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Transformation of levofloxacin during water chlorination

Posted on 20. December, 2012.

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Information on chlorine reaction with pharmaceutical compounds is scarce. An investigation reported in Progress in Reaction Kinetics and Mechanism quantifies the kinetics for reactions of levofloxacin with free available chlorine and also identifies associated transformation, mechanisms, degradation products, and evaluates thermodynamic activation parameters relevant to chlorine based municipal waste water and drinking water disinfection processes.

Transformation of Levofloxacin During Water Chlorination Process: Kinetics and Pathways

2.1 Materials and methods
2.2 Kinetic Measurements
3.1 Product analysis
3.2 Reaction order
3.3 Effect of pH on the reaction
3.4 Effect of varying ionic strength and dielectric constant
3.5 Effect of initially added product
3.6 Effects of temperature
3.7 Kinetic modelling
3.8  Environmental implications of fluoroquinolone degradation products

Kinetics and mechanism of removal of fluoroquinolone antibacterial levofloxacin (LFC 1) by free available chlorine (FAC) during water chlorination processes was investigated for the first time between the pH values 4.2 and 8.5. The pH dependent second order rate constants were found to decrease with increase in pH. (e.g. Apparent second order rate constant; K"app = 20 dm3 mol-1 s-1 at pH 4.2 and k"app = 1 dm3 mol-1 s-1 at pH 8.5 and at 25 oC). The products of the reaction were determined by Liquid chromatography and high resolution mass spectrometry. There are two plausible pathways for the LFC chlorination. The major channel is electrophilic halodecarboxylation of quinolone moiety in which, HOCl reacts at tertiary N(4) amine to form a reactive chlorammonium intermediate (R3N(4)Cl+) that can catalytically halogenate LFC and the minor channel is chlorination at piperazinyl moiety in which the HOCl reacts at tertiary N(4) amine to form a reactive chlorammonium intermediate (R3N(4)Cl+) followed by intermediate degradation both at piperazinyl and quinolone moiety with successive chlorination. The effect of temperature on the rate of the reaction was studied at four different temperatures and rate constants were found to increase with increase in temperature and the thermodynamic activation parameters Ea, ΔH#, ΔS# and ΔG# were evaluated for the reaction and discussed.


M. S. Gudaganatti1 , M. S. Hanagadakar1 , R. M. Kulkarni1* , R. S. Malladi1, R. K. Nagarale2
1 Department of Chemistry, Gogte Institute of Technology, Belgaum- 590 008, Karnataka, India,        *
2 Department of Chemical Engineering, The University of Texas at Austin, University Station C0400, Austin, TX 78712, USA

Keywords:  Kinetics,  Chlorination, Levofloxacin, Emerging contaminant, Pathways

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