Reactivity of BrCl, Br2, BrOCl, Br2O, and HOBr Toward Dimethenamid in Solutions of Bromide plus Aqueous Free Chlorine
Reactivity of BrCl, Br2, BrOCl, Br2O, and HOBr Toward Dimethenamid in Solutions of Bromide plus Aqueous Free Chlorine
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DOI：
10.1021/es302730h
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发表时间：
2013-02-05
影响因子：
11.4
通讯作者：
Roberts, A. Lynn
中科院分区：
文献类型：
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作者：
Sivey, John D.;Arey, J. Samuel;Roberts, A. Lynn
HOBr 是通过游离有效氯 (FAC) 氧化溴化物而形成的，通常被认为是产生溴化消毒副产物 (DBP) 的唯一物质。我们的研究表明，在添加了 FAC 的 -8 溴化物溶液中，BrCl、Br-2、BrOCl 和 Br2O 也可以作为除草剂噻吩草胺的溴化剂。系统地改变影响溴形态的条件（pH、总游离溴浓度（[HOBr](T)）、[Cl-]和[FAC](o)），并测量噻吩草胺溴化速率。 [HOBr](T) 中的反应级数范围为 1.09 (+/-0.17) 至 1.67 (+/-0.16)，在 HOBr 的 pK(a) 附近达到最大值。这种对 [HOBr](T) 的复杂依赖表明 Br2O 作为活性溴化剂。溴化速率随着 [Cl-]、[PAC](o)（[HOBr](T) 恒定）和过量溴化物（其中 [Br-](o)>[FAC](o)）的增加而增加，分别表明 BrCl、BrOCl 和 Br-2 作为溴化剂。由于 Br2O 和 BrOCl (aq) 形成的平衡常数之前尚未报道，因此我们使用基准质量量子化学方法 [CCSD(T) 直至 CCSDTQ 计算加上溶剂化效应] 计算了这些值（及其气相类似物）。结果使我们能够计算溴的形态，从而计算二阶速率常数。固有溴化反应活性按以下顺序增加：HOBr
HOBr, formed via oxidation of bromide by free available chlorine (FAC), is frequently assumed to be the sole species responsible for generating brominated disinfection byproducts (DBPs). Our studies reveal that BrCl, Br-2, BrOCl, and Br2O can also serve as brominating agents of the herbicide dimethenamid in -8 solutions of bromide to which FAC was added. Conditions affecting bromine speciation (pH, total free bromine concentration ([HOBr](T)), [Cl-], and [FAC](o)) were systematically varied, and rates of dimethenamid bromination were measured. Reaction orders in [HOBr](T) ranged from 1.09 (+/-0.17) to 1.67 (+/-0.16), reaching a maximum near the pK(a) of HOBr. This complex dependence on [HOBr](T) implicates Br2O as an active brominating agent. That bromination rates increased with increasing [Cl-], [PAC](o) (at constant [HOBr](T)), and excess bromide (where [Br-](o)>[FAC](o)) implicate BrCl, BrOCl, and Br-2, respectively, as brominating agents. As equilibrium constants for the formation of Br2O and BrOCl (aq) have not been previously reported, we have calculated these values (and their gas-phase analogues) using benchmark-quality quantum chemical methods [CCSD(T) up to CCSDTQ calculations plus solvation effects]. The results allow us to compute bromine speciation and hence second-order rate constants. Intrinsic brominating reactivity increased in the order: HOBr