Predicting Gaseous Reaction Rates of Short Chain Chlorinated Paraffins with center dot OH: Overcoming the Difficulty in Experimental Determination

Short chain chlorinated paraffins (SCCPs) are under evaluation for inclusion in the Stockholm Convention on persistent organic pollutants. However, information on their reaction rate constants with gaseous (OH)-O-center dot (k(OH)) is unavailable, limiting the evaluation of their persistence in the atmosphere. Experimental determination of k(OH) is confined by the unavailability of authentic chemical standards for some SCCP congeners. In this study, we evaluated and selected density functional theory (DFT) methods to predict k(OH) of SCCPs, by comparing the experimental k(OH) values of six polychlorinated alkanes (PCAs) with those calculated by the different theoretical methods. We found that the M06-2X/6-311+G(3df,2pd)//B3LYP/6-311 +G(d,p) method is time-effective and can be used to predict k(OH) of PCAs. Moreover, based on the calculated k(OH) of nine SCCPs and available experimental k(OH) values of 22 PCAs with low carbon chain, a quantitative structure-activity relationship (QSAR) model was developed. The molecular structural characteristics determining the (OH)-O-center dot reaction rate were discussed. logk(OH) was found to negatively correlate with the percentage of chlorine substitutions (Cl%). The DFT calculation method and the QSAR model are important alternatives to the conventional experimental determination of k(OH) for SCCPs, and are prospective in predicting their persistence in the atmosphere.