Photodegradation of Dichlorprop and 2-Naphthoxyacetic Acid in Water. Combined GC-MS and GC-FTIR Study

Article abstract of DOI:10.1021/jf960699l

We have examined the photochemical transformations of dichlorprop (1) and 2-naphthoxyacetic acid (2) in aqueous solution, by means of combined GC-MS and GC-FTIR analysis. Photolysis of 1 under oxygen atmosphere led to 2-chlorophenol (5), 2,4-dichlorophenol (6), 4-chlorophenol (7), 2,4-dichlorophenyl acetate (8), the lactone of 2-(4-chloro-2-hydroxyphenoxy)propionic acid (9), and 2-(2-chlorophenoxy)propionic acid (10). Irradiation under argon atmosphere led again to 5, 6, 7, and 10 together with 2,4-dichlorophenyl ethyl ether (11). Photolysis of 2 under aerobic conditions gave β-naphthol (12), together with minor amounts of 2-hydroxy-1-naphthaldehyde (13) and naphtho [2,1-b]furan-2(1H)-one (14). Under argon atmosphere only 12 and 14 were detected. Therefore, the most general processes were photolytic cleavage of the aryl-halogen bond (route i) and the aryloxy-carbon bond (route ii). Similar photodegradation pathways had been previously observed for 2,4-D and 4-CPA and were confirmed in this work. The formation of 8, 11, and 13 must occur via cleavage of the carbon-carbon bond a to the carboxy group (route iii). Formation of this type of photoproducts in phenoxyalkanoic acid pesticides is unprecedented. Its structure was further assessed by alternative synthesis.