Transformation Reactions of Radicals from the Oxidation of Diphenhydramine: Pulse Radiolysis and Mass Spectrometric Studies

Abstract Mechanistic aspects of diphenhydramine (DPH) oxidation induced by hydroxyl ( • OH) and sulfate (SO 4 •− ) radicals have been explored in detail by pulse radiolysis technique and high resolution mass spectrometry (HRMS). The transient absorption spectrum along with HRMS analysis undoubtedly established the non‐position selective hydroxylation of DPH by • OH ( a ; k 2 = (1.08 ± 0.06) × 10 10 dm 3 mol −1 s −1 ; λ max : 335 nm) led to various transformation products ( i ‐ vii ) including isomeric mono ( I a‐d ), di ( II a‐c ) and tri ( VII a‐e ) hydroxylated analogues. On the other hand, SO 4 •− (specific one electron oxidant) ultimately generates another hydroxylated adduct radical ‘c’ λ max : 330 nm, k 2 =(5.70 ± 0.03) × 10 9 dm 3 mol −1 s −1 ) which is formed as a result of preferential hydroxylation of initially formed radical cation ‘ b ’ at ipso position. The mechanism leading to the formation of various transformation products induced by • OH and SO 4 •− are thoroughly discussed. The mechanistic findings obtained from our studies (especially in the case of less investigated oxidant like SO 4 •− ) are capable to enrich the fundamental understanding on environmentally relevant reactions initiated by • OH and SO 4 •− .