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Permanganate oxidation of diclofenac: The pH-dependent reaction kinetics and a ring-opening mechanism.
Chemosphere. 2015 Oct; 136:297-304.C

Abstract

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.

Authors+Show Affiliations

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. Electronic address: owenchy@163.com.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. Electronic address: songdean07@mails.ucas.ac.cn.Key Laboratory of Drinking Water Science and Technology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China. Electronic address: hjliu@rcees.ac.cn.Key Laboratory of Drinking Water Science and Technology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China. Electronic address: jhqu@rcees.ac.cn.

Pub Type(s)

Journal Article
Research Support, Non-U.S. Gov't

Language

eng

PubMed ID

25522850

Citation

Cheng, Hanyang, et al. "Permanganate Oxidation of Diclofenac: the pH-dependent Reaction Kinetics and a Ring-opening Mechanism." Chemosphere, vol. 136, 2015, pp. 297-304.
Cheng H, Song D, Liu H, et al. Permanganate oxidation of diclofenac: The pH-dependent reaction kinetics and a ring-opening mechanism. Chemosphere. 2015;136:297-304.
Cheng, H., Song, D., Liu, H., & Qu, J. (2015). Permanganate oxidation of diclofenac: The pH-dependent reaction kinetics and a ring-opening mechanism. Chemosphere, 136, 297-304. https://doi.org/10.1016/j.chemosphere.2014.11.062
Cheng H, et al. Permanganate Oxidation of Diclofenac: the pH-dependent Reaction Kinetics and a Ring-opening Mechanism. Chemosphere. 2015;136:297-304. PubMed PMID: 25522850.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Permanganate oxidation of diclofenac: The pH-dependent reaction kinetics and a ring-opening mechanism. AU - Cheng,Hanyang, AU - Song,Dean, AU - Liu,Huijuan, AU - Qu,Jiuhui, Y1 - 2014/12/15/ PY - 2014/06/29/received PY - 2014/11/24/revised PY - 2014/11/27/accepted PY - 2014/12/20/entrez PY - 2014/12/20/pubmed PY - 2016/2/18/medline KW - Diclofenac KW - Permanganate KW - Ring-opening mechanism KW - pH-dependent kinetics SP - 297 EP - 304 JF - Chemosphere JO - Chemosphere VL - 136 N2 - 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. SN - 1879-1298 UR - https://www.unboundmedicine.com/medline/citation/25522850/Permanganate_oxidation_of_diclofenac:_The_pH_dependent_reaction_kinetics_and_a_ring_opening_mechanism_ L2 - https://linkinghub.elsevier.com/retrieve/pii/S0045-6535(14)01385-X DB - PRIME DP - Unbound Medicine ER -