Oxidation of Flame Retardant Tetrabromobisphenol A by Aqueous Permanganate: Reaction Kinetics, Brominated Products, and Pathways

In this work, the most widely used brominated flame retardant tetrabromobisphenol A (TBrBPA) was shown to exhibit appreciable reactivity toward potassium permanganate [Mn­(VII)] in water over a wide pH range of 5–10 with the maxima of second-order rate constants (<i>k</i>_Mn(VII) = 15–700 M^–1 s^–1) at pH near its p<i>K</i>_a values (7.5/8.5). A novel precursor ion scan (PIS) approach using negative electrospray ionization-triple quadrupole mass spectrometry (ESI-QqQMS) was adopted and further optimized for fast selective detection of brominated oxidation products of TBrBPA by Mn­(VII). By setting PIS of <i>m</i>/<i>z</i> 79 and 81, two major products (i.e., 4-(2-hydroxyisopropyl)-2,6-dibromophenol and 4-isopropylene-2,6-dibromophenol) and five minor ones (including 2,6-dibromophenol, 2,6-dibromo-1,4-benzoquinone, and three dimers) were detected and suggested with chemical structures from their product ion spectra and bromine isotope patterns. Reaction pathways mainly involving the initial one-electron oxidation of TBrBPA and subsequent release and further reactions of 2,6-dibromo-4-isopropylphenol carbocation intermediate were proposed. The effectiveness of Mn­(VII) for treatment of TBrBPA in real waters was confirmed. It is important to better understand the reactivity and toxicity of primary brominated products before Mn­(VII) can be applied for treatment of TBrBPA-contaminated wastewater and source water