Reactivity of polychlorinated biphenyls in nucleophilic and electrophilic substitutions

• Quantum chemical calculations were carried out for PCBs congeners. • Calculated descriptors were used to explain the PCBs reactivity in S N and S E substitutions. • Obtained data were used to estimate the PCBs reactivity in the S N reactions. • Calculated descriptors were insufficient to explain the PCBs reactivity in the S E reactions. • New neutralization methods of the large-capacity PCBs were discussed. To explain the chemical reactivity of polychlorinated biphenyls in nucleophilic (S N ) and electrophilic (S E ) substitutions, quantum chemical calculations were carried out at the B3LYP/6-31G(d) level of the Density Functional Theory in gas phase. Carbon atomic charges in biphenyl structure were calculated by the Atoms-in-Molecules method. Chemical hardness and global electrophilicity index parameters were determined for congeners. A comparison of calculated descriptors and experimental data for congener reactivity in the S N and S E reactions was made. It is shown that interactions in the S N mechanism are reactions of the hard acid – hard base type, these are the most effective in case of highly chlorinated substrates. To explain the congener reactivity in the S E reactions, correct descriptors were not established. The obtained results can be used to carry out chemical transformations of the polychlorinated biphenyls in order to prepare them for microbiological destruction or preservation.