Elucidation of fipronil photodegradation pathways

The phenylpyrazole insecticide fipronil (I) photolyzes to its desthio produ ct (II) in aqueous solution. However, the necessity of an intervening oxida tion to a sulfone intermediate (III) has not been resolved, and the photode gradation products of II have not been identified. Using GC-MS, HPLC-UV/vis , electrospray MS, F-19 NMR, and GC-TSD, our objective was to characterize the photodegradation pathways of I, which would clarify the role of III, id entify products of II, and explain unbalanced mass accounts in previous stu dies. Findings showed that II is formed directly and photochemically from I , confirmed by the greater stability of III (t(1/2) 112 h), and that succes sive oxidations of I to III and then a sulfonate (IV) comprise a second pat hway. Compound II underwent photodechlorination, substitution of chlorine b y trifluoromethyl, and pyrazole ring cleavage. This work is significant to understanding the photochemistry of novel phenylpyrazole pesticides in the environment.