Pyrogallol red and bromopyrogallol red in new optical methods for the determination of molybdenum(VI) and tungsten(VI)

The complexation of molybdenum(VI) and tungsten(VI) with pyrogallol red (PR) and bromopyrogallol red (BPR) in the presence of a cationic surfactant, cetylpyridinium bromide was studied. Conditions of the preconcentration of molybdenum(VI) and tungsten(VI) as complexes with PR and BPR on Silochrom S-120 were found. The concentration coefficients were no lower than 67 for a volume of the aqueous phase of 20 mL and a mass of the sorbent of 0.3 g. Chromaticity characteristics of the complexes in solutions and on the sorbent were determined. It was demonstrated that the complex of molybdenum(VI) with BPR in the presence of cetylpyridinium bromide should be used in the analysis of materials with low concentrations of molybdenum.     

Chelating behavior of macroreticular hydroxamic acid resin towards molybdenum(VI), tungsten(VI), uranium(VI) and vanadium(V)

Summary The properties and behaviour of the hydroxamic acid resin have been studied and shown to be an highly selective resin for molybdenum(VI), tungsten(VI), uranium(VI) and vanadium(V) ions. The stability constants of these metal ion complexes with the resin have been determined. The sorption and desorption characteristics of these metal ions on this resin and the methods for the separation of these metal ions from each other on a short column of such resin were also developed.

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Komplexierungsverhalten von makroretikularem Hydroxamsäureharz gegenüber Molybdän(VI), Wolfram(VI), Uran(VI) und Vanadium(V)

Zusammenfassung Die Eigenschaften und das Verhalten von Hydroxamsäureharz wurden untersucht. Das Harz erwies sich als hochselektiv für Mo(VI), W(VI), U(VI) und V(V). Die Stabilitätskonstanten der Komplexe wurden bestimmt, die Sorptions- und Desorptionscharakteristica wurden untersucht und Trennungsmethoden für die genannten Ionen an einer kurzen Säule entwickelt.

     

Extraction of phosphorus(V), molybdenum(VI), and tungsten(VI) from fluoride solutions

The influence of titanim(IV) and silicon(IV) on the extraction of phosphorus(V), molybdenum (VI), and tungsten(VI) fluoride complexes by tributyl phosphate was studied.

     

Reactions of tungsten(VI) and molybdenum(V) chlorides,and tungsten(VI) and molybdenum(VI) oxychlorides,with azoxybenzene

Reactions of W^VI and Mo^V chlorides with azoxybenzene yield ionic species of W^VI and Mo^VI oxychlorides in which the cation is a protonated azobenzene. The reaction between MoCl₅ or MoOCl₄ and azoxybenzene gives, after extraction with methylene chloride—ethanol mixture, the complex [trans-MoOCl₄(OC₂H₅)]^? [C₁₂H₁₀N₂H]⁺. In contrast, WOCl₄ reacts with azoxybenzene to give a stable non-ionic adduct in which the organic moiety is coordinated through its oxygen atom trans to the WO bond. Several complexes of substituted azoxybenzene having similar structures are described.     

Sorption of Mo(VI), W(VI), Cr(VI), and V(V) anions on a silica gel modified with immobilized polyionene

The sorption of polyionene 1,4-MePh on the silica gel surface was studied. The silica gel modified with polyionene sorbed was used for sorption preconcentration of MoO ₄ ^2? , WO ₄ ^2? , Cr₂O ₇ ^2? , and VO ₃ ^? anions from aqueous solutions. The sorption isotherms of these anions on the initial and modified silica gels were obtained and analyzed.     

Thermometric titration in investigation of the formation of polyanions of molybdenum(VI), tungsten(VI), vanadium(V), and chromium (VI)-I: comparison of thermometric and potentiometric titration curves

A new twin-cell thermometric titrator has been devised and used for thermometric titration of solutions of sodium molybdate, sodium tungstate, sodium orthovanadate, ammonium metavanadate, and potassium chromate with perchloric acid. The thermometric titration curves were compared with corresponding pH-titration curves for elucidation of the reactions occurring in the titrations. Thermometric titrimetric methods have been developed for the determination of tungsten, vanadium and chromium.     

Monohydrazido(2-)-complexes of molybdenum and tungsten (IV), (V) and (VI)

Summary Reaction of MoCl₅ or WCl₆ with 1-methyl-1-phenylhydrazine or 1, 1-diphenylhydrazine hydrochloride results in the formation of M^VI species [MCl₄(NNRR)]. These react with tertiary phosphines PR₃ to form M^V species [MCl₃(NNRR)(PR₃) _n ] (n=1 or 2).[MoCl₃(NNMePh)(PMe₃)₂] can be reduced in the presence of PMe₃ to the Mo^IV speciescis-mer-[MoCl₂(NNMePh)(PMe₃)₃].     

