| Abstract
| - We have examined the photochemical transformations of dichlorprop(1) and 2-naphthoxyaceticacid (2) in aqueous solution, by means of combined GC−MSand GC−FTIR analysis. Photolysis of1 under oxygen atmosphere led to 2-chlorophenol(5), 2,4-dichlorophenol (6), 4-chlorophenol(7),2,4-dichlorophenyl acetate (8), the lactone of2-(4-chloro-2-hydroxyphenoxy)propionic acid (9),and2-(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 aerobicconditionsgave β-naphthol (12), together with minor amounts of2-hydroxy-1-naphthaldehyde (13) andnaphtho[2,1-b]furan-2(1H)-one (14).Under argon atmosphere only 12 and 14 weredetected. Therefore,the most general processes were photolytic cleavage of thearyl−halogen bond (route i) and thearyloxy−carbon bond (route ii). Similar photodegradationpathways had been previously observedfor 2,4-D and 4-CPA and were confirmed in this work. The formationof 8, 11, and 13 mustoccurvia cleavage of the carbon−carbon bond α to the carboxygroup (route iii). Formation of this typeof photoproducts in phenoxyalkanoic acid pesticides is unprecedented.Its structure was furtherassessed by alternative synthesis. Keywords: Dichlorprop; 2-naphthoxyacetic acid; 2,4-D; 4-CPA;GC−MS; GC−FTIR; photodegradation; photodecarboxylation; photodehalogenation;photorearrangement
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