Oxidative Transformation Of Fluoroquinolone Antibacterial By Permanganate-kinetics And Mechanistics

Fluoroquinolones （FQs） residues in the environment pose threats to the health ofecological systems and human. The increasing antibacterial resistance gene abundanceand persistence in the environment has become a global issue. The chemical oxidationprocess is more feasible in drinking water process than adsorption and biologicaldegradation because of its merits such as completely removal and easily handling.Potassium permanganate has high redox potential and slow rate ofdecomposition, and can also be easily monitored, in addition, compared with otheroxidant potassium permanganate oxidation produces fewer by-products. This studyexamined for aqueous reactions between potassium permanganate and FQs. Detailedkinetics experiments of Ofloxacin and Norfloxacin were conducted to characterizereactions, including examining the effects of the oxidant concentration, pH andtemperature. The mechanistic investigation of the oxidation of Enrofloxacin,Ciprofloxacin, Ofloxacin and Norfloxacin by Potassium permanganate was also studied.The results showed that the oxidation reaction of Ofloxacin and Norfloxacin bypotassium permanganate in aqueous solution followed second-order kinetics. Whenpotassium permanganate was excessive, the second-order reaction rate constant was80M^-1·min^-1and12M^-1·min^-1, respectively. The second-order reaction rate constrant wasinfluenced by pH values. The rate of Ofloxacin and Norfloxacin oxidation by potassiumpermanganate increased with the increase of the water temperature, and the reactionactivation energy was29.6kJ·mol^-1and27.2kJ·mol^-1, which reveals that the oxidationreaction of Ofloxacin and Norfloxacin by potassium permanganate is feasible underusual water treatment condition.The reaction kinetics and product characterization point to a reaction mechanismthat the piperazine ring is the reactive site. Mn（VII） was mainly targeting the tertiaryaromatic amine （N1site） on the piperazine ring. The initiation step of Mn（VII）-FQsreactions is proposed to be the oxidative formation of an enamine from the aromaticamine group, there are three pathways for the further oxidation of the enamine product.Pathway Ⅰis a N-dealkylation process, the partially dealkylated product is formedwhen the enamine undergoes two consecutive hydrolysis steps, and then the fulldealkylated product is formed by the further oxidation of the partially dealkylatedproduct. Pathway Ⅱ is a hydroxylation process,in which the enamine was hydrolyzed tomonohydroxylated intermediates and a1,2-diolintermediate, futher oxidation of themyields the amide products and a dialdehyde product, respectively. The twomonoaldehyde products were formed by the further oxidation of the dialdehyde product. The two pathways above are suitable for the oxidation of the four compounds in thisstudy.But there are another pathway （pathway Ⅲ） for Enrofloxacin and Ciprofloxacin.Pathway Ⅲ is the oxidation of cyclopropyl group. The hydroxylation process andN-dealkylation process was concured initially，and then the cyclopropyl group inEnrofloxacin/Ciprofloxacin was oxidized to yield aldehyde and carboxylic acidproducts.Potassium permanganate can remove fluoroquinolones rapidly and efficiently. Inthis study the reaction rate constrant was influenced by the reaction temperature, pHvalue and the concentration of potassium permanganate.At least ten kinds of oxidationproduct and three pathways were found in this study. This research provided aneffective method of removing fluoroquinolones from aquatic environment.