Ashutosh Srivastava

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 sulphur functions with N-iodosuccinimide.

Titrimetric determination of thioureas, thiols, xanthates and dithiocarbamates with N-iodosuccinimide (NIS) is described. The method for xanthate can be applied to carbon disulphide (converted into xanthate with potassium ethoxide). Acidic and non-aqueous solutions of the oxidizing agent are stable. The procedures are rapid and accurate to 0.1% with a precision of 0.2%. Hydrogen sulphide and thiocarbonyl compounds interfere. The behaviour of N-bromosuccinimide and NIS with thiols in aqueous medium is compared. It is shown that iodine is the oxidizing species in both cases. The limitations of iodine as a reagent for thiol determination are discussed. Cysteine, which cannot be determined with iodine, can be determined with NIS. The role of methanol in non-aqueous determination of thiols is discussed. Methanol accelerates the oxidation, which is otherwise slow in acetonitrile medium.

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.

Determination of vitamin C in chemical, pharmaceutical and biological samples by spectrophotometric titrimetry with o-diacetoxyiodobenzoate. Analysis of mixtures of vitamin C with methionine and cysteine or glutathione

A method has been developed for the determination of vitamin C in pharmaceutical preparations, foodstuffs and biological fluids based on titrimetry with o-diacetoxyiodobenzoate (o-DIB) with spectrophotometric (λmax. 600 nm) or visual detection of the end-point using leuco-2,6-dichlorophenolindophenol and potassium iodide as indicator. Sulphur-containing amino acids such as cysteine and glutathione interfere quantitatively and can be masked by cyanoethylation; the cyanoethylated product and methionine have also been determined with o-DIB in the presence of acidified potassium bromide with methyl red as indicator. Procedures are given for the analysis of mixtures of vitamin C with sulphur-containing amino acids. The effect of a number of interferents has also been studied.

Determination of organotrithiocarbonates with o-diacetoxyiodobenzoate and N-chlorosuccinimide in aqueous and non-aqueous media

The determination of organotrithiocarbonates with o-diacetoxyiodobenzoate and N-chlorosuccinimide in aqueous and non-aqueous media using visual and potentiometric methods is described. The visual end-point is indicated by a sharp colour change from straw yellow to deep yellow caused by the first drop of oxidant solution in excess. Potentiometric titrations were performed with antimony or modified calomel reference electrodes and a bright platinum wire as the indicator electrode. The proposed method is simple, rapid, requires the minimum of apparatus and is also applicable to the determination of β-carboxythiols, 1-thioglycerol and carbon disulphide.

RETRACTED ARTICLE: Determination of sulpha drugs and ascorbic acid, individually or in mixture, withN-chlorosuccinimide

New spectrophotometric and titrimetric methods for the determination of sulphonamides withN-chlorosuccinimide (NCS) were developed. The spectrophotometric measurements can be made at 324–395 nm at pH 7.4 at room temperature, the stoichiometry being 1: 2, (p-H2N-C6H4-SO2NHR): (NCS) forming a dibromination product in presence of acidified potassium bromide. Potentiometrically or visually using methyl red as indicator, sulphonamides are titrated in pharmaceutical preparations by NCS always in presence of acidified potassium bromide. Ascorbic acid is determined alone and also in combinations, by first titrating it using potassium iodide and starch or 2,6-dichlorophenolindophenol as indicator. Acylation or diazotization of the aromatic amino groups that prevents substitution at the two ortho positions, is used as additional prereaction to analyze various binary and ternary mixtures of certain sulphonamides. These methods are accurate, simple, rapid, reproducible, useful at higher concentrations, do not involve any preseparation, and can tolerate several compounds that cause interference in other methods.

Determination of sulphur functions with iodoso-compounds

Iodoso derivatives, e.g., m- and p-chlorophenyl, m- and p-methylphenyl and p-nitrophenyl-iodosoacetates and o-diacetoxyiodobenzoate, have been thoroughly investigated as oxidants and are proposed as analytical reagents for the determination of thiols, thioureas, isothiocyanates, organic sulphides, disulphides, xanthates, dithiocarbamates, amines and alcohols in aqueous and non-aqueous (acetic acid, acetonitrile, dimethylformamide) media. The error of the determination of thiols is 0.2% thioureas 0.5%, organic sulphides and disulphides 0.4%, isothiocyanates 0.4%, dithiocarbamates 0.4%, and xanthates 0.5%. All the methods are precise to 0.2-0.5%. It is also shown that the properties of the o-derivatives differ markedly from those of the m- and p-derivatives. The o-derivatives contain a 1-substituted 1,2-benzoiodoxilin-3-one ring system. The stability of this system is apparently associated with the size of the five-membered ring; other compounds in which iodine is apparently part of larger rings are less stable. o-Diacetoxyiodobenzoate appears to be the best analytical reagent of the iodoso series. The m- and p-iodosobenzoates are found unsuitable for quantitative oxidation of cysteine.

Titrimetric determination of organic derivatives of dithiocarbonic acid and carbon disulphide by interhalogens

Zu 50 ml einer bei 25~ an Kochsalz ges~ttigten und die eingangs genannten Metallionen enthaltenden L6sung, die mit 2 ml konz. HC1 anges/iuert wird, werden 10 ml einer Mischung von ct-Benzoinoxim und Chloroform zugegeben und alles 2 min geschiittelt. Das c~-Benzoinoxim-Reagens wird durch Aufl6sen von 0,15 g in 100 ml Chloroform hergestellt. Nach Abtrennung des Chloroformextraktes wird die w/iBrige Phase noch mit 5 ml Reagens nachextrahiert. Die gesammelten Extrakte werden, zur Entfernung eventuell vorhandenen Wassers, mit 2 ml 0,5 N HC1 geschfittelt. AnschlieBend wird der Extrakt rnit Hilfe eines Hochtemperaturstrahlers eingeengt. Nach Abkiihlung werden je 10 Tropfen konz. HNO3 und konz. H2SO4 zugegeben und die L6sung wird abgeraucht. Nach dem Abkfihlen wird der Riickstand mit 5 ml einer 1 N NaOH-L6sung gel6st und nach Uberffihrung in einen 50 ml-Kolben mit 2 ml einer 10%igen KSCN-L6sung und 15rot einer 5%igen Zinn(II)-chloridl6sung in konz. HC1 versetzt. Nach 1 h Stehen werden 0,5 ml einer 7%igen Eisen(II)ammoniumsulfatl6sung zugetropft und die L6sung mit H2O auf 50 ml aufgeftillt. Nach nochnals 1 h Stehen wird die L6sung in einem Scheidetrichter mit 5 ml Diisopropyl/ither geschfittelt und die Atherphase direkt in 5 cm-Ktivetten bei den Wellenl/ingen 405 bzw. 490 nm gemessen.