Kinetics and mechanism of benzene derivative degradation with Fenton's reagent in aqueous medium studied by MIMS

Membrane introduction mass spectrometry (MIMS) was used to investigate kine tic and mechanistic aspects of the reaction of benzene derivatives with Fen ton's reagent (Fe2+/H2O2) in water. Under the conditions employed, the reac tion rate showed a first-order dependence on the aromatic compound concentr ation. The order of reactivity observed was C6H5Cl > C6H5Br > C6H6 > C6H5CH 3 > C6H5OCH3 > C6H5NO2) C6H5OH, and, with the exception of C6H5NO2, a linea r Hammett relationship (log k(X)/k(H) versus sigma(p)) was observed. This f act suggests that electronic factors significantly influence reactivity wit h the Fenton's reagent. Experiments with C6H6 and C6D6 showed the presence of an isotopic effect of k(H)/k(D) = 1.7, suggesting that cleavage of the b enzene C-H bond occurs in the reaction rate controlling step. Mechanistic s tudies with chlorobenzene showed that mineralization to CO2 and chloride pr oceeds via hydroxylation steps producing phenolic, hydroquinonic, and quino nic intermediates.