Resistance of alkyl chloride on chloramphenicol to oxidative degradation by sulfate radicals: Kinetics and mechanism

Release and rechlorination of chlorine atoms on the benzene ring have been observed during advanced oxidation processes (AOPs), while the dechlorination on the side chain of the benzene ring has not been fully investigated previously. The degradation and dechlorination processes of chloramphenicol (i.e., thiamphenicol (TAP) and florfenicol (FFC)) were assessed through generation of the sulfate radical from Co(II)-mediated activation of peroxymonosulfate (PMS). High-resolution mass spectrometry (HRMS) analysis detected a few chlorinated and dechlorinated products during the Co²⁺/PMS reaction. The low efficiency of total organic carbon (TOC) removal in conjunction with slightly decreased absorbable organic halogen (AOX) values with high degradation rates, indicate that TAP and FFC could be degraded via the destruction of a small portion of the carbon moiety rather than through complete mineralization. The possible degradation pathways of TAP and FFC are proposed. All experimental results and further quantum chemistry calculations indicate dechlorination on the side chain of the benzene ring is more difficult than that directly on the benzene ring. This suggests organic pollutants containing chlorine atoms on the side chain of the benzene ring will be more resistant to oxidative attack and deserve more attention.