Photodegradation of metolachlor: Isolation, identification, and quantification of monochloroacetic acid

The photolysis of metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-met hoxy-1-methylethyl) acetamide] in a sunlight simulator under actinic radiat ion was investigated. The focus of the study was to determine the extent of monochloroacetic acid (MCA) production. MCA was concentrated and derivatiz ed from photolysate as the n-propyl ester using propanol and sulfuric acid and then identified as the ester using GC/MS and GC/ECD. On the basis of re gression analysis, it was shown that the direct photodegradation of similar to 10 mu M metolachlor followed pseudo-first-order kinetics with respect t o the metolachlor concentration, and the half-life of the herbicide (simila r to 74 h) was independent of the pH of the medium. Photolysis in synthetic held water (SFW) resulted in a significant reduction of photolysis time (t (1/2) similar to 9 h). Direct photolysis experiments indicate a 5.19 +/- 0. 81% (n=3) conversion of metolachlor to MCA, while photolysis in synthetic f ield water and in a Don River water sample resulted in 29.8 +/- 4.6% (n = 3 ) and 12.6 +/- 4.1% (n = 3) conversion, respectively; MCA was shown to be h ydrolytically stable over the time course of the photoreaction. The photode gradation of alachlor, butachlor and a model chloroacetanilide, 2-chloro-N- methylacetanilide, in SFW were also investigated.