Photodehalogenation of Aryl Halides

Schutt, Leah; Bunce, Nigel J.

doi:10.1201/9780203495902.ch38

Cited by 11 publications

(20 citation statements)

References 80 publications

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“…A possible reason could be the red-shift in the spectrum of PBB compared to PCB as well as the lower bond dissociation energy of C-Br (331–343 kJ/mol) compared to C-Cl (~350–400 kJ/mol) in aryl halides (16, 36), as proposed (37). The ether bridge in PBDE further increases the red shift, accompanied by an increased yield of radicals compared to PBB 209.…”

Section: Resultsmentioning

confidence: 95%

UVA/B-Induced Formation of Free Radicals from Decabromodiphenyl Ether

Suh

Buettner

Venkataraman

et al. 2009

Environ. Sci. Technol.

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Polybrominated diphenyl ether (PBDE) flame retardants are ubiquitous in the environment and in humans. A decabromodiphenyl ether mixture (deca-BDE) is the dominating commercial PBDE product today. Deca-BDE is degraded by UV to PBDEs with fewer bromines. We hypothesized that photodegradation of deca-BDE results in the formation of free radicals. We employed electron paramagnetic resonance (EPR) with spin trap agents to examine the free radicals formed from UV irradiation of a deca-BDE mixture (DE-83R). The activating wavelength for deca-BDE photochemistry was in the UVA to UVB range. The yields of radicals from irradiated deca-BDE in tetrahydrofuran (THF), dimethylformamide (DMF), and toluene were about 9-, 4-, and 7-fold higher, respectively, than from irradiated solvent alone. Radical formation increased with deca-BDE concentration and irradiation time. The quantum yield of radical formation of the deca-BDE mixture was higher than with an octa-BDE mixture (DE-79; ~2-fold), decabromobiphenyl (PBB 209; ~2-fold), decachlorobiphenyl (PCB 209; ~3-fold), and diphenylether (DE; ~6-fold), indicating the positive effects of bromine and an ether bond on radical formation. Analysis of hyperfine splittings of the spin adducts suggests that radical formation is initiated or significantly enhanced by debromination paired with hydrogen abstraction from the solvents. To our knowledge this is the first report that uses EPR to demonstrate the formation of free radicals during the photolytic degradation of PBDEs. Our findings strongly suggest the potential of negative consequences due to radical formation during UV exposure of PBDEs in biological systems.

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Section: Resultsmentioning

confidence: 95%

UVA/B-Induced Formation of Free Radicals from Decabromodiphenyl Ether

Suh

Buettner

Venkataraman

et al. 2009

Environ. Sci. Technol.

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“…15 A multitude of homolytic and heterolytic pathways that can be accessed from singlet and triplet excited states affords numerous synthetic possibilities. A number of photoinduced processes have been successfully adapted in the chemical industry (e.g.…”

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confidence: 99%

Scalable, Metal- and Additive-Free, Photoinduced Borylation of Haloarenes and Quaternary Arylammonium Salts

et al. 2016

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“…13 In addition to homolytic cleavage of the Ar–X bond, photoheterolysis of haloarenes produces π 5 σ 1 triplet aryl cations. Due to the combined radical and cationic character of these species, their reactivity is distinctively different from the reactivity of the ground state aryl cations and aryl radicals.…”

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confidence: 99%

“…Photoinduced homolysis is very efficient for bromo- and iodoarenes in low- and medium polarity solvents. 13,14 Following the initial homolytic substitution at B 2 pin 2 with the photogenerated aryl radical, 19,22 addition of the Bpin radical to PhBpin may be enabled by the cage effect of the more confining medium (e.g. compare viscosities of acetonitrile 0.377 cP, 23 and isopropanol 2.859 cP, 24 at 15 °C).…”

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confidence: 99%