Microdetermination of certain mercaptans and carboxylic acids present in a mixture

An oxidimetric method is described for the determination of certain mercaptans based on their titration with standard potassium iodate in presence of 4–6 N hydrochloric acid. This procedure in conjunction with a method for determining mercaptans involving mercaptide formation with mercuric chloride can be used for the microanalysis of a mixture containing a mercaptan and a carboxylic acid.     

Gas-chromatographic determination of volatile sulfur-containing impurities in industrial emissions and aqueous solutions

Procedures are developed for determining volatile sulfur-containing impurities, hydrogen sulfide, simple mercaptans, sulfides, and disulfides in air and aqueous solutions. The procedures are based on the principle’s headspace gas chromatography and equilibrium preconcentration. The procedures differ from the officially approved ones in that the operations of sampling and sample preparation to gas-chromatographic analysis considerably reduce the loss of hydrogen sulfide and mercaptans unstable in humid air. The procedures provide the determination of sulfur-containing substances at the level of their maximum permissible concentrations (MPC) in industrial emissions and natural waters and the analytical range of four orders of magnitude; they can be implemented on gas chromatographs with flame ionization and flame photometric detectors, a quartz capillary column, and a thermostated gas-sampling valve.     

Zur colorimetrischen Bestimmung flüchtiger Schwefelverbindungen in Lebensmitteln

The quantitative determination of volatile mercaptans and hydrogen sulphide with bis-(p-nitrophenyl)-disulphide is described. The influence of various other volatile sulphur compounds, which may be found in food, and of ethanol has been examined. It is possible to determine down to 0.1 mMol/kg of mercaptans and hydrogen sulphide in food with a standard deviation of 8.4%. A few examples are given.     

Alkalimetric determination of mercaptans through trithiocarbonic acid formation

A simple and rapid alkalimetric method for the determination of mercaptans through trithiocarbonic acid formation is described. The mercaptans are titrated in tert.-butanol in the presence of carbon disulphide with standard aqueous sodium hydroxide, with phenolphthalein as indicator. The -SH group is smoothly, rapidly and quantitatively transformed into the group under the specified conditions. The method has been extended to the analysis of mercaptan-carboxylic acid and mercaptan-trithiocarbonate mixtures.     

Semiconductor gallium arsenide electrodes for the potentiometric titration of mercaptans in raw hydrocarbons

Electrochemically modified electrodes based on gallium arsenide (GaAs) were designed for the potentiometric determination of mercaptans in raw hydrocarbons. The main electrochemical characteristics (linearity range of the electrode function, limit of detection, and slope of electrode function) were studied. The argentometric titration of mercaptans in a gas condensate was performed using the GaAs electrodes prior to and after modification. The use of the electrochemically modified electrode ensures a more reliable determination of the titration end-point.     

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.     

Chromatographic location and colorimetric determination of mercaptans, prolines and free radical precursors

A new reagent, 7,7,8,8-tetracyanoquinodimethan (TCNQ), is introduced for the colorimetric determination of free radical precursors, such as cysteine, proline, hydroxyproline, the phenoxazine family and mercaptans. TCNQ is also useful in the location and characterization on paper or thin-layer chromatograms of proline, hydroxyproline, cysteine, polynuclear compounds, mercaptans, thiocarbonyl amides and thiosemicarbazones. In addition, aminoacid derivatives, such as the N-(phenylthiocarbamyl) amino-acids and the 3-phenylthiodantoins, can be located and characterized on chromatograms. TCNQ has been applied to the location and characterization of atmospheric proline, carbazole and 11H-benzo[a]carbazole. For characterization purposes absorption spectra were obtained directly from glass-fibre, paper, or thin-layer chromatograms from about 300 to 900 mmu.     

