The solvent extraction of cobalt(iii) from a trisoxalatocobaltate(iii) solution into chloroform containing acetylacetone

The rate of the extraction of cobalt(III) from aqueous solutions containing trisoxalatocobaltate(lll) into chloroform containing acetylacetone has been investigated. The effects of pH, acetylacetone concentration, oxalate concentration, complex concentration, temperature, and possible change in oxidation state are reported.     

Solvent extraction of Sb(III) with malachite green into chloroform

A rapid and selective method for the solvent extraction of Sb(III) using malachite green (C. I. Basic green 4) has been described. Effect of different parameters affecting the extraction coefficient value of Sb(III) such as acidity, time of equilibration, KI concentration, solvents, anions, etc. has been studied. For various elements the separation factor has been evaluated. The stoichiometry of the extracted species has been determined by the method of substoichiometric extraction. The decontamination factor for some elements using substoichiometric quantities of the extracting agent has been evaluated. Radiotracers were employed for the extraction studies. The method elaborated has been employed for the quantitative determination of antimony in normal, benign and cancerous tissues of the human brain.     

The solvent extraction of Ir(III) with 2-mercaptobenzothiazole into chloroform

Ideal conditions for the extraction of Ir(III) with 2-mercaptobenzothiazole (2-HMBT) into chloroform have been established. The effects of various parameters such as pH, time of equilibration, time of heating, solvents, cation and anion interferences have been studied. The stoichiometry of metal to reagent has been evaluated.     

Substoichiometric extraction of chromium(III) with 2-picolinic acid into n-butanol

A substoichiometric radiochemical extraction procedure has been designed for the estimation of trace amounts of chromium(III). The method employs the extraction of spiked (⁵¹Cr) chromium by chelation with 2-picolinic acid in n-butanol solvent at pH 4. The interference effects of various closely related foreign ions on the extraction efficiency were found to be negligible, thus establishing the selectivity of the proposed technique over other standard analytical procedures available for the estimation of chromium(III). The validity of this method has been established by successful estimation of chromium present in various certified alloys. Investigations have been made to understand the parameters controlling the extraction of chromium(III).     

Radiochemical solvent extraction of Cr(III) using51Cr tracer by 8-hydroxyquinoline and acetylacetone as mixed ligands in chloroform

A radiochemical solvent extraction method has been developed for the determination of Cr(III) using⁵¹Cr tracer. It is based on the complexation of Cr(III) with 8-hydroxyquinoline (oxine) and acetylacetone as mixed ligands at pH 3.8 and extraction in chloroform. Effect of various parameters such as pH, time of equilibration, nature of solvent, quantitative nature, effect of diverse ions has been studied. The method can be used up to 200 ng of Cr.     

Spectrophotometric determination of chromium(III) and rhodium(III) after extraction with oxine into molten naphthalene

Conditions have been developed for the extraction of chromium(III) and rhodium(III) as their 8-hydroxyquinolinates into molten naphthalene. The naphthalene is allowed to solidify, separated by filtration, dried with filter paper and dissolved in chloroform. The solution is diluted to 10 ml and its absorbance measured at 410 nm for chromium and 425 nm for rhodium, against a reagent blank. In both cases the solution is stable for 24-36 hr. Beer's law is obeyed over the range of 2.7-48.6 mug of chromium or 2.7-57.5 mug of rhodium in 10 ml of the chloroform solution. The molar absorptivity is 3 x 10(3) l. mole(-1) . cm(-1) for chromium and 3.6 x 10(4) for rhodium. Solutions containing 27.0 mug of chromium or 10.95 mug of rhodium give a mean absorbance of 0.140 and 0.395 respectively, with standard deviations of 0.002(2) and 0.004(7). Most metal ions that form oxinates may interfere, but can be removed beforehand by normal liquid-liquid extraction.     

