Transformation of linezolid during water treatment with chlorine ─ A kinetic study

Abstract

The experimental studies on transformation of emerging contaminant linezolid during water chlorination process have been carried out using UV-Visible spectrometer. The pseudo-first order rate constants of linezolid reaction with free available chlorine (FAC) at 5.0 - 8.8 <i style="mso-bidi-font-style:normal">p</i>Hhave been determined. The second order rate constants are found to decrease with increase in <i style="mso-bidi-font-style:normal">p</i>H (e.g. apparent second rate constant; k”_app=2.88 dm³mol^-1s^-1at <i style="mso-bidi-font-style:normal">p</i>H 5.0 and k”_{app =} 0.076 dm³mol^-1s^-1at <i style="mso-bidi-font-style:normal">p</i>H 8.8 at 298K). Monochlorinated reaction product has been identified by LC/ESI/MS spectra under the experimental conditions. A mechanism involving electrophilic halogenation is proposed based on the kinetic data and LC/ESI/MS spectra. The effect of temperature on the rate of the reaction has been studied at four different temperatures. It is observed that rate constants increase with the increase in temperature and the thermodynamic activation parameters <i style="mso-bidi-font-style:normal">E_a, ΔH^#, ΔS^#</i> and <i style="mso-bidi-font-style:normal">ΔG^#</i>are evaluated for the reaction and discussed. The product of the reaction between linezolid and FAC retains the antibacterial activity. The geometry optimization of the reactants and the products has been done using dispersion corrected density functional (DFT-D) method. All the DFT calculations are accomplished using the TurboMole-5.10 package.