Silver (I) catalyzed and uncatalyzed oxidation of levofloxacin with aqueous chlorine: A comparative kinetic and mechanistic approach

Abstract

The kinetics and mechanism of the Ag (I) ion catalyzed reaction of levofloxacin (LFC) by free available chlorine (FAC) during water chlorination processes was investigated for the first time between the pH values 4.2 and 8.2. The pH dependent second order rate constants were found to decrease with increase in pH. (e.g. Apparent second order rate constant for Ag (I) catalyzed reaction , k” app = 114.40 dm-3 mol-1 sec -1 at pH 4.2 and k” app.= 8.72 dm-3mol-1 sec -1 at pH 8.2 and at 25±0.20C). The reaction rates revealed that Ag (I) catalyzed reaction was about six-fold faster than the uncatalyzed reaction. The products of the reaction were determined by Liquid chromatography and high resolution mass spectrometry. The reaction proceeds via formation of intermediate complex between Ag (I) ion and levofloxacin, then HOCl reacts with the complex to form chlorinated product. The effect of catalyst, effect of initially added product, effect dielectric constant and effect ionic strength on the rate of reaction was also studied. 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 , ∆H # , ∆S # and ∆G # were evaluated for the reaction and discussed.