Carbon fibers modified with molybdenum for sorption of arsenic(V)

Procedure for obtaining new hybrid sorbents based on carbon fibers and chitosan-carbon materials modified with molybdenum, which determines the affinity of the sorbents for arsenate ions, is described. The surface morphology was examined and a qualitative chemical analysis of the surface of the composite sorbents was made by the method of scanning electron microscopy–energy-dispersive analysis. Sorption isotherms were obtained for unmodified materials, carbon fibers and chitosan-carbon materials, and hybrid sorbents in twicedistilled and tap water at low As(V) concentrations.     

Vibrational spectra of hepta- and octafluorocomplexes of molybdenum(VI), tungsten(VI) and rhenium(VI)

The alkali salts of the seven- and eight-coordinated fluoro-complexes of Mo, W and Re have been prepared. Their vibrational spectra were recorded. The spectra of all ElF^n-₈ are consistent with a square antiprismatic arrangement of the fluorine ligands. The spectra of Cs ElF₇ (El = Mo, W, Re) and Rb ReF₇ are similar to those known for ReF₇ and JF₇ and can be interpreted on the basis of pentagonal bipyramid (D_5h). If Cs⁺ is replaced by lighter alkali ions in Me ElF₇ (El = Mo and W), a lowering of symmetry is apparent from the number of bands observed in the vibrational spectra.     

Potentiometric studies of the complexes of chromium(VI), molybdenum(VI) and tungsten(VI) with some Azoxine S dyes

The equilibrium constants of the complexation reactions of Cr(VI), Mo(VI) and W(VI) with 8-hydroxyquinoline-5-sulphonic acid (OXS), 7-phenylazo-8-hydroxyquinoline-5-sulphonic acid (PAZOXS), 7-(4-sulphophenylazo)-8-hydroxyquinoline-5-sulphonic acid (SPAZOXS) and 7-(4-sulphonaphthylazo)-8-hydroxyquinoline-5-sulphonic acid (SNAZOXS) have been determined by potentiometric pH titration. The values in the case of chromate are different from those for molybdate and tungstate. The order of stabilities is OXS > PAZOXS > SPAZOXS > SNAZOXS.     

Anderson-type heteropolyanions of molybdenum(VI) and tungsten(VI)

The previously reported preparation of some Anderson-type molybdopolyanions containing divalent metal ions (Zn, Cu, Co or Mn) as a heteroatom has been reinvestigated. The molybdopolyanions of Zn(II) and Cu(II) were confirmed, although the Cu(II) polyanion was not stable and could not be recrystallized. On the other hand, the polyanions of Co(II) and Mn(II) could not be reproduced. Another type of heteropoly compound, [X(H₂O)_6-x(Mo₇O₂₄)]⁴⁻ [X = Cu(II), Co(II) or Mn(II)], was isolated as solids, which are not stable thermally. The mixed-type Anderson polyanions, [Ni(II)Mo_6-xW_x,O₂₄H₆]⁴⁻, which have been questioned as mixtures of species with different x values, were also reinvestigated using IR, UV absorption and MCD spectra. They are single species, but not mixtures, although some positional isomers may be present for the compounds where x = 2-4. The possibility of oxidation of the heteroatom with the Anderson structure maintained was examined. The oxidation of [Ni(II)Mo₆O₂₄H₆]⁴⁻ by the S₂O²⁻₈ ion in aqueous solution gave the Waugh-type [Ni(IV)Mo₉O₃₂]⁶⁻ polyanion, whereas the oxidation of [Ni(II)W₆O₂₄H₆]⁴⁻ gave no heteropoly compound.     

Simultaneous polarographic determination of micro amounts of vanadium(V) and molybdenum(VI)

A simple and sensitive polarographic method has been developed for the determination of micro quantities of vanadium(V) and molybdenum(VI), based on the reduction of bromate, which is catalysed by these metal ions in the presence of 2,4-dihydroxyacetophenone oxime. Interference by various cations and anions has been investigated.     

