Optimization of nucleophilic dechlorination of polychlorinated biphenyls: calculation and experiment

The nucleophilic substitution of aromatic chlorine atoms in polychlorinated biphenyls structures for non-toxic substituents was investigated. The reaction of industrial polychlorobiphenyls mixture Sovol with sodium methoxide in bipolar aprotic solvent was studied. Thermodynamic modeling and the HSC software were used to evaluate the reactivity of polychlorobiphenyls congeners from mixture Sovol toward sodium methoxide in dimethyl sulfoxide, and the calculation results were compared with experimental data. The reactivity of polychlorinated biphenyls was evaluated using gas chromatography and gas chromatography/mass spectrometry. Experimental and computational studies confirm that under the reaction conditions, the most reactive congeners are hepta-, hexa- and pentachlorobiphenyls, and the trichlorinated congeners represent the lowest reactivity. The tetrachlorobiphenyls possess an intermediate position. The optimal thermodynamic and chemical conditions at which occurs complete dechlorination of toxic chlorinated aromatic compounds under the conditions of nucleophilic substitution were proposed. The optimal conditions for the complete replacement of chlorine atoms in polychlorinated biphenyls congeners with methoxy groups were detected: temperature = 170 °C, ratio of polychlorinated biphenyls/sodium methoxide was 1:6 and reaction time was 4 h.