Electrically generated lead(IV) acetate and manganese(III) acetate as reagents for coulometric redox titrations in acetic acid

Summary The conditions were investigated for electrochemical generation of lead(IV) acetate in acetic acid by oxidation of lead(II) acetate on a lead dioxide electrode and on a platinum electrode. Bivalent manganese ions are quantitatively oxidized on a platinum electrode to the tervalent state in the same solvent. Coulometric titration methods for the determination of small amounts of hydroquinone in acetic acid were developed on the basis of the electrically generated oxidizing agents. Better results were obtained in titration with electrogenerated manganese(III) acetate. The titration end-point was detected by the biamperometric method. Suitable redox indicators were found.

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Zusammenfassung Die Bedingungen zur elektrochemischen Pb(IV)-Acetatherstellung aus Pb(II)-Acetat in Eisessig durch Oxydation an der Blei(IV)-oxid-Elektrode und an der Pt-Anode wurden untersucht. Auch Mn(II)-Ionen wurden in diesem Lösungsmittel quantitativ zu Mn(III) an der Pt-Elektrode oxydiert. Mit diesen auf elektrochemischem Wege erhaltenen Oxydationsmitteln wurden coulometrische Titrationsmethoden für die Bestimmung kleiner Hydrochinonmengen ausgearbeitet. Bessere Resultate wurden mit Mn(III)-Acetat erhalten. Die Endpunktbestimmung wurde durch biamperometrische Anzeige oder mit Hilfe visueller Redoxindikatoren durchgeführt.

     

Determination of organic bases in non-aqueous solvents by catalytic thermometric titration

Catalytic thermometric titrations have been developed for bases (brucine, diethylaniline, potassium acetate and triethylamine) in acetic acid by continuous and discontinuous addition of the standard solution and automatic temperature recording. The determination of weak bases, e.g., antipyrine, unsuccessful in acetic acid by catalytic thermometric titration, has been achieved by using nitromethane or acetic anhydride as solvent. Catalytic thermometric titrations were also performed by coulometric generation of hydrogen ions for the determination of micro amounts of weak bases in a mixture of acetic anhyride and acetic acid.     

Application of the aldehyde reactions for the endpoint detection in the catalytic thermometric titration of acids

Exothermic reaction of formaldehyde polymerization in alcoholic medium which is catalyzed by diluted solutions of strong bases was used for catalytic thermometric endpoint indication in titrations of organic acids. The amounts of 7.80–23.10 mg of various organic acids were determined with a relative standard deviation less than 0.9%. The developed method was successfully applied also to determination of free acid content (formic acid) in aqueous solutions of formaldehyde of various manufacturers.Also investigated were the possibilities of the application of two new indicator reactions in catalytic thermometric titrimetry: the exothermic reactions of aldolic addition of both benzaldehyde and acetophenone, and benzaldehyde and methylethylketone, which are catalyzed in alcoholic medium by diluted solutions of strong bases.The influence of concentration of indicator reaction components, the solvent and the titrant, on the shape of catalytic thermometric curves was explored.The obtained results were compared to those of potentiometry and other standard methods.     

Coulometric generation of hydrogen ions by oxidation of mercury in anhydrous acetone

The application of a mercury anode for the quantitative generation of H(+) ions in anhydrous acetone has been investigated. From the changes of anode potential with current density in 0.25M sodium perehlorate in anhydrous acetone it has been established that in this solvent mercury is oxidized at a potential which is much more negative than the oxidation potentials of the bases to be titrated, the indicator used and the solvent. Protons generated in this way have been used for titration of some organic bases, with either visual or potentiometric end-point detection. The oxidation of mercury in anhydrous acetone and the reaction of mercury ions with acetone have been found to proceed with 100% current efficiency.     

The application of deuterium-palladium electrodes in the coulometric-potentiometric determination of bases in ketone media

The application of deuterium-palladium electrodes as generator, indicator and reference electrodes for the determination of organic bases in acetone and methyl ethyl ketone has been investigated. Deuterium dissolved in palladium is oxidized at a potential that is close to the oxidation potential of hydrogen in palladium and more negative than the oxidation potentials of the bases titrated, indicator, and the solvents used. The anodic oxidation of deuterium dissolved in palladium proceeds with 100% current efficiency in the solvents investigated. The relative errors for the determination of 5 x 10(-4)M solutions of bases are less than 1%.     

Coulometric bipotentiometric titration of bases and their mixtures in acetic anhydride in the presence of two pretreated metal (Au,Pd)- quinhydrone electrodes

Summary The possibility of application of gold and palladium as the metal phase of quinhydrone electrodes in coulometric bipotentiometric titrations of bases alone and of some of their two-component mixtures in acetic anhydride was investigated. The effect of activation of these electrodes, by heating in an alcohol flame, on the shape of the titration curve is discussed. The amounts of bases determined were 5.0–10.0 eq. Errors did not exceed ±2%.

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Zusammenfassung Die Möglichkeit der Verwendung von Gold und Palladium als Metallphase von Chinhydronelektroden bei coulometrischen bipotentiometrischen Titrationen von Basen allein oder Gemischen zweier Basen in Essigsäureanhydrid wurde untersucht. Der Einfluß der Aktivierung dieser Elektroden durch Glühen in einer Alkoholflamme auf die Form der Titrationskurve wurde diskutiert. Die Mengen der analysierten Basen entsprach 5,0–10,0 Mikroäquivalenten. Die Ermittlungsfehler liegen innerhalb ± 2%.

     

Determination of tertiary amines and salts of organic acids in acetic acid by catalytic thermometric titration

A new method of determination of tertiary amines and salts of organic adds in acetic acid solution, to which about 2 % of water and 8% acetic anhydride are added, is described. After the equivalence point, the excess of perchloric acid catalyses the exothermic reaction of water with acetic anhydride. The end-point is determined from the graph of temperature against volume of added titrant. If a slightly soluble compound is produced during the titration, the precision of the new method is superior to that of the potentiometric method.     

International student competitions in Analytical Chemistry

Summary Competition can play a very positive role of university, stimulating students to extra efforts. The international student competition in Analytical Chemistry as performed at Belgrade university is discussed in detail.Presented at Euroanalysis III conference, Dublin, August 20–25, 1978     

Coulometric generation of acetylions by oxidation of mercury in acetic anhydride and in acetic acid/acetic anhydride mixture

Coulometric generation of acetyl (CH₃CO⁺) ions by oxidation of mercury in acetic anhydride and in acetic acid/acetic anhydride (5:95, v/v) is described. Current/potential curves for solvents, titrated bases, indicator and mercury showed that in both these solvents mercury is oxidized at potentials which are much more negative than those for the titrated bases and other components present in the solution. Quinoline, triethanolamine, triethylamine, pyridine and quinolin-8-ol in acetic anhydride, as well as triethylamine, 2,2′-bipyridine, 2,4,6-collidine, pyridine and sodium acetate in acetic acid/acetic anhydride were titrated with acetyl ions generated by the oxidation of mercury. In this way, it was established that the oxidation of mercury to mercury (I) ions proceeds quantitatively with 100% current efficiency.