Tibor J. Pastor

The quantitative electrochemical generation of bromine in acetic acid

Abstract The quantitative electrochemical generation of bromine at a platinum electrode in acetic acid is described. Coulometric methods for the determination of hydroquinone and 2-methylhydroquinone are reported. The best results are obtained with 0.7–1.1 M potassium acetate solutions as supporting electrolyte, and biamperometric end-point detection. The effects of water and acetic anhydride on the accuracy of titrations are discussed. Determination of the formal redox potential of the Br2/Br- system in a 0.9 M potassium acetate solution in acetic acid showed that bromide is oxidized directly to bromine at a platinum electrode with 100% current efficiency.

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

SummaryThe 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.ZusammenfassungDie 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.

Behaviour of membrane graphite electrodes in potentiometric titration of bases and reducing substances in acetic acid media

Abstract Potentioimetric titrations of bases with perchloric acid, and of reducing substances with lead(IV) acetate, in acetic acid medium and in a mixture of acetic acid and acetic anhydride are discussed. The indicator electrodes used were: a Radelkis membrane graphite electrode (OP-C-7112 C), laboratory-prepared silicone rubber-based graphite electrodes, an Elektrokarbon graphite electrode (SU 106), a Radiometer glass electrode (G 200 B), and a platinum electrode. In addition, new types of silicone rubber-based electrodes were prepared by incorporating mixtures of graphite and manganese dioxide, graphite and quinhydrone, and manganese dioxide in their membranes. A manganese dioxide electrode was also prepared by electrolytic precipitation of manganese on a platinum anode. The properties of all the cited electrodes are compared. The influence of oxidants, especially potassium permanganate, on the behaviour and sensitivity of graphite membrane electrodes in the potentiometric acid—base and redox titrations is described.

Derivative polarographic titration of tertiary amines and salts of organic acids in acetic acid in the presence of antimony and quinhydrone electrodes

Abstract Derivative polarographic titration of some tertiary amines and salts of organic acids with perchloric acid in a mixture of glacial acetic acid and acetic anhydride, with two antimony or quinhydrone electrodes is described. The advantages of the method over potentiometric titration are that a sharper end-point is obtained and the use of a reference electrode and a salt bridge is avoided. The rather long time required for the titration of certain systems is a disadvantage. Quinhydrone electrodes give sharper titration end-points than antimony electrodes, but titrations with the latter can be accomplished more rapidly. The results obtained are in very good agreement with those obtained by potentiometric titration and afford excellent reproducibility.

The role of manganese(IV) compounds as oxidants : a review

A historical review of the development of manganese(IV) chemistry and its application in analytical chemistry is presented. A brief presentation of the presence and importance of manganese(IV) in other areas of chemistry is also given.

Coulometric determination of thiols and hydrazines with electrogenerated iodine in methanol in the presence of potassium acetate

SummaryConditions have been established for the quantitative electrochemical generation of iodine in methanol in the presence of potassium acetate. The conditional redox potentials of the iodine/iodide system in the same supporting electrolyte have been determined. With increasing concentration of potassium acetate in the solutions, the conditional redox potentials of the iodine/iodide couple were only negligibly decreased. In the presence of sodium perchlorate the redox potentials were noticeably increased. Anodically generated iodine has been applied to coulometric titration of thiols and hydrazines. The error of the determinations did not exceed ±2%.ZusammenfassungDie Bedingungen zur quantitativen elektrochemischen Erzeugung von Jod in Methanol in Anwesenheit von Kaliumacetat wurden untersucht. Das formale Redoxpotential des Systems Jod-Jodid wurde in der selben Grundlösung bestimmt. Durch Erhöhung der Konzentration des Kaliumacetats in der Lösung kommt es zu einer geringen Verminderung des Formalpotentials des Redoxpaares. In Anwesenheit von Natriumperchlorat sind die gefundenen Werte für das Redoxpotential bedeutend höher. Mit anodisch erzeugtem Jod wurden Thiole und Hydrazine bestimmt. Die erhaltene Fehlergrenze überschritt nicht ±2%.

Coulometric redox titrations of hydrazine, phenylhydrazine and isoniazid with electrogenerated lead(IV) acetate and manganese(III) acetate in acetic acid

SummaryThe conditions fox coulometric determination of small quantities of hydrazine, phenylhydrazine and isoniazid in glacial acetic acid with electrogenerated manganese(III) acetate and lead(IV) acetate were investigated. With the direct coulometric method at room temperature, good results were obtained in the determination of hydrazine and isoniazid with lead(IV) acetate and in the determination of phenylhydrazine with manganese(III) acetate. Hydrazine and isoniazid can also be determined by the coulometric back-titration method if the oxidation with manganese(III) acetate is performed at elevated temperature.ZusammenfassungDie Bedingungen für die coulometrische Bestimmung kleiner Mengen Hydrazin, Phenylhydrazin und Isoniazid mit elektrolytisch erzeugtem Mangan(III)-Acetat und Blei(IV)-Acetat in Eisessig wurden untersucht. Bei Zimmertemperatur wurden gute Resultate durch direkte coulometrische Titration des Hydrazins und Isoniazids mit Blei(IV)-Acetat und bei Titration des Phenylhydrazins mit Mangan(III)-Acetat erhalten. Durch coulometrische Rücktitration können bei höheren Temperaturen Hydrazin und Isoniazid mit Mangan(III)-Acetat erfolgreich bestimmt werden.

The growth of ADP crystals in the presence of manganese ions

Abstract Ammonium dihydrogen phosphate monocrystals have been grown in the presence of manganese(II) salts, permanganate and mixtures of the two. The concentration and oxidation state of the incorporated manganese ions have been determined. The corresponding effects on crystal habit, as well as kinetic data for growth of the {100} faces of monocrystals, were also studied.

Coulometric titrations of arsenic(III) and antimony(III) with electrically generated bromine in acetic acid

Abstract Conditions for the coulometric titrations were investigated. Arsenic(III) could be titrated by continuous or discontinuous generation of bromine, and antimony(III) by discontinuous generation or back-titration. The accuracy and reproducibility depend on the pretreatment of the platinum electrodes.

Electrogeneration, behaviour and applications of cobalt(III) in perchlorate solutions in acetic acid

Abstract Conditions for the electrochemical generation of cobalt(III) in acetic acid—perchlorate media were determined. The current efficiency depended on the current density at the working electrode and on the amounts of water or acetic anhydride in the solution. The stability of cobaltl(III) decreased with increasing content of water and perchloric acid in the solution, but increased with increasing content of acetic anhydride. The biamperometric system with the electrodes immersed in a solution of sodium perchlorate, cobalt(II) and cobalt(III) in acetic acid, in the presence of a definite amount of water, behaved as an electrochemical oscillator. Coulometric titration methods were developed for the determination of reducing substances with cobalt(III), the end-point being detected by the biamperometric and potentiometric methods. Errors in the determinations were less than ±2%.