Pathways, by-products, reaction intermediates, and kinetics study of degradation of profenofos via photo-assisted peroxidation

This article presents, in detail, the paths and mechanisms, main by-products, and a kinetic study of the oxidation of profenofos (PFF) by HO center dot radicals. Photo-assisted peroxidation was the precursor reaction for generation of radicals; the effect of UV-C (245 nm) radiation was evaluated. The results of the kinetics study indicated that the best fit for the experimental data was the pseudo-first-order model; further, that oxidation occurs in a fast initial stage and a slow final stage. In an acidic environment, the fast oxidation stage was favored over the slow stage; while in the basic medium the opposite behavior was observed. Eight oxidation by-products and 29 reaction intermediates were identified. The main mechanisms involved in the mineralization of PFF were reactions of electron abstraction, HO center dot abstraction, H-center dot abstraction, substitution, displacement, and addition of electrons. The rapid oxidation step was related to the mining of the O-C2H5 and S-C3H7 chains of the intermediate O-ethyl S-propyl phosphonothioate. The slow oxidation step included the mineralization of 4-bromo-2-chlorophenyl and derivatives.