Abstract
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•A QSPR model to predict the photolysis rates of 25 PCDPSs was developed.•Thirteen intermediates of PeCDPS were detected by LC-Q-TOF-MS.•The photolysis of PeCDPS mainly involves hydroxylation, direct photooxidation, C–S bond cleavage and hydroxyl substitution.•Density functional theory was employed to determine the reaction sites of PeCDPS.
The direct photolysis of 25 individual polychlorinated diphenyl sulfides (PCDPSs) substituted with 1–7 chlorine atoms was investigated using a 500-W Xe lamp. Photolysis of PCDPSs followed pseudo-first-order kinetics, with the higher chlorinated diphenyl sulfides generally degrading faster than the lower chlorinated congeners. A quantitative structure-activity relationship model to predict the photolysis rates of PCDPSs was developed using 16 fundamental quantum chemical descriptors. We found that the substitution pattern for chlorine atoms, the dipole moment, and ELUMO − EHOMO were major factors in the photolysis of PCPDSs. The reaction kinetics, products, and photodegradation pathways of 2,2′,3′,4,5-pentachlorodiphenyl sulfide (PeCDPS) suggest hydroxylation, direct photooxidation, the C–S bond cleavage reaction, and hydroxyl substitution were mainly involved in the photodegradation process, leading to the formation of 13 intermediates, detected by an electrospray time-of-flight mass spectrometer. The initial reaction sites of PCDPSs under photolysis were rationalized by density functional theory calculations. Anions (Cl−, SO42−, NO3−, and HCO3−) and Co2+ had no influence on the removal of PeCDPS, while Fe3+, Cu2+, and HA decreased the photolysis efficiency of PeCDPS. This report is the first to develop a logk quantitative structure–property relationships (QSPR) model of 25 PCDPSs and to describe mechanistic pathways for the photolysis of PeCDPS.