Reaction of Tetrabromobisphenol A (TBBPA) with Manganese Dioxide: Kinetics, Products, and Pathways

Abstract

Birnessite (delta-MnO2) is a naturally occurring soil and sediment component that has been shown to oxidize organic compounds containing phenolic or aniline moieties. In this study, for the first time we explored the oxidation reaction of tetrabromobisphenol A (TBBPA), the most heavily used brominated flame retardant, with MnO2. TBBPA rapidly dissipated from the reaction solution and the process was accompanied by the dissolution of Mn2+. Dissipation of 50% of TBBPA occurred in less than 5 min in a system (pH 4.5) containing 625 microM MnO2 and 3.50 microM TBBPA at 21 degrees C, and the removal further increased to as high as 90% when the reaction was prolonged to 60 min. Analysis of initial reaction kinetics showed that the reaction orders with respect to TBBPA, MnO2, and H+ were 1.0, 0.8, and 0.25, respectively. Higher initial concentrations of TBBPA and MnO2 both enhanced the reaction. In addition, reaction rates increased as pH decreased. A retarded first-order model was found to closely describe the long-term reaction kinetics (R2 > or = 0.99), from which initial half-lives of TBBPA under different reaction conditions were estimated. A total of 7 reaction products were identified and a tentative reaction scheme was proposed. This study suggests that oxidative transformation of TBBPA by MnO2 may play an important role in the natural attenuation of TBBPA. The reaction may be further optimized for treatment of TBBPA-containing wastewater or remediation of TBBPA-polluted environmental matrices.

Kinetics of tetrabromobisphenol A (TBBPA) reactions with H2SO4, HNO3 and HCl: Implication for hydrometallurgy of electronic wastes

“…Product 3 was tentatively identified as 4-isopropyl-2,6-dibromophenol in comparison with published mass spectrum data [21]. Product 5 had a similar mass spectrum as of silylated 4-(2-hydroxyisopropyl)-2,6-dibromophenol reported by Lin et al [22] (Fig. S3).…”

“…In pathway one, TBBPA was initially oxidized by H 2 SO 4 to loss an electron and proceeded via ␤-cleavage (cleavage between one of the benzene rings and the isopropyl group of TBBPA) to form 4-isopropyl-2,6-dibromophenol and 2,6-dibromophenol. This degradation pathway has been established in the oxidation of TBBPA by other oxidizer such as hydroxyl radical [24] and manganese dioxide [22]. 4-isopropyl-2,6-dibromophenol was further oxidized by concentrated H 2 SO 4 to form 4-(2-hydroxyisopropyl)-2,6-dibromophenol, 3,5-dibromo-4-hydroxybenzaldehyde, and methyl 3,5-dibromo-4-hydroxybenzoate.…”

Ferrate(VI) oxidation of tetrabromobisphenol A in comparison with bisphenol A

“…Initially, Fe(VI) oxidizes the phenol moiety of TBBPA by one electron transfer generating a phenoxyl radical and Fe(V) as the first step (Rush et al, 1995;Huang et al, 2001;Li et al, 2008;Yang et al, 2011b). The phenoxy radical is stabilized by electron resonance within the phenol ring and forms radical R1, which supported by the calculation of charge distribution and spin densities via molecular modeling (Lin et al, 2009;Feng et al, 2013;Pang et al, 2014). Radical R1 undergoes bscission (cleavage between one of the benzene rings and the isopropyl group) and releases a new radical 2,6-dibromo-4-isopropylphenol carbocation (R2).…”

“…1). The t 1/2 for Fe(VI) reaction with TBBPA (1.7 s, pH 7.0) is magnitude lower than that of the permanganate (29.8 s, pH 7.0) (Pang et al, 2014), manganese dioxide (1.79 min, pH 4.5) (Lin et al, 2009) and photochemical (30 min, pH 7.1) (Eriksson et al, 2004), indicating that Fe(VI) treatment technology appears to be a promising tool for the removal of brominated flame retardant TBBPA in water.…”

“…R2 may react with water to form the product A, or substitution with the methanol cosolvent (stock solution was prepared in methanol) to yield the product B (Feng et al, 2013). The pathway of product A has been extensively reported in the oxidative degradation of TBBPA by permanganate, manganese dioxide, UV/Fenton, and UV irradiation (Eriksson et al, 2004;Lin et al, 2009;Zhong et al, 2012;Pang et al, 2014). For product B, this is probably not valid in a potential real water treatment.…”