Epr of luminescent glasses containing chromium(III)

The EPR spectrum at 9 19 GHz has been examined for a series of chromium(III)-doped glasses. The S = $\text{3}\text{2}$ chromium ion site in all the glasses displays two prominent transitions in the g = 6 and g = 2 region. Concentration-dependent broadening observable in the glasses at g = 2 is associated with isotropic spin exchange and provides evidence that the concentration-dependent quenching of chromium luminescence in glasses is due to an ion pairing mechanism     

Kinetics of anation of chromium(III) by L-phenylalanine

Summary The kinetics of anation of chromium(III) species, [Cr(H₂O)₆]⁴⁺ and [Cr(H₂O)₅OH]²⁺, by L-phenylalanine in aqueous acid has been studied spectrophotometrically. Effects of varying [substrate], [ligand], [H⁺], , % ethanol and temperature were investigated. The kinetic data suggest a mechanism where outersphere-associations [between chromium(III) species and phenylalanine in the zwitterionic form] precede anation. Comparison of the results with published data suggest an I_a path for the [Cr(H₂O)₆]³⁺ reaction and I_d path for the [Cr(H₂O)₅OH]²⁺ reaction.     

Thermal and magnetic studies of mixed ligand complexes of chromium(III) containing dithiocarbamate and acetylacetone/oxine/glycine moieties

Chromium(III) complexes of the type Cr(A)(A′)2, Cr(A)2(A′) and Cr(A)3 have been prepared (whereA is either piperidyldithiocarbamate or morpholyldithiocarbamate andA′ is glycine or oxine or acetylacetone moiety). The mixed ligand complexes have been charac terized by elemental analyses, magnetic susceptibility measurements and thermal studies. The complexes show magnetic moment in the range of 3.5–4.3 B.M. which corresponds to three unpaired electrons. TG studies have also been carried out, in order to study the mode of decomposition of the complexes and to evaluate various kinetic parameters.     

The extraction of iron(III) by dioctylarsinic acid in chloroform

Dioctylarsinic acid, HDOAA, in chloroform solution has been investigated as a reagent for the extraction of iron(III) chloride. The extraction coefficient reaches two maxima, one of 1.5 at 8.5 M hydrochloric acid and another of 7 at pH 2.3. Experiments in the range 4–8 M for sulfuric, nitric and perchloric acids showed no extraction of iron(III) from these solutions for extraction times of 6 h. Evidence for the extraction of H₃FeCl₆ from 4–9 M hydrochloric acid solutions as [(H₂DOAA)⁺]₃FeCl₆^3- is presented. The species extracted from aqueous solutions of pH 1–2.3 is probably a hydroxy complex of the composition [Fe₂(DOAA)₂(HDOAA)X₄(H₂0)₂ ](X = OH and/or Cl).     

In-situ separation of chromium(III) and chromium(VI) and sequential ETV-ICP-AES determination using acetylacetone and PTFE as chemical modifiers

Electrothermal vaporization-inductively coupled plasma-atomic emission spectrometry (ETV-ICP-ES) has been used for the sequential determination of Cr(III) and Cr(VI). The method is based on the difference between the chelate reactions of the two Cr species and acetylacetone. Cr(III) chelate was separated from Cr(VI) and determined with use of acetylacetone as chemical modifier. The retained Cr(VI) in graphite tube was analyzed subsequently, after addition of polytetrafluoroethylene (PTFE) as chemical modifier. The different factors affecting the vaporization behavior of Cr(III) acetylacetonate were investigated in detail. The detection limits for Cr (III) and Cr(VI) were 0.56 and 1.4 ng mL(-1), respectively, and relative standard deviations for 0.1 microg mL(-1) Cr(III) and 0.1 microg mL(-1) Cr(VI) were 2.5% (n = 6) and 4.8% (n = 6), respectively. The linear ranges of the calibration curve for both Cr(IIl) and Cr(VI) covered three orders of magnitude. The proposed method was used to analyze water samples with satisfactory results.     

