R. Mihajlović

Coulometric generation of protons by oxidation of hydrogen dissolved in palladium, in non-aqueous media

Coulometric generation of H(+) ions by the oxidation of hydrogen dissolved in palladium, in media such as acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, acetic anhydride and acetic acid-acetic anhydride mixture, for use in titration of bases, has been investigated. The hydrogen is oxidized at potentials which are much more negative than those of the bases and other components present in the solution. Titrations of numerous bases have established that the oxidation is quantitative and proceeds with 100% current efficiency.

Coulometric titration of salts of strong mineral acids in acetic anhydride by application of a hydrogen/palladium electrode

The application of H2/Pd electrodes as generator and indicator electrodes is described for coulometric titrations of alkali metal halides and trivalent metal sulphates in acetic anhydride with potentiometric end-point detection. In acetic anhydride, sodium fluoride is a strong enough base to be titrated directly with H+ ions obtained by anodic oxidation of hydrogen dissolved in palladium. Other halides (NaCl, KCl, LiCl, KBr and NaBr) can be determined, after reaction of halides with mercury (II) acetate, by coulometric titration of the liberated base. Potentiometric end-point detection with a H2/Pd-mercury(I) acetate electrode pair is satisfactory. Sulphates of Fe(III), Cr(III) and Al(III) are determined by back-titrating the excess of barium acetate after precipitation of barium sulphate. The errors in these determinations are < 1% for concentrations ranging from 0.001 to 0.003 M.

Natural monocrystalline pyrite as a sensor in non-aqueous solution: Part I: Potentiometric titration of weak acids in, N,N-dimethylformamide, methylpyrrolidone and pyridine

The possibility of applying natural monocrystaline pyrite as a sensor for the potentiometric titration of weak acids in N,N-dimethylformamide, methylpyrrolidone and pyridine was investigated. The potential of this electrode in N,N-dimethylformamide, methylpyrrolidone and pyridine exhibits a sub-Nernst dependence. In N,N-dimethylformamide the slope (mV/pH) is 39.0 and in methylpyrrolidone it is 45.0. The potential jumps at the titration end-point obtained in the titration of weak acids are higher than those obtained by the application of a glass electrode as the indicator electrode The potential in the course of the titration and at the titration end-point (TEP) are rapidly established. Sodium methylate, potassium hydroxide and tetrabutylammonium hydroxide (TBAH) proved to be very suitable titrating agents for these titrations. The results obtained in the determination of the investigated weak acids deviate by 0.1-0.35% with respect to those obtained by using a glass electrode as the indicator electrode.

Natural monocrystalline pyrite as electrode material for potentiometric titrations in water

The possibility of applying natural monocrystalline pyrite as sensor for the potentiometric titration of acids in water was investigated. The potential of this electrode in aqueous solutions exhibits a sub-Nernst dependence. In fresh solutions the slope (mV/pH) is 33.9. The potential jumps at the titration end-point obtained in titrations of HCl, H(3)PO(4) and CH(3) COOH do not differ much from those obtained by the application of the glass electrode as the indicator one. The potentials in the course of the titration and at the titration end-point (TEP) are rapidly established. The results obtained in the determination of the investigated acids deviated for 0.16-0.34% with respect to those obtained by using the glass electrode as the indicator one.

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%.

Application of hydrogen—palladium and deuterium—palladium electrodes in the coulometric—potentiometric determination of bases in some dipolar aprotic solvents

The application of H2Pd and D2Pd electrodes as indicator, generator and reference electrodes in coulometric—potentiometric titrations of bases in acetonitrile, benzyl cyanide, nitromethane, ethylene carbonate and sulfolane, was investigated. Current—potential curves for hydrogen and deuterium dissolved in palladium, titrated bases, indicator and solvents show that hydrogen and deuterium are oxidized at potentials which are more negative than those of the titrated base and other components present in the solution. The generated H+ and D+ ions were used for the titration of organic bases (tributylamine, collidine, 2,2-bipyridine, cyclohexylamine, N,N-diphenyl guanidine, butylamine and quinoline) with visual and potentiometric titration end-point detection. The current efficiency was 100%. H2Pd and D2Pd electrodes were applied as indicator and reference electrodes.

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

Abstract Coulometric generation of acetyl (CH 3 CO + ) 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.

Coulometric generation of hydrogen ion by anodic oxidation of ascorbic acid and naphthohydroquinones in acetonitrile and in acetic acid-acetic anhydride

Abstract Coulometric generation of hydrogen ions by the oxidation of ascorbic acid, 1,4-naphthohydroquinone and 2,6-naphthohydroquinone in anhydrous acetonitrile and in acetic acid-acetic anhydride is described. Current—voltage curves for solvents, indicator, titrated bases and depolarizer show that all three depolarizers are oxidized at potentials more negative than those of bases and other components in the solution. Titrations of sodium acetate and potassium hydrogenphthalate in acetic acid-acetic anhydride (1:6), and of triethanolamine, p -toluidine and γ-picoline in acetonitrile, with hydrogen ions generated at a platinum anode by the oxidation of these depolarizers, proved that ascorbic acid and 1,4-naphthohydroquinone are successful. With ascorbic acid, the current efficiency was 100 ± 0.3%.

Potentiometric determination of pKA of organic bases in acetone by the application of coulometry

A coulometric-potentiometric method for the determination of pK(A) values of organic bases in anhydrous acetone is described. The bases were titrated with protons obtained by anodic oxidation of hydrogen dissolved in palladium, in the presence of sodium perchlorate as the supporting electrolyte. A pair of glass electrodes was used for measuring directly the difference between the half-neutralization potentials of the standard and the base being studied. The pK(A) values obtained were close to those reported in the literature. The effect of the supporting electrolyte concentration on the pK(A) values of some of the bases was also studied.

Coulometric generation of hydrogen ions by anodic oxidation of some organic compounds in nitromethane, sulpholane, acetonitrile and acetic acid-acetic anhydride

Abstract The coulometric generation of hydrogen ions by anodic oxidation of cyclohexa-1,4-diene, cyclohexa-1,3-diene, 9,10-dihydroanthracene, cyclohexene and 1,2,3,4-tetrahydronaphthalene in acetonitrile and acetic acid—acetic anhydride (1 + 6, v/v) is described. The coulometric generation of protons by anodic oxidation of 2,3,4-trihydroxybenzoic acid, some dihydric and trihydric phenols and esters of gallic acid, in nitromethane and sulfolane as solvents is also reported. The current—potential curves recorded for these depolarizers, the titrated bases, indicators and solvents showed that the investigated depolarizers are oxidized at more negative potentials than the oxidation potentials of the titrated bases and other components present in the solution. The generated hydrogen ions were used for the titration of some organic bases ( p -toluidine, triethanolamine, sodium acetate, potassium hydrogenphthalate, pyridine, piperidine, tributylamine, collidine and 2,2′-bipyridine) with visual and potentiomeric end-point detection. The current efficiency was 100% for dienes, 2,3,4- and 3,4,5-trihydroxybenzoic acid, phenols and esters of gallic acid.