Identification of Components of Commercial Alkylsalicylaldoxime Based Reagents by GC–MS

A simple gas chromatographic-mass spectrometric (GC–MS) method for the identification of components present in alkylsalicylaldoximes based metal extractants LIX860, LIX622, LIX622N, Acorga PT5050 and Acorga P5100 is described. These reagents have been developed for removing copper in hydrometallurgical processes. The extractants were analyzed by GC–MS in the Full Scan mode without any derivatization step. 5-Nonylsalicylaldoxime in the extractants LIX622N, Acorga PT5050 and Acorga P5100 and 5-dodecylsalicylaldoxime in the extractants LIX622 and LIX860 were found to be present as a mixture of alkyl isomeric compounds. The extractant Acorga P5100 also contains a large amount of p-nonylphenol isomers whereas LIX622, LIX622N and Acorga PT5050 contain tridecyl alcohol isomers. In addition, the presence of small amounts of alkylphenol isomers was detected in all LIX reagents. The GC–MS study has revealed that the major fragmentation ions of the alkylsalicylaldoximes can be classified into two types: the molecular ion less C _n H_2n+1 and the molecular ion less C _n H_2n+1 and water. Cleavage of the benzylic bond predominates, resulting in the base peak. The identified compounds have been classified in different types that show different base peaks and the possible structures of the alkyl groups based on the substitution of the alpha-carbon are proposed.     

Extraction of copper(II) with N-(para-tert-butylbenzoyl)-N′,N′-dialkylhydrazines

Extraction of Cu(II), Co(II), Ni(II), and Zn(II) with N-(para-tert-butylbenzoyl)-N??,N??-dialkylhydrazines was studied. In contrast to other listed elements, copper(II) is extracted with these reagents in a wide pH range and NH₃ concentrations, which provides its selective separation. Effect of chain length of the N??,N??-alkyl groups and solvent nature on copper extraction and its stripping conditions were determined. Extraction constants were calculated. Ammonium salts decrease the extraction degree of copper(II). The studied reagents are superior to the known industrial reagent of ??-diketone class, LIX 54, in terms of copper(II) extraction efficiency from ammonia media.     

Multicommutated generation of concentration gradients in a flow-batch system for metronidazole spectrophotometric determination in drugs

The titration by using the perchloric acid as titrant and malachite green as indicator is the classical method for the determination of metronidazole, 2-(2-methyl-nitroimidazol-1-yl) ethanol, in drugs. However, this procedure is slow, laborious and consumes great amount of reagents and samples. Moreover, it requires careful manipulation because the reagents cause irritation in the skin and in the eyes. To overcome these drawbacks an automatic system is proposed. It uses three-way solenoids valves, an open chamber and it exploits concentration gradients generated into the chamber in a multicommutated way. As the proposed system embodies the characteristics of flow-batch systems and of multicommutation techniques in flow, it is here named flow-batch-multicommutated titrator. The system is fully controlled by microcomputer running software written in LabView 5.1 graphic language. It processes 60 samples per hour with relative standard deviation smaller than 2.3% (n=6) and in each titration it consumes 2.5 and 1.5 ml of sample and titrant, respectively. By applying the paired t-test, no statistic differences at the 95% probability level between the results of the proposed system and classical titration were observed.     

Potentiometric determination of potassium ferricyanide

A rapid and accurate electrometric method for the determination of potassium ferricyanide solutions has been investigated. It consists in titrating ferricyanide solutions potentiometrically against standard AgNO₃, using a silver indicator electrode in conjunction with a saturated calomel electrode connected by a KNO₃ bridge. Either of the reagents may be used as the titrant. A marked change in e.m.f is observed at thc end-point corresponding to the formation and precipitation of Ag³[Fe(CN)₆]. The curves have a regular form, a pronounced maximum in dE/dV occurs at the end-point and the results are very accurate and reproducible. The reaction, though simple, affords a quantitative method for the determination of ferricyanide or silver. The effect of neutral salts and ethanol on the accuracy of the end-point has been studied.     

