Reduction Of Dicarbonyl Compounds Research Articles

Reduction of dicarbonyl compounds on the dme: Part VII. Electrochemical behaviour of glyoxal

Polagraphic and kinetic studies of both the first and the second reduction waves of glyoxal have been carried out in aqueous solutions in the pH range 0 – 11. Tafel slopes and reaction orders with respect to glyoxal, H + ion and proton donors present in solutions have been obtained at potentials corresponding to the foot of the waves. Reactions mechanisms are proposed for this potential zone. The proposed mechanism accounts both for our experimental data and for those previously reported in the literature.

Reduction of dicarbonyl compounds on a DME: Part VI. A comparative study of the electrochemical behaviour of aromatic dicarbonyl compounds

Polarographic and voltammetric studies have been carried out on the reduction of benzyl and acetylbenzoyl in a basic medium. The effect of pH, reactant concentration, drop time and ethanol content on the polarographic and kinetic parameters is shown. The occurrence of adsorption phenomena is inferred from C - E curves. The degree of adsorption decreases as the ethanol content increases. Tafel slopes and reaction orders have been obtained at potentials corresponding to the foot of the wave. On the basis of these experimental data, reduction mechanisms are proposed in the zone where Tafel's law is obeyed. The results obtained here and those corresponding to the acidic medium, together with those concerning phenylglyoxal and phenylglyoxylic acid reported in the literature, are thoroughly discussed. A parallelism in the electrochemical behaviour of these compounds is made evident.

Reduction of dicarbonyl compounds on a mercury electrode. II. Reduction mechanism of acetylbenzoyl

A study on the electrochemical reduction of acetylbenzoyl on a mercury electrode has been carried out in the pH range 0–9 in buffered aqueous solutions. The effect of pH, drop time, temperature, and acetylbenzoyl concentration on polarographic and kinetic parameters has been studied. The occurrence of adsorption phenomena is inferred from the recordings of C–E curves. Tafel slopes and reaction orders have been obtained at potentials corresponding to the foot of the wave. On the basis of these experimental data, a reaction mechanism is proposed for the zone of potentials where Tafel's law is satisfied.

Reduction of dicarbonyl compounds on the DME: Part V. Experimental verification of the theoretical equations for CEC mechanisms

The theoretical equations for CEC mechanisms are applied to the reduction of phenylglyoxal, acetylbenzoyl and the glyoxylate ion, where the second chemical step is a first-order reaction. The experimental results obtained from the i – t and E 1 2 − t recordings agree with these equations. Likewise, the experimental results indicate that in the case of phenylglyoxal and acetylbenzoyl, the rate constants of these first-order reactions are sufficiently high that the reaction takes place on the electrode surface, while in the case of the glyoxylate ion, this reaction takes place in the reaction layer.

Reduction of dicarbonyl compounds on the DME: Part IV. Electrochemical behaviour of phenylglyoxal: Second wave

Polarographic (dc and DP), chronoamperometric and kinetic studies of the second reduction wave of phenylglyoxal have been carried out in the 0–12 pH range. At potentials corresponding to the limiting current, this process is governed by diffusion, although the i L − t recordings indicate the existence of an adsorption process. DP polarography indicates that in the 4–6 pH range two processes at very similar reduction potentials take place on the electrode surface, the electroactive species being the protonated and unprotonated forms of hydrated phenylglyoxal. Above pH 9, a new process takes place at potentials close to the supporting electrolyte discharge, due to the reduction product of phenylglyoxal. The Tafel slopes and reaction orders with respect to phenylglyoxal and H + ion have been obtained at potentials corresponding to the foot of the wave. The values of these parameters and their variations with the ethanol content and phenylglyoxal concentration agree with those expected from the application of the “combined isotherm” given by Gileadi. Reaction mechanisms are thus proposed in this zone of potentials.

Reduction of dicarbonyl compounds on the DME: Part III. Electrochemical behaviour of phenylglyoxal: First wave

Polarographic (dc and DP), voltammetric and kinetic studies of the first reduction wave of phenylglyoxal have been carried out in the 0–12 pH range. The effect of pH, drop time and temperature on the limiting current, half-wave and peak potentials, as well as the E vs. log[ i/( i L − i)] plots, is shown. Voltammetric results confirm the conclusions obtained from the polarographic data: in the 0–7 pH range, the charge transfer is in quasi-equilibrium whereas over the pH range of 8–12 it is irreversible. Moreover, in the 5–7 pH range, the current at the foot of the wave is controlled by a subsequent chemical reaction. We have also recorded the differential capacity curves at different pH values. The difference between these curves and those obtained in the absence of phenylglyoxal are negligible for pH < 4, and significant for pH > 7. The Tafel slopes and reaction orders with respect to phenylglyoxal, H + ion and proton donors present in solutions have been obtained at potentials corresponding to the foot of the wave. The influence of temperature and ethanol content on the kinetic parameters has also been calculated. Reaction mechanisms are thus proposed in this zone of potentials.

Reduction of dicarbonyl compounds on a mercury electrode—I. Reduction mechanism of diacetyl

A polarographic and kinetic study of the reduction of diacetyl has been carried out in the 0 < pH < 10 range in buffered aqueous solutions. The effect of pH, the diacetyl concentration, the height of the mercury column, the drop time, and temperature on the limiting current is studied. A discussion of the obtained results and the data reported in the literature is made. The Tafel slopes and reaction orders with the respect to diacetyl and H + ion are obtained for the first reduction wave at potentials corresponding to the foot of the polarographic wave, and a reaction mechanism according to the experimental data is proposed in this zone of potentials.

Effect of proton donors on the mechanism of the electrochemical reduction of some dicarbonyl compounds in dimethylformamide

1. The mechanism of the electrochemical reduction of aromatic dicarbonyl compounds of the\(R - CO - \begin{array}{*{20}c} { / / \_\_\_} \\ { \setminus \_\_\_\_\_\_} \\ \end{array} \begin{array}{*{20}c} { \setminus \setminus } \\ / \\ \end{array} - CO - R\) type in media with depressed proton donor activity (dimethylformamide plus phenol) consists in the formation and dual reaction of ambident enolate-anions just as in buffer aqueous organic solutions. 2. Predominant reaction of the carbanion center of the enolate anion with solvated proton is proposed.