A new mechanism for the reaction of direct (additive) chlorination of ethylene with chlorine from the formation of 1,2-dichloroethane in the presence of FeCl 3 catalyst promoted by NaCl has been proposed. It was found that the rate depends on the active phase concentration of the catalyst and the promoter, as well as the formation of the Na[Fe(C 2 H 4 Cl) 4 ] complex, which is a surface intermediate of the reaction. The heterogeneous-homogeneous mechanism of the process, according to which the reaction begins on the surface of the catalytic complex and lasts in a solution of dichloroethane, has been substantiated. A stabilizer of the catalyst complexthe sodium salt of perforated sulfonic acid, which accelerates the process of dissolution of sodium chloride,increases the selectivity of 1,2-dichloroethane formation and reduces the number of by-products of trichloroethane and other chlorine derivatives.