Oxidation of Sulfonamide Antibiotics of Six-Membered Heterocyclic Moiety by Ferrate(VI): Kinetics and Mechanistic Insight into SO2Extrusion

This work presents ferrate(VI) (FeVIO42–, FeVI) oxidation of a wide range of sulfonamide antibiotics (SAs) containing five- and six-membered heterocyclic moieties (R) in their molecular structures. Kinetics measurements of the reactions between FeVIand SAs at different pH (6.5–10.0) give species-specific second-order rate constants, k5and k6of the reactions of protonated FeVI(HFeO4–) and unprotonated FeVI(FeVIO42–) with protonated SAs (HX), respectively. The values of k5varied from (1.2 ± 0.1) × 103to (2.2 ± 0.2) × 104M–1s–1, while the range of k6was from (1.1 ± 0.1) × 102to (1.0 ± 0.1) × 103M–1s–1for different SAs. The transformation products of reaction between FeVIand sulfadiazine (SDZ, contains a six-membered R) include SO2extrusion oxidized products (OPs) and aniline hydroxylated products. Comparatively, oxidation of sulfisoxazole (SIZ, a five-membered R) by FeVIhas OPs that have no SO2extrusion in their structures. Density functional theory calculations are performed to demonstrate SO2extrusion in oxidation of SDZ by FeVI. The detailed mechanisms of oxidation are proposed to describe the differences in the oxidation of six- and five-membered heterocyclic moieties (R) containing SAs (i.e., SDZ versus SIZ) by FeVI.