MECHANISM OF CHLORINATION OF AROMATIC-COMPOUNDS ADSORBED ON THE SURFACE OF FLY-ASH FROM MUNICIPAL INCINERATORS

Aromatic substrates were adsorbed on the surface of fly ash from a municipal incinerator. Treatment with gaseous hydrogen chloride gave aromatic chlorination. Relative yields and isomer distributions indicate that an electrophilic mechanism is likely for the chlorination reaction. Inverse addition experiments were used to show that a surface-bound chlorinating agent is produced by the interaction of hydrogen chloride with the fly ash surface. Recycling experiments indicate that the fly ash surface functions as a stoichiometric oxidant, and not a catalyst, in promoting aromatic chlorination by HCl. The yields of aromatic chlorination on three different fly ash samples were found to be quite different. A variety of physical and chemical characterizations revealed no simple relationship between properties and yields. It was noted that the reaction of hydrogen chloride with the fly ash surface led to release of metal ions from the surface upon solvent extraction. It was found that the release of iron from the surface corresponded to the changing yields noted. Based on the known chlorinating ability of iron(III) chloride, as well as other data from aromatic chlorinations on fly ash surfaces, reaction of HCl with iron(III) sites on the fly ash surface could produce surface-bound iron(III) chloride species that are the actual chlorinating agents. © 1990, American Chemical Society. All rights reserved.