Extraction and spectrophotometric determination of vanadium(V) with ferron

Various metal complexes of 7-iodo-8-hydroxyquinoline-5-sulphonic acid (ferron) were found to be selectively extracted into immiscible alcohols. Vanadium(V) is almost completely extracted into n-butanol in a single extraction from solutions which are 0.05 M in sulphuric acid. A sensitive and selective spectrophotometric method can be based on this extraction. Beer's law is obeyed up to 15.3 μg of vanadium per ml; the sensitivity of the color reaction is 0.011 μg of vanadium per cm² at 430 mμ. The interference of iron(III) can be eliminated by adding excess pyrophosphate. The extracted species appears to contain vanadium, ferron and n-butanol in the ratio 1:2:4.     

Extraction of amino acid (L-aspartic acid) from aqueous stream using trioctylamine

L-aspartic acid is an α-amino acid that is primarily used in protein biosynthesis. It can be manufactured via protein extraction, chemical synthesis, fermentation, and enzymatic processes. L-aspartic acid separation from protein hydrolysates, fermentation broths, and aqueous streams are rather difficult. In the current study, trioctylamine (TOA) is used as an extractant in a variety of solvents, including 1-octanol, 1-decanol, and cyclohexane, to extract aspartic acid from aqueous solutions. Different parameters, including the distribution coefficient, loading ratio, extraction efficiency, and number of stages, were used to explain the results. The maximum extraction efficiencies were found to be 86.25%, 67.25%, and 58.50% with 1-octanol, 1-decanol, and cyclohexane by trioctylamine, respectively.     

Precipitation of molybdenum(V) as the hydroxide and its separation from rhenium

A study of the conditions for precipitation of molybdenum(V) hydroxide shows that for Mo concentration 1 mg ml about 97.5% of the Mo can be precipitated between pH 5 and 5.8. Lower concentrations of molybdenum(V) or molybdenum(VI) can be precipitated quantitatively by using 20 times the amount of zirconium as collector, at the same pH. On this basis, a simple method is given for quantitative separation of rhenium from large amounts of molybdenum and is attested by analysis of synthetic and molybdenite samples.     

Oxidation of malic acid by vanadium (V) in sulphuric acid medium: A kinetic and mechanistic investigation

The oxidation kinetics of malic acid by vanadium(V) in aqueous sulphuric acid was investigated at 303 K by monitoring the appearance of vanadium(IV) at 760 nm. The reaction showed first-order behavior with respect to vanadium(V), malic acid, and hydrogen ion concentration, respectively, regardless of the ionic strength. The reaction rate is enhanced by an increase in ionic strength and a decrease of the dielectric constant of the medium by addition of methanol. The activation parameters were estimated by varying the temperature in the range of 293 K to 313 K to 313 K. An oxidation mechanism is proposed, involving different vanadium(V) species produced in the presence of sulphuric acid. © 1995 John Wiley & Sons, Inc.     

Thermal decomposition of the solvent extracted molybdenum (VI) complexes from hydrochloric acid solutions with trioctylamine and trioctylmethylammonium chloride

The complexes of molybdenum(VI) with trioctylamine (TOA, R₃N) and trioctyl methylammonium chloride (TOMAC, R₃R'NCl) were prepared by drying in vacuo the organic solutions for the extraction of molybdenum(VI) from hydrochloric acid solutions at low and higher acidities, respectively, by TOA and TOMAC in benzene. The resulting complexes were examined by thermal analysis (TG and DTA) in air and under the atmosphere of nitrogen, and their thermally decomposed products such as volatile matters and residues by gas chlomatography, X-ray diffraction study and infrared spectrophotometry. It was found that their complexes decompose thermally to MoO₃ by cracking of alkyl groups combined with molybdenum(VI) ion. Accordingly the thermal decomposition process of those complexes is discussed and the probable structure of the complexes is proposed on the basis of the results obtained.

