Titrimetric determination of mercaptans with chloramine-T

Propyl mercaptan, allyl mercaptan, 2-mercaptoethanol, cysteamine hydrochloride, thio-p-cresol, 2-aminobenzenethiol, 2-mercaptopropionic acid and thioglycollic acid react with chloramine-T in 2:1 molar ratio in the presence of iodide, forming the corresponding disulphides. Mercaptans having a free beta-carbonyl group do not react quantitatively. The oxidation of the mercaptans is a function of time, and the corresponding sulphonic acids are formed on allowing them to stand with excess of chloramine-T. The oxidation to sulphonic acid is, however, instantaneous in the presence of iodine cyanide which acts as a catalyst and preoxidizer. This method is simple, accurate and rapid, and as little as 0.5 mg of the mercaptan can be determined with +/- 0.25% error.     

Titrimetric determination of mercaptans with potassium persulphate

Summary 2- and 3-Mercaptopropionic acids, thiomalic acid, 2-mercaptoethanol and propyl mercaptan have been determined by direct titration with potassium persulphate in the presence of iodide in acidic aqueous medium. These mercaptans react with the oxidant in 2 1 molar ratio forming corresponding disulphides. The reaction of thio-p-cresol, thioglycollic acid and thioacetic acid with persulphate is too slow to be followed titrimetrically. However, they are oxidised to disulphide when allowed to stand with excess persulphate for 2.0, 1.75 and 0.75 hours respectively. The reaction stoichiometry is not a function of time. 2- and 3-Mercaptopropionic acids, cysteamine hydrochloride, thiomalic acid, thioacetic acid and thioglycollic acid react with potassium persulphate in acidic medium in the presence of iodine cyanide which acts as preoxidiser and catalyst, in the molar ratio 1 3 forming corresponding sulphonic acids. As little as 0.50 mg of the mercaptan can be determined in 50 ml solution with ± 0.25 % error.

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Zusammenfassung Durch direkte Titration mit Kaliumpersulfat in Gegenwart von Jodid kann man in saurem Medium 2- und 3-Mercaptopropionsäure, Thiomalonsäure, 2-Mercaptoäthanol und Propylmercaptan bestimmen. Diese Thiole reagieren mit dem Oxydationsmittel im Molverhältnis 2 1 unter Disulfidbildung. Die Umsetzung von Thio-p-kresol, Thioglykolsäure und Thioessigsaure mit Persulfat verläuft für maßanalytische Zwecke zu langsam. Die genannten Verbindungen werden von überschüssigem Persulfat in 2,0, 1,75 bzw. 0,75 Stunden zu Disulfiden oxydiert. Die Stöchiometrie der Reaktionen ist zeitunabhängig. 2- und 3-Mercaptopropionsäure, Cysteaminchlorhydrat, Thiomalonsäure, Thioessigsäure und Thioglykolsäure reagieren mit Kaliumpersulfat in saurer Lösung in Gegenwart von Jodcyan, das als Voroxydationsmittel und Katalysator füngiert, im Molverhältnis 1 3 unter Bildung von Sulfonsäuren. Nur 0,25 mg Mercaptan in 50 ml Lösung sind mit ± 0,25% Fehler bestimmbar.

     

Titrimetric determination of some organic compounds with bromine chloride

Bromine chloride is used in hydrochloric acid medium as a standard reagent for the rapid and precise determination of organic compounds by direct or indirect titrimetric methods. Hydrazine and its aryl derivative undergo a 4-electron change. Carbonyl compounds are determined by reaction with excess of 2,4-dinitrophenylhydrazine and estimation of the surplus. Sulphanilamide undergoes a substitution reaction in 1:3 molar ratio to bromine chloride. Thiobarbituric acid and thiourea or its alkyl derivatives show an 8-electron change but aryl thioureas also undergo nuclear bromination. Thiosemicarbazide and semicarbazide give a 10- and a 2-electron change respectively. In the direct titration, methionine is oxidized to its sulphoxide whereas cystine and cysteine form cysteic acid. In presence of bromide, glutathione forms the sulphonic acid but in the presence of iodide the product is the disulphide. The analytical results obtained by bromine chloride method are compared favourably with those afforded by established procedures.     

Titrimetric determination of silver,chloride and bromide in glasses

Titrimetric methods are described for the determination of total silver, free silver or free halide (Cl, Br and I), and bromide (or iodide) in glasses. Total silver is titrated potentiometrically with standard bromide solution after hydrofluoric—sulfuric acid sample decomposition followed by sodium hydrogensulfate fusion for volatilizing hydrogen halide. Free silver is determined similarly on a separate sample without the fusion step. For glasses containing excess of halide, free halide is titrated potentiometrically with standard silver(I) solution after dissolution of the sample in ice-cold hydrofluoric—nitric acid. Total bromide (or iodide) is determined by iodometric titration after oxidation to bromate (or iodate) with hypochlorite solution. The methods have been applied to a wide range of complex glass compositions and results are compared with values obtained by controlled-potential coulometry and x-ray fluorescence analysis.     

