Oxidation of Sulfonamide Antibiotics of Six-Membered Heterocyclic Moiety by Ferrate(VI): Kinetics and Mechanistic Insight into SO 2 Extrusion.

This work presents ferrate(VI) (FeVI O4 2- , 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 FeVI and SAs at different pH (6.5-10.0) give species-specific second-order rate constants, k5 and k6 of the reactions of protonated FeVI (HFeO4 - ) and unprotonated FeVI (FeVI O4 2- ) with protonated SAs (HX), respectively. The values of k5 varied from (1.2 ± 0.1) × 103 to (2.2 ± 0.2) × 104 M-1 s-1 , while the range of k6 was from (1.1 ± 0.1) × 102 to (1.0 ± 0.1) × 103 M-1 s-1 for different SAs. The transformation products of reaction between FeVI and sulfadiazine (SDZ, contains a six-membered R) include SO2 extrusion oxidized products (OPs) and aniline hydroxylated products. Comparatively, oxidation of sulfisoxazole (SIZ, a five-membered R) by FeVI has OPs that have no SO2 extrusion in their structures. Density functional theory calculations are performed to demonstrate SO2 extrusion 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 .