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Zusammenfassung Komplexe von Molybdän(VI) mit Trioktylamin (TOA, R₃N) und Trioktylmethylammoniumchlorid (TOMAC, R₃R'NCl) wurden hergestellt, mittels TG und DTA in Luft und in Stickstoffatmosphäre untersucht. Die thermischen Zersetzungsprodukte der Komplexe (flüchtige Substanzen und Rückstände) wurden mittels Gaschromatographie, Röntgendiffraktion und IR-Spektroskopie untersucht. Es wurde gezeigt, daß die Komplexe thermisch zu MoO₃ zerfallen, indem die an das Molybdän(VI)-Ion gebundenen Alkylgruppen abgekrackt werden. Die Ergebnisse der thermischen Zersetzungsprozesse wird diskutiert und auf der Basis der erhaltenen Ergebnisse die wahrscheinliche Struktur der Komplexe dargelegt.

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Dedicated to Professor Dr. H. J. Seifert on the occasion of his 60^th birthday

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The author wishes to thank Dr. H. Watanabe and Mr. T. Takahashi for assistance with experimental work, and also the Koei Chemical Co., Ltd. for samples of TOA and TOMAC.     

Hydroxamic acid dinuclear complexes of molybdenum(V) and molybdenum(III)

Summary Molybdenum(V) and molybdenum(III) complexes [Mo₂O₃L₄] and [Mo₂L₆] derived from hydroxamic acids (HL) were prepared and identified by Raman, i.r., e.s.r., electronic spectra and analytical data. The low magnetic moments of the dinuclear complexes are due to in part to intramolecular interactions. Electronic spectra and vibrational studies indicate the presence of a Mo₂O₃ core in the molybdenum(V) complexes. The relative intensities of the, main and satellite peaks in e.s.r. spectra indicate the dinulcear nature of molybdenum(III) hydroxamates.     

Analytical separation of rhenium by extraction with n-benzylaniline in chloroform from sulphuric acid media

Analytical separation of rhenium(VII) is achieved by solvent extraction with N-benzylaniline in chloroform from sulphuric acid media. Few cations interfere: common anions such as phosphate, tartrate, citrate, oxalate, fluoride, EDTA and ascorbic acid do not interfere. A simple method is described for the separation of micro amounts of rhenium from macro amounts of molybdenum, tungsten, niobium and tantalum. The method also separates rhenium from V, Cr, Se, Te, Os, Ru, Rh, Pd and Pt. The molar absorptivity of rhenium thiocyanate complex in butyl acetate and diisopropyl ether is 40280 ± 280 at 430 nm.     

Extraction of chlorinated hydrocarbons from fish with sulphuric acid

A method is described for extraction of chlorinated hydrocarbons (DDTs and PCBs) from fish samples with sulphuric acid of various concentrations. The results are better than those obtained by an official method using Soxhiet extraction with n-hexane, especially with 9.5-13M sulphuric acid. The relative standard deviation is about 12% for analysis of portions of a homogenized single sample taken from the dorsal flesh of the same fish. Drawbacks and advantages in comparison with other methods are discussed.     

Dimerization of electrogenerated Mo(V) in sulphuric acid solutions

The electrochemical behaviour of molybdenum(VI) in sulphuric acid solutions was investigated by cyclic voltammetry. In the reduction of Mo(VI) to Mo(III) a dimerization reaction of Mo(V) is involved; the rate constant for the reaction was estimated to be 2.79×10² M⁻¹ s⁻¹ and the activation energy was ca. 35 kJ mol⁻¹ in 0.1 M H₂O₄. Oxidation of the monomer and dimer Mo(V) species take place at −0.31 and +0.18 V (vs. SCE), respectively.     

Extraction of rhenium(VII) and molybdenum(VI) with hexabutyltriamide of phosphoric acid from acid media

Extraction of rhenium(VII) and molybdenum(VI) from sulfuric, hydrochloric, and nitric acid solutions with hexabutyltriamide of phosphoric acid was studied. The influence exerted on the extraction of Re(VII) and Mo(VI) by the nature and concentration of an acid in the aqueous phase, temperature, time of contact between phases, and concentration of the extracting agent in the organic phase was analyzed. Isotherms of extraction of rhenium(VII) and molybdenum(VI) with solutions of hexabutyltriamide phosphoric acid in kerosene were obtained, the composition of the complexes being extracted was determined, the enthalpies and entropies were evaluated, and the concentration constants of extraction of the metals were found.     

