Kinetics and Equilibrium of the Dehydration-Hydration and Recombination-Dissociation Reactions of Glyoxylic Acid Investigated by Electrochemical Methods

Equilibrium constants of the glyoxylic acid hydration have been defined more precisely taking into account the values of the DC polarographic limiting kinetic current and the dimerization effect. For the correct calculation of the rate constants for the glyoxylic acid dehydration and recombination reactions, the diffusion contribution of the dehydrated anions into the limiting kinetic current of the first and total DC polarographic waves was considered and the concept of the preceding consecutive rate determining reactions of the dehydration and recombination was used. The rate constants from the DC polarographic data have been obtained that are close to the ones from the pulse polarographic and spectrophotometric data. On the basis of a comparison with the linear-sweep voltammetric data, intermolecular catalysis of the dehydration reaction was noted. The recombination stage corresponds to protonation of the carboxylate group. The fast intramolecular protonation of the carbonyl group after the recombination stage has been considered

Polarographic Kinetic Currents of Formaldehyde and Kinetics of the Electrode Chemical Reactions

New approaches to the analysis of the polarographic (DCP) kinetic currents of formaldehyde have been developed. Anomalously high limiting kinetic current in strongly acidic media has been explained by catalytic hydrogen evolution upon CH2OH+ discharge after the protonation of CH2O. On the other hand, the diffusion contribution of CH2O from the bulk solution to the total limiting kinetic and diffusion currents should be taken into account for a correct determination of the rate constants of CH2(OH)2 dehydration reaction in the catalysis by H2O molecules in neutral and weakly acidic media. At the same time, the electrode reaction of the direct formation of CH2O from CH2(OH)O- can be neglected in alkaline Solutions. Thus, the two consecutive reactions, i.e. the formation of CH2(OH)2 from CH2(OH)O- and H2O and the dehydration reaction of CH2(OH)2 to CH2O, proceed at the electrode in alkaline Solutions. Detailed analyses of the diffusion coefficient and diffusion current of formaldehyde as well as equilibrium constants of the dimerization and acidic dissociation reactions of CH2(OH)2 and the hydration and protonation reactions of CH2O allowed us to choose the most correct values for kinetic calculations

Acids Extraction from Vegetable Oils for Acid Value pH-metric Determination without Titration

Theoretical and experimental analysis of free fatty acids extraction from vegetable oils into a reagent containing triethanolamine for pH-metric acid value determination without titration was carried out. Practically complete extraction of the free fatty acids in the form of triethanolammonium salts was demonstrated. The obtained results allow to understand more possibilities of the pH-metric and other methods for acid value determination in different oils