Formation of hydrates from asymmetric and cyclic ketones in their oxidation by alkaline hexacyanoferrate(III)

Abstract

Alkaline hexacyanoferrate(III) oxidizes 2-methyl-3-pentanone and 2-methylcyclohexanone quite rapidly. Kinetic data show second-order kinetics with respect to hydroxide ion concentrations indicating the formation of hydrates by ketones in aqueous alkaline medium before their reaction with the oxidant. The rate follows direct proportionality with respect to the concentrations of hexacyanoferrate(III) and ketones. Externally added hexacyanoferrate(II) does not affect the reaction velocity indicating the reduction of oxidant takes place after the rate determining step. Orders with respect to various reactants were confirmed by various methods and the overall rate constant of the reaction was calculated by three different variations. Thermodynamic data suggest that 2-methyl-3-pentanone forms the activated complex more easily compared to 2-methylcyclohexanone. Second-order in [OH−] in the oxidation of 2-methyl-3-pentanone and methyl cyclohexanone by alkaline hexacyanoferrate (III) indicates that oxidation proceeds through the formation of hydrates. Rate constant and thermodynamic parameters at five temperatures were calculated. Mono and dicarboxylic acids were confirmedto be the final oxidation products. Rate law given was— $$ -\frac{\hbox{d}[\hbox{Fe}(\hbox{CN})_{6}]^{3-}}{\hbox{d}t}=k \hbox{K}_{1} \hbox{K}_{2} \frac{[\hbox{S}][\hbox{OH}]^{2}[\hbox{Fe}(\hbox{CN})_{6}]^{3-}} {[\hbox{H}_{2}\hbox{O}]^{2}}$$