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 kinetic and mechanistic aspects of the reaction of benzene derivatives with Fenton's reagent (Fe 2+ /H 2 O 2 ) in water. Under the conditions employed, the reaction rate showed a first-order dependence on the aromatic compound concentration. The order of reactivity observed was C 6 H 5 Cl > C 6 H 5 Br > C 6 H 6 > C 6 H 5 CH 3 > C 6 H 5 OCH 3 > C 6 H 5 NO 2 > C 6 H 5 OH, and, with the exception of C 6 H 5 NO 2, a linear Hammett relationship (log k X / k H versus σ p ) was observed. This fact suggests that electronic factors significantly influence reactivity with the Fenton's reagent. Experiments with C 6 H 6 and C 6 D 6 showed the presence of an isotopic effect of k H / k D = 1.7, suggesting that cleavage of the benzene C−H bond occurs in the reaction rate controlling step. Mechanistic studies with chlorobenzene showed that mineralization to CO 2 and chloride proceeds via hydroxylation steps producing phenolic, hydroquinonic, and quinonic intermediates.