Oxidation of Sulfonamide Antibiotics of Six-Membered Heterocyclic Moiety by Ferrate(VI): Kinetics and Mechanistic Insight into SO2 Extrusion

• Published in: Environmental science & technology Vol. 53; no. 5; pp. 2695 - 2704
• Main Authors: Feng, Mingbao, Baum, J. Clayton, Nesnas, Nasri, Lee, Yunho, Huang, Ching-Hua, Sharma, Virender K
• Format: Journal Article
• Language: English
• Published: Easton American Chemical Society 05-03-2019
• Subjects: Aniline; Antibiotics; Density functional theory; Extrusion; Kinetics; Oxidation; Rate constants; Reaction kinetics; Sulfadiazine; Sulfisoxazole; Sulfonamides; Sulfur dioxide
• ISSN: 0013-936X; 1520-5851
• DOI: 10.1021/acs.est.8b06535

This work presents ferrate­(VI) (FeVIO4 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, k 5 and k 6 of the reactions of protonated FeVI (HFeO4 –) and unprotonated FeVI (FeVIO4 2–) with protonated SAs (HX), respectively. The values of k 5 varied from (1.2 ± 0.1) × 103 to (2.2 ± 0.2) × 104 M–1 s–1, while the range of k 6 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.