Alpha-benzoinomixe: Extracting agent for uranium(VI), tungsten(VI), molybdenum(VI) and some transition metals of the iron family

The effect of pH on the percent extraction of vanadium(V), iron(II), cobalt(II), nickel(II), copper(II), molybdenum(VI), tungsten(VI) and uranium(VI) by -benzoinoxime in different solvents has been studied. The maximum recovery is not appreciably affected by the nature of the solvent, but occurs at different pH values for different metals. The pH corresponding to maximum extraction increases with increasing hydrolysis pK of the species in aqueous solution, and decreases with increasing stability constant of the complexes formed. Alpha-benzoinoxime allows the separation of these metal ions into three groups: V(V), Mo(VI) and W(VI) are extracted at pH=2, U(VI) at pH=5, Fe(II), Cu(II), Co(II) and Ni(II) at around pH=10.     

Determination of vanadium(V) and molybdenum(VI) by means of a Landolt reaction

The determination of vanadium(V) and molybdenum(VI) by a Landolt-type reaction with bromate, iodide and ascorbic acid is reported. For the determination of vanadium(V) the molybdenum(VI) is masked with citrate-citric acid buffer, which also controls the pH. Molybdenum(VI) is determined in the presence of thiourea as masking agent for vanadium(V).     

Kinetic-spectrophotometric determination of molybdenum (VI) and tungsten (VI) in mixtures

A simple kinetic-spectrophotometric method is described for the determination of molybdenum(VI) and tungsten(VI) in mixtures, without prior separation. The method is based on the catalytic effect of molybdenum(VI) and tungsten(VI) on the oxidation of 2,4-diaminophenol dihydrochloride (DAP) by hydrogen peroxide in acidic medium. The reaction was followed spectrophotometrically by measuring the rate of change in absorbance with time at 500 nm. A partial inhibition in the catalytic activity of each catalyst, when the other one is present, at all ratios of Mo(VI) W(VI) mixtures studied was observed. On the other hand, the catalytic activity of tungsten(VI) dropped to zero whilst that of molybdenum(VI) decreased slightly, in the presence of citrate ions. Two sets of experiments were carried out, the first in the absence and the other in the presence of citrate, and the resolution of Mo(VI)/W(VI) mixtures was achieved by solving two simultaneous equations. Various molar ratios of Mo(VI) W(VI), at the 10^–6 M level, from 0.2 1 to 5 1 can be determined with satisfactory precision and accuracy. The selectivity of the method was investigated and the method was applied successfully to the determination of molybdenum and tungsten in each other's presence in steel.     

Mononuclear and homobinuclear vanadium(IV), chromium(III), molybdenum(III), and uranium(VI) chelates with ortho-cresolphthalein complexone

Mononuclear and homobinuclear o-cresolphthalein complexone complexes with VO²⁺, Cr³⁺, MoO⁺, and UO₂ ²⁺ have been prepared and their structures investigated. The empirical formulas, the mode of bonding, and the geometry of the complexes were obtained from elemental and thermal analyses, IR, electronic and ESR spectra, magnetic moment determinations, DC and CV polarographic studies.     

Some aspects of estimation of extraction selectivity under the conditions of competitive sorption on modified silica gels

Systematic studies of silica gels with covalently immobilized thiosemicarbazide and formazan groups under the conditions of competitive sorption from multicomponent systems were conducted. A methodological approach to determine the selectivity of the modified sorption material with regard to Cu(II), Ni(II), Co(II), Cd(II), and Zn(II) was proposed. Solid-phase extraction in equilibrium conditions of Cu(II), Zn(II), Co(II), Cd(II), and Ni(II) on a silica gel with covalently immobilized thiosemicarbazide and formazan groups in the conditions of competitive sorption was studied. The possibility to use the pseudo-second-order kinetic equation for assessment of mutual influence at competitive sorption has been shown. We found that sorption from multicomponent solutions proceeds as a non-additive process under the conditions of an excess of functional groups.

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Silver(I) sorption by silica gels chemically modified with mercaptopropyl or dipropyl disulfide groups

The sorption of silver(I) from nitric and hydrochloric acid solutions with silica gels chemically modified with mercaptopropyl groups (MPSG) and dipropyl disulfide groups (DDSG) has been studied. For nitric acid solutions, the highest silver(I) recovery factor (99.0–99.9%) is reached in the acidity range between 5 M HNO₃ and pH 8 for MPSG and between 2 M HNO₃ and pH 8 for DDSG. In the sorption of silver(I) from hydrochloric acid solutions with MPSG, the recovery factor is 99% at pH 2–7. The recovery of silver(I) from chloride solutions with DDSG depends significantly on the chloride ion concentration. The treatment of silver-containing DDSG with a water-ethanol or water-dimethylformamide solution of Michler thioketone yields an intensely colored, reddish claret, mixed-ligand silver(I) complex on the sorbent surface. The diffuse reflectance spectrum of this complex shows a band peaking at 520 nm.