Outer‐sphere reduction of hexacyanoferrate(III) by enolizable and nonenolizable aldehydes in alkaline medium

Abstract

Outer‐sphere reduction of hexacyanoferrate(III) by some enolizable/nonenolizable aldehydes (viz., aliphatic, heterocyclic, and aromatic aldehydes) in alkaline medium has been studied spectrophotometrically at λmax = 420 nm. The reactions are first order each in [aldehyde] and [Fe(CN)63−]. The rate increases with an increase in [OH−] in the oxidation of aliphatic and heterocyclic aldehydes, whereas it is independent of [OH−] in the reaction with aromatic aldehydes. The intervention of free radicals in the reaction mixture was carried out using both acrylonitrile and acrylamide scavenger in two different experiments. The kinetic results indicate that the oxidation of benzaldehyde in aqueous medium proceeds at a slower rate than the aliphatic aldehydes (other than formaldehyde) and furfural. The values of third‐order rate constant (k3) at 308 K in the oxidations of some aliphatic aldehydes and furfural follow the order (CH3)2CH > CH3CH2 > CH3 > C4H3O > H. The rate constants correlate with Taft's σ* value, the reaction constant being negative (–9.8). The pseudo–first‐order rate constants in the oxidations of benzaldehyde and substituted benzaldehydes follow the order NO2 > H > Cl > OCH3. The Hammett plot is also linear with a ρ value (0.6488) for meta‐ and para‐substituted benzaldehydes. The kinetic isotope effect for benzaldehyde (kH/kD = 1.93 at 303 K) was obtained. The rate‐determining step is the outer‐sphere formation of Fe(CN)64− and free radicals, which is followed by the rapid oxidation of free radicals by Fe(CN)63− to give products. The kinetic data and hence thermodynamic parameters have been used to distinguish enolizable and nonenolizable aldehydes. An attempt has also been made to correlate kinetic data with hydration equilibrium constants of some aliphatic aldehydes. © 2012 Wiley Periodicals, Inc. Int J Chem Kinet 44: 494–505, 2012

Influence of Microheterogeneous Environments of Sodium Dodecyl Sulfate on the Kinetics of Oxidation of l-Serine by Chloro and Chlorohydroxo Complexes of Gold(III)

“…The nature of a substrate in combination with the experimental conditions in a reaction controls the behavior of gold­(III) to serve as either a one or two electron transfer oxidant. , Since the reaction mixture upon contact with acrylonitrile or acrylamide afforded a polymeric white suspension, the reaction obviously passes through the free radical intermediate. This observation consequently rules out the conversion of gold­(III) to gold­(I) in a single-step two electron reduction process.…”

A promising methyl ester of pectic acid polysaccharide in biomedicine and pharmaceutics applications: Oxidation of methyl ester of pectic acid by alkaline hexacyanoferrate(III). A kinetic and mechanistic orientation

“…Although hexacyanoferrate(III) is known as a weak oxidant with redox potential of 0.36 and 0.4 V for [Fe(CN) 6 ] 3− /[Fe(CN) 6 ] 4− couple in acidic and alkaline solutions, respectively. 9,10 A considerable amount of work has been reported on the oxidation kinetics of organic 11,12 and inorganic [13][14][15][16][17][18] substrates by this oxidant. Therefore, redox reactions involving this oxidant are considered as a tool for chemical kinetics inception.…”

Mechanistic Investigation of the Oxidative Cleavage of the Carbon–Carbon Double Bond in α,β‐Unsaturated Compounds by Hexachloroiridate(IV) in Acetate Buffer

“…The reaction rate was found to be enhanced with an increase in solvent polarity (Table ). The result was expected if one assumed that the interaction took place between the π‐electron cloud of the substrates' double bond and the negatively charged oxidant . Moreover, in the rate‐determining step the intermediate complex decomposes to a number of charged species, which might come from the polar transition state.…”

“…The unsaturated compounds (e.g., acrylamide, acrylonitrile), in general, are susceptible to radical‐induced polymerization. Such a possibility may not be applicable under the present experimental conditions where the concentrations of the unsaturated compounds are quite low [(2.5–25) × 10 −2 mol dm −3 ] . Again, if these unsaturated compounds might have played a significant role in induced polymerization in the reaction mixture, it would have resulted in the decrease of the reaction rate with the increase in the concentration of the each substrate .…”