Oxidation of clindamycin phosphate by chromium(VI) in aqueous sulfuric acid medium—A kinetic and mechanistic study

Amar K Durgannavar,Sharanappa T Nandibewoor,Manjunath D Meti,Shivamurti A Chimatadar,Mark Russell Stjohn Foreman

doi:10.1080/23312009.2015.1115210

Amar K Durgannavar, Sharanappa T Nandibewoor + Show 3 more

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https://doi.org/10.1080/23312009.2015.1115210

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Abstract

AbstractKinetics and mechanism of oxidation of clindamycin phosphate by potassium dichromate in aqueous sulfuric acid medium is studied spectrophotometrically at 25°C at a constant ionic strength of 3.60 mol dm−3. The stoichiometry of the reaction is determined and it was found that one mole of clindamycin phosphate consumes two moles of chromium(VI) (1:2). The oxidation products are characterized and confirmed by spectral studies such as IR, GC-MS and LC-MS. The reaction is first order each in chromium(VI) and clindamycin phosphate concentrations. An increase in the sulfuric acid concentration causes an increase of the reaction rate. The order with respect to acid concentration is found to be 1.65. From the results of kinetic studies, reaction stoichiometry and product analysis a suitable free radical mechanism is proposed. Based on investigation of the reaction at different temperatures, computation of the activation parameters with respect to the slow step of the proposed mechanism was evaluated.

Highlights

Chromium(VI) is widely used in organic chemistry, due to its versatile oxidative mechanistic pathways, which makes them inherently interesting
Effect of [clindamycin phosphate] on rate of oxidation The effect of clindamycin phosphate concentration on the rate was studied in the range of 5.0 × 10−4 to 5.0 × 10−3 mol dm−3 retaining concentrations of all other reaction components constant
The results indicate that H2CrO4 reacts with clindamycin phosphate forming a complex, The formation of complex is evident kinetically by a Michaelis–Menton plot, i.e. a non zero intercept of the plot of 1/kobs vs. 1/[CP] (Figure 6)

Summary

Introduction

Chromium(VI) is widely used in organic chemistry, due to its versatile oxidative mechanistic pathways, which makes them inherently interesting. Among various oxidation states of chromium, Cr(VI) and Cr(III) are stable oxidation states. In acidic medium the reduction potential of Cr(VI)/Cr(III) couple is 1.33 V (Chimatadar, Basavaraj, & Nandibewoor, 2006; Day & Selbin, 1964). Kinetics and oxidation of organic compounds by chromic acid has been the subject of large number of investigators (Das, 2004; Wiberg & Mukherjee, 1974). Interest has been shown in the chemistry of the intermediate oxidation states, Cr(V) and Cr(IV), due to their observation during the oxidation of organic substrates by Cr(VI) and implication in the mechanism of Cr-induced cancers (Fawzy, Ashour, Musleh, Hassan, & Asghar, in press)

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