Free-radical-induced oxidative degradation of antibacterial drug, methylparaben by permanganate in alkaline medium: A kinetic and mechanistic approach

The kinetics of oxidation of an antibacterial drug, methylparaben by permanganate in alkaline medium at a constant ionic strength of 0.80 mol dm⁻³ was studied spectrophotometrically at 25°C. The stoichiometric ratio between permanganate and methylparaben was found to be 2:1 in alkaline medium. The main products were identified by NMR, IR, and GC–MS spectral studies. The reaction showed first-order kinetics in permanganate, fractional order in methylparaben, and OH⁻ concentrations under the experimental conditions. Ionic strength and dielectric constant did not affect the rate of reaction. The added products did not have any significant effect on the rate of reaction. Based on the rate experimental results, a suitable mechanism is proposed. Investigations at different temperatures allowed the determination of the activation parameters with respect to the slow step of the proposed mechanism. The reaction constants involved in the mechanism were evaluated. The results of this study provide fundamental mechanistic parameters and degradation efficiencies of drug by advanced oxidation processes.

在离子强度固定为0.80 mol dm⁻³的碱性介质中，于25℃下采用分光光度法研究了抗菌药物对羟基苯甲酸甲酯（methylparaben）被高锰酸盐（permanganate）氧化的反应动力学。实验测得碱性介质中高锰酸盐与对羟基苯甲酸甲酯的化学计量比为2:1。通过核磁共振波谱（NMR）、红外光谱（IR）及气相色谱-质谱联用（GC-MS）的谱学分析，对反应主要产物进行了结构鉴定。在实验条件下，该反应对高锰酸盐浓度表现为一级动力学，对对羟基苯甲酸甲酯和氢氧根离子（OH⁻）浓度均为分数级动力学。离子强度与介电常数均未对反应速率产生显著影响，外加产物亦未对反应速率造成明显作用。基于上述速率实验结果，本文提出了合理的反应机理。通过开展不同温度下的实验研究，确定了所提机理决速步的活化参数，并对机理中涉及的各反应常数进行了求解。本研究所得结果可为高级氧化工艺（advanced oxidation processes）降解该类药物提供基础的机理参数与降解效率数据。