Determination of some steroidal bases in non-aqueous media by potentiometric titrations at a small constant current

In this work the volumetric and coulometric titrations of some newly synthesized androstene steroidal compounds with pyridine ring are carried out. The titrations were followed potentiometrically at a small constant current using pairs of identical platinum or glassy carbon electrodes, both in presence of quinhydrone. As the titration reagent, in volumetric titrations served 0.01 mol dm^?3 perchloric acid, and in coulometric titrations hydrogen ions were anodically generated in situ from quinhydrone at the platinum electrode. Sodium perchlorate served as the supporting electrolyte.Amounts of 1.18-5.35 mg of the investigated steroidal compounds were determined with a relative standard deviation less than 1.4% at volumetric and 1.2% at coulometric determinations. A negative influence of the supporting electrolyte on magnitude of the signal change in potentiometric determinations was observed. Glassy carbon electrodes are more advantageous over platinum ones.The achieved results are in good agreement with those of catalytic thermometric titrations.     

Coulometric titration of bases in acetic acid and acetonitrile media

The working conditions and the results for coulometric titration of milligram amounts of some bases in 0.1M sodium perchlorate in a mixture of acetic acid and acetic anhydride (1:6), are given. Determinations were made both by coulometric back-titration or direct titration at the platinum anode. Back-titration was done in the catholyte, by coulometric titration of the excess of added perchloric acid. The titration end-point was detected photometrically with Crystal Violet as indicator. The direct titration of bases was done at the platinum anode, in the same electrolyte, to which hydroquinone was added as anode depolarizer and as the source of hydrogen ions, Malachite Green being used as indicator. Similarly, bases can be determined in acetonitrile if sodium perchlorate, hydroquinone and Malachite Green are added to the solvent. Errors are below 1 %, and the precision is satisfactory.     

Coulometric-acidimetric titrations in anhydrous acetic acid

A technique for the coulometric generation of hydrogen ions in an acetic acid-acetic anhydride-sodium perchlorate electrolyte by anodically oxidizing a mercury electrode is described. Accurate coulometric titrations of sodium acetate and potassium hydrogen phthalate have been carried out. The technique should be applicable to many of the basic substances which can be titrated volumet-rically in acetic acid.     

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.     

Anodically generated cobalt(III) acetate as reagent for coulometric titrations in acetic acid

Summary Conditions for the anodic generation of cobalt(III) acetate with high current efficiency in non-aqueous solutions of potassium acetate in acetic acid have been investigated. The presence of water or acetic anhydride in the anolyte diminishes the amount of the generated oxidant. The stability of the generated cobalt(III) acetate solution is decreased in the presence of water and at elevated temperatures. Procedures for coulometric titrations of reducing substances with cobalt(III) acetate, using the biamperometric or the potentiometric end point detection, are described.Presented at the Fifth European Conference on Analytical Chemistry-EUROANALYSIS V, Cracow, Poland, August 26–31, 1984.     

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.     

Biamperometric end-point detection with quinhydrone electrodes in coulometric neutralization titrations in nonaqueous media

Some new possibilities for continuous coulometric titration of bases, alone and in mixture, as well as of mineral acids, alone and in mixture, were investigated with acetic anhydride-anhydrous acetic acid as solvents. The titration end point was determined biamperometrically. It was established that quinhydrone electrodes with platinum, palladium, and gold as the metal phase can be equally satisfactorily applied to the end-point determination of both the titrations of bases or acids alone, and of their two-component mixtures. Amounts of 6–10 μequiv. of bases, i.e., 20–47 μequiv. of mineral acids, were determined with the maximal average deviation of 1.4%. Results of biamperometric determinations of bases are compared to those of catalytic thermometric determinations, while those of acids are compared with the results of photometric titrations. The agreement between the methods is satisfactory.     