The use of naphthalene derivatives in inorganic analysis : The effect of substituents in the naphthalene nucleus on the fluorimetric detection of tin

Fourteen substituted nitronaphthalene derivatives have been examined as reagents for the fluorimetric detection of tin. The compounds investigated included dinitronaphthalenes, dinitronaphthylamines, halogen substituted mononitronaphthylamines, mononitroso- and dinitro-naphthols and their sulphonic acid derivatives. Four of these reagents have been found to exhibit strong fluorescence and another four to give moderate fluorescence with stannous tin. All reagents are capable of detecting l0^-4 g stannous tin and with four of them, 10^-5 g is capable of detection in 0.01 ml of solution. The results indicate that two of the most important factors relating structure of reagent to intensity of fluorescence are (a) the position of the nitro group in the naphthalene nucleus, i.e., whether it is α- or β- or whether it is sterically hindered and (b) the electropositive or electronegative character of other substituent groups in the reagent     

Hetero-molecular association in binary mixtures of solvent extractants and diluents at temperature 303.15 K

Ultrasonic velocity and viscosity measurements have been made for binary liquid mixtures of solvent extractants, LIX reagents such as LIX 84 and LIX 984 in benzene, amyl alcohol and tri-n-butyl phosphate (TBP) at temperature 303.15?K and at atmospheric pressure. The measured values of ultrasonic velocity, density and viscosity have been utilised to compute various thermo-acoustic parameters and their excess functions, which provide information about the nature and strength of intermolecular interactions present in the systems.     

Lower limits of the potentiometric microtitration of chloride with silver ions

The lower levels of the potentiometric titration of chloride with silver ions were investigated. The titrant was 0.001 N acetonic silver perchlorate. The titration media were acetone and acetic anhydride:acetone (4:1). A silver sulfide ion-selective indicator electrode and a double-junction reference electrode were use to monitor emf's. This titration is limited only by the trace amounts of chloride in the reagents used. Satisfactory results and well-defined titration curves were obtained down to 7 μg of chloride per 50 ml of solution (0.2 μmol; 4 × 10^?6N).A small polarization current can be used to enhance the potentiometric breaks of this titration. In an 80% methanolic medium with 0.001 N aqueous silver nitrate and a polarization current of ?0.4 μA, the lower practical limit of this titration was near 22.3 μg of chloride (1.26 × 10^?5N).     

Development and validation of HPLC‐MS/MS method for the determination of lixivaptan in mouse plasma and its application in a pharmacokinetic study

The aim of the present study was to develop a simple, sensitive and accurate liquid chromatography–electrospray ionization tandem mass spectrometry (ESI‐MS/MS) method for the determination of lixivaptan (LIX) in mouse plasma using vildagliptin as the internal standard (IS). A precipitation procedure was used for the extraction of LIX and vildagliptin from mouse plasma. Chromatographic separation of LIX was achieved using a C₁₈ analytical column (50 × 2.1 mm, 1.8 μm) at 25°C. The mobile phase comprised acetonitrile and ammonium formate (10 mm , pH 3.1; 40:60, v /v) pumped at a flow rate of 0.3 mL min⁻¹. A tandem mass spectrometer with an electrospray ionization source was used to perform the assay. Quantification of LIX at m/z 290 → 137 and IS at 154 → 97 was attained through multiple reaction monitoring. The investigated method was authenticated following the bio‐analytical method of validation guidelines of the US Food and Drug Administration. The developed method showed a good linearity over the concentration range from 5 to 500 ng mL⁻¹, and the calibration curve was linear (r = 0.9998). The mean recovery of LIX from mouse plasma was 99.2 ± 0.68%. All validation parameters for LIX were within the levels required for acceptance. The proposed method was effectively used for a pharmacokinetic study of LIX in mouse plasma.     

Introduction of N,N'-disulfonylhydrazines as new sulfonylating reagents for highly efficient synthesis of (E)-β-iodovinyl arenesulfones under mild conditions

N,N'-Disulfonylhydrazines have been proven to be the most reactive precursors of the sulfonyl radicals among all types of sulfonyl substituted hydrazines as early as half a century ago. However, the sulfonyl radicals generated from these compounds have not been used in organic synthesis except the simple self-dimerization synthesis of disulfones controlled by the “solvent-cage-effects”. In this article, N,N′-disulfonylhydrazines were introduced as new sulfonylating reagents and their combinations with NIS were disclosed as new iodosulfonylating reagents of alkynes. Finally, a highly efficient method for the synthesis of (E)-β-iodovinyl arenesulfones was developed by mixing an alkyne, a N,N′-disulfonyl-hydrazine and NIS in aqueous THF at room temperature for 5 min.     

