Document 2X3pwJBR1NN0ZVEK25ML8qg5

Polyhalogenated Biphenyls: Photolysis of Hexabromo and Hexachlorobiphenyls in Methanol Solution by Luis Octavio Rezo* and Matthew J. Zabik* Deportment of Entomology Pfiii'eiVf Hetearch Center Michigan State Vnivertity E<ut Canting, Mich. 4SU4 Polyhalogenated biphenyls have been reported in various biolog ical systems, such as human milk (ACKER and SCHULTE, 1970) and adipose tissue (BIROS et al, 1970). Recently In Michigan several herds of dairy cows were accidentally fed a commercial (Firemaster BP-6) hexabromobiphenyl fire retardant (LASSITER, 1974). The metabolic pathways of chlorobiphenyls have been reported (SAFE et al, 1973) yielding hydroxylated biphenyls as major products. It was of interest to compare the photoreactivity of hexabromobi phenyl with that of PCB, and to investigate the possibility of photonucleophilic reactions involving the solvent. In a similar manner hydroxybiphenyls have been isolated from PCB photolysis in aqueous media (HUTZINGER and SAFE, 1972). ' We have photolyzed 2,2',4,4',S,5'*hexachlorobiphenyl and Fire- aaster BP-6 in methanol and found them to undergo reductive dehalo- genition and ring methoxylation. The reactivity of the brominated biphenyls is far greater than that of the PCB. METHODS and MATERIALS Firemaster BP-6 (1) was obtained from Michigan Chemical Co. 2,2',4,4',S,S'-Hexachlorobiphenyl (II) was purchased from Analabs, Inc. S^'fA^'-Tetrachlorobiphenyl was synthesized in our labora tory (RUZO et al, 1974). Methanol solutions (2X10~*M) of I and II were photolysed (X>28( nm) for periods of 0.5-2.0 hrs in sealed borosilieste test tubes, using a Rayonette Reactor equipped with B1 RUL 3000 lamps. (The Southern N.E. Ultraviolet Co.). Samples were either aerated or degassed by nitrogen flushing. A Beckman GC-65 gas chromato graph Interfaced with a DuPont 21-490 mass spectrometer end a PDP-12 (Digital) computer was used for analysis. A 6 ft X 1/8 in stain less steel column pecked with 10% DC-200 on Ges Chrom Q (80-100 mesh) with a helium flow of SO ml/mln maintained isothermally at 220 or 250 was used for seperetion of the photoproducts. The injector and detector temperatures were 280 and 300 respectively. icraduate Research Assistant `Associate Professor of Entomology BaUfii* *1 Et.kaaatalil C*l<iaia*ilia 4 TaiUalefy, Vat. II, Ha. I emi I, Sptlapr-VtilM Na* Yarh la*. 181 08X575 Thin-layer chromotagraphy was accomplished by developing with 4:1 bcneene-methtnol on precoated Silica-Gel F2S4 plates (EM Reagents). RESULTS After 1 hour of irradiation in degassed methanol compound II . yielded 2,3',4,4',5-pentachlorobiphenyl and 3,3*,4,4'-tetrachlorobiphenyl. These were identified from their mass spectra and by comparison with an authentic sample of 3,3*,4,4'-TCB. The molecular ions appeared at o/e 324 and 290 respectively. The pentachlorobiphenyl showed the expected M2, M+4, M+6, M-8, M+10, M-3S and M-70 signals. The tetrachlorobiphenyj showed a retention time and mass spectrum identical with that of a standard (Rt 13 min). After one hour of irradiation approximately 10% of I had reacted to give 70% tetrachlorobiphenyl and 30% pentachloTobiphenyl. The rapid loss of ortho chlorines in biphenyl systems is well supported in the literature (L.O. RUZO et, 1974). It has been postulated that the excited PCB triplet is planar and can thus be stabilized from the pare position and destabilised by ortho substituents. 2,4,disubstltuted biphenyls such as II combine both effects and show greatest reactivity. Compound 1 after 45 minutes of irradiation (70% reacted) yielded as major products oenta- and tetra-bromobiphenyls with retention times of 25 and 16 minutes respectively. These showed character istic mass spectra (M at 544 and 466 a/e). Compound I also yielded >1% methoxylated product. A compound with M at m/e 526 identified tentatively as dlaethoxy tetrabromobiphenyl was observed after separa tion of the reaction mixture by preparative thin layer chromatography followed by gas chromatographic analysis (R( 16 min). By measuring the amounts of I and II reacted it is observed that the brominated biphenyl is about seven times as reactive as its chloro counterpart, an increase in reactivity which can be attributed to its lower bond energy. Over similar time periods dark controls did not show reaction. When I and II were irradiated In aerated solution the rates of reaction decreased considerably ('50%), as would be expected with a triplet intermediate. REFERENCES L. ACKER and E. SCHULTE, Naturwiss. 57^, 497 (1970). F.J. BIROS et al. Bull, Environ. Contam. Toxicol., S, 317 (1970) C. LASSITER, Dept, of Dairy Science, Mich. State UnTv., private communication. L.O. RUZO et al, J. Agr. Food Chem. 22, 199 (1974). S. SAFE et al, 21st Annual Conference on Mass Spectrometry and Allied Topics, May, 1973, San Francisco, Cal. p 486. S. SAFE and 0. HUTINCER, Environmental Health Perspectives, 1, 15 (1972). " Michigan Agricultural Experiment Station Journal Article No.6853 . 182 HONS 081576