Coulometric generation of H+ ions by oxidation of thiols at a platinum anode and by oxidation of mercury in acetic acid—acetic anhydride

The coulometric generation of hydrogen ions by anodic oxidation of propane-1-thiol, butane-1-thiol, 2-mercaptopropionic acid, heptane-1-thiol, 2-mercaptoethanol, methyl and ethyl thioglycollate and p-thiocresol in acetic acid—acetic anhydride (1 + 6 v/v) is described, together with the possibility of coulometric generation of protons by mercury oxidation in the presence of p-thiocresol in the same solvent system.Current-potential curves for the solvent, indicator, titrated bases, mercury and the investigated thiols showed that in acetic acid—acetic anhydride (5 + 95, v/v), mercury and the investigated thiols are oxidized at potentials which are much more negative than those of the titrated bases and other components present in the solution.Titration of potassium hydrogenphthalate and sodium acetate with protons generated by the oxidation of thiols, and of sodium acetate, lithium acetate and pyridine with protons generated by the oxidation of mercury, demonstrated that the oxidation of both thiols and mercury proceeds quantitatively with 100% current efficiency.     

Determination of total free acid in formaldehyde by coulometric catalytic thermometric titration

Coulometric catalytic thermometric titration of the total free acid (HCOOH) in formaldehyde of various manufacturers was successfully performed. The indicator reaction was the exothermic polymerization of formaldehyde in the presence of ethanol, catalyzed by strong base. In the titrations, a cathodically polarized platinum generator electrode was employed. The content of free acid in various formaldehyde samples ranged between 0.018 and 0.044 %, and was determined with a standard deviation less than 1.5%. Good agreement was obtained with the results of coulometric photometric and volumetric titrations.     

1-Acyl-3-arylazoindoles in the synthesis of indolo[1,2-c]quinazolines

Treatment of 1-aeyl-3-arylazoindoles with zinc in acetic acid in the presence of acetic anhydride and sodium acetate leads to 12-acetamidoindolo [1,2-c]quinazolines. 12-Aminoindolo[1,2-c]quinazolines are obtained when the reaction is carried out in the absence of acetic anhydride and sodium acetate.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 377–379, March, 1977.     

Electrochemical generation of manganese(III) and behaviour of the generated oxidant in acetic acid in the presence of perchlorate ions

Summary Research was carried out to determine conditions for the anodic generation of manganese(III) with high current efficiency in solutions of sodium perchlorate in acetic acid, and to examine the behaviour of the oxidant thus generated. The effects of water and acetic anhydride on current efficiency in the generation of the oxidant was also examined. The formal redox potential of the Mn(III)/ Mn(II) system is decreased with increasing concentrations of sodium acetate in the solution. The effect of sodium perchlorate and perchloric acid concentrations is the reverse. Procedures for coulometric titrations of a number of substances with the generated oxidant were developed, end point being detected using biamperometric and potentiometric methods. Perchloric acid accelerates the oxidation of certain substances with manganese(III) in acetic acid and increases the sensitivity of end-point detection using the potentiometric method.

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Elektrochemische Erzeugung von Mangan(III) und das Verhalten dieses Oxydationsmittels in Essigsäure bei Gegenwart von Perchlorat

Zusammenfassung Die Bedingungen der anodischen Erzeugung von Mangan(III) mit hoher Stromausbeute in Essigsäure, nach Zugabe von Natriumperchlorat wurden untersucht; das elektrochemische Verhalten des so dargestellten Oxydationsmittels wurde ebenfalls untersucht. Der Einfluß von Wasser und Essigsäureanhydrid auf die prozentuelle Stromausbeute des erwähnten Oxydationsmittels wurde verfolgt. Das Formalredoxpotential des Systems Mn(III)/ Mn(II) sinkt bei Erhöhung der Konzentration an Natriumacetat in der Lösung. Perchlorsäure wie auch Natriumperchlorat üben eine entgegengesetzte Wirkung aus und führen zur Steigerung des Formalredoxpotentials bei Erhöhung ihrer Konzentration. Verfahren zur coulometrischen Titration verschiedener Substanzen mittels biamperometrischer oder potentiometrischer Erfassung des Titrationsendpunktes wurden ausgearbeitet. In Gegenwart von Perchlorsäure wächst die Geschwindigkeit der Oxydation einiger Substanzen in Essigsäure in Gegenwart von Mn(III) und auch die Empfindlichkeit der Endpunktbestimmung verbessert sich.

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Presented at the 9th International Symposium on Microchemical Techniques, Amsterdam, August 28–September 2, 1983.     