Extraction of iridium (IV) from hydrochloric acid media with crown ether in chloroform, and its determination by ICP-AES

A new method for the quantitative extraction and determination of trace amounts of iridium from hydrochloric acid media has been established based on the formation of an ion-association complex of iridium hexachloro anion IrCl6(2-) with dicyclohexyl-18-crown-6 (DC18C6) oxonium cation in chloroform, then determination by inductively coupled plasma atomic emission spectrometry (ICP-AES). The effect of various factors (solvent, acid concentration, crown ether, reagent concentration, shaking time, composition of the extracted species, foreign ions, etc.) on the extraction and back-extraction of iridium has been investigated. The procedure was used to determine traces of iridium in palladium chloride and rhodium chloride.     

The extraction of niobium (V) and Tantalum (V) by Octylarsinic acid in chloroform

Dioctylarsinic acid (HDOAA) in chloroform solution extracts Nb(V) and Ta(V) efficiently from solutions containing oxalate and oxalic acid at hydrochloric acid concentrations greater than 1M.The extraction coefficients are 92.5 at 7M hydrochloric acid and 251 at 6M hydrochloric acid for niobium and tantalum, respectively. These metals can be extracted even more efficiently from sulfuric acid solutions. The results of the reagent- and pH-dependence studies suggested that a trimeric, monobasic oxoacid of niobium, associated with ten HDOAA molecules, is extracted. Tantalum appears to be present in the organic phase as (H₂DOAA)⁺ [Ta(C₂O₄)₃ (HDOAA_n] (n=l or 2).     

Synergistic extraction of copper(II) from sulfate medium with capric acid and tri-n-octylphosphine oxide in chloroform

The synergistic solvent extraction of copper(II) from 0.33?mol?dm^?3 Na₂SO₄ aqueous solutions with capric acid (HL) in the absence and presence of tri-n-octylphosphine oxide (TOPO) in chloroform at 25°C has been studied. The extracted species when capric acid was used alone is CuL₂(HL)₂. In the presence of TOPO, the extracted complex is CuL₂(HL)₂(TOPO). The TOPO–HL interaction strongly influences the synergistic extraction efficiency. The extraction constants were calculated.     

Separation of molybdenum (VI) by extraction withn-octylaniline from hydrochloric acid medium

n-Octylaniline in bezene was used for the extractive separation of molybdenum (VI) from hydrochloric acid medium. Molybdenum(VI) was extracted quantitatively from 10 ml aqueous solution 1.5M in hydrochloric acid and 10M in lithium chloride into 10 ml of 10%n-octylaninline in benzene. It was stripped from the organic phase with 5% aqueous ammonia solution and estimated spectrophotometrically with thiocyanate at 465 nm. The interference of various ions has been studied in detail and conditions have been established for the determination of molybdenum(VI) in synthetic mixtures and alloy samples.     

Oxidation ofL-tyrosine by vanadium (V) in presence of sulphuric acid

Oxidation ofL-tyrosine with vanadium (V) in sulphuric acid medium at constant ionic strength is first order in oxidant and H⁺. The order in tyrosine varies from 1 to 0. A mechanism consistent with the kinetic results is proposed in which the rate determining step is the decomposition of the complex formed in the prior equilibrium.

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Oxidation vonL-Tyrosin mit Vanadium (V) in Gegenwart von Schwefelsäure

Zusammenfassung Die Oxidation vonL-Tyrosin mit V(V) in schwefelsaurem Medium bei konstanter Ionenstärke ist erster Ordnung bezüglich Oxidationsmittel und H⁺. Die Ordnung bezüglich Tyrosin variiert zwischen 1 und 0. Es wird ein Mechanismus vorgeschlagen, der mit den kinetischen Ergebnissen konsistent ist. Der geschwindigkeitsbestimmende Schritt ist dabei die Zersetzung eines Komplexes, der in einem vorgelagerten Gleichgewicht gebildet wird.