Differential determination of selenium(IV) and selenium(VI) with sodium diethyldithiocarbamate, ammonium pyrrolidinedithiocarbamate and dithizone by atomic-absorption spectrophotometry with a carbon-tube atomizer

The extraction behaviour of selenium(IV) and selenium(VI) with sodium diethyldithiocarbamate, ammonium pyrrolidinedithiocarbamate and dithizone in organic solvents has been investigated by means of flameless atomic-absorption spectrophotometry with a carbon-tube atomizer. The selective extraction of selenium(IV) and differential determination of selenium(IV) and selenium(VI) have been developed. With sodium diethyldithiocarbamate and carbon tetrachloride, when the aqueous phase/organic solvent volume ratio is 5 and the injection volume in the carbon tube is 20 microl, the sensitivity for selenium is 0.4 ng/ml for 1% absorption. The relative standard deviations are ca. 3%. Interference by many metal ions can he prevented by masking with EDTA. The proposed methods have been applied satisfactorily to determination of Se(IV) and Se(VI) in various types of water.     

Extraction and preconcentration of selenium from aqueous solutions and its determination in water and hair samples by atomic-absorption spectrophotometry

Several organic solvents, including benzene, xylene, toluene, nitrobenzene, chloroform, carbon tetrachloride, chlorobenzene and high molecular-weight pyridines such as 4-(5-nonyl)pyridine, 2-hexyl-pyridine and benzylpyridine have been investigated as components of systems for the extraction and preconcentration of selenium from nitric acid solutions containing iodide. The results are discussed in terms of choice of reagents and the acid and iodide concentrations, and of several other parameters affecting the extraction. The utility of the method for separation of selenium from aqueous solution has been evaluated. The method has been used for preconcentration of trace levels of selenium from water and hair samples for determination by atomic-absorption spectrophotometry.     

Simple method for determination of selenium in biological materials by flameless atomic-absorption spectrometry using a carbon-tube atomizer

A method for determination of selenium in biological materials by flameless atomic-absorption spectrometry using a carbon-tube atomizer is described. The sample is burned by an oxygen-flask combustion procedure, the resulting solution is treated with a cation-exchange resin to eliminate interfering cations, the selenium is extracted with dithizone in carbon tetrachloride and the resulting selenium dithizonate is combined with nickel nitrate in the carbon tube to enhance the sensitivity for selenium and avoid volatilization losses. The method measures selenium concentrations as low as 0.01 mug/g with a relative standard deviation of 8%.     

Spectrophotometric determination of selenium with dithizone

Microgram amounts of selenium(IV) are determined by measuring the decrease in absorbance of dithizone in carbon tetrachloride solution at 620 nm. Relative standard deviations for samples containing 0.20 and 1.00 μg of selenium(IV) are 0.6% and 0.4%, respectively. Of several metals tested only copper (at the 1.0-μg level) and iron (at the 100-μg level) interfere but high concentrations of nitric or perchloric acid cause low results. A reinvestigation of the reaction of selenium(IV) with dithizone suggests a formula Se(HDz)₄ for the dithizonate.     

Synthesis of Fused Compounds on the Basis of Chalcogen Chlorides and 2-Allylphenols

Efficient methods have been developed for regioselective synthesis of new organochalcogen compounds containing 2,3-dihydro-1-benzofuran-2-ylmethyl and 7-methyl-2,3-dihydro-1-benzofuran-2-ylmethyl substituents by reactions of selenium and sulfur dichlorides and tellurium tetrachloride with 2-allylphenol and 2-allyl-6-methylphenol.     

