Characterization of the photolysis of 2,4,5,2',4',5'-hexabromobiphenyl.

2,4,5,2',4',5'-Hexabromobiphenyl (2,4,5-HBB) was irradiated with ultraviolet light in hexane with stirring, and photolysis was monitored by gas chromatography (GC). 2,4,5-HBB decomposed at an average rate of 0.66 +/- 0.02 mumol/min and the reaction appeared zero order from 0.159 to 1.59 mM 2,4,5-HBB. Several polybrominated biphenyl (PBB) congeners were identified as photoproducts of 2,4,5-HBB. 2,4,5,2',5'-Pentabromobiphenyl (-PBB), formed by para debromination, accumulated at a higher rate than did 2,4,5,3',4'-PBB, formed by ortho debromination. 2,4,5,2',4'-PBB was formed by meta debromination. 3,4,3',4'-Tetrabromobiphenyl (-TBB) was found as a secondary photoproduct, formed by ortho debromination of 2,4,5,3',4'-PBB. 2,5,2',5'-TBB and 2,4,2',5'-TBB were formed by debromination of 2,4,5,2',5'-PBB para and meta, respectively. 2,5,3',4'-TBB could be formed by either ortho debromination of 2,4,5,2',5'-PBB or para debromination of 2,4,5,3',4'-PBB. Rates of degradation and accumulation of the penta- and tetrabrominated biphenyls were also studied. The ultraviolet spectra of the 2,4,5-HBB photolysis mixture, as well as the purified components, were studied and are also reported.