Emerging investigators series: comparing the inherent reactivity of often-overlooked aqueous chlorinating and brominating agents toward salicylic acid
Emerging investigators series: comparing the inherent reactivity of often-overlooked aqueous chlorinating and brominating agents toward salicylic acid
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DOI：
10.1039/c7ew00491e
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发表时间：
2018-03-01
影响因子：
5
通讯作者：
Sivey, John D.
中科院分区：
文献类型：
--
作者：
Broadwater, Matthew A.;Swanson, Tyler L.;Sivey, John D.
氯化和溴化形式的水杨酸(SA)最近被确定为饮用水中一类新的消毒副产物(DBPs)。在这里，我们报告了几种卤化试剂在环境条件下对水杨酸氢盐的固有反应性，水杨酸的主要物种。利用合成水，测量了与3-氯、5-氯、3-溴和5-溴水杨酸酯形成有关的卤化速率随pH、[Cl-]、[Br2-]、游离氯剂量和SA初始浓度的变化。测定了卤代剂的二级速率常数，其大小顺序为：BrClGT；BrOClGT；Br2>；Br2O>；Cl2>；Cl2O>；HOBrGT；HOCl2。氯能够加快溴化和氯化的速度，表面上是通过促进BrCl2和Cl2的形成，这两种物质本身的活性分别比HOBr2和HOCl高几个数量级。动力学数据也支持水杨酰次氯酸盐作为氯化中间体，能够在pH>；8时影响氯化速度。改变缓冲液浓度的实验表明，磷酸盐缓冲液可以提高SA溴化反应的速度，但不能提高氯化反应的速度；碳酸盐和硼酸盐缓冲液对溴化或氯化反应速度没有明显影响。在具有代表性的氯化饮用水条件下，SA的溴化速率通常会超过SA的氯化速率。本文讨论的结果表明，在开发动力学模型来描述和预测含有游离氯的水体中的卤化速率和选择性时，考虑HOBr2和HOCl2以外的卤代剂的重要性。
Chlorinated and brominated forms of salicylic acid (SA) have recently been identified as a new class of disinfection byproducts (DBPs) in drinking water. Herein, we report the inherent reactivity of several aqueous halogenating agents toward hydrogen salicylate, the predominant species of salicylic acid under environmental conditions. Using synthetic waters, halogenation rates associated with the formation of 3-chloro, 5-chloro, 3-bromo, and 5-bromosalicylate were measured as a function of pH, [Cl-], [Br-], free chlorine dose, and the initial concentration of SA. Halogenating-agent specific second-order rate constants were determined and decrease in the order: BrCl > BrOCl > Br-2 > Br2O > Cl-2 > Cl2O > HOBr > HOCl. Chloride is capable of enhancing rates of bromination and chlorination, ostensibly by promoting the formation of BrCl and Cl-2, both of which are several orders of magnitude more inherently reactive than HOBr and HOCl, respectively. Kinetic data also support the participation of salicyloyl hypochlorite as a chlorination intermediate capable of influencing chlorination rates at pH >8. Experiments in which buffer concentrations were varied indicate that phosphate buffers can enhance rates of SA bromination but not chlorination; carbonate and borate buffers did not appreciably influence rates of bromination or chlorination. Under conditions representative of chlorinated drinking water, rates of SA bromination will generally exceed rates of SA chlorination. The results discussed herein demonstrate the importance of considering halogenating agents beyond HOBr and HOCl when developing kinetic models to describe and predict halogenation rates and selectivity in waters containing free chlorine.