.9 M-1 s(-1) and k(HSO5-/CET-) of 36.6 +/- 0.16 M-1 s(-1). The addition of 100 mu M Fe(II) promoted (OH)-O-center dot mediated degradation of H-1-antihistamines and their N-oxide products. This study demonstrated selective transformation with the potential for extensive degradation employing both the direct and catalytic PMS oxidative processes.