Sameer Bose

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.

Determination of thiol groups with o-diacetoxy-iodobenzoate

o-Diacetoxyiodobenzoate is used for determining thiol groups by two procedures. In the first, thiols are titrated directly with the reagent at pH 6-8, with leuco-2,6-dichlorophenolindophenol and potassium iodide as indicator. In the second, thiols are treated at pH 7 with an excess of the reagent, the surplus being determined by reaction with excess of mercaptoacetic acid followed by back-titration of the latter with iodine. Both procedures yield results within 0.2% of the theoretical.

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.

Determination of cysteine, 3-mercaptopropionic, and mercaptosuccinic acid with neutral hexacyanoferrate(III)

Two procedures are proposed for the determination of -SH groups. In both a known amount of hexacyanoferrate(III) is added to the sample and the excess is then determined. In one procedure an excess of ascorbic acid is added and the excess of that is titrated with iodine. In the other, the excess is determined by direct titration with ascorbic acid. Both procedures avoid errors resulting from side-reactions of iodine which takes place if the excess of hexacyariofcrrate(III) is reacted with potassium iodide.

Determination of thiourea and its organic derivatives with iodine trichloride

Thiourea and its organic derivatives and thiosemicarbazide are determined in water, methanol or glacial acetic acid medium by reaction with an excess of iodine trichloride in the presence of mercuric chloride. The reaction is complete in 15 min. The excess of iodine trichloride is evaluated by adding potassium iodide and titrating the liberated iodine with thiosulphate. A variety of organic thioureas can be determined with an average accuracy and precision of 0.2%.

Detection of aromatic amines using lead tetraacetate as the reagent

SummaryIntense colors are immediately produced when primary, secondary and tertiary aromatic amines are reacted with lead tetraacetate in glacial acetic acid, methanol, acetonitrile, benzene or dioxane. This color reaction forms the basis of a rapid spot test for the detection of aromatic amines.ZusammenfassungPrimäre, sekundäre und tertiäre aromatische Amine reagieren mit Bleitetraacetat in Eisessig, Methanol, Acetonitril, Benzol oder Dioxan unter sofortiger intensiver Farbbildung. Auf der Grundlage dieser Reaktion lassen sich aromatische Amine rasch auf der Tüpfelplatte nachweisen.

Titration of thiol groups with cupric ion

Procedure. Take an aliquot of sample dissolved in water or dimethylformamide containing 0.1-0.3 meq of mercaptan in a 150-ml Erlenmeyer flask. Add 25 ml of water, 1 g of potassium iodide and 1 ml of 1 ~ starch solution. Titrate with 0.02 M solution of cupric sulphate taken in a 10-ml burette (graduated at 0.02 ml). Shake the solution vigorously during titration. At the end point a blue colour is formed. Under the described conditions of titration no cuprous mercaptide is formed. Cuprous iodide precipitates during the course of titration.

Determination of formates by oxidation with iodine

Abstract A selective determination of formates based on oxidation with iodine at 100° in presence of potassium hydrogen tartrate, and final titration with thiosulphate solution, is described. The error is below 0.5% for 25–90 mg of formic acid. Few other organic acids interfere.

Milligram amount determination of thiol groups with ferricyanide. Use of 2,6-dichlorophenolindophenol as titrant

SummaryThiols are reacted at pH 7 with an excess of ferricyanide. The excess of reagent is determined by adding a measured excess of ascorbic acid followed by back titration of ascorbic acid with 2,6-dichlorophenolindophenol. A correction can be made for ascorbic acid, if present with thiols. Tested with dilute solutions of cysteine, glutathione, mercaptoacetic acid and some other water-soluble thiols gave results which are accurate to 0.1%. Glycine, cystine, methionine, etc. do not interfere.ZusammenfassungThiole reagieren bei pH 7 mit überschüssigem Cyanoferrat (III). Der Überschuß läßt sich durch Zusatz einer gemessenen Menge Ascorbinsäure und deren Rücktitration mit 2,6-Dichlorphenolindophenol bestimmen. Ist neben Thiol bereits Ascorbinsäure zugegen, so ist eine entsprechende Korrektur anzubringen. Die Anwendung auf Lösungen von Cystein, Glutathion, Mercaptoessigsäure und einigen anderen wasserlöslichen Thiolen erbrachte auf 0,1% genaue Ergebnisse. Glycin, Cystin, Methionin usw. stören nicht.