Reactivity of 3H-1,2,4-dithiazole-3-thiones and 3H-1,2-dithiole-3-thiones as sulfurizing agents for oligonucleotide synthesis

The reactivity of 5-amino-3H-1,2,4-dithiazole-3-thiones substituted at their amino group and 5-amino-3H-1,2-dithiole-3-thiones substituted at their amino group and C4 toward compounds containing P(III) atoms has been studied. N,N-Disubstituted-N′-(3-thioxo-3H-1,2,4-dithiazol-5-yl)methanimidamides were selected as novel efficient sulfur transfer reagents suitable for DNA and RNA synthesis.     

A simple photo-electric carbon dioxide titrator

A simple photo-electric apparatus is desscribed for the automatic titration of small amounts of carbon dioxide The apparatus is based on automatic titrant shut-off controlled by a photoresistor and is used for the non-aqueous titration proposed by Blomet al. (pyridine/monoethanolamine medium, sodium methanolate titrant).     

Continuous on-line feedback based flow titrations. Complexometric titrations of calcium and magnesium

The methodology of continuous feedback-based flow titrations and the principle of compensating errors [Anal. Chem. 72 (2000) 4713; Anal. Chim. Acta 435 (2001) 289] were applied to the determination of calcium and magnesium ions with EDTA. The flow of the titrant, EDTA, varied linearly in response to a controller output voltage while the total flow (F_T, the sum of the metal ion sample flow and the titrant flow) was held constant. The sample was pre-doped with a metal ion indicator; the status of the indicator color in the mixed stream was monitored by an optical detector and was used for governing the controller output as well as for interpreting the results of the titrations. The titrant flow initially ramped upward linearly. As a change in the color corresponding to the equivalence point was sensed by the detector, the controller output (instantaneous value V_H) reversed its ramp direction, thus decreasing the titrant flow linearly at the same ramp rate. When the predefined absorbance corresponding to the equivalence point was sensed again, the controller voltage (instantaneous value V_L) was ramped in reverse once more, going upward. Because of the lag time between a change in the controller output and its effect being sensed by the detector, the controller voltage corresponding to the actual equivalence point was the average of V_H and V_L. Continuous sensor-governed operation of the controller resulted in a triangular waveform. The mean of this waveform during any cycle gives the equivalence point controller voltage V_E. This principle allowed true titrations with good reproducibility (0.2-0.7% R.S.D.) and throughput (33-42 s per titration).     

Selenium promoted synthesis of enantiopure pyrrolidines starting from chiral aminoalcohols

Starting from commercially available enantiomerically pure aminoalcohols and using simple conversions promoted by organoselenium reagents, several enantiomerically pure substituted pyrrolidines were prepared. After double protections (R)- or (S)-2-phenylglycinols were converted into the β-amino selenides by displacing the tosyl group with phenyl selenolate anions. The phenylseleno group was then substituted by an allyl group by treatment with allyltributyltin and AIBN. The reaction of these allylic derivatives with electrophilic phenylselenium reagents afforded selenium containing pyrrolidines as the result of a 5-exo-trig cyclization. The pyrrolidine derivatives thus obtained were reductively deselenylated with triphenyltin hydride and AIBN. Moreover, the selenides were converted into the selenones, which easily gave substitution with different nucleophiles. Enantiopure 2,5-pyrrolidines containing azido, methylthio, cyano and iodo groups were thus obtained.     

Pd(OAc)2-catalyzed domino reactions of 1,2-dihaloarenes and 2-haloaryl arenesulfonates with Grignard reagents: efficient synthesis of substituted fluorenes

Pd(OAc)₂-catalyzed domino reactions of 1,2-dihalobenzenes and 2-haloaryl arenesulfonates with hindered Grignard reagents to form substituted fluorenes, which are believed to occur through palladium associated aryne intermediates, are described. Such palladium associated aryne reaction pathway was found to be favored by omitting the use of phosphine and N-heterocyclic carbene ligands for palladium catalysts and with better leaving groups. Our study suggested that Pd(leaving group)X associated arynes should be formed first and the sp³ C-H activation preferentially occurred at benzylic C-(1°)H bonds. The work described here provides a high yield, one-step access to substituted fluorenes from readily available 1,2-dihalobenzenes and 2-haloaryl arenesulfonates and hindered Grignard reagents, and this substituted fluorene-making method may find applications in the preparation of substituted fluorene-containing molecules including polymers.     

