Aquatic Thermaland Photochemical Reactivity of N‑(1,3-Dimethylbutyl)‑N′‑phenyl‑p‑phenylenediamine(6PPD), N‑Isopropyl‑N′‑phenyl‑p‑phenylenediamine(IPPD), and 6PPD-quinone

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A ubiquitously used tire rubber antidegradant, 6PPD (N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine), and its toxic ozonation product, 6PPD-quinone(N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine quinone), have become recognized as importantenvironmental pollutants since 6PPD-quinone (6PPD-Q) was identifiedas the likely cause of decades of mass Coho salmon kills. The reactivityof 6PPD, 6PPD-Q, and similar phenylenediamines requires study to betterunderstand their environmental fate. This study explores the aquaticreactivity of 6PPD, N-isopropyl-N′-phenyl-1,4-phenylenediamine (IPPD), and 6PPD-Q through thermaland photochemical pathways using both steady-state photochemistryand time-resolved laser spectroscopy techniques. 6PPD was found torapidly degrade in the dark, with its degradation rate being highlydependent on the pH, temperature, and oxygen concentrations. IPPDbehaves similarly to 6PPD. In contrast, 6PPD-Q is much more stablein the dark. All three chemicals are degraded via direct photochemistry.Regarding indirect photochemistry, 3CDOM* plays a rolein the degradation of 6PPD and IPPD but not 6PPD-Q, while 1O2 does not play a significant role for any of the compounds.Reaction rate constants are reported as well as 6PPD-Q molar yieldsfrom 6PPD, which were minimal for all aqueous pathways examined. 6PPD-Qmay have a longer environmental lifetime as there are fewer degradationpathways. This research will help us to better understand and controlthese chemicals in the environment.