Quantitative anodic generation of cobalt (III) at glassy carbon in acetic acid. Coulometric titrations with the generated reagent

Conditions are established for quantitative electrochemical generation of cobalt (III) at a glassy carbon working electrode in anhydrous acetic acid in the presence of potassium acetate, sodium acetate or sodium perchlorate. In anhydrous alkali-metal acetate solutions cobalt (III) is as stable as in the presence of acetic anhydride. The concentration of cobalt(III) in the solution is considerably decreased in the presence of small amounts of water. This phenomenon is much more pronounced in sodium perchlorate supporting electrolyte. Coulometric titration methods for the determination of hydroquinone, 2-methylhydroquinone and ascorbic acid with the generated oxidant have been developed. The errors of the determinations are less than ±2%.     

Rearrangement of the benzidine type in the indole series

12-Acetamidoindolo[1,2-c]quinazolities were obtained by treatment of 3-arylazoindoles with zinc in acetic acid in the presence of acetic anhydride and sodium acetate. The products were converted to the corresponding amines by hydrolysis.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1096–1098, August, 1975     

Antianexiety activity of pyridine derivatives synthesized from 2-chloro-6-hydrazino-isonicotinic acid hydrazide

A series of oxadiazole pyridine derivatives were synthesized by using 2-chloro-6-hydrazinoisonicotinic acid hydrazide as starting material. Treatment of the hydrazide with carbon disulfide to afford the oxadiazole derivative, which was treated with 5-methyl-2-furancarbaldehyde, formic acid, acetic acid/acetic anhydride, or phthalic anhydride to yield the corresponding pyridinodiazoles and on imide. Condensation of the hydrazide with p-fluorobenzaldehyde in ethanol or acetic acid in the presence of sodium acetate afforded hydrazone and oxadiazole derivatives, which were acetylated and cyclized with acetic anhydride to N-acetyloxadiazole derivatives. The hydrazone was treated with acetic acid in the presence of sodium acetate, or bromine water/sodium acetate to give on oxadiazole, while it was cyclized with chloroacetyl chloride in the presence of TEA to oxoazetidinaminoisonicotinamide. Finally, condensation of the hydrazide with acid anhydrides in refluxing glacial acetic acid afforded the corresponding bisimide derivatives. The pharmacological screening showed that many of these obtained compounds have good antianexiety activity comparable to diazepam^® as positive control.     

Biamperometric neutralisation titrations in non-aqueous solvents applying tin electrode pair for the end-point detection

Summary Tertiary amines and salts of organic acids in acetic anhydride with 5% of acetic acid were titrated applying a biamperometric indicating system consisting of a polarised or unpolarised pair of tin electrodes by means of 0.1 N perchloric acid in glacial acetic acid. Amounts of 15.4–29.8 mg were analysed with average deviations of <0.6%, the results obtained being in a good agreement with those of potentiometry. The biamperometric end-point detection using an indicating system of polarised pair of tin electrodes can be applied for coulometric determinations of these bases with satisfying accuracy. By means of anodic generation of hydrogen ions in the presence of hydroquinone amounts of 0.5–1.0 mg were titrated with average deviations of < 1.3%. The results obtained were compared with those obtained of catalytic thermometric and photometric titrations.

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Biamperometrische Neutralisationstitrationen in nichtwärigen Lösungsmitteln unter Anwendung eines Zinn-Elektrodenpaares als Indicatorsystem

Zusammenfassung Tertiäre Amine und Salze organischer Säuren werden in Acetanhydrid mit 5% Essigsäure durch Titration mit einer 0,1 N Lösung von Perchlorsäure in Essigsäure bestimmt. Das verwendete biamperometrische Indicatorsystem besteht aus einem Paar polarisierter oder nichtpolarisierter Zinnelektroden. Mengen von 15,4–29,8 mg wurden mit einer mittleren Abweichung von <0,6% analysiert. Die Ergebnisse stimmen gut mit denen von potentiometrischen Titrationen überein. Die biamperometrische Endpunkttechnik mit polarisierten Zinnelektroden kann für coulometrische Bestimmungen dieser Basen mit zufriedenstellender Genauigkeit benutzt werden. Durch anodische Erzeugung von Wasserstoffionen in Gegenwart von Hydrochinon wurden Mengen von 0,5–1,0 mg mit einer mittleren Abweichung von < 1,3% titriert. Die Ergebnisse wurden mit denen von katalytisch-thermometrischen und photometrischen Titrationen verglichen.

