Photochemical degradation of acifluorfen in aqueous solution

To elucidate the photochemical behavior of diphenyl ether herbicides in sup erficial waters, the photodegradation of acifluorfen, 5-[2-chloro-4-(triflu oromethyl)phenoxy]-2-nitrobenzoic acid (CAS Registry No. 50594-66-6), was s tudied in water and acetonitrile. All experiments were carried out under la boratory conditions using a solar simulator (xenon are) or jacket Pyrex rea ction cell equipped with a 125 W high-pressure mercury lamp. The calculated polychromatic quantum efficiencies (Phi (solvent)) of acifluorfen in diffe rent solvents are as follows (units are degraded molecules photon(-1)): Phi (water) = 10(-4), Phi (acetonitrile) = 10(-4), Phi (methanol) = 10(-4), an d Phi (hexane) = 10(-2). The results obtained in this work are in good agre ement with the literature value of monochromatic quantum yield. HPLC-MS ana lysis (APCI and ESI in positive and negative modes) was used to identify ac ifluorfen photoproducts. These results suggest that the photodegradation of acifluorfen proceeds via a number of reaction pathways: (1) decarboxylatio n, (2) dehalogenation, (3) substitution of chlorine group by hydroxyl or hy drogen groups, and (4) cleavage of ether linkage, giving phenols. Photorear rangement products were studied by other investigators. No such products we re observed. In addition, it was found that the trifluoro functional group on acifluorfen was not affected by any transformation, and no products of a nitro group reduction were found.