Titrimetric determination of thallium

Summary Titrimetric determination of thallium(I) is carried out by treating the sulfate with reducing sugars in alkaline medium either at room temperature or by boiling. The metal obtained is oxidised with an excess of ferric ammonium sulphate at room temperature. The ferrous ion formed, corresponding to the thallium metal oxidised, is titrated against a standard solution of ceric sulphate using N-phenyl anthranilic acid as indicator. Metallic thallium has been observed to exist in three varieties under different conditions. The presence of potassium chloride protects the metal from aerial effects. Li⁺, Ca²⁺, Sr²⁺, Ba²⁺, Mg²⁺, Cd²⁺, Zn²⁺, Be²⁺, Ni²⁺, Co²⁺, Al³⁺, and Zr⁴⁺ interfere with the determining but Pb²⁺ and Th⁴⁺ do not.

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Zusammenfassung Zur maßanalytischen Bestimmung von Thallium(I) behandelt man zunächst dessen Sulfat in alkalischem Medium mit reduzierenden Zuckern bei Raumtemperatur oder im Sieden. Das dabei entstandene elementare Metall wird mit überschüssigem Eisen(III)-ammoniumsulfat bei Raumtemperatur oxydiert und die äquivalente Menge Eisen(II) mit einer Standardlösung von Cersulfat gegen N-Phenylanthranilsäure als Indikator titriert. Metallisches Thallium liegt je nach den vorliegenden Bedingungen in drei verschiedenen Formen vor und wird durch Kaliumchlorid gegen Lufteinwirkung geschützt. Li⁺, Ca²⁺, Sr²⁺, Ba²⁺, Mg²⁺, Cd²⁺, Zn²⁺, Be²⁺, Ni²⁺, Co²⁺, A1³⁺ und Zr⁴⁺ stören die Bestimmung im Gegensatz zu Pb²⁺ und Th⁴⁺.

     

Titrimetric determination of hydrazines with sulfatoceric acid

Titrimetric methods for the determination of hydrazine and some simple alkyl and aryl derivatives are described. Iodine monochloride serves as pre-oxidant and indicator, and sulfatoceric acid as the titrant. Mercury(II) is added to ensure complete oxidation of some compounds.     

Semimicro determination of mercaptans with copper(II)

A rapid and precise titrimetric method for the determination of mercaptans on the semimicro scale is described. Samples dissolved in water, methanol. dimethylformamide or acetonitrile are treated with a measured excess of cupric sulphate. After 1 min, the excess of copper(II) is back-titrated with standard mercaptoacetic acid solution. At the end-point the violet complex first formed changes to a permanent yellow. The method is applicable to a variety of mercaptans and accurate to 0.2%. It is relatively free from interferences.     

Titrimetric determination of gold by precipitation with hydroquinone

A rapid method for the volumetric determination of gold is described. Gold(III) is reduced to metal with excess of hydroquinone at room temperature and the excess is titrated with ceric sulphate. The effect of chloride ion on the reducibility of gold(III) to the metal is discussed. This method can be successfully employed for the determination of gold in presence of certain base and noble metals. The method was successfully adopted for the determination of gold in a commercial sample.     

Titrimetric determination of aminobenzoic acids

A novel titrimetric method for determination of aminobenzoic acids is based on their reaction with excess of bromine to form N-bromo-2,4,6-tribromoaniline, which liberates an equivalent amount of iodine when treated with iodide. The method is applicable to the aminobenzoic acids in the range 0.1-5.0 mg, with a recovery ranging from 96 to 99.7% and a coefficient of variation of 0.2-2.0%, depending on the concentration level.     

Titrimetric determination of chloramphenicol in pharmaceuticals

The simple titrimetric procedure to be described is based on acid hydrolysis of chloramphenicol and quantitative oxidation of the product by potassium dichromate in one step.     

Titrimetric determination of some phenothiazine derivatives, with ferricyanide

Six phenothiazine drugs (chlorpromazine hydrochloride, promethazine hydrochloride, promazine hydrochloride, perphenazine, acetophenazine maleate and trifluoperazine hydrochloride) have been determined by titration with potassium ferricyanide in phosphoric acid medium with Methylene Blue as a screening indicator. The results were in agreement with those obtained by the official methods.