Photoreduction of the chloropropionic acid of carfentrazone-ethyl in sodium sulfide [corrected].

The purpose of this study was to determine whether the conversion of carfentrazone-chloropropionic acid to carfentrazone-propionic acid in sunlit rice paddies is attributed to photoreduction. Model solutions (Na2S with quinoids) irradiated by laboratory ultraviolet light dechlorinated carfentrazone-chloropropionic acid (1.6-28.4% yield of carfentrazone-propionic acid), though Na2S alone was also reactive. Minor conversion (0-2.5%) occurred in the dark, along with dehydrochlorination to carfentrazone-cinnamic acid. Carfentrazone-propionic acid formed proportionally to the Na2S concentration (0-50.7% at 1.3-91 mM), whereas acidic pH inhibited reactivity. Photoreduction with Na2S was verified with 2-chloropropionic acid conversion to propionic acid (53.5%) and by minor 4-chlorophenoxyacetic acid dechlorination. Dissolved Na2S was the primary photoreductant, whereas reduced quinones degraded carfentrazone-chloropropionic acid by an alternate reaction. A survey of ambient rice field conditions indicates that carfentrazone-chloropropionic acid photoreduction is not directly attributed to H2S/HS- in this environment, though reduced quinones may be involved to an unknown extent.