Abstract
The kinetics of oxidation of the antibiotic drug chloramphenicol (CHP) by hexacyanoferrate(III) (HCF) has been investigated spectrophotometrically both in the absence and presence of ruthenium(III) catalyst in aqueous alkaline medium at 25 °C and at constant ionic strength of 1.10 mol dm−3. The stoichiometry is identical in both cases, i.e. [CHP]/[HCF] = 1:2. The oxidation products were identified by TLC and spectral studies such as GC–MS, IR, and 1H NMR. In both catalyzed and uncatalyzed reactions, the order with respect to the concentration of HCF is unity, whereas the order with respect to the concentration of CHP and the concentration of OH− is less than unity over the concentration range studied. The order with respect to the concentration of Ru(III) is unity. The reaction in the presence of Ru(III) is approximately tenfold faster than the uncatalyzed reaction. The active species of oxidant and catalyst are [Fe(CN)6]3− and [Ru(H2O)5(OH)]2+, respectively. On the basis of experimental results suitable mechanisms are proposed. The reaction constants involved in the different steps of the reaction mechanisms were calculated for both cases. The catalytic constant was also calculated for the catalyzed reaction at different temperatures. The activation parameters with respect to the slow step of the mechanism and thermodynamic quantities are also determined.Graphical abstract Electronic supplementary materialThe online version of this article (doi:10.1007/s00706-014-1208-7) contains supplementary material, which is available to authorized users.
Highlights
Hexacyanoferrate(III) [HCF(III)] has been widely used to oxidize numerous organic and inorganic compounds in alkaline media
The mechanism of the catalysis depends on the nature of the substrates, oxidant, and experimental conditions, it has been shown [10] that metal ions acts as catalysts by one of several different paths, such as the formation of complexes with reactants or oxidation of the substrate itself or through the formation of free radicals
The main reaction product was identified as p-nitrobenzaldehyde. This was the only organic product obtained in the oxidation which was confirmed by a single spot on thinlayer chromatography and was characterized by spectral investigations
Summary
Hexacyanoferrate(III) [HCF(III)] has been widely used to oxidize numerous organic and inorganic compounds in alkaline media. Some authors [1, 2] have suggested that alkaline HCF(III) ion acts as an electron-abstracting reagent in redox reactions. Singh et al [4] while discussing the oxidations of formaldehyde, acetone, and ethyl methyl ketone by HCF(III) suggested that the oxidation takes place via an electron transfer process resulting in the formation of a free radical intermediate. The mechanism of the catalysis depends on the nature of the substrates, oxidant, and experimental conditions, it has been shown [10] that metal ions acts as catalysts by one of several different paths, such as the formation of complexes with reactants or oxidation of the substrate itself or through the formation of free radicals. Ruthenium(III) catalysis in redox reactions involves different degrees of complexity, owing to the formation of different intermediate complexes and different oxidation states of ruthenium
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