Effect of tin tetrachloride on thermal decompositions of α,α′-azobisisobutyronitrile and dimethyl α,α′-azobisisobutyrate

Thermal decomposition of α,α′-azobisisobutyronitrile (AIBN) and dimethyl α,α′-azobisisobutyrate (MAIB) in the presence of a large amount of tin tetrachloride was investigated to determine the effect of complex formation on the decomposition rates and yields of the recombination products. The addition of tin tetrachloride significantly increased the decomposition rates; the observed first-order rate constant increased by factors of 4.5 and 17 at molar ratios of [SnCl₄]/[AIBN] = 21.65 and [SnCl₄]/[MAIB] = 19.53, respectively. It was found that the decomposition of these azo compounds was also accelerated by the addition of a comparable amount of donor solvent such as ethyl acetate or propionitrile to tin tetrachloride and that the enhancement in rate was accounted for by a larger frequency factor in the Arrhenius equation. Furthermore, the addition of tin tetrachloride seemed to suppress the formation of recombination products, tetramethyl succinonitrile and dimethyl tetramethylsuccinate, of the radicals produced by decomposition.     

1,4,6,9‐Tetraoxa‐5λ4‐selena‐spiro[4.4]nonane – A Combined Theoretical and Experimental Study

The symmetric spiro‐selenurane derived from ethylene glycol, 1,4,6,9‐tetraoxa‐5λ⁴‐selena‐spiro[4.4]nonane, was prepared from selenium tetrachloride and ethylene glycol and its molecular structure was determined by single crystal X‐ray diffraction. NBO analyses for the title compound and a related compound were conducted to assess the role of the stereochemical active lone pair on the selenium atom on the structure.     

Simultaneous spectrophotometric determination of tetravalent and hexavalent selenium

Two rapid, accurate and reproducible methods are reported for the simultaneous spectrophotometric determination of tetravalent and hexavalent selenium in the presence of each other. Both procedures involve the sequential complexation and solvent extraction of the selenium(IV)-diethyldithiocarbamate complex by chloroform in the presence of perchlorate ions followed by reduction of hexavalent selenium in the remaining aqueous phase to tetravalent selenium by 25% hydrobromic acid and its subsequent determination after complexation with 3,3′-diaminobenzidine or sodium diethyldithiocarbamate.     

Syntheses of dibenzo[c,e][1,2]diselenin and related novel chalcogenide heterocyclic compounds

Reaction of 2,2′-dilithio-1,1′-binaphthyl with selenium followed by air oxidation gives a mixture of dinaph-thoselenophene and dimer and oligomers of 2,2′-diseleno-1,1′-binaphthyl. 2,2′-Dilithio-1,1′-biphenyl reacts with selenium to afford dibenzo[c,e][1,2]diselenin. Structures of the dimeric 2,2′-diseleno-1,1′-binaphthyl and dibenzo[c,e][1,2]diselenin have been confirmed by X-ray crystallographic analyses. Similar reaction of 2,2′-dilithio-1,1′-binaphthyl with sulfur or tellurium gives a mixture of dinaphthothiophene and dinaphtho[2,1-c:-1′,2′-e][1,2]dithiin or a mixture of dinaphthotellurophene and oligomer of 2,2′-ditelluro-1,1′-binaphthyl, respectively. Dibenzotellurophene and oligomer of 2,2′-ditelluro-1,1′-biphenyl are obtained from reaction of 2,2′-dilithio-1,1′-biphenyl with tellurium.     

Liquid-phase microextraction and gas-chromatographic determination of selenium(IV) in aqueous samples

A liquid-phase microextraction (LPME) method was employed for preconcentration of selenium as piazselenol complex in aqueous samples. The samples reacted with o-phenylenediamine in 0.1?M HCl at 90°C for 15?min, and then LPME was performed. A microdrop of carbon tetrachloride was applied as the extracting solvent. After extraction, the microdrop was introduced directly into the injection port of gas chromatography for analysis. Several important extraction parameters such as the type of organic solvent, sample and organic drop volumes, salt concentration, stirring rate, and exposure time were controlled and optimized. In the proposed LPME, the extraction was achieved by suspending a 3?µL carbon tetrachloride drop from the tip of a microsyringe immersed in 12.5?mL of aqueous solution. Under optimized conditions, a dynamic linear range was obtained in the range of 20–1000?µg?L^?1. The preconcentration factor and the limit of detection of selenium in this method were 91 and 0.9?µg?L^?1, respectively. The optimized procedure was successfully applied to the extraction and determination of selenium in different types of real samples. The relative standard deviations for the spiking levels of 50–100?µg?L^?1 in the real samples were in the range of 3.2–6.1%, and the relative errors were located in the range of ?5.4 to 5%.     