The extraction of thulium(III), dysprosium(III) and samarium(III) by dioctylarsinic acid in chloroform

Dioctylarsinic acid, HDOAA, in chloroform (0.1 M) extracts thulium(III), dysprosium(III) and samarium(III) from their aqueous solutions in the pH ranges 1–6.5, 2–7 and 4–8, respectively, with extraction coefficients of approximately 0.1 for the lowest and 10 for the highest pH. The extractability increased with increasing ionic strength for each ion and decreased in the order ClO₄^- > NO₃^- > Cl^- > SO₄^2- > acetate for solutions of the same molarity. pH-Dependence curves had slopes ranging from 1.05 to 1.87. The reagent-dependence studies gave curves with slopes between 3.60 and 5.30. The general formula [MX_n(DOAA)_m(HDOAA)_p(H₂O)_q] (X = Cl^-. NO₃^-, SO₄^2-/2, ClO₄^-, acetate, OH^-; n+m=3, m+p=4 or 5, q?0)is suggested for the extracted species.     

Solvent extraction of lanthanum(III), europium(III) and lutetium(III) with fluorinated 1-phenyl-3-methyl-4-benzoyl-5-pyrazolones into chloroform

A series of chelating reagents, 1-phenyl-3-methyl-4-(2-fluorobenzoyl)-5-pyrazolone, 1-phenyl-3-methyl-4-(3-fluorobenzoyl)-5-pyrazolone and 1-phenyl-3-methyl-4-(4-fluorobenzoyl)-5-pyrazolone, has been synthesized. The extraction of Ln(III), (Ln = La, Eu and Lu) into chloroform with these reagents at 30 +/- 1 degrees has been studied. The composition of the complexes extracted has been determined by the slope method, and the extraction constants K(ex), were measured. The presence of the fluorine atom in the reagents does not make the K(ex), values much different from those obtained with the parent pyrazolone.     

Solvent extraction of Zn(II), Cu(II) and Sb(III) with N-m-tolyl-p-methoxybenzohydroxamic acid (TMBHA) into chloroform

Rapid methods have been described for the quantitative extraction of milligram amounts of Zn(II), Cu(II) and Sb(III) with TMBHA into chloroform. The separation factor for many elements was found to be at least greater than 10⁴. The metal: reagent stoichiometry determined by methods like slope ratio, mole ratio and substoichiometric extraction were found to be 12 for Zn(II) and Cu(II), and 23 for Sb(III).     

Solvent extraction of Os(IV) with 2-mercaptobenzothiazole into chloroform

2-mercaptobenzothiazole has been used for the solvent extraction of Os(IV) in acidic medium. The extraction of Os(IV) was found to be better than 90% over the pH range of 3.0 to 5.0 with an equilibration time of 5.0 minutes. The stoichiometry of metal:reagent determined by substoichiometric extraction and slope ratio method was found to be 1∶4. Decontamination factor for various elements in the substoichiometric extraction of Os(IV) were also evaluated.     

Kinetics and mechanism of a macrocyclic chromium(III) complex oxidation to chromium(IV) by hexacyanoferrate(III) in strongly alkaline media

Oxidation of the macrocyclic Cr(III) complex cis-[Cr(cycb)(OH)₂]⁺, where cycb=rac-5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane, by an excess of the hexacyanoferrate(III) in basic solution, slowly produces Cr(V) species. These species, detected using e.p.r. spectroscopy, are stable under ambient conditions for many hours, and the hyperfine structure of the e.p.r. spectrum is consistent with the interaction of the d-electron with four equivalent nitrogen nuclei. Electro-spray ionization mass spectrometry suggests a concomitant oxidation of the macrocyclic ligand, in which double bonds and double bonded oxygen atoms have been introduced. By comparison basic chromate(III) solutions are oxidized rapidly to chromate(VI) by hexacyanoferrate(III) without any detectable generation of stable Cr(V) intermediates.Kinetics of oxidation of the macrocyclic Cr(III) complex in alkaline solution has been studied under excess of the reductant. Rate determining formation of Cr(IV) by a second order process involving the Cr(III) and the Fe(III) reactants is seen. This reaction also involves a characteristic higher order than linear dependence on the hydroxide concentration. Reaction mechanisms for the processes, including oxidation of the coordinated macrocyclic ligand – under excess of the oxidant- are proposed.     