Palladium-catalyzed benzylation of N-Boc indole boronic acids

The direct benzylation of indole 2-boronic acid can be efficiently achieved using trans-PdBr(N-Succ)(PPh₃)₂, alleviating the need for strong bases or toxic organotin reagents. Under these reaction conditions substituted indole-2-boronic acids and substituted benzyl bromides are cross-coupled to afford aryl(indolo)methanes in good yield.     

Tracer-monitored flow titrations

The feasibility of implementing tracer-monitored titrations in a flow system is demonstrated. A dye tracer is used to estimate the instant sample and titrant volumetric fractions without the need for volume, mass or peak width measurements. The approach was applied to spectrophotometric flow titrations involving variations of sample and titrant flow-rates (i.e. triangle programmed technique) or concentration gradients established along the sample zone (i.e. flow injection system). Both strategies required simultaneous monitoring of two absorbing species, namely the titration indicator and the dye tracer. Mixing conditions were improved by placing a chamber with mechanical stirring in the analytical path aiming at to minimize diffusional effects. Unlike most of flow-based titrations, the innovation is considered as a true titration, as it does not require a calibration curve thus complying with IUPAC definition. As an application, acidity evaluation in vinegars involving titration with sodium hydroxide was selected. Phenolphthalein and brilliant blue FCF were used as indicator and dye tracer, respectively. Effects of sample volume, titrand/titrant concentrations and flow rates were investigated aiming at improved accuracy and precision. Results were reliable and in agreement with those obtained by a reference titration procedure.     

Emulsion membrane extraction of cobalt using aromatic beta-hydroxyoxime

A batch pertraction (liquid membrane extraction, MX) of cobalt has been studied, with industrial reagent LIX 64N and ABF (USSR) as a carrier. The influence of cobalt, reagents and acid concentration has been searched. The kinetic and hydrodynamic characteristics of the emulsion were optimized. In one batch pertraction process it is possible to reach 100-fold cobalt preconcentration with 93–98% yield from 1 dm³ sample volume.     

Synthesis and analytical applications of sodium N-bromo-p-nitrobenzenesulfonamide

Sodium N-bromo-p-nitrobenzenesulfonamide (bromamine-N) is useful as an oxidizing titrant. The synthesis, composition and structure are reported. Direct titrations of ascorbic acid, glutathione, thioglycolic acid, methionine, sulfite and arsenite are described. The procedures are simple and rapid; errors are within ± 0.5%. The compound is a somewhat better titrant for those species than the chlorine analogs such as chloramine-T and chloramine-N.     

The effect of ethylenediaminetetraacetic acid on the ferrous/ferric and cuprous/cupric redox systems

The effect of ethylenediaminetetraacetic acid on the redox systems Fe⁺²/Fe⁺³ and Cu⁺/Cu⁺² has been examined. In each case the oxidation potential of the system was markedly reduced, thus making the lower valency state a more powerful reductant. It has been established that the oxidation potentials of the two systems, in the presence of EDTA, at PH 4–5, are 0.12 and 0.13 v respectively.Because of these enhanced reducing powers, attempts were made to use ferrous-EDTA and cuprous-EDTA as reductimetric reagents. A variety of oxidants was in fact successfully titrated, but neither titrant possessed any advantage over existing reagents.The reducing properties of both systems lie intermediate between those of stannous and titanous chlorides.Theoretical considerations suggest the existence of a cuprous-EDTA complex with a formation constant of ca. 10¹⁸.     

Reversible stereocontrol in the Lewis acid promoted reaction of alkoxyaldehydes toward various allyltins

In the reactions of variously substituted allyltin reagents toward achiral alkoxyaldehydes, one of the diastereomeric homoallyl alcohols was stereoselectively obtained by the help of BF₃, while TiCl₄ preferentially gave the other diastereomer, though (E)- and (Z)-3-monoalkylallyltin reagents were exceptional. This reversible diastereoselectivity can be explained by the coordination geometry (anti or syn) of the Lewis acids toward alkoxyaldehydes.