Oxidation of Flame Retardant Tetrabromobisphenol A by Singlet Oxygen

Abstract

Wide use of flame retardants can pose an environmental hazard, and it is of interest to investigate how they may degrade. We report here that 3,3',5,5'-tetrabromobisphenol A (TBBPA) is subject to photosensitized oxidation involving singlet molecular oxygen ((1)O2). By using visible light and rose bengal or methylene blue as 102 photosensitizers, we have found that TBBPA is a 102 quencher. The quenching rate constant, k(q), depends on TBBPA ionization (pK = 7.4). In acetonitrile, where TBBPA is undissociated, the kq value is 6.1 x 10(5) M(-1) s(-1) for a TBBPA monomer and decreases to 2.9 x 10(4) M(-1) s(-1) for TBBPA dimers and/or aggregates. TBBPA dissociates in aqueous solutions, and its kq value is 1.44 x 10(9) M(-1) s(-1) in alkaline solution, decreasing to 3.9 x 10(8) M(-1) s(-1) at pH 7.2. The strong 102 quenching by TBBPA anion initiates an efficient oxidation of TBBPA, which results in oxygen consumption in aqueous micellar (e.g., Triton X-100) solutions containing photosensitizer. This oxygen consumption is mediated by transient radical species, which we detected by using EPR spectroscopy. We observed two major radicals and one minor radical generated from TBBPA by reaction with 102 at pH 10. One was identified as the 2,6-dibromo-p-benzosemiquinone radical (a2H = 2.36 G, g = 2.0056). A second radical (aH = 2.10 G, g = 2.0055) could not be identified butwas probably a 2,6-dibromo-p-benzosemiquinone radical containing an EPR-silent substituent at the 3-position. Spin trapping with 5,5-dimethyl-1-pyrroline N-oxide (DPMO) showed that other minor radicals (hydroxyl, carbon-centered) are also generated during the reaction of TBBPA with (1)O2. The photosensitized production of radicals and oxygen consumption were completely inhibited by the azide anion, an efficient physical (1)O2 quencher. Because TBBPA is a stable compound that at neutral pH does not absorb much of the atmosphere-filtered solar radiation, its photosensitized oxidation by (1)O2 may be the key reaction initiating or mediating TBBPA degradation in the natural environment.

Troubleshooting the dichlorofluorescein assay to avoid artifacts in measurement of toxicant-stimulated cellular production of reactive oxidant species

“…Specifically, MEHP did not significantly affect DCF fluorescence in either HBSS or RPMI assay solutions lacking serum when compared to the solvent control in the same type of assay solution. Additionally, similar to previous research demonstrating that type of assay solution can impact DCF fluorescence (Han, et al, 2008; Han, et al, 2009; Kalinich, et al, 1997; Korystov, et al, 2007), we observed significantly lower DCF fluorescence for all treatment groups when HBSS was used as the buffer compared to RPMI or RPMI + serum.…”

Mechanochemical degradation of tetrabromobisphenol A: Performance, products and pathway

“…Therefore the debromination accounted only for a part of the degradation mechanism and in addition another degradation mechanism was involved. These results are similar with the studies on the degradation of TBBPA by oxidation, photochemical transformation and catalytic degradation, in which the reactions were dominated by a radical mechanism [55][56][57].…”

“…8) which was possibly the precursor of products A and B, resulting from its dehydrogenation or reaction with methanol during the extraction. A similar observation of radical M and product B was reported in the study of oxidation and photochemical transformation of TBBPA, in which a radical reaction were proven [56,61]. Therefore, during the MC process of Fe + SiO 2 , the zero valent iron could get activated to give electrons and quartz could generate radicals, both of which would make the reaction with target pollutants take place.…”

Photolysis Kinetics, Mechanisms, and Pathways of Tetrabromobisphenol A in Water under Simulated Solar Light Irradiation

“…The degradation of TBBPA by 1 O 2 was well-studied by Bilski and will be described in the following part. 28 Interestingly, TBBPA exhibited significant photolysis under N 2 atmosphere with a rate slightly lower than that under air atmosphere, as shown in Figure 2A. The results indicated that dissolved oxygen was not required for the photolysis of TBBPA.…”