     

Catalytic Thermometric Titrations of Various Mixtures of Nitrogen Bases

The reactions of acetylation of hydroquinone and quinhydrone with acetic anhydride, catalysed by perchloric acid, were used to determine the end point of catalytic thermometric titrations of a number of different amines and amides dissolved either in acetic anhydride or in acetic acid-acetic anhydride (10+1) mixture. In the majority of cases primary and secondary amines could be successfully determined if pKb_b≤9.3, tertiary amines if pK_b≤14, and amides if pK_b≤l5. Thanks to the difference in behaviour of organic bases in acety lation reaction, it was possible in some instances to determine selectively the individual bases in their mixtures. Catalytic titrations appeared to be especially suitable for the determination of extremely weak bases, even in the case of using mixtures of organic solvents, when Potentiometrie titrations could not be employed. Amounts of 2.5·10^?6-8·10^?5 mole of bases were determined with a maximal relative standard deviation less then 2%.     

Peculiarities of the chemical properties of vicinally disubstituted veratrole and synthesis of 1-methyl-4,5-dimethoxybenzimidazole derivatives

Various paths for the synthesis of 4-methylamino-3-aminoveratrole (I) from 4-amino-3-nitroveratrole (II) were investigated, and it was found that I can be obtained in a high overall yield of 65% through the tosyl derivative of II. 1-Methyl-4,5-dimethoxybenzimidazolone, 1-methyl-4,5-dimethoxybenzimidazole and its 2-phenyl-, 2-chloro-, and 2-dimethylamino derivatives were synthesized on the basis of I in order to investigate their biological activity. It was established that the chemical properties of vicinally disubstituted veratrole, particularly the increased basicity of II, are determined to a significant degree by steric strains caused by bulky substituents. It is shown that 85% formic acid can be successfully used in place of 98–100% formic acid for the N-formylation of aromatic amines with a mixture of formic acid and acetic anhydride.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1387–1392, October, 1970.     

Potentiometric titration of peptides and the starting materials and intermediates of their synthesis. I. Acidimetric determination of N-acetylamino acids

The potentiometric titration of N-acetylamino acids and their sodium salts in nitromethane-acetic anhydride (2:1) with a nitromethane solution of perchloric acid has been investigated. A procedure has been developed for the quantitative determination of N-acetylamino acids in the presence of acetic acid in aqueous solutions. A differentiation determination of N-acetylamino acids and their salts in the presence of sodium acetate has been carried out.All-Union Scientific-Research Institute of Applied Biochemistry, Biolar Scientific-Industrial Association, Olaine. Translated from Khimiya Prirodnykh Soedinenii, Vol. 6, pp. 830–834, November–December, 1989.     

Catalytic acetylation of flavonoids

Conclusions On catalytic acetylation in the presence of magnesium perchlorate, flavonoids do not react with the catalyst. The highest yield of product was found when using the smallest amount of acetic anhydride (1 · 10^–1 mole per 1 · 10^–3 mole of quercetin) and 3 · 10^–4 mole of Anhydrone.Khimiya Prirodnykh Soedinenii, Vol. 6, No. 4, pp. 418–421, 1970     

Efficient One-Step Conversion of Tetrahydropyranyl Ethers into Acetates and Formates in the Presence of Potassium Dodecatungstocobaltate K<Subscript>5</Subscript>CoW<Subscript>12</Subscript>O<Subscript>40</Subscript> · 3H<Subscript>2</Subscript>O

Tetrahydropyranyl ethers derived from primary alcohols were directly and efficiently converted into the corresponding acetates and formates by the action of ethyl acetate, acetic acid, acetic anhydride, and ethyl formate in the presence of a catalytic amount of potassium dodecatungstocobaltate K₅CoW₁₂O₄₀ · 3H₂O. Tetrahydropyranyl ethers derived from secondary alcohols and phenols can also be transformed into the corresponding acetates with the use of acetic anhydride, but K₅CoW₁₂O₄₀ · 3H₂O was ineffective for esterification with ethyl acetate, acetic acid, and ethyl formate.__________From Zhurnal Organicheskoi Khimii, Vol. 41, No. 3, 2005, pp. 403–405.Original English Text Copyright © 2005 by Rafiee, Tangestaninejad, Habibi, Mohammadpoor-Baltork, Mirkhani.The original article was submitted in English.