Controllable Pyridine N-Oxidation–Nucleophilic Dechlorination Process for Enhanced Dechlorination of Chloropyridines: The Cooperation of HCO₄^– and HO₂^–

Abstract

Dechlorination of chloropyridines can eliminate their detrimental environmental effects. However, traditional dechlorination technology cannot efficiently break the C−Cl bond of chloropyridines, which is restricted by the uncontrollable nonselective species. Hence, we propose the carbonate species-activated hydrogen peroxide (carbonate species/H 2 O 2 ) process wherein the selective oxidant (peroxymonocarbonate ion, HCO 4 −) and selective reductant (hydroperoxide anion, HO 2 − ) controllably coexist by manipulation of reaction pH. Taking 2-chloropyridine (Cl−Py) as an example, HCO 4 − first induces Cl−Py into pyridine Noxidation intermediates, which then suffer from the nucleophilic dechlorination by HO 2 − . The obtained dechlorination efficiencies in the carbonate species/H 2 O 2 process (32.5−84.5%) based on the cooperation of HCO 4 − and HO 2− are significantly higher than those in the HO 2 − -mediated sodium hydroxide/hydrogen peroxide process (0−43.8%). Theoretical calculations confirm that pyridine N-oxidation of Cl−Py can effectively lower the energy barrier of the dechlorination process. Moreover, the carbonate species/H 2 O 2 process exhibits superior anti-interference performance and low electric energy consumption. Furthermore, Cl−Py is completely detoxified via the carbonate species/H 2 O 2 process. More importantly, the carbonate species/H 2 O 2 process is applicable for efficient dehalogenation of halogenated pyridines and pyrazines. This work offers a simple and useful strategy to enhance the dehalogenation efficiency of halogenated organics and sheds new insights into the application of the carbonate species/H 2 O 2 process in practical environmental remediation.