Impact of micelles on the periodate oxidation of cobalt(II)-trans-cyclohexane-1,2-diamine-N,N,N’,N’-tetraacetate: a kinetic and mechanistic study
摘要
The current study intends to investigate the impact of neutral, cationic, and anionic surfactants on the IO4− oxidation of cobalt(II)-trans-cyclohexane-1,2-diamine-N,N,N’,N’-tetraacetate ([CoIICYDTA]2−). The kinetics of [CoIICYDTA]2− oxidation in both aqueous and CTAB micellar mediums is determined by quantifying a spike in absorbance at a wavelength of 538 nm, serving as a measure of the concentration of [CoIIICYDTA]−. In the acidic medium periodate ion predominantly exists as octahedral H4IO6− ion. The electron transfer reaction involving [CoIICYDTA]2− and H4IO6− proceeds preferentially through an outer-sphere mechanism via the formation of ion-pair. Throughout the range of concentration analyzed, the reaction exhibits first order dependence both on [CoIICYDTA2−] and [IO4−]. The observed constancy in reaction rate within the examined pH range supports the dominant presence of the unprotonated form of [CoIICYDTA]2− and the single species of periodate ion. The linear increase in oxidation rate with the addition of electrolytes indicates a positive salt effect. The CTAB micellar media facilitates an approximate 2.5-fold enhancement in the rate of [CoIICYDTA]2− oxidation. TX-100 promotes the oxidation of [CoIICYDTA]2−, while SLS, an anionic surfactant, acts as an inhibitor. The calculated activation parameters further corroborate the suggested mechanistic framework.