INVESTIGATION OF PRECURSOR REACTIONS IN THE DE-NOVO-SYNTHESIS OF PCDDPCDF ON FLY-ASH/

At 300 degrees C thermal experiments are performed with fly ash which had been spiked with C-12-C-13 mixtures. The resulting isotopically la beled PCDD/PCDF were analyzed by HRGC-HRMS. With PCDD besides C-12(12) and C-13(12) structures also substantial fractions of mixed species ( C-12(6)-C-13(6)) were formed, indicating that dioxins are formed partl y via condensation of phenyl rings. In contrast to that no such mixed species were obtained with PCDF. Consequently the synthesis of furans proceeds directs from preformed biphenyl structures. (C) 1997 Elsevier Science Ltd.