Dechlorination helps defluorination: Insights into the defluorination mechanism of florfenicol and DFT calculations on the reaction path-ways
Abstract
Defluorination of organic chemicals is challenging under ambient conditions. Florfenicol (C12H14Cl2FNO4S, FF) is a broad-spectrum antibiotic and a ubiquitous environmental contaminant that can be effectively dechlorinated by sulfidated nanoscale zerovalent iron (S-nZVI), yet a comprehensive investigation of the defluorination mechanism is lacking. Herein, we used experimental data and density functional theory (DFT) calculations to reveal how defluorination of alkyl F in FF is facilitated by dechlorination through four pathways. We found sequential and complete dechlorination of FF by S-nZVI to form deschloro (dFF) and dideschloro FF (ddFF) within 24 hours and up to 37.0% of defluorination in 15 days. The dominant pathway to defluorination is the indirect hydrolysis of ddFF, which is initiated by an intramolecular substitution attack from the carbonyl O to alkyl F, resulting in hydrolyzed ddFF. This pathway does not rely on the presence of S-nZVI and is limited for dFF and FF because of the electron-withdrawing Cl. The removal of Cl also makes the reductive defluorination of ddFF by S-nZVI amenable, as indicated by the unique byproduct. The other two minor but more rapid defluorination pathways occur in synergy with the dechlorination of FF and dFF and involve the nucleophilic substitution of alkyl F mediated by the reactive carbanion intermediates, resulting in the corresponding hydrolyzed byproducts. The reliability of the proposed pathways was demonstrated by the consistency of theoretical calculations with experimental data. These dechlorination-facilitated defluorination mechanisms are first identified, providing valuable insights into the degradation of Cl and F-containing chemicals.
Jingdan Chen 陈敬丹
Chemistry Undergraduate
My previous research concentrate on computational chemistry, while I would like to contribute to general data-driven chemical research.