Accuracy and precision of a coulometric titration technique with mercaptans as test compounds

A coulometric determination of mercaptan sulfur, concentrating on the effect of quantity and structure of mercaptans on the accuracy and reproducibility of their quantitative determination, is described. A series of pure mercaptans were used as test compounds. A potentiometric endpoint detection technique was devised consisting of a sulfide-sensitive electrode as the indicator electrode and a calomel electrode as the reference electrode. A silver electrode acted as the generator anode and a platinum electrode as the cathode. The measurements were performed in an ethanolic solution of NH₄OH and NH₄NO₃ as supporting electrolytes. The accuracy of mercaptan determination corresponding to 168.20–15.00 μg of mercaptan sulfur varied from ±1 to ±4% except for sec- and tert-butyl mercaptans at their lowest concentrations. Furthermore, the presence of a branched alkane chain increased the percentage error, while the presence of a phenyl group decreased the error.     

Extraction of Mercaptans from Light Hydrocarbon Mixtures with Aqueous Ammonia

Results of laboratory studies of the extraction of light mercaptans (methyl, ethyl, and propyl mercaptans) from hydrocarbons mixtures with a 25% aqueous solution of ammonia (caustic ammonia) are presented and discussed. It is shown that aqueous ammonia can in principle be used for controlled demercaptanization of light hydrocarbon fractions and liquefied hydrocarbon gases containing hydrogen sulfide and lower mercaptans. The advantage of this demercaptanization method over the conventional processes of alkali treatment is that there is no stage of oxidative catalytic regeneration of a spent alkali and there are no its highly toxic wastes, sulfurousalkaline waste waters. The regeneration of a spent (saturated with sulfurous compounds) aqueous ammonia can be comparatively easily performed by its heating (boiling), which leads to a hydrolytic decomposition of ammonium sulfides and mercaptides to release their constituent gases: hydrogen sulfide, mercaptans, and ammonia. Ammonia is recycled into the process as freshly prepared (regenerated) caustic ammonia.

     

Coulometry applied to gas-phase chromatograpy

It has been found that coulometry is an excellent procedure for identification and quantitative determination of the components of an organic mixture, separated by vapor-phase chromatography. A millicoulometer is described which can be used either for manual or automatic titration. The eluted components are absorbed in a suitable solution where they are continuously titrated by an electrolytically generated reagent. Photometric, amperometric and potentiometric end-points may be used for the titration of compounds with an active functional group such as volatile acids, bases, mercaptans and aldehydes. The procedure can be extended to all organic vapors by burning them at the end of the column and converting them into carbon dioxide which can be coulometrically titrated.     

Analytical applications of mercaptan-carbon disulphide reaction: Determination of mixtures containing mercaptans

Summary A method is described for the determination of mercaptans by alkalimetric titration of trithiocarbonic acids formed through their reaction with carbon disulphide in tert.-butanol. The method has been applied to the analysis, on the same sample solution, of mixtures of mercaptans containing titrable hydrogen and those containing nontitrable hydrogen, mercaptans and alkali mercaptides, and mercaptans and mercaptopyrimidines.

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Analytische Anwendung der Merkaptan-Schwefelkohlenstoff-Reaktion: Bestimmung von Merkaptan in Gemischen

Zusammenfassung Ein Verfahren zur Merkaptanbestimmung durch alkalimetrische Titration der Trithiokohlensäure auf der Grundlage seiner Reaktion mit Schwefelkohlenstoff in tert. Butanol wurde beschrieben. Es eignet sich zur Bestimmung von Gemischen aus Merkaptanen mit titrierbarem Wasserstoff und solchen ohne titrierbaren Wasserstoff sowie von Merkaptanen und Merkaptiden, weiters von Merkaptanen und Merkaptopyrimidinen.

