he reaction of a technical mixture of polychlorobiphenyls Sovol with sodium methoxide in dimethyl sulfoxide and methanol was studied using the thermodynamic modeling method. The optimal process conditions were determined: 1 atm, 115°C, 0.25 mol of dimethyl sulfoxide, 0.085 mol of methanol, the molar ratio of polychlorobiphenyls:sodium methoxide = 1:4. Experimental data obtained using theoretically selected conditions for the interaction of polychlorobiphenyls with sodium methoxide show a spectrum of positive effects: savings of reagents, exhaustive conversion, and the formation of potentially less toxic substances. The studied interaction can serve as a stage for the pretreatment of toxic polychlorinated biphenyls for the pyrolytic method of destruction.