Oxidative catalysis
is becoming a leading trend in fighting
environmental
pollution created, inter alia, by numerous pesticides. Among them
are carbendazim (Cbz), a benzimidazole fungicide and the metabolite
of other fungicides, including thiophanate methyl (Tpm). We investigated
the oxidative degradation of Cbz and Tpm by H2O2 catalyzed by TAML activators including a bis-amide bis-sulfonamide
variant [Fe{4-NO2C6H3-1,2-(NCOCMe2
NSO2)2CHMe}(OH2)]− (1).
Studies were performed in water at pH 7.0 and 25 °C, i.e., under
the conditions that correspond best to environmental demands. Two
major parallel catalytic pathways were identified for Cbz, viz. typical
of TAMLs’ deep oxidative destruction and rare catalytic nitration
of Cbz by nitrite liberated on the oxidation of Cbz. Catalyst 1 is 4.6 times more reactive than its tetra-amide rival [Fe{4-NO2C6H3-1,2-(NCOCMe2
NCO)2CF2}(OH2)]− (2b). Kinetic, fluorescence, DFT
methods all were used to understand the advantages of 1, which are discussed in detail. Several degradation products of
Cbz were identified. Tpm is rapidly transformed into Cbz by 1/H2O2, mimicking metabolic processes.
Mechanisms of Cbz oxidation and nitration, as well as of Tpm to Cbz
conversion, are discussed.