Cheng Hanyang, Song Dean, Liu Huijuan, Qu Jiuhui
Key Laboratory of Drinking Water Science and Technology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China; University of Chinese Academy of Sciences, Beijing 100039, China.
Key Laboratory of Drinking Water Science and Technology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China.
Chemosphere. 2015 Oct;136:297-304. doi: 10.1016/j.chemosphere.2014.11.062. Epub 2014 Dec 15.
In this work, the fate of diclofenac (DCF) during permanganate (Mn(VII)) oxidation was investigated at environmentally relevant pH conditions (from 5 to 9). The batch experiments showed that the kinetics of the Mn(VII)/DCF reaction follows a second-order rate law with an apparent rate constant of 1.57±0.02 M(-1) s(-1) at pH 7 and 20 °C. The half-value of DCF was calculated to be 37.5 min, when the concentration of Mn(VII) (0.4 mM) was 20-fold excess of DCF. The pH-dependence of the reaction kinetics was investigated, and the DCF reactivity with Mn(VII) was found to decrease with increasing pH. The second-order rate constants were then quantitatively described by incorporating the species distribution of DCF. A lower reactivity of the anionic DCF (DCF(-)) in comparison with its neutral counterpart (DCF(0)) was most likely attributable to the interaction between the ionized carboxylate group and amine nitrogen position, which can reduce the nucleophilicity of amine nitrogen by inductive and resonance effects. Moreover, a range of degradation products and the corresponding structures were proposed on the basis of the LC-Q-TOF-MS analysis. A detailed ring-opening reaction mechanism was proposed as follows: Mn(VII) acts as an electrophile to attack the amine moiety, leading to the formation of the primary intermediate products 2,6-dichloroaniline and 5-hydroxy-diclofenac, which can be further transformed. The further degradation proceeded through a multistep process including ring-opening, decarboxylation, hydroxylation, and cyclation reactions.
在本研究中，考察了在环境相关pH条件（5至9）下双氯芬酸（DCF）在高锰酸盐（Mn(VII)）氧化过程中的归宿。批次实验表明，Mn(VII)/DCF反应动力学遵循二级速率定律，在pH 7和20℃时表观速率常数为1.57±0.02 M⁻¹ s⁻¹。当Mn(VII)浓度（0.4 mM）为DCF浓度的20倍过量时，DCF的半衰期经计算为37.5分钟。研究了反应动力学的pH依赖性，发现DCF与Mn(VII)的反应活性随pH升高而降低。通过纳入DCF的物种分布对二级速率常数进行了定量描述。与中性形式（DCF(0)）相比，阴离子型DCF（DCF(-)）反应活性较低，这很可能归因于离子化的羧基与胺氮位置之间的相互作用，这种相互作用可通过诱导效应和共振效应降低胺氮的亲核性。此外，基于液相色谱-四极杆-飞行时间质谱（LC-Q-TOF-MS）分析提出了一系列降解产物及其相应结构。提出了详细的开环反应机理如下：Mn(VII)作为亲电试剂攻击胺部分，导致形成初级中间产物2,6-二氯苯胺和5-羟基双氯芬酸，它们可进一步转化。进一步的降解通过包括开环、脱羧、羟基化和环化反应的多步过程进行。
