Regioselective oxidation of tetracycline by permanganate through alternating susceptible moiety and increasing electron donating ability |
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Authors: | Xiaohua Jiang William A Jefferson Dean Song Hanyang Cheng Fengmin Li Zhimin Qiang Aiqian Zhang Huijuan Liu Jiuhui Qu |
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Institution: | College of Environmental Science and Engineering, Ocean University of China, Qingdao 266100, China;The State Agriculture Ministry Laboratory of Quality & Safety Risk Assessment for Tobacco, Tobacco Research Institute, Chinese Academy of Agricultural Sciences, Qingdao 266101, China;Key Laboratory of Drinking Water Science and Technology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China;The State Agriculture Ministry Laboratory of Quality & Safety Risk Assessment for Tobacco, Tobacco Research Institute, Chinese Academy of Agricultural Sciences, Qingdao 266101, China;College of Environmental Science and Engineering, Ocean University of China, Qingdao 266100, China |
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Abstract: | Permanganate has attracted much attention in wide range of chemistry and particularly in degradation of environmental pollutants.However,few studies have discussed the feature of regioselective reactivity of permanganate with specific moiety of the target compound.Herein,we studied the reaction between permanganate and tetracycline that is an emerging micropollutant with different species containing several electron-rich groups.The second-order rate constants increased from 6.0 to 9.0 and could be quantitatively modeled by considering the speciation of both reactants,yielding k_(TC)~0= 11.7(mol/L)~(-1) sec~(-1),kTC-= 35.7(mol/L)~(-1) sec~(-1),k_(TC)~(2-)= 43.1(mol/L)~(-1) sec~(-1) for individual reaction channels.Degradation products were then identified as the hydroxylated and demethylated compounds.The result suggested a rate-limiting step of simple hydroxylation at the phenolic and/or alkene moieties,while the demethylation should be caused by the unavoidably formed manganese oxide via single electron oxidation.This is supported by the DFT calculation,indicating the primary oxidation of phenolic group of T_C~0 with activation barrier of 44.5 kcal/mol and of alkene group of TC~- and TC_2~- with activation barriers of 44.0 and 43.4 kcal/mol,respectively.This is in agreement with the experimental results,implying the alternation of regioselectivity associated with the deprotonation process.The result was further supported by performing the Fukui function and electrostatic potential analysis,reflecting the more probable site and better electron donating tendency beneficial to the permanganate oxidation. |
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Keywords: | Corresponding authors Permanganate oxidation of tetracycline Regioselective reactivity Rate-limiting hydroxylation step Altered susceptible moiety Increased electronegativity |
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