Beiträge zur Chemie der Silicium—Stickstoff-Verbindungen. XC. Reaktionen des Lithium-bis(trichlorsilyl)amids mit rein anorganischen Halogensilanen

Lithium bis(trichlorosilyl)amide decomposes in the presence of silicon tetrachloride, tetrabromide, iodotrichloride or germanium tetrachloride, giving only decachloro-N,N′-bis(silyl)-cyclodi(silaz)ane. With iodosilane it reacts to bis(trichlorosilyl)-silyl-amine. With silicon tetrafluoride the product of reaction is bis(trichlorosilyl)-trifluorosilyl-amine. The latter compound rearranges already during its formation to give a nonseparable mixture with trichlorosilyl-dichlorosilyl-chlorodifluorosilyl-amine and tris(dichlorofluorosilyl)amine.     

Electrophilic reactions of halides of group vi elements. 7. Reactions of allylbenzene and allyl phenyl ether with selenium tetrahalides

The reaction of selenium tetrachloride with allylbenzene and allyl phenyl ether proceeds in accordance with the Markownikoff rule to give 1:2 adducts. The use of selenium tetrabromide changes the course of the reaction and leads to the production of a mixture of adducts in accordance with and counter to the Markownikoff rule, as well as products of cyclization of the intermediate monoadducts to 2-bromomethyl-2,3-dihydrobenzo[b]selenophene or 2-bromomethyl-benzo-1,4-selenoxane derivatives.See [1–6] for previous communications.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 911–913, July, 1982.     

Studies on 3,3′-dichloro-, 4,4′-dichloro- and 5,5′-dichloro,2-2′-dimethyldithizone and their reactions with metal ions

Three new derivatives of dithizone are reported, with their electronic and i.r. spectra, acidity constants and partition coefficients between 0.5 M sodium perchlorate and chloroform or carbon tetrachloride. The extraction equilibria with Cd, Co(II), Hg(II), Ni, Pb, Tl(I), Zn and Bi and the spectrophotometric characteristics of the extractable metal chelates are described. Complete extraction of these complexes requires higher pH than that needed with dithizone itself. The 4,4′-dichloroisomer is more efficient than the 3,3′ and 5,5′-isomers, or dithizone itself, for the separation of cadmium from zinc or cobalt from nickel.     

Monitoring of selenium in water samples using dispersive liquid-liquid microextraction followed by iridium-modified tube graphite furnace atomic absorption spectrometry

A simple and powerful microextraction technique was used for determination of selenium in water samples using dispersive liquid-liquid microextraction (DLLME) followed by graphite furnace atomic absorption spectrometry (GF AAS). DLLME and simultaneous complex formation was performed with rapid injection of a mixture containing ethanol (disperser solvent), carbon tetrachloride (extraction solvent) and ammonium pyrrolidine dithiocarbamate (APDC, chelating agent) into water sample spiked with selenium. After centrifuging, fine droplets of carbon tetrachloride, which were dispersed among the solution and extracted Se-APDC complex, sediment at the bottom of the conical test tube. The concentration of enriched analyte in the sedimented phase was determined by iridium-modified pyrolitic tube graphite furnace atomic absorption spectrometry. The concentration of selenate was obtained as the difference between the concentration of selenite after and before pre-reduction of selenate to selenite. Some effective parameters on extraction and complex formation, such as extraction and disperser solvent type and their volume, extraction time, salt effect, pH and concentration of chelating agent were optimized. Under the optimum conditions, the enrichment factor of 70 was obtained from only 5.00 mL of water sample. The calibration graph was linear in the range of 0.1-3 μg L^− 1 with detection limit of 0.05 μg L^− 1. The relative standard deviation (RSDs) for ten replicate measurements of 2.00 μg L^− 1 of selenium was 4.5%. The relative recoveries of selenium in tap, river and sea water samples at spiking level of 2.00 μg L^− 1 were 106, 96 and 98%, respectively.     