     

镍基催化剂上硫醇与异戊二烯硫醚化反应的研究

在上流式气-液-固三相固定床微型反应装置上，对Ni／Al2O3催化剂上硫醇与异戊二烯硫醚化反应进行了研究，并考察了反应温度、压力、空速、临氢条件对催化剂二烯硫醚化反应性能的影响。结果表明，异戊二烯与硫醇在镍基催化剂的作用下，可以发生反应生成高沸点的硫醚化合物，反应温度和空速对催化剂二烯硫醚化活性有明显的影响，提高反应温度和降低空速有利于提高硫醇在二烯硫醚化反应过程中的转化率，在临氢反应条下，可以提高催化剂二烯硫醚化反应的活性和稳定性。     

Polarographic study of bis(2-pyridyl)disulphide di-N-oxide and bis(2-quinolyl)disulphide di-N-oxide in aqueous ethanol

The polarographic reduction of bis(2-pyridyl)- and of bis(2-quinolyl)disulphide di-N-oxide in aqueous alcohol yields aryl mercaptans. The electrode reaction is kinetically controlled by an initial one-electron transfer step, and values for the transfer coefficients and the specific heterogeneous rate constants for the forward reactions are presented. The polar N-oxide function in the alpha-position withdraws electrons from the disulphide bond, making the half-wave potential less negative than that of the diphenyl disulphide. The pk(a) values of the mercapto compounds formed have been evaluated and the low values obtained for the heterocyclic N-oxides are further evidence for tautomerism in these compounds.     

Titrimetric determination of certain mercaptans with mercuric chloride

A procedure is described for the semimicro determination of certain mercaptans, by means of their reaction with mercuric chloride. The acid liberated during the reaction is titrated with standard alkali after addition of sufficient potassium iodide to convert the surplus mercuric chloride into a stable soluble complex. The procedure has been applied to determine 0.12-1 mmole of these compounds; the results are accurate to within 0.5%.     

Cyclic flow-injection photometric determination of mercaptans in hydrocarbon gases

A procedure for the automated photometric determination of mercaptans in hydrocarbon gases was developed using sodium nitroprusside as a photometric reagent. The analytical range was from 10 to 150 mg/m³ at a sample volume of 0.4 L and preconcentration time of 2 min.     

Determination of cyanide in the presence of mercaptans with a selective-electrode

The interfering action of mercaptans on determinations of cyanide with a cyanide-selective electrode can be eliminated by oxidation or by distillation. The procedures are supplied to the analysis of waste waters.     

The indirect determination of organic compounds by atomic absorption spectrometry

The feasibility of determining indirectly certain organic compounds by precipitation of insoluble silver compounds and determining the excess silver(I) by atomic absorption spectrometry (AAS) has been demonstrated. The determination of other compounds, such as alkylated barbiturates and mercaptans by similar methodology should be possible. Although direct AAS methods are preferable to indirect methods, the insolubility of many silver salts, the inherent sensitivity of the AAS method for silver, and the speed and convenience of AAS methodology suggests that under certain conditions, an indirect AAS method may be appropriate and the method of choice.     

Flow-injection photometric determination of mercaptans in light oil products with chromatomembrane extraction

A procedure was developed for the flow-injection photometric determination of mercaptans in light oil products. The use of sodium nitroferricyanide as the photometric reagent at 540 nm provides a detection limit of mercaptan sulfur of 0.3 mg/L at a volume of the sample of 3 mL; the analytical range is from 1 to 50 mg/L.     

Periodatometric determination of organotrithiocarbonates and mercaptans (via trithiocarbonate formation)

A method has been described for the direct visual and potentiometric determination of organotrithiocarbonates in bicarbonate medium in the presence of potassium iodide, using potassium periodate as an oxidimetric reagent. The method was extended to the determination of mercaptans after their quantitative transformation to the corresponding organotrithiocarbonates through reaction with carbon disulfide in the presence of alkali. The resulting trithiocarbonates are titrated with periodate in the manner described herein. The excess of carbon disulfide does not interfere in these determinations. Organotrithiocarbonates are smoothly, rapidly, and quantitatively oxidized to the corresponding bis(alkyl/aryl mercapto thiocarbonyl) disulfides with the oxidant under the specified conditions.     

Facile Synthesis of Alkylthiobenzaldehydes

Alkoxyl alkylthiobenzaldehydes can be readily prepared from the corresponding bromobenzaldehydes and the sodium salt of primary mercaptans in DMF.