Kinetic-mechanistic study of the chlorpromazine-hydrogen peroxide reaction catalyzed by molybdenum(VI) and tungsten(VI), and their differential determination

A simple and sensitive kinetic-catalytic method was developed for differential determination of molybdenum(VI) and tungsten(VI). The proposed method was based on their catalytic effect on oxidation of chlorpromazine by hydrogen peroxide. The reactions, which could be followed by measuring the increase in absorbance at 344 nm of the sulfoxide formed, were studied kinetically by an initial-rate method in 0.12 mol 1−1 hydrochloric acid solution (40 °C). The rate equations of each catalyzed reaction showed that the kinetic contributions to the total rate of these catalysts changed with reaction conditions; the reaction was first-order with respect to each of the two catalysts and the ratio of the apparent rate constant for molybdenum(VI) to that for tungsten(VI) decreased with an increase in the hydrogen peroxide concentration. Based on this kinetic difference, molybdenum(VI) and tungsten(VI) can be determined differentially. The method developed here utilizes the initial rates measured at two different hydrogen peroxide concentrations and the corresponding rate equations. Their mixtures at approximately equimolar concentrations (in the 10−7 mol 1−1 range) are determined an error of < 10%.