Kinetics and mechanism of oxidation of (ethylenediaminediacetato)chromium(III) by N-bromosuccinimide

The kinetics of oxidation of (ethylenediaminediacetato)-chromium(III), [Cr(EDDA)(OH2)2]+, by N-bromosuccinimide (NBS) in aqueous solution to yield CrVI have been studied spectrophotometrically over the 20–40°C range. The reaction rate is first order with respect to both [NBS] and [CrIII], and increases with pH over the range 4.8–5.8. The activation parameters were calculated. A mechanism in which deprotonated [CrIII(EDDA)(OH2)(OH)] is the reactive species is suggested. The electron transfer may proceed via an inner sphere mechanism through bridging of the two reactants by the hydroxo ligand.     

Heterotri- and -tetrametallic alkoxides of chromium(III) containing aluminium(III), gallium(III) and niobium(V)

CrCl₃ · 3THF reacts with two equivalents of potassium alkoxometallates K{M(OPr ⁱ ) _x } [M = Al(A), Ga(B), x = 4; M = Nb(C), x = 6] to give heterobimetallic chloride isopropoxides [Cr{M(OPr ⁱ ) _x }₂Cl(THF)] [M = Al(A – 1), Ga(B – 1), and Nb(C – 1)], in which the replacement of the chloride with an appropriate alkoxometallate (tetraisopropoxoaluminate, tetraisopropoxogallate, or hexaisopropoxoniobate) results in the formation of novel heterotrimetallic derivatives. The 'single pot synthesis of an heterotetrametallic isopropoxide [Cr{Nb(OPr ⁱ )₆}{Al(OPr ⁱ )₄}{Ga(OPr ⁱ )₄}] (7) has been carried out by the sequential addition of (A), (B), and (C) to a benzene suspension of CrCl₃ · 3THF. Alcoholysis of [Cr{Al(OPr ⁱ )₄}₂{Nb(OPr ⁱ )₆}] (1) and [Cr{Al(OPr ⁱ )₄}₂{Ga(OPr ⁱ )₄}] (5) with t-BuOH has also been studied and the derivatives characterized by elemental analyses, molecular weight determinations, spectroscopic [Electronic, i.r., ²⁷Al-n.m.r.] and magnetic susceptibility studies.     

Kinetics and mechanism of the oxidation of nitrilotris(methylenephosphonato)chromium(III) by periodate

The kinetics of oxidation of nitrilotris(methylenephosphonato)chromium(III), Cr^IIINTMP, by periodate to yield Cr^VI have been studied spectrophotometrically over the 5.80–6.85 pH range at 22–33 °C. The reaction rate, which is first-order with respect to [Cr^IIINTMP] and [IO^– ₄] and inversely dependent on [H⁺], obeys the rate law:-d[Cr^IIINTMP/dt=kKK_h[IO^- ₄] [Cr^III]_T/K_h+ [H⁺] +KK_h[IO^- ₄] The values of the intramolecular electron transfer, k, and the formation constant of the intermediate complex, K, were determined at various temperatures. The hydrolysis constant for Cr^IIINTMP, K _h , was determined spectrophotometrically and is in agreement with the value estimated from the kinetic data. The activation parameters were calculated from the temperature dependence of the specific rate constants. A mechanism is proposed in which the hydroxo complex, [CrHNTMP(OH)]^3–, is the reactive species. The results support a mechanism where intramolecular electron transfer is the rate-determining step.