The pyrolytic degradation of decachlorobiphenyl (PCB 209) in the tempe
rature range of 700 - 1000 degrees C and at a pyrolysis time of 10 sec
onds generated one main chloroaromatic product. This compound has been
identified by HPLC-UV, GC-MS, GC-FTIR and C-13-NMR as octachloroacena
phthylene (OCAN). The mechanism of the nearly quantitative formation o
f octachloroacenaphthylene (OCAN) occurs via a nonachlorobenzobarrylen
e radical (ZIR) as an intermediate followed by a rearrangement and fur
ther dechlorination to form OCAN, Calculations with the program THERM
based on the Benson-group-theory indicated that this mechanism is not
possible for lower or nonchlorinated biphenyls. (C) 1997 Elsevier Scie
nce Ltd.