Synthesis,spectroscopic, and molar conductance characterization of selenium(IV) vitamin B6 complex as prospective antioxidant agent

Selenium(IV) complex of vitamin B₆ has been prepared using Se(IV) tetrachloride and characterized using spectroscopy (IR, UV-Vis, H NMR), molar conductance measurements, thermal analysis (DTA and TGA) and SEM imaging. Micro-analytical and spectral data show that the formed selenium(IV) complex is 1 : 2 (Se : vitamin B₆) molar ratio. Vitamin B6 and its selenium complex were screened for in vitro antioxidant activity. The complex exhibited stronger antioxidant activity in 2.2-diphenyl-1-picrylhydrazyl (DPPH) radical assay compared to the free vitamin B6 ligand.     

Regioselective addition of sulfur dichloride and selenium tetrachloride to diallyldimethylsilane as the method of preparation of eight-membered heterocycles containing silicon and chalcogens

The electrophilic additiob of sulfur dichloride and selenium tetrachloride to diallyldimethylsilane proceeds strictly according Markownikoff rule and results in the formation of previously unknown saturated siliconcontaining heterocycles, 5,5-dimethyl-3,7-dichloro-1,5-thiasilacyclooctane and 5,5-dimethyl-1,1,3,7-tetrachloro-1,5-selena(IV)silacyclooctane. The structure of heterocycles obtained was confi rmed by ¹H, ¹³C NMR spectra, in the case of selenium-containing heterocycle, by ⁷⁷Se NMR spectrum, among them the 2D HMBC spectrum.     

Cathodic stripping voltammetry and adsorptive stripping voltammetry of selenium(IV)

Cathodic stripping voltammetry of selenium(IV) in 0.1 M hydrochloric acid media yielded a nonlinear calibration graph for the concentration range 10^?9?10^?8 M. In this concentration range, adsorptive stripping voltammetry based on adsorption of the selenium/3,3′-diaminobenzidine complex on the surface of the hanging mercury drop electrode at the deposition potential of +0.05 V (vs. SCE) is more convenient. A linear calibration graph is obtained for selenium concentrations of 3×10^?9?3×10?8 M, with an accumulation time of 300 s.     

Relation between preferential solvation and intrinsic viscosity of polymers in solvent mixtures

Preferential solvation and intrinsic viscosity measurements are reported for three systems: polystyrene + benzene + methanol, polystyrene + carbon tetrachloride + methanol, and poly(2-vinylpyridine) + ethanol + cyclohexane. Plots of the coefficient of preferential solvation λ′ as a function of variation of the segment density Δ_ρ for a given ternary system, give a single curve for a large range of molecular weight and solvent mixture composition. This correlation between λ′ and Δ_ρ is verified in previously published data.     

Preparation of Hydrazides Using Silicon Tetrachloride as Coupling Agent1

Silicon tetrachloride proved to be an effective reagent for the preparation of hydrazides from carboxylic acids. Yields were comparable to those obtained via N,N′-dicyclohexylcarbodiimide (DCC) and the procedure was used to synthesize some hydrazides which are difficult to obtain otherwise.     

Benzodiselenagermoles and spirobisbenzodiselenagermoles

Synthesis of benzodiselenagermoles and bisbenzodiselenagermoles was carried out by transmetallation group 4 → group 14 between diselenophenylenezirconocenes and dialkyl-, diaryl- or alkylaryldichlorogermanes, aryltrichlorogermane or germanium tetrachloride. The new compounds were studied by ¹H, ⁷⁷Se NMR and mass spectrometry. In the case of compounds with substituted phenyl groups, double irradiation and 2D NMR experiments were performed to determine the chemical shifts of the two selenium atoms. The crystal structure of a spirobisbenzodiselenagermole has been